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hell fine grain powder is of a size to pass through a ieve of 44 meshes to the inch, and retained upon one of 72, and is used for the bursting charges of all hrapnel shell, powder channels of fuzes, and cartridges or pistols. I believe that this powder, in future, is to De calle 1 "service pistol-powder." BLUE JACKET.

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"F.R.A.S." v. CAPTAIN SMYTH. [1514] REFERRING to a statement made by F.R.A.S." on p. 491, of the current volume of the ENGLISH MECHANIC, allow me to ask that gentleman, in what part of the world, and under what sky, he can see the companion to à Cygni, perfectly well with one of Dallmeyer's 4in. achromatics"? Loomis, in his "Practical Astronomy," p. 26, says that Captain Smyth, who had a celebrated object-glass of 5 9-10in. (more than double the size, in superficial measure, of the instrument belonging to " F.R.A.S.) declares that "it required the full aperture and powers of from 240 to 300, with favourable circumstances, to scrutinize satisfactorily" the particular star in question.

Now, of these two gentlemen-Captain Smyth or
F.R.A.S."-to which am I to pin my faith?
CUPIO SCIRE.

CHEAP SPECULA.

[1515] WHY does not Edwin Holmes (let. 1415, p. 517) give an order for (say) a dozen first-class specula on "spec." He might get them cheaply enough then I dare say. His suggestion has long ago been forestalled; the moulds of all my cast glass specula being dished out to the proper curves. In regard to his other suggestions, I think that a very soft glass is undesirable; and he would find, also, that a silver face deposited upon a copper or brass base would not answer for large mirrors, there being many serious objections to it; while, for the production of "flats," I have for some time used a similar plan.

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BICYCLE WHEELS.

E. TYDEMAN.

stellar map, also punctured, but showing in white lines on blue ground merely the separations and positions of the different groups, the stars being also punctured variously and coloured according to their colour and magnitude. I mentioned above that the principal stars are punctured, but in. fact, all stars visible to the naked eye are so, and the whole of the plates seem to be most carefully done, and worthy of being generally known. Now here is the obvious advantage of this system. Suppose a lady wishes you to show her the different constellations, their names, shapes, and relative position to each other, &c., &c., instead of poring over a common map or globe, and then running in and out to compare the heavens with the map, to the manifest discomfort of others, through draughts, &c., you simply take with you your collection of 30 plates into the garden, or out for a walk, and by even the feeble light of the darkest star-lit night, by holding the plates to this light you can, with every facility and comfort, continue your studies with out the possible chance of a mistake-the punctured outline at once proclaims the name of the constellation, whilst the larger punctures show the different stars in the positions as seen in the heavens.

The veriest child can learn with these; and if not yet known in England it would be well worth the while to draw Mr. Proctor's attention to the system, as although these plates are apparently very good and complete, yet, with very little trouble, they might in conjunction with the inventor, be made most exact and

valuable to all.

Being at Gundlach's (whose address by the way is changed) the other day, I asked him about the microscope drawing-prism (so-called Nachet) spoken of by Dr. Anthony in your columns, page 251, No. 378, wishing to get one made; but though I described it as there stated, Gundlach knew nothing about form of drawing-prism. I however, subsequently by mere chance, found the very prism ready mounted at another optician's, whose address I here give for the benefit of any who should wish to get one sent, as after careful trial of the same-having purchased one, price 12s. I can fully endorse the glowing verdict of its advantages, as stated by Dr. Anthony. The opticians are Messrs. Krügelstein & Magen, 130, Leipziger Strasse, Berlin.

cient to move the turbine and pumps alone, without raising any water. And let me say that these rams, though there was some difficulty at first in regulating the recoil, really worked very well, giving little trouble; only getting exhausted of air about once in ten days all summer, and putting up one gallon for every four wasted. Though but a bit of common piping and only held in place by screw bolts, the Nasmythean quality is so well curbed, that you may stand on the bare pipe in full work and hardly feel the tremor.

I suspect Mr. R.'s ram would cut but a sorry figure in the same position. No doubt, as he seems to feel, it would knock itself to pieces in a week. If it can only work profitably at from 5ft. to 10ft. fall, which I well believe, it is of no use here, as the waste must be from three to six times as great. The idea of working the dash-valve under water is clearly caused by defect in design, as by placing it on opposite side of airvessel (as in my drawing) no air could possibly follow the valve, which will not be instantly ejected by next stroke. I also notice that in the engraving both valves appear to open one way, but perhaps that is only an error in copying.

I should like to see a table of results with this horizontal drive-pipe and large cistern, as I must confess for the reasons given in my last, and unanswered, I think it a most awkward and expensive arrangement; and I am sure the sloped pipe of proper length, at 5ft. or 10ft. fall, will and does work as well as it can do. The recoil even in this present instance of high fall can be managed from the dead lock of nothing, to making the water spring a yard back into supply cistern, by other means quite as well as angle of drivepipe. It would surely be better for all readers to have a plain scientific answer to simple queries, though they may appear in a long letter of explanation, rather than be dogmatically asked to substitue a design, which, on his own showing, is useless for the place, instead of this despised machine, of the capabilities of which he is evidently entirely ignorant.

HYDRAULIC.

BAROMETER OSCILLATIONS.

[1516] HAVING had experience with both the "Spider" and "Phantom" bicycles, I, in reply to "J. H." (let. 1828, p. 471), can assure him that the Spider" is, in my opinion, by far the best wheel of the two. I consider that the wheels are the most important part of a bicycle, and it is requisite that they should be perfectly sound and made to keep so, to of their make, the most practical I have yet seen, and readings on a diagram, according to locality, I found

ensure a good machine. The "Phantom" that I had in use very quickly gave signs of giving way in the spokes; in fact, they became quite loose in a short time, and made travelling on that machine very uncomfortable. The principle of the " Spider" is, I am inclined to think, a much better one, and gave me more satisfaction. But that has its weak points, and being an expensive machine, it should not have many. A really good bicycle should be strong and yet light, compact and sound; and these requirements I have discovered in a machine that I have been using since Christmas. It is called the Ariel Lever Wheel Machine. I will endeavour to give a short description of the wheel. In the first place, the felloe is formed out of light angle iron, and from the inside of this are suspended narrow strips of thin rolled steel. These are connected to the hub, projecting from the centre of which is a lever, by a long screw fixed one end to the felloe, and the other end passing through the top of the lever; a thumb-nut then takes its place on the screw-end; as that is screwed up the hub is forced round, which causes the whole of the spokes to tighten up equally. This wheel, when screwed up in this manner, forms one of the strongest and best wheels that was ever made of bicycle pattern. The whole is surmounted by an india-rubber tire of the best quality. It must be so, for in all the wear I have had out of this machine there is not the slightest cut or damage

They tell me the prism is not known as the Nachet, but cannot tell me who the inventor is, nor have they any special name for it, but simply they make it. They showed me also a "Demonstration Microscope"

I have seen many forms.

I know not whether the suggestion be of use, but would it not answer (qy. 6804, p. 432) to dispense with chains, rods, &c., and simply take the readings of his pole anemometer by means of a small powerful telescope-"the rifle tele." fixed anywhere convenient, so as to command a good view of his dials, if necessary by the aid of a mirror at a proper angle. This idea struck me at once on reading his difficulty, as I used to set my watch in that manner from a distant clock, but I did not care to venture this suggestion till others more competent had offered their advice.

(6635.) Steamed Windows.-I saw in a shop in Hamburg the show window at bottom kept completely free from ice crystals by a number of jets of gas (mere holes in the pipe) tolerably near the glass, from a gas pipe passing along window bottom frame.

(6611.) Amber Varnish.-Pound or grind fine the amber, use best chloroform, and set the whole in a warm place, shaking frequently.

(6423.) Electrotyping. A full, but long description, especially silvering glass in "British Journal Photo. Almanac," 1869, page 145; authority, Baron Liebig.

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(6597.) Lichtdruck and Heliotype. -The querist will find long description in Almanac," 1871, page 151.

British Journal Photo.

