of any one who could, give him a satisfactory reply. Magnetism is generally ranked in the same category as light, heat, electricity, gravitation, &c., as a something which decreases in force as the square of the distance from the centre of force increases, and this holds true if we could only find the centre of the force, which must be a mathematical point, and yet infinite as regards the peculiar power it is supposed to exert, be it attraction or repulsion, as T. A." and others may ultimately determine. All that we know is that we know nothing about what an electro-magnet will do when an armature is removed a given distance from its poles, whether these poles are on the surface or removed an indefinitely small distance below that surface; but we have that great lever of Archimedes handed down to us by Bacon, which has been the mainspring of all worth calling improvements in every branch of scientific research, wo have the power to try for ourselves stop by step every suggestion that offers, and we have the privilege of holding fast to that which seems good. (6234.) Kitchen Boiler Taps.-In reply to the first query of "Clericus," I beg to say that there are such taps to be found, since my own, which has been in daily uso for over seventeen years, has never yet shed a tear, when not compelled to weep a torrent. Secondly, the suggestion contained ia query No. 2 should always be carried out in order not only to allow of the boiler being fillel while hot, by gradually adding cold water to that already left in, and by this means continuously kept there, but it also admits of any stray impurities, such as soot, dast, &c., quietly finding their way to the bottom, and remaining there in calm repose, while the pure water is being drawn off. It might appear harsh towards his servants at first, but certainly were I in "Clericus's" position I should issue an imperative should be filled before a fire was lighted, and have a written agreement signed by the servant upon whom such duty devolved, rendering her liable for the cost of repairs or renewals due to the omission of this duty. I do not mean that I would enforce such an instrument in a court of law-by no means; but I believe its bare existence would suffice to ensure constant attention to the performance of this necessary duty. There can only be three causes, so far as I can see, for the difficulty "Clericus" plains of, viz., ill-usage by the servants, bad material to begin with, and worse workmanship in those who grind the plugs in the taps; and he himself can alone order that all such boilers in the establishment com. determine to which of these causes the fault is attributable. I, for one, know that good gunmetal taps properly made will last at least twelve months, even in a locomotive boiler, with steam at 120lb. or more, without requiring to have the plags re-ground, always provided that you have careful men footplate, who are far-sighted enough to see that their own welfare is inseparable from that of their employers, and plenty of such can be found. on the (6295.) I see no reason why soaking the points of the type in turpentine for a short time and then well orushing them should not succeed in cleaning them without injury. (5833.) Elementary Mathematics (U. Q.)—If "T. S. H." will purchase "Plane Geometry," Chambers's course, price 2s. 6d., he will find at the end of the "first book" 28 problems given as exercises upon the propositions of that book. Let him bring these one by one before his "science class," that the members may exercise their ingenuity in trying to demonstrate them, and in the event of their failure, and it being beyond his powers, if he will send those problems which they cannot solve one at a time to "Our Paper," I believe I can answer for the Editor admitting them, and feel quite sure demonstrations will be given by some of our contributors. When these 28 exercises are thoroughly mastered by the "class" it will be fully prepared to enter upon the "second book." I will offer one exercise which I have never seen published, but I do not claim having originated it. "The semicircle upon the hypothesis of a rightangled triangle is equal to the sum of those formed upon the base and perpendicular, and if the semicircle upon the hypothenuse be continued, the sum of the two lunes thus formed is equal to the original triangle." I have several more in my repertoire all of which will be at the disposal of "T. S. H." from time to time if he should continue his class, and if he will urge upon those who constitute it the great necessity that each and all should get for themselves a demonstration worked out by their own industry, totally independent of adventitious aid, for by such means only can a usefnl knowledge of any science be obtained. Still there are difficulties insurmountable to the unaided in their first struggles with every science; my will is good to lend a helping hand in all such cases, and I do not think the lever has yet grown too rusty on its falcrum, so as to render it unavailable (in geometry at all events). Hence I even apologize to "T. Š. H." for having allowed his query to remain so long unnoticed. WM. TONKES. [We have omitted the introductory passages of the above letter as they consisted of sundry raps on the respective knuckles of J. Howard, J. Barwick, and Bernardin. Had they been printed, probably each of these correspondents would have returned the compliment, and so space would be almost unproductively occupied.-ED.] MOUNTING IN CANADA BALSAM. [1340] HAVING had some years experience in mounting microscopic objects in Canada balsam, I have read with interest the letters of Mr. White (1156) and "H. P. H." (1251), on the subject. They show how we each succeed in different ways if we set rightly to work. During the first few years of my work I used pure balsam, and experienced the inconveniences so well described by "H. P. H.," and in a while my balsam got too thick to use without heat. At this time a friend told me of thining it with chloroform, which I at once did, and have ever since used it in this way with perfect satisfaction. The convenience in mounting delicate objects when you have to let the balsam flow under the cover-glass by capillary attraction from one edge for fear of displacing the objects, is very great. As to evaporation, Mr. White's friend who pulled a long face at the disappearance of his chloroform, could not have had it in a proper sort of bottle. If kept in one of those made for the purpose, with glass cap ground to fit correctly, it will remain fluid for any reasonable time. By my side is one of these bottles with balsam thined with chloroform two years ago still in a nice state for mounting. Of course the cap is only lifted off for a moment just while the dipping tube can be lifted out and a drop deposited on the slide. I do not estimate my expenditure in chloroform at fourpence a year. I hope Mr. White will be enabled ere long to introdace his new medium, so kindly hinted at, to his fellowlabourers in microscopy. MODERN ARTILLERY. E. G. [1341] WOULD you allow me to call Artillery Captain's" attention to the following facts ?-He says (let. 1223) a grape shot consists of iron balls held between circular plates of cast-iron. The plates he mentions are perforated with six large holes, for the sand shot to rest in, but the bottom plate is a strong solid wrought-iron disc, to act as a wad. If a cast-iron plate was placed next the charge, it would be broken up, the greater part of the gas escaping through the fragments and balls, and not giving the shot the full effect of the charge. The powder channels of common fazes are filled with rifle powder. Mealed powder damped with spirits of wine would burn too slow, and interfere with the ARTILLERY GUNNER. action of the fuze. THE DIFFICULTIES OF METEOROLOGICAL OBSERVATIONS IN COLD CLIMATES. [1342] MOST meteorological text books give very little information on special points to be considered in taking observations in cold climates, or perhaps pass over the question by some such remark, under hygrometry, as, when the thermometer is below freezing point, the wet bulb will often read higher than the dry I find by careful observation, that except when the wet bulb is passing the freezing point, there ought to be no more uncertainty when the temperature is below than above 32 Fahr., but that a difficulty exists when the temperatare is passing this point. I have had this exemplified a few times this winter: on December 13th, with a rising thermometer, the wet bulb was covered with ice at 9 a.m., the readings being dry 33-2 Fahr., wet 32° Fahr.; but by 11.30 a.m. the dry bulb had risen to 36-2 Fahr., the temperature of evaporation still reading 32° Fahr., but the ice melting about that time, the readings at 1.30 p.m. were again probably correct, being dry 376 Fahr.) thus showing that for some hours wet 354 Fahr.) after the air temperature passes the freezing point, the readings are unreliable. On the 18th ult., with a falling thermometer, although at 9 a.m. the wet bulb was covered with ice, the readings were dry 27 Fahr. The conclusions to be drawn are identical with those of December 13th, that these difficulties, arising from latent heat, can hardly be overcome, but should be carefully watched. wet 27-3 Fahr. I