[1519] I VENTURE to trouble you to say in response to "J. B. T." (let. 1144), that I made the matter he alludes to the subject of a similar comparison a few years ago, with the additional difference that I took the whole of the places included in the weather reports of the late Admiral Fitzroy. Ranging the an almost entire coincidence in the respective curves, but more particularly in the depressions denoting the passage of storms. The only difference was in the time of the extremes, which ranged over an interval of about 36 hours, representing the time occupied by the passage of the "wave of pressure," as it is termed,

between the extreme stations in the tables. In the

reports lately published this time, difference is exemplified in the "f" and "v" at the side of the barometer readings. If "J. B. T." chooses any time connected with the positions given in my paper, he will observe all the diversities of movement arising from the passage of such an extreme over a large tract. The approach of this disturbance, storm, or cyclone," as it is sometimes termed, is often immediately preceded by the finest of weather, with a not unfrequent rise in the barometer of a few hundredths. A few hours, and we have its full violence, which, passing away, is followed by a belt of atmosphere, so exhausted of its vapour and electricity, as to produce often the more sudden and intense frost. In fact, these extremes may be in existence at the same moment of the opposite" sides" of the storm, and hence the same day may be totally different in the north and south of kingdom, and with merely the slightest difference in berometric reading.

I am also able to verify his observation as to the simultaneousness of the extremes over a large tract of

done to the tire. I can get a greater speed out of this task for contributing my mite to the general informa- country for an entire year, in the form of a large dia

bicycle than any other that I have tried. The spokes, presenting a knife-edge, considerably reduce the re

I trust, Mr. Editor, you will not take me to tion.

CIREB.

P.S. (6071.)-Apropos of "bullet proof armour," I sistance to the air in travelling. I am well pleased read in one of the German papers that an individual, and proud of my machine, and consider it vastly actually in such, received a full volley à bout portant superior to any machine that is at present known; and rolled over and over, but otherwise uninjured, and and I have reason to know that it is cheaper. Multi-that on being captured and taken before the General, plying wheels can be applied, I am given to understand, "Old Moltke" gravely put the armour, or whatever it at a trifle more expense; and the makers guarantee was, on, and examined it most carefully. The "Iron fourteen or fifteen miles per hour with a tolerably good Duke" would have found the joke against him in this case apparently.

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[1518] IN answer to Mr. Reveley's last, may I also INDIAN MODE OF CASTING DELICATE OBJECTS in my turn tell him that the queries and complaint are amply detailed in original and other letters to which he has referred. The simple request was," that some subscriber who might have the practical knowledge, should explain the reason, if there was any special difficulty, in regulating the supply of air to rams of high fall."

The whole consists of a strong portfolio, enclosing1st: a pamphlet-reference or description, with other matter, to the following 80 plates of blue cardboard, The answer, so far as I can make it out, seems to be independent of each other, on which are drawings in that the generality of makers know nothing about the ink of the various principal constellations as repre- theory, which may be true; that they are wrongly sented on celestial globes, i.e., the full detailed figures; erected, which is likely to follow; and that the present e.g, Orion with his left foot just above the hare, &c. example is a model of error in every part, which it On holding each plate up to the light, you find that the would be impossible to make work; that the use at all ontlines are, besides drawn in ink, also punctured of water at higher pressure than 12ft. is against all in very fine pricks, whilst the principal stars are the laws of nature and science; and gravely recomeach in its respective place also punctured accord-mended to substitute a water-wheel and pumps, as the ing to their respective magnitude, and are besides best thing under the circumstances, because the plan backed with coloured paper to indicate, where pecu- was 2,000 years old. liar, their respective colour, all others being yellow; the ground, as we know, a piece of tolerably thick blue card. Added to the whole is an ordinary

Now if Mr. R. had not been writing at random, he would have known that the small quantity of water which could do duty through a ram would not be suffi

[1520] THE goldsmiths and silver workers always prefer the curious clay compound prepared by the white ants, and taken out of their huge honey comb abodes, for forming the tiny crucibles used in their arts';fit burns beautifully without cracking when taken from a proper locality, but is more frequently found as here-in Jubbulpoor-full of grit, and too friable even after repeated washings, to hold together. The stomachs of these" white ants" are evidently supplied with a powerful chemical secretion, and this, doubtless combining with certain clays and earths constitutes the useful crucible product I now speak of. It burns to a hard white vessel, on which the borax of the artisan gives a brilliant internal glaze; but I have never seen this earth used for any but the diminutive melting pots alluded to. White ants, if they "swarm" "lodge" for a short time on sheet glass, corrode the same in zigzag patterns, as if etched by fluoric acid; occasionally these marks resemble Persian characters or Egyptian hieroglyphics. Hence some

or

potent chemical acid enters into their building composition, of which the tenacity in some countries, when it has been well kneaded, pounded, and sun-dried, renders it a fine cheap flooring for settlers' houses. It is very generally used in South Africa, where I employed it for the upper portion of a rough stone floor to my verandah. But I must return to my artistic Indians and their primitive" dodges." In casting small articles in brass, and the cheaper metals, they fix the mould with iron wire to the mouth of the melting-pot, well lating the connections repeatedly with a mixture of stiff clay and cow-dung kneaded together, till quite strong and safe, gradually warming the luting at the mouth of the furnace, and repairing all cracks and fissures as they may appear; when thoroughly dry the whole mass is put in the rude native furnace of common clay, and on the contents of the melting pot being fused, it is turned gently "topsy turvy" and the metal runs from its inverted month into the attached mould. For articles of ornament and elaborate design, of any size, even to a field-piece, the native workman makes a composition of two parts "dammer" resin, and one part bee'swax (common resin will replace the first in England); these are very slowly and carefully melted over charcoal, and stirred together (in the open air, and not under a roof), and when almost hard are moulded by the hands, the lathe, or in metallic shapes. These models in their turn are then encased in suitable mould clay, and very carefully and slowly dried in a shady spot until perfectly hard and seasoned. The workman then, over charcoal, gently heats the mould and pours out the composition from the hole he left as a future "ingate ;" when every particle of the mixture has flowed out into a vessel held to catch it for future use, he increases his fire till smoke rises from the interior of his mould, and it is gradually brought to a condition to receive the molten metal. From an earring to an idol this is the favourite modus operandi of casting, and I can most thoroughly recommend it to the ingenious amateur, if not already practising it. Bismuth is so very highly priced in India that I never employ" fusible metal;" the present mode, besides being cheaper, gives a sharper casting, especially for small jewellery, tiny silver ornaments, to say nothing of avoiding the contamination of precious metals by the lead of the alloy.

There is great reason for supposing that in the days of "human sacrifices," models of the entire figure were obtained by casts of the victims who were immolated in substantial clay coverings, which, when red hot, were filled with molten gold or silver, and gave the perfect images required by the priesthood. The delicate German castings of flowers and insects are nowadays cast in the same fashion-" burning out." Fish and reptiles, such as snakes and lizards, may be so cast very life-like in tin, and afterwards bronzed. I lately amused myself by getting the perfect nature model of a water snake about 2ft. long in the above manner. I got a split bamboo equally divided; I placed good fire-clay in each half of this bamboo; I then put the snake carefully between the two pieces secured the halves of bamboo firmly by binding wire at intervals of a few inches; I dried the whole slowly before a fire; I then slowly in a long charcoal stove of clay gradually burnt out the snake, and poured in pewterer's solder-i.e.,2 parts tin, 1 part lead.

I have a small box in " ormolu" of foreign mannfacture, surmounted by a "horned beetle," evidently modelled in this fashion, which I recommend to the amateur mechanic as a most satisfactory and interesting amusement. Eos.

THE LUNULE OF HIPPOCRATES (Lette p. 520).-M. Paris says: "Surely there must be a take here; Hippocrates was the celebrated p of Cos, not Chio. Hipparchus, of Nicea, was the fa mathematician and astronomer," the father of 1 nomy, and the discoverer of the precession of equinoxes, of equation of time, of parallax, and mode of geometrically measuring distances; make e a catalogue of stars, and who first laid the sonde dations of geometrical and trigonometrical s Vide Lemprière-Art. Hipparchas.

patches of colour, formed by the film of oxide which is perpetually forming; a white vapour will also be seen EXTRACTS FROM CORRESPONDENCE. rising from the cupels or "lists," as they are sometimes called. This is cansed by the volatilization of a small portion of the lead. When this vapour is thin and rises very rapidly the heat in the muffle is too great; while, on the other hand, when it is heavy and hangs over and around the cupel it is a sign that the temperature is too low. In the former case, the draught must be checked; in the latter, increased. When nearly the whole of the lead has been absorbed the heat is gently raised, and when the bead-like "prill" of silver can be plainly distinguished the door of the muffle is closed for about a minute to drive off the remaining portion of litharge. It is then opened, the cupels withdrawn, and in order to prevent loss from "spitting" empty cupels inverted over them. A wellmade cupel will absorb, as a rule, about its own weight of melted litharge, but the power of absorption is not quite regular. A small portion of silver is always ab. sorbed, but it is so small in ores of a lower produce than 350oz. per ton of stuff, as to be seldom taken into account by the practical assayer. As the loss from absorption is very regular, most assayers have tables calculated, by the aid of which they can always know what to add for loss from that cause.

The colour imparted to the cupel by the different kinds of ore gives a means whereby one can judge of the nature of the other metals which may be present besides lead and silver, par example :— Pure lead stains the cupel a yellow straw-like colour; copper gives a dark brown colour if in quantity, otherwise a grey tint. Iron forms a dark rim round the sides of the cupel; zinc gives a yellowish stain; and, during cupellation, forms a bright white flame, which occasions loss of silver, if not carefully watched.

Tin produces a grey scoria, and antimony a spongy yellow one, which causes the circumference of the cupel to split off. The two metals last mentioned require a considerable quantity of lead for proper cupellation, in order to carry off insoluble oxides.

In concluding my papers on Lead and Silver Assaying, I feel it necessary to state that I did not undertake in commencing them to do more than give a brief outline of the dry methods of estimating these metals. It requires time, patience, and practice to make a good assayer; and therefore let no reader be disap. pointed by one, two, or more failures; but if there be anything which is not quite plain to him I shall be only too happy to explain it.

I must also apologize for the long intervals at which my papers have appeared; but I have a great deal of business to attend to, and it is only now and then that I can find time to write. However, I shall not commence my papers on Copper Assaying for some time, but when I do commence them I shall endeavour to have them appear as regularly as possible. UN IRLANDAIS. P.S.-The printer has made me call a pennyweight each of carbonate of soda and of borax a pennyworth each, in my description of the reduction of silver ore by scorification. I find "Urban" is perfectly right about the NHO in copper assaying. I added very much the same quantity to the test solution as to the ore solution, although I never measured it. Will do so for the future. Never too late to mend."

STEREOSCOPES.-"E. L. G."—(LET. 1477, p. 544.) [1522] I APOLOGIZE to "E. L. G." for my mistake with regard to his use of the word "portion;" but with him, I otherwise rejoice, as it affords me another opportunity of correcting his erroneous views. I never ASSAYING.-THE SILVER ASSAY.-No. III. supposed perspective as an exact science to be required by artists. I used the word in its ordinary sense; and [1521] THE final operation by which the lead is besides, it is well-known that a strict adherence to the separated from the silver with which it is alloyed is laws of the science is in many cases to be avoided. termed cupellation, and is conducted in a muttle. A "E. L. G." appears to be affected with that great small round vessel formed of bone-ash, called a cupel, infirmity of noble minds employed in mathematical is used to contain the lead alloy, and as the current of studies, of looking at matters too much from a matheheated air passes through the muffle it oxidizes thematical point of view. Dr. Lardner, in his tract on lead and other metallic impurities that may be present, the stereoscope, has the following passages.—“The when they are immediately absorbed by the cupel. The stereoscope has the property of exaggerating the nasilver, which does not oxidize at any temperature, is tural effects of perspective and relief." Again, "It is left behind in the form of a small bead or "prill," then rigourously true, that the surprise and admiration easily detached from the cupel after cooling. excited by the stereoscope does not arise from the truth of the picture which it presents, but from the strong exaggeration of perspective and relief which it exhibits. It is very true that no art of the dranghtsman or painter could produce any such effects, but it is equally true that no such effects could be produced by the objects themselves."

The cupels are made of the best bone-ash moistened with water and mixed with about one-fortieth part by weight of American pearl-ash, or one-tenth by measure of fern-ashes. The mixture, sufficiently moist to cohere, is pressed into a mould of brass or cast-iron, open at each end, the diameter of the cavity being slightly less at the bottom than at the top. The usual dimensions are interior diameter at bottom in., ditto at top 1 9-16in., depth 2in. When in use, a small thin plate forming a false-bottom is inserted through the larger end, the cavity is then filled with bone-ash pressed down hard, and by means of a die, termed a "plunger," which fits the mould and has its lower end turned convex, a cup-like cavity is formed, very shallow, being not more than three-quarters of an inch deep. The cupels are dried perfectly before being used. Capellation is conducted as follows:-When the muffle has become red-hot, from four to eight cupels are placed in it by means of slight tongs made for the purpose. The door of the muffle is then closed, the damper drawn, and the cupels exposed to the influence of the heat for about twenty minutes, when the buttons of alloy to be cupelled are introduced into them by means of a pair of slight tongs.

When the assays have been placed in the cupels the

tacles are.

I can

As to Apille's paintings we do not know, I believe, what his knowledge of perspective was. It is asual to consider Ulbaldi and Perussi as the pioneers of the science, but I have "jumped to the conclusion" that it was nearly as well known to the ancients as now.

TELESCOPIC.-Mr. Holmes (let. 1415, p. 519 why metallic reflectors cannot be produced by el deposition. Was not this M. Foucault's plan plained to the British Association about the yearb cheap speculum of glass and, I believe, with cu M. Foucault deposited a thin film of silver as able success.-M. PARIS.

METEOR.-Mr. George Stedham, of Tra says:-" The brilliant meteor, seen by your or dent of last week, I happened to see on tea evening; Greenwich time, 8min. past 9. B near Belatrix in Orion, altitude 85. It left be it a train of bright colours, the colour greas, wee, being prominent. I agree with your correspondin E. Spiller, as to no sound being heard; it be b ever, been said by many that a crackling soi va heard. The meteor passed due west. A: if great brilliancy was also seen this time in the me position last year."

REVOLUTION OF THE EARTH (L 121, tion appears to me to be the true one-, 1876, 1396, p. 546).-M. Paris says:-'K' cxpiata, as Mr. Ginger, would say, 'there was a mirtie

REPLIES TO QUERIES.

In their answers, Correspondents are repe requested to mention in each instance the tea number of the query asked.

[5473.] RAPID FIRING.-Fifty-five shots in thi seconds were fired at Montreal from a single breech-loading, rifle, known as the "Meyer Gar has an outer casing of brass, and when in act barrel is surrounded by water to the depth of a On one occasion 450 rounds were tired rapidly any cessation, for the purpose of cleaning the barrela fair performance for a single barrel-MoNT Canada.

[5602.]-VIOLIN (U. Q.).-Harshiness of tone may ceed from various causes.-1, bad strings; 2. inequa in the finger board, remedy obvious; 3, the back or i may be partly separated from the rim. Use a little d glue and clamp tight till set. If all exterior mese the instrument had better be entrusted to fessional repairer. Erect sound-post under string, or towards central line, a little d the bridge; no glue required. The introd of a longitudinal rod is a very questionable proce seeing that so many violins produce good tones it has also been shown by the experiments of M. Savark, as already much that is unnecessary. -IRIOSAL

[6000.]-HUMAN HAIR (U. Q.).-M. P.," in sto this query, says that a certain hair-dresser throws hair away. Allow me to state that hair-dressers ready sale for it here. It is bought by builders 8348 used in mortar.-F. W. SHEARING.

[6139.]-BOILER PRESSURE (U. Q.).—I! J. Hed will give the length of his boiler flue I may be able form him the collapsing pressure of such flue; o means the safe working pressure it will be 150-151b. cording to Fairbairn, we have 29 =

=

261

28 24

=16-5 and 18

34000 238000 = 901.5lb. bursting pressure of fae, and allowing of that pressure we have 150-51b. safe writing pressure. As regards the rule to find the dis flue in proportion to the diameter of the boiler, 1. there is no rule laid down. I think it is left to the jai ment of engineer in charge of the construction-b

JACKSON.

[6145.]-SIZE AND STRENGTH OF BOILERS (U.QL -From the earliest numbers of "our" MECHANIC, With respect to there being no instrument made to to the present time there have been many inquiries ab obviate the varying distances of the pupils of different boilers as well as sewing machines, without a persons, think I have seen one advertised. at anything definite. Will you be kind enough to all See also very well with some stereoscopes and not at self-help. How to make and test boilers for " Jacar "Jack" to give them a lift and put them in the way all with others, as they are made to suit sights as spec- a boiler maker too-with a very little trouble ander any risk o pense. They, our readers I mean, will be able to ascer life or limb. The enclosed will be found equal to antes for steaming and strength, I think. It is a tabalar ber with a corrugated fire-box; you or some of our readers will say that is not new; but I think, take the things as they stand, it is a new design-plenty of steam room, dry, no priming. Fig. 1 and 2; see crown of botler and bottom of fire-box. Can be all built and put into its POSTAL FACILITIES.-Eight hundred letters, find the best plan to make it a good at in the parts, ces To make small boilers for models I says the Rappel, have lately reached Paris from the pro- the junctions, tin them, put them together persung vinces by a singular mode of transport. The carriage rivets, and sweat them together. Method of operating which brought them was a zinc ball twenty-five centi- for boiler such as is here shown. metres in diameter, and the rail on which it ran was copper skeet, gauge 14; rivets; brass wire, cold draw so that this ball thrown into the Seine moved at a

M. PARIS.

and riveted.

Scale lin. to foot;

door of the muffle is again closed in order that the the current of the Seine. The weight was calenlated 10 or il gauge. Bend the wire at right angles, Gin, each

alloy may more easily melt. After a minute or two it

way, after having cut it up into foot lengths; screw it op as close to the angle as you can; having screwed a tap them; use your wire alternate ends, that you

is once more opened and air admitted freely. The sur- certain depth below the surface. The current striking ends they are ready for operation. Drill your holes and

face of the melted alloy will then be found covered with

little wings made it progress rapidly.

may have a lever to work with to the last. With a knife, mirror. Let a and b be the two points given, and C
file, or half round, or a fine hack-saw, nick the screw be-
fore you enter it of the length to admit of 1-16in.
projecting inside, and the same out. After screwing in,
cut off at the nick; proceed until you have it all to-
gether, with the exception of putting it into the
jacket. Having tried it before, make it hot over a light,
wood fire, or a fire of shavings, sufficiently hot to run
soft solder, not more, and with a bit make all your joints
sound. You can let your rivets rest at that inside, and
the fire-box; but outside, for neatness, they should be
shaped or rounded off, either with a punch or drill.

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scription 2, is the ash pit; there are lugs in the fire-box side to carry frame for fire-bars; M mud hole; A water space between barrel and fire-box; and see, from Fig. 2, transverse section; corrugations only being in the water, running out at both ends to a circle at the tube collar T; and for C the corrugations being tied together at A by rivets or bolts, and washers; T'I tube collar; T T are tubes screwed taper, passing through the chimney end tube plate at E; the arrows show the circulation of fire; SS is a double dome, which constitutes a part of the boiler, the tube-plate being pierced with holes BB to allow the steam to enter, and by that means becoming superheated. In connection with the same I forward a sketch of a simple apparatus by which I have tested one made of 14 gauge brass, one to 3000lb. to square inch. A piece of stick brass or Muntz metal, in., Sin. long. Bore it up 5in. with a quarter hole, the rest with an eighth. Drill a quarter hole about in. in the bottom; for the valve F take a piece of gin. brass wire, and make valve-box and stud in one as at D. Twopennyworth of india-rubber tube that is used for Maw's feeding bottles, that is your suction; and a very good To the plunger is made of in. steel rod, turned as represented; E is, a piece of leather screwed upon the plunger, the grain outside. By pulling the grain of the leather well forward be fore entering the bell-mouth of the pump-barrel, you form a very nice little cup leather; with that a man of ten stone can use a force of 3000lb. per square inch. The handle C is of wood-a gimlet handle. So far so good, a simple thing, but very dangerous if not careful how used. Air compressed to 3,000 is nothing to laugh at; if it were to explode it would as surely drill a hole in you as a rifle ball; so exclude all air when testing your boilers large or small; throw your valves open, and fill to the brim before using the pump. Then screw your pump in to a place that you have made for its reception. Close your valves and cocks, load your valves to what you want to press it, and out of a can, bucket, or jug, into which you have dropped your section, you may pump away to your heart's content without fear of doing more damage than bursting your boiler.-JACK OF ALL

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centre of circular profile. Join Ca, Cb, and bisect each. From the points of bisection erect perpendiculars towards D and d. Find two points D and d, so that CD:Cd:: Ca: Cb, and the line joining Ddtangential to the arc r, drawn with half radius of profile. This may be done in a few trials, either by laying off equal arcs A A, B B', or by drawing parallels to a b, and marking off with centre C. With centre D draw Cca, and similarly from draw Cc b. The intersection of these arcs will mark the point required, as it is evident that the segments on Ca and Cb are similar, and contain equal angles. In the method of " E. L. G."I think the limits assigned to his trial are will not always hold good, since the radius must vary with the angles of incidence and reflection. If any contributor could give a true geometrical solution by ratios, or the application of a curve, I should feel obliged.-IRIOSAL.

nace. The principal ingredients are potter's clay, ground flint, and borax, with a glaze of borax and Cornish stone. The Patent Enamel Company produce enamel surfaces on iron for use as street name plates; the lettering being accomplished by means of stencil plates.-H. U.

[6336.]-CHOICE OF TELESCOPE.-In answer to "T. H." I must apologize for not replying earlier, but pressure of business matters is my excuse; and moreover, the very few spare hours I have had since the period referred to have not been favourable for any further testing of my Wray's 8fin. object glass, except on two or three occasions, when I obtained fine views of the moon. Judging from the ease with which very minute points and shadows could be seen, I feel confident the instrudment is an excellent one: however, when I have an opportunity of severely testing it, I shall be pleased to give the result if desired. For " Amateur's" satisfaction I will at once admit that notwithstanding its fine definition under favourable circumstances, when the objectglass is thickly covered with moisture and used with high powers on objects near the horizon, the definition is simply wretched. To prevent such a deposition of moisture, I have a piece of brass tube 8in. long to slide over the end of the telescope. As to the question of cost, the O. G. stands for £7 10s., mounted in a cell. For this cell to screw into, I had a piece of tubing Jin. long; this I found to be almost essential for the purpose of centering, as the main tube in my case-of zinc and made by an ordinary tinman-was by no means so accurately turned out of hand as optical science requires. Those tubes, together with excellent rack-work for focussing, and screwing into the eye end of the telescope, cost about £2 more; morocco covering for same and some other pieces of brass, &c., another 10s., which completed the outlay, except for the eyepieces-suppose four be obtained at a cost of 15s. each, the total cost will be about £13. Of course, my labour in mounting it equatorially on a strong tripod does not count. In centering, I tried several methods, but did not succeed well until I tried the method given in these pages by "F. R. A. S." on a fixed star. I selected the pole star, with a power of 286, and succeeded admirably.-B.

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[6253.]-EXPRESS ENGINES.-The most powerful express engines in existence are those recently constructed for the Great Northern line. The diameter of the cylinder is 18in., and a stroke of 28in., the steam pressure in boiler being 1401b. to the square inch. The diameter of the driving wheels is 8ft. lin., and the tractive force which the engine is capable of exerting is 1081b. for each pound of effective pressure per square inch on the pistons. The cylinders are outside, and are held in openings in the frame between the two foremost wheels. The leading end of the engine is carried on a four-wheel bogie; the weight on the driving wheels is 15 tons, and the total weight of the locomotive in working order is 38 tons 9 cwt., whilst the tender has a weight of 26 tons 10 cwt. The boiler contains 217 tubes, of an outside diameter of 19-16in., the total heating surface being 1165 square feet. Apropos of the "speed" question, I find the following:- The express traffic of the Great Northern line necessitates the running of trains consisting of from 15 to 26 carriages from King's Cross to Peterborough at a mean speed of 47 miles per hour." SAUL RYMEA.

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coopers place slips of dried bulrush between the joints. When you have rounded your bottom, which must be a little larger than old one, you must shave the circumpails, &c., are rotten at the bottom, the crease, or ference to the thickness of crevice. Sometimes, when groove, is cut off, and a fresh one made higher up; this I have not made a is done with a tool called a cressett (see figure). The two years. When yon bott om hoops must be taken off, to take old bottom out. Place the new bottom in and hoops on again. The hoops are drove on tight by a tool called a hoop-dreft (see Fig. 3). This is made of iron.-FREDERIC W. SHEARING.

[6262.]-BREWERS' QUESTIONS.-I do not think
you have carefully read chapter XII. in the book to which
I referred you, as it is especially adapted to your sized
plant. However, I will give you an outline of the prin-
cipal process. Your mashing heat should not be above
1710, if a degree or two lower all the better; now turn
into mash tun, which ought to be previously warmed,
three barrels, and mash well for about 39 min., when
you may run on one barrel more at 185° or 190°, and stir
up, the mash well whilst running on; now cover up for
into the copper. At the same time commence sparging,
2 hours. At the end of that time set tap and pump
and keep the sparge working, so that at the time the re-
quired amount of wort is drained off the goods for the
in the tun; then if you mash again turn off taps and
first copper, the goods have not dropped more than 84in.
mash with about 13 barrels at 185°, but I prefer only
mashing once and sparge the rest.
second mash for the last
set taps again your sparging water may be as
hot as 190 without doing any harm. It appears you have
only one boiling, as you say you pump both together
into the copper; whatever do you do with your first wort
the two hours your second mash is standing on the
goods? I should advise you to have two boilings; it is
much more profitable, as the second wort mashes out a
large proportion of the saccharine matter left in the hops
by the first wort, which would be about 361b. per barrel
by saccharometer; the second probably 181b. As you pro-
ceed, the wort left in the hops weighs about 31°, provided
you do not make any table beer. The first wort ought
to be boiled between 1h. 30m.; the second 2h., and run
into gyle tun between 60 and 64°, according to weather,
&c. I do not admire your rule for cleansing your beer
always at 70°, as sometimes they may weigh by saccha-
rometer 20; at another time, perhaps 10; that rule
of worts rising 1 for 1lb. saccharine matter at-
tenuated is not infallible, as you will find out if you use
the saccharometer as a standard to cleanse by, as most
brewers generally do. There is no necessity to skim off
the head before cleaning. If the cleanse looks at all
sluggish by all means give it a good rousing up.
expect you do not pay enough attention to
beer after it is in the casks, because there it
wants more attention than in any other part of the
process; and I should not be at all surprised
them up every two hours the first twenty-four hours
if your beer did not go bright if you do not top
not topped up at stated intervals, but not oftener than
after cleansing, as the yeast is liable to drop through if
two hours. You say you get 11 kilderkins to the 2
quarters; at that rate they ought to weigh in the gyle
tun 30lb. or 31lb. per saccharine; for that strength beer
you ought to use between 3lb. and 4lb. yeast per barrel
(never measure yeast, always weigh it), but you must
use your judgment about the quantity, as locality, &c.,
make so much difference in fermentations, but the
amount I state ought to attenuate the beer to about
71b. or 8lb. per saccharine. When finished working
should advise you to cleanse your beers when they weigh
about '131b. or 141b. per saccharine, and then the final
attenuation will be about 7. If you find that your wort
is not down to 131b. when the heat of the gyle is 70°, do
not cleanse it. I have had them get up to 75° before
attenuating to the required point. Finings will not
touch beer that has not finished fermenting, so I advise
you to look sharp after the fermenting process, and
try to find out where the fault lies. There is one thing
in a brewery you cannot pay too much attention to,
that is, to keep everything clean and sweet, especially
wort pumps. In conclusion, I should advise you to read
the "Brewer" again thoroughly.-AROMA.

I

the

thankful to Carl Dittenhoffer for his kindly promised assistance. 1. The exact internal dimensions are, width, 39gin.: length, 11in., about 4in. from bottom board, the length increases to 13in. owing to a crossbar which stands inside at the back of instrument. 2. Width of space for blowing pedals 33in.: height 8in. I may also say that the bottom-board projects 7in. from front of instrument, and is of good thickness. 3. Say about 18in. when closed, and allowing about 7in. or 8in. motion. They are not yet added, and will be made to order by a practical person, and so "C. D." can suit himself, as I am not tied to an inch or two. 4. The wind reservoirs will be up the sides.-JAS. W. WORSEY.

[6409.]-HARMONIUM PEDALS.-I am exceedingly

very successful with the plan he proposes for rustic
[6411.] RUSTIC AQUARIUM.-"S. T." will not be
aquaria. A small pond might succeed for fresh-water
animals and plants, but, sunk in the earth, and sur-
rounded by rockwork it would be inconvenient for pur-
poses of observation and study. Most of the pleasure a
well-kept aquarium can give would be lost, and un-
checked confervoid growths would soon excite a feeling
would be less likely to succeed than the above; so many
of disgust and disappointment. A marine aquarium
to be under careful and proper control that without the
conditions of light and shade, temperature, &c., require
shelter of a building and the choice of a proper aspect-
a situation without sun or strong daylight is most suit-
able-it would be impossible to succeed; in fact,
to fail is more common than to succeed with a
marine aquarium, because these things do not re-
ceive sufficient attention. A small vessel holding 2 or
3 gallons of sea-water, and capable of keeping in health,
say, a dozen specimens of marine life, such as anemones
pleasure and enjoyment to the student of nature the
a star-fish or two, madrepores, &c., would give a real
largest tub could not impart. The best of all vegetation
for an aquarium is the natural confervoid growths
which are sure to come if sufficient time be given. A
formula for the manufacture of artificial sea-water will
be given if required; real sea-water is much better, and
requires less time to fit it for the reception of animal
life than the other.-J. G.

[6411.)-RUSTIC AQUARIUM.-See Mr. A. S. Liggatt's letter.-ED.

[6425.]-SPECTROSCOPY.-I think "J. V." has not yet received a satisfactory answer to his query. Let him turn the lever of his spectroscope to the full extent both to right and left. He will find that there are two coloured spectra, one a broad and the other a narrow one. The latter is the one he wants. Let him then focus.

[6281.]-ENAMELLED IRON.-Does Mr. Glazier
mean the enamel used for saucepans and other hollow
ware, or the enamelled iron advertising tablets? I am
not aware that there is any enamel which can be success.
fully applied without a properly constructed muffle fur--X, Y, Z.

[6430.]-STREET TELESCOPE. Several correspondents seem inclined to recommend Mr. Shepherd to have a reflector for this purpose, but if he does not wish to be put to serious loss, he had better give up all idea of having a reflector, because such an instrument would be utterly useless in the public streets. Reflectors require to be remarkably steady to do anything at all with them, and in the streets the rumbling and shaking caused by vehicles and passengers would effectually prevent the slightest steadiness. As one residing in London, I know that although removed & little way back from the road, I am sometimes even unable to use my refractor, which, as every one knows, can be used when, from unsteadiness, a reflector cannot. Moreover, reflectors require steady air, and it stands to reason that in the streets, what with the gas, the chimneys, and possibly a crowd of spectators, the air would not be steady, but on the contrary, would cause such an image that would puzzle even an astronomer to make out, much less the general public. A reflector for London streets (or indeed a public thoroughfare anywhere) would be a certain loss. Mr. Shepherd had much better take the advice of "F.R.A.S." and get a refractor of about 3in. aperture, and mount it on a very firm stand.-ALBERT P. HOLDEN.

[6436.1-RUST JOINTS.-I am afraid if "One in a Fog" follows "Manager's" advice he will become involved next in a "Scotch mist." By referring back to No. 277, Vol. XI. (answer to qy. 4169), he will, no doubt, see the reason why his joints crumble away, as well as ascertain how to make them correctly. I do not know where "Manager" has found his recipe, but he has failed to perceive that sal ammoniac and muriate of ammonia, or the chloride of ammonium, are one and the same thing, so that what he recommends is simply 4 oz. of sal ammoniac to 14lb. of iron borings, where foz. would be much nearer the mark.-MATRIX.

[6439.]-POWER OF WATER WHEELS.-In answer to the above query respecting the power (effective I judge) to be obtained by using water wheels upon the three principles, I find the average amount obtained from each class as follows: Overshot from 45 per cent. to 50 per cent.; undershot from 25 per cent. to 30 per cent.; and for breast-wheels, 35 per cent. to 40 per cent. These are alone obtainable under favourable circumstances. A turbine will give out about 70 per cent. of the theoretical power of stream. The latter part of your correspondent's question "as to how measurements are usually taken, whether from the inner or outer circumference of the floats," I find the inner circumference spoken of generally; but I have myself inclined to adopt a mean as is usual in setting out teeth-gearing, calling such the "pitch line," which would be more convenient for practical purposes.-L. G. [6443.]-TURNING WITH THE SLIDE REST.-In my opinion, the proper height for the tool for turning is the centre; if the tool be higher, and the piece to be turned weak, it will most likely spring up and cause the tool to "dig in; " or the same thing may happen, if the tool springs from being too far away from the toolholder. If the tool be higher, and the cut keeps increasing, as sometimes happens, it will cause the tool to take too much off, as it will force it down unless every the heel may be nearly in a vertical position, thus:

ounce and a half of nitric acid, and when cold 2oz. of spirits of wine are added, and the whole put into a perfectly clean vessel, and placed in the open air, when copious fumes pass off, and a violent action takes place, during which a white crystalline powder is deposited: as soon as all action has ceased, and the liquid cooled, the whole is filtered through blotting-paper, the powder which remains is then washed with a little water, and dried without heat. The varnish is made by dissolving shellac in spirits of wine. -DELATEUR.

[6489.]-CHINESE WHITE.-Chinese White is made from white oxide of zinc mixed with liquid gum.-W. BELFIELD.

[6495.]-CYANIDE OF MERCURY.-It is obtained by boiling together two parts of bisulphate of mercury and one of ferrocyanide of potassium in eight of water, evaporating the solution and crystallising.-SIGMA. by saturating dilute bydrocyanic acid (prussic acid) with [6495.]-CYANIDE OF MERCURY-May be prepared finely divided mercuric oxide, filtering, evaporating and crystallizing the filtrate.-J. W. W.

[6503.]-ECCALOBION, OR EGG HATCHING.-I send a rough section of Cantelo's one-tray HydroIncubator. A, zinc cistern with hollow cylinder in centre from top to bottom; B, sheet iron tube or furnace fitted to go into the above cylinder, it is charged with charcoal; C, small trough for med in top of cistern time to gain strength; D, tray to contain 100 eggs. It in which the newly hatched chicks are placed for a short would be about 20in. square, and that will regulate the size of machine front to back, about 3in deep, filled with any number of brass springs which are covered over with canvas on which the eggs are laid. hinged to cross piece. It will be seen that when they are E, bearers, laid down the tray D will be lowered, and can then be

[6520.]-ALLOY.-"Hammersman" is not sufficiently concise; he should have stated the purpose to which be wished to apply his alloy. I could fill a page or two of the MECHANIC with the composition of a series of allers each of which should be both hard and tough; but a hard and tough bell-metal would not have precisely the same composition as a hard and tough type-metal and neither would fulfil the conditions required by a hard and tough gun-metal. What is "H." going to do with his alloy when he gets it ?-B. C. E. BRODIE

[6521.] SAFETY VALVES.-Read my reply "Young Hand," p. 501, No. 807, and that by Brumhall to him, same page. The ares of a read surface is found by multiplying the square of diameter by 11, and dividing the result by i The square of a number is found by multiplying number by itself, thus 6 times 6 are 36. 36 is the sare of 6, written 62. If the area in inches be multiplied by the pressure in pounds per square inch, it will give the hinges is called its fulcrum; then if "H." multiplies the whole pressure. Now, the point upon which the lever distance between the fulcrum and the valve, by the sure upon the valve, and will divide the result by the weight of his "load," he will find the distance from fulcrum of the point on the lever at which he requires se apply his "load." If instead of fixing the "load," he had determined the point at which he intended to apply then, instead of dividing by the weight, he would have need to have divided by the distance of the fixed m in diameter, the square of this is 1-16th, and its point from the fulcrum. In "H.'s" case, his valve is m therefore 864 say of a square in the pressure 62 11 will, therefore, be Tolb., or 82 ib. = fox.and 33 8 10oz. respectively. If "H." will "think over the b ject carefully, he will soon find his seeming dificaties vanish. There is no subject over which so much doubt exists in the beginner's mind as in this; and there none in which, by a little thought, that doubts se som dispelled.-B. C. E. BRODIE.

11

10

1

N

5

20

=

5

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[6521.]-SAFETY VALVES.-Suppose "Baners man" has a safety valve, its diameter being equal to 25in., length of the lever 8in., and the distance brom the fulcrum to the centre of the valve in, the wet to be placed on the end of the lever to be equal to 20 per square inch would be found as follows, viz.-1 find the area of the valve thus, 252 x 7854-1402, 49 which is a little less than the th part of a square 1000

inch. Then the direct weight which should be placed

49 on the valve is found by taking the th part d 1003

201b., which is equal to 1568oz.; but since the weight to be placed on the end of the lever, this weight at be divided by 6, i.e., the ratio of the length of the lever to the distance from the fulcrum to the centre of the valve, which gives 2-613 oz. Therefore a weight ey to 2-613 oz. placed on the end of the lever would k equal to 20lb. per square inch, not taking into acc O'CONNOR.

part is very rigid. When the tool is placed this height, drawn out. F, return-pipes, 6 or 8 in number, they also friction, nor the weight of the lever.-TuoxAJ

MACHINIST.

[6470.]-REGELAT ION.-I think the inherent tendency mentioned by "CM. Hc." is not due to the thawing state, or to welding. Two pieces of lead will join cold by pressure, so will panes of glass. I have often seen a glacier split to fragments in turning a corner united firmly soon after passing; here, from its position, it was unlikely any thaw otherwise than surface thaw ever occurred.-M. P.

[6478.]-POISONOUS GAS FROM BATTERIES.-The Daniell, as to which the question is specially put, gives off no gas whatever, except a little hydrogen, due to its local action. The Grove and Bunsen cells give off nitrous fumes, which, though scarcely poisonous, are unwholesome and even dangerous in confined spaces. The Smee gives offhydrogen, and if" brown vitriol" be used with it, this hydrogen may be charged with arsenic, and so become poisnous, arseniuretted hydrogen being a deadly poison. But I have never heard of any one having been thus poisoned. The hydrogen thus given off is, however, unpleasant when abundant, and produces painful pimples inside the nostrils, and no doubt from its chemical action, would interfere with the full and proper oxidation of the blood.-SIGMA.

[6482.]-BOOKBINDING." Robinson Crusoe's" re

marks on the practical replies of a bookbinder of thirty-six years' working experience," compel me to decline answering his queries.-AB INITIO.

[6484.]-GUN CAP AND LOCKS-Are made of thin copper, punched into shape. The explosive compound inside is composed of six parts chlorate of potash, four parts mercury, and two parts ground glass.-A. B. B.

[6484.] - GUN CAPS AND LOCKS.- They are produced by pressure. The blanks, in the form of a cross, are punched out of thin rolled copper; then, by means of dies, the arms are folded up and united into a short tube, whilst the central portion of metal forms the top, the inside of which is touched with a solution of glue, into which the fulminating powder is dropped. They are, when dry, coated with varnish to protect them from damp.-STEWART WILLIAMSON. [6484.]-GUN CAPS AND LOCKS.-At the Arsenal at Woolwich is a machine, which makes the caps complete. It is fed with a band of thin copper, about 2in. wide, out of which pieces are punched in the form of a thick cross. These pieces are punched or " struck up," and expelled as perfect caps at the rate of about 1,000 per minute. The fulminating powder is then put in and rammed down, and a minute portion of varnish dropped in. This varnish dries in a few minutes, and causes the fulminating powder to adhere; the caps are then complete. To prepare the fulminating powder for these caps, 100 grains of mercury is dissolved in a measured

form the artificial mother; under the said pipes is spread a layer of sand; G, glass, a flange is formed in the zinc on which the glass is bedded in redlead putty; H, cover or lid to furnace in which is a small slide for regulation of draught for fire, for it must be remembered that the heat must be kept regular at 104°; I, panelled framing of 14in stuff with which the whole is enclosed, save that portion back and front of egg tray; J, covers the right hand one is hinged at the back, the left hand is in two parts, slide right and left. A thermometer is placed in some convenient position, with the ball in the warm water to register the degree of heat. It will be understood that the water being heated at the furnace B, will rise, flow over the glass plate (to the underside of which the eggs are pressed by the springs in tray) in the direction of the arrows through the return pipes (or artificial mother) to the bottom of cistern again. Such was Mr. Cantelo's, and as an egg-hatching machine highly successful; but with regard to the healthiness or longevity of the poor little orphans, I say nothing.-AN

ENGLISH MECHANIC.

[6509.]-GRINDING GLASS STOPPERS.-Faraday says that the best thing is sea-sand, or coarse emery and water. It should be quickly inserted into and removed from its place, and burned at the same time. In this manner the glass is in part worn away and the stopper made tight; but care should be taken that during the grinding the bottle be shifted now and then in the hand, that different parts of the neck and stopper may work against each other at different times, and thus mutually correct the existing inequalities.

AROMA.

The use of hot

[6513.]-INFLAMMATION OF CUTICLE.-I suffered from the same thing, as far as I can judge, for nearly ten years. A weak white precipitate ointment applied Occasionally at night did good, but the pimples always water at night, and cold in the morning for nearly a returned, and at last got very bad. year, and an application of the same ointment at times, routed the enemy at last. Perhaps a little pure carbolic acid and water lotion, added to the morning bath, might prove useful; and, of course, the general health should be attended to.-AMICUS.

[6521.]-SAFETY VALVES.-In reply to " Hammers man" suppose he requires to work his boiler at 10 pe square inch, the..iameter of the safety valve being j to find the weight necessary to counteract the pressure he must first ascertain the area of the vane and then multiply this area by the pressure in pode per square inch, the result will give him the din weight to be placed upon the valve. The calculatzen as follows:- x x ·7854 = 1-16th x 7864 = 19:25 = area of valve. Then '0490875 x 10 = 4963 lb. nearly. I think" Hammersman" will find the ordinary method of obtaining the area as simple as any that is by squaring the diameter and multiplying y 7854.-W. MOOR, Jun.

[6521.]-SAFETY VALVES.-First square 25x5= 625 x 7854 = 0.04908 the area x 20, the pressure re quired = 0:98160 x 16 14-68 or 1402. 5drs.-JACK

ALL TRADES.

[6522.]-PLASTER CAST.-"A Working Shoemaker" must first oil the foot all over, to prevent the plaster from sticking to it. The plaster of Paris being mi with water to a consistency should then be poured o In a few minutes it will become hard, and may them be removed.-L. R. C.

[6524.]-LINEAR PERSPECTIVE. - If the gi diagonal is parallel to the picture plane, the pote distance will be the vanishing points for the the cube, and of course the length of these is the height of the cube; but if the given diaginal is not parallel with the picture, then find its washing point, and draw a line to the station point, and make an angle of 45° with the line, right and left, and conting the lines forming the angles till they cut the herstel line, which will be the vanishing points for the edges –

T. M.

[6524.]-LINEAR PERSPECTIVE.-The diagonal of cube, "given in perspective," may, like any other per spective line, represent an actual line of one foot long or a hundred miles. What is to determine then the size of our cube? And supposing the size and actual diagonal given, it may turn on this line as on an as What is to determine its position?-E. L. G.

cured himself some years ago of a disease, apparently
[6513.]-INFLAMMATION OF CUTICLE.-The writer
similar to the one "F. C. D. is suffering, from by the not given enough conditions; he has only given
[6524.]-LINEAR PERSPECTIVE.-"Thomas" has
following means:-He took about one grain of precipi- diagonal, but the elevation of a diagonal may be giv
tated sulphur dry on the tongue twice a day; anointed and the cube assume a variety of positions by revolving
the affected parts every morning with the smallest round that diagonal. If, however, the elect
portion of a lotion made with equal parts of glycerine two such diagonals is given, the perspective projection
and spirits of wine, faintly perfumed with oil of lavender; of the solid can be obtained. In doing so Thomas
and wore every night a cap made of macintosh cloth. must must use a very fine-pointed pencil, owing to the
He found water always disagree with the disease, but as great number of lines he will have to draw. Let he
a matter of cleanliness he made a point of washing the perspective representations of the two diagonalar
head with warm water and honey-soap once a week.- a bed; through those points, i. c., a bed, drawi
CALIADA.
pendiculars a a, b b, c c, d d', meeting the ground pla
[6513.]-INFLAMMATION OF CUTICLE.- Use a in a' b c and d'; through P, the point of sight, dr
lotion composed of sulphurous acid two parts; glyce- Para", Pb, b", Pec", P dd", meeting the Padicalers
rine, one part; water, four parts. Rend Dr. Dewar's "d"; through a" be" d draw the perpendic
pamphlet oh the subject of sulphurous acid and the a" a", "b","c", d" d", and throngu P draw
treatment of all cutaneous diseases, as well as of Sore Pb b", P c c", Pd d", meeting a"a", "b"
throat, &c., with this great specific.-COMUS.
and dd, in a b c and d respectively; j

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no account allow the water to freeze in his boiler, be-
cause water, when freezing, expands considerably on
approaching the freezing point, and would therefore be
certain of injury to the boiler. I am sure "Steam"
often heard of water-pipes bursting in frosty weather.-
THOMAS J. O'CONNOR.

5ft. lengths diagonally-from one corner to the other; join these pieces edgeways to the two 5ft. pieces, for ming the sides, 22in. at back, 11in. at the front. Mitre or dovetail together, and plane the top surface level. The lights, whether two or one, should be made of wood 1jin. thick, moulded to hold the glass. Join the two back corners; but the front piece should be fastened en underneath, so as to fit into the frame, and form a ledge preventing the "light" from slipping down. It thus carrying off the rain and preserving the frame. also allows of the glass projecting from the woodwork, mortise these in according to the width you desire the Get some sash bars, and cut to the length required;

a" b and e" d", then a"" b" and c" d" will form the orthographical elevation of the given diagonals; to find their plan proceed thus:-Join P with the station point, let the joining line cut the P P in O, then let M and M be the two measuring points; for parallel perspective join M with a' and d', produce M b and M d to cut the PP in land m, and join M with a' and c'; produce M' a' and Me to cut the PP in n and o; produce the lines a" a', b' b", e" c", and d" d", downwards ton lo =a" n, b" l' = "bl, c" o' and m', making a" n' c"o,d" m = d" m; join n'l', and o' m', then n' l' and o' m' will be the orthographical plan of the two diagonals; from these the orthographical plan and elevation of the entire solid can be easily deduced, and the radial both eavalry and infantry. A great advantage in a glass. Give the frame three coats of paint outside; the projection can easily found from this. If "Thomas" experiences any further difficulty, and will apply to me, I will set him right.-B. C. E. BRODIE.

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[6525.]-CAST OF SEALS.-Get some new bread, and rub it up with a little gum-water about the consistence of stiff putty, and press it well into the seals; leave it to dry of itself. You can strike them in fusible metal not with a hammer, but with the hand, just before the alloy sets, the same that you would with a soft medal

lion.-JACK OF ALL TRADES.

[6525.]-CASTS OF SEALS.-If "Beta" would try isinglass or plaster of Paris he would be more likely to succeed. If he uses the latter he must take care to oil the seal first.-L. R. C.

[6526.]-LATHE CEMENT. See my reply to qy. 5423, p. 880. It is a pity that querists do not refer to back numbers before putting their queries. If they did they would save themselves postage and our editor valuable space.-No. 170.

[6526.]-LATHE CEMENT.-Take one part beeswax, E two parts common rosin, two parts whiting; melt the first two together, make the whiting hot, and dry in a shovel or upon a piece of sheet iron; crush it well and mix; pitch and gutta-percha, equal parts, will do, but I do not like it.-JACK OF ALL TRADES.

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[6531.]-FUMIGATION.-It W. Ryan will read let. 1286, p. 449, he will see reason not to rely upon his fumigation solely. All the bedding should be scalded or subjected to the action of steam, the room thoroughly washed, and if possible, re-papered. There is no proof that the vapour of chlorine kills or neutralizes the poisons of small-pox or scarlet fever, or any other animal poison.-M. PARIS.

[6534.]-GREAT PACIFIC RAILROAD.-Precisely speaking, there is no Great Pacific Railroad. I presume that "P. R. R." means the Great Railroad Route

various routes; but the best and most practicable route

[6548]-WAR ROCKET.-The composition used in a war rocket consists of saltpetre 68 parts, sulphur 12 parts, charcoal, or mealed powder, 82 parts. As missiles, these rockets are found to annoy most seriously bardment they speedily set fire to buildings. In the the defenders in any fortified work, and, in a bomfield, the plunging ricochetting motion greatly disturbs rocket is, that it has no recoil against the stand from which it is fired.-DELATEUR.

[6544.]-MAIN STREET GAS-PIPE.-The consumption would be the same in each case, depending only upon the pressure in the main and the size of the aperture. Theoretically, the discharge would be slightly greater from the larger pipe, but the same from each in practice; the increase would be owing to the diminished friction in the large pipe for the same supply -B. C. E. BRODIE.

[6544.]-MAIN STREET GAS-PIPE.-If "Inquisitor"
means only one No. 2 burner, my answer is, the differ-
ence would be scarcely perceptible. Had he said ten,
then I should reply, he would burn more by the in.
than the fin. pipe, supposing the pressure upon the main
to be the same. On account of friction, the longer a pipe
is through which gas is transmitted, the less will be
the quantity delivered, the pressure remaining the
same. Also, a greater proportion of gas will pass
through the larger size pipes. For instance, a lin.
pipe has only four times the area of a fin., but it will
pass nearly six times as much gas; so that it follows,
that the consumption being in proportion to the pres
sure upon the burner, and the larger pipes facilitating
that pressure, you would burn more gas by the larger
pipe.-J. BUTCHER.

[6547.]-THE SLIDE-RULE.-If " Alpha" will turn
to page 356, Vol. XII., of the ENGLISH MECHANIC,
he will find some of the uses of the slide-rule described
there. There are many other problems which can be
worked out with the slide-rule, which I will most wil-
lingly explain for the benefit of "Alpha" and my fellow
subscribers to the ENGLISH MECHANIC. But I think
this subject would be much better treated by Mr.
McEwen, president of the English Mechanic Scientific
and Mechanical Society, Manchester, or some more able
correspondent than myself.-FRANK CHESSELL.
the following methods :-(a.) By heating a mixture of
[6548.]-OXYGEN GAS-May be prepared by one of
ganese. This gives the gas nearly pure, and is the
method generally employed. (b.) When black oxide of
manganese is heated in an iron tube or mercury bottle
in a furnace, oxygen is evolved. The oxygen is never
This process is sometimes employed when large quan-
pure, containing a large quantity of carbonic anhydride.
tities of oxygen are wanted. (c.) When concentrated
sulphuric acid is dropped slowly into a red-hot plati-
num retort, it is decomposed into water, sulphurous
anhydride, and oxygen. The sulphurous anhydride is
absorbed by milk of lime, or a solution of caustic soda.
(d.) Oxygen is also liberated when chlorine gas is passed
through a solution of caustic soda in which a little
carbolic acid has been placed. The solution of caustic
soda is to be gently heated; oxygen is given off in
abundance.-J. W. W.

lights may have one before glazing, and two afterwards. Lime-white the inside after one coat of paint, or without, as you please. If you do the work well, you will have a strong and serviceable frame for about 15s., which would cost, to buy, 303.-SAUL RYMEA.

[6554.]-PASSAGE OF AIR THROUGH FLUES.

Dr. Hayward wishes the best method for calculating the above. The formula given in Ganot and Deschane acceleration of gravity, a the coefficient of expansion is v = 2ga (tt) h, where v = the velocity, g the of air, t' the temperature in the flue, t temperature of surrounding air, h the height of the flue. In the present case g = 82 1724, a = 008665 (t-t)= 10 F., or reduced to centigrade 5.59 C, h = 100, there fore

or

v = √2 × 82-1724 x 003665 x 5'5 × 100
129-7030306 = 11:389

11.389ft. per second.-GEORGE E. DAVIS.
[6556.]-RAISING WATER.-No; you would require
more speed and power to return it.-JACK OF ALL
TRADES.

[6559.]-PURIFYING OIL.-Get a flask of salad oil place it in a cold situation, pour off the liquid, place it in a bottle with some zinc and lead shavings, and in a very little time it will be quite white and fit for use.

JACK OF ALL TRADES.

[6564.]-ENGINE QUERIES.-By placing the slideValve, or plunger (if it be for the pump), in the centre of the stroke, and measuring from the centre of crankshaft. There are numbers of works on engineering that give instructions for getting the horse-power of an engine. The stroke of piston is double the throw of crank.-MACHINIST.

[6564.]-ENGINE QUERIES.-"Willing Parter of 2d. per Week's" first question is rather an out-of-the-way one, for no mechani c would ever think of commencing the engine. If "Willing Parter of 2d. per Week" is to make an engine with the excentric rod. The length of the excentric rod must depend on the construction of

sign and size, and forward them to our editor for insertion, when he will be certain of obtaining all information respecting the length of his excentric rod. In reply to his second question-first find the average multiply this pressure by the number of square inches pressure in the cylinder by means of the indicator, then contained in the piston, and the result by the velocity of the piston in feet per minute, and divide by 33,000, which will give the horse-power. In answer to his last question, all he has to do is to double the length of the crank; thus, if the crank of an engine is 7in., its stroke will be equal to 14in. Further information if required. -THOMAS J. O'CONNOR.

to the Pacific. He would derive a far clearer notion of route, distance, stations, &c., &c., by purchasing for himself "Appleton's Railway Guide," "The Traveller's equal parts of potassic chlorate and black oxide of man- desirous to make a model engine, let him select the deGuide," or "Colton's Hand-maps of Railroads," than from any answer in this way. It would not be difficult for him to get these, should he apply to any map-dealer in London, Liverpool, or Glasgow. Suppose he has reached St. Louis; he may then reach Cheyenne by is that by the way of Kansas City to Omaha, Naebraska, and then on by the Union Pacific Railroad to Salt-lake City, Utah; then by the Central Pacific Railroad to San Francisco. As to the stations on the route, they are not of any great importance or interest, if we except St. Louis and Salt-lake City. From the southern border of Nebraska, all the way to California, the country is barren and exceedingly monotonous. The Rocky Mountains are grand, but dreary-looking. The distance between St. Louis and San Francisco is not far from 2,000 miles. I am sorry that I have not the means just now at hand by which I might ascertain the exact number of miles; but 2,000 is a close approximation. If you should prefer going by way of Chicago, you might find it less tortuous than through St. Louis. There is a railroad running direct from Chicago to Council Bluffs, over against Omaha, Nebraska. As there is hardly anything like first, second, and third class on the American railroads, you would find the fare or charge about one English penny per mile; sometimes a fraction over that; and once in awhile about twopence. I think you can pass from St. Louis to San Francisco for about five English pounds. Stoves, couches, refreshments, water-closets, &c., on board the trains. I give you this information from more or less personal experience.-CAMBRO.

[6535.]-MACHINERY FOR THE PREPARATION OF RHEA.-There is no restriction against foreigners competing for the prize offered.-A. B. B.

[6537.]-LIFT FOR VALVE.-The height to which a valve must be lifted to allow an escape equal to its area may be found by dividing the diameter of valve by [4. The proper lift, therefore, for a 8in. valve is in., for a 4in. valve 4-4in. lin., and so on for valves of any size.-W. MOOR, Jun.

[6537.]-LIFT FOR VALVE.-All Frederick Malvern requires to know is the rule for finding to what height. a valve must be raised to allow a free escape to the steam equal to the area of the valve. This is done by dividing the diameter of the valve by 4; therefore, 3 divided by 4 equals 75in., which is the proper lift the valve should have.-THOMAS J. O'CONNOR.

[6539.]-MANGANESE BATTERY.-The cell is of little consequence; any open porous material will serve, as its object is not to separate solutions, as in other cases, but merely to sustain the solid material.-SIGMA.

[6539.]-MANGANESE BATTERY.-I have, as a rule, found the pink porous cells, which are usually of open texture, to give the best results; but if "Lea" has not commenced to fit them up, and does not object to a little extra trouble, he would do well to read and act upon the letter of Geo. Fox (1386), substituting graphite for the ordinary earthenware.-SIGNUS.

[6542.1-ICE IN BOILER-will certainly strain it dangerously, if it does not fracture it. If you are in the habit of working up to high pressure, an explosion would inevitably follow, unless the leakages were discovered before getting up steam to high pressure. If boiler is weak, the freezing will make it weaker. Blow out when you have drawn your fire.-B. C. E. BRODIE.

[6542.]-ICE IN BOILER.-"Steam" must have a very slight knowledge of water and its properties by the nature of his question at page 504. "Steam" must on

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[6548.]-OXYGEN GAS.-The best thing I can do is
to refer you to Roscoe's excellent little book, "Lessons
in Elementary Chemistry," p. 11:-"Oxygen gas can be
prepared from the air, but it is more easily obtained
from many compounds which contain it in large quan-
tities.
Oxygen can be more cheaply obtained by
heating potassium chlorate (commonly called chlorate
of potash), a white salt which yields on heating 39-2 per
cent. of its weight of this gas. In order to collect the
oxygen thus given off, powdered potassium chlorate is
placed in a small thin glass flask, furnished with a well-
fitting cork, into which a bent tube is inserted. The
lower end of the tube dips under the surface of water
in a pneumatic trough, and the gas, on being evolved
bubbles out of the end of the tube, and is collected in
jars or bottles filled with water, and placed with their

mouths downwards in the trough. The above figure

shows the arrangement of the apparatus. If a small
quantity of manganese di-oxide be mixed with the
potassium chlorate, the oxygen is given off at a much
lower temperature."-A. D. C. C.

[6552.]-CUCUMBER FRAME.-" E. L. D." will find
5ft. too wide for sashes; 4ft. is much the best and
handiest. A 3-light frame, with sashes 6ft. by 4ft.,
glazed and painted ready for use, would cost about £8
108.-UN JARDINIER.

[6552.]-CUCUMBER FRAME. - Get 84ft. of deal, 1 in. thick bv 11in. broad. Cut off three pieces 6ft. long and three 5ft. long. Plane; join two of the 6ft. pieces edgeways to form the back, 22in. high. Cut one of the

[6568.]-COPPERPLATE PRINTING.-Heat the back of your plate gently over a clear flame; then rub your ink into it, and polish it clean. When you have done this, put your prépared paper on it, and roll it through your press two or three times. If you do not succeed, try again.-WILLIE SCORER.

[6569.]-FROSTED SILVER-Use cyanide of potassium with a brush, but do not handle it more than you can help. Get a piece of lance-wood or box and make a pair of wood pliers. An ounce dissolved in a half pint of water. It is very poisonous.-JACK OF ALL TRADES.

fully explained by "Nobody," let. 781, p. 204, ante.-S. R.

[6572.]-THE PEDOMETER.-This instrument was

[6578.]-LETTERING COFFIN PLATES.-Write the letters with gold size, and when getting dry, rub bronze powder over them.-G. F. B.

[6574.]-FROZEN FOTATOES-Are said to be cured

by keeping them in cold water for two or three days

before using them.-G. F. B.

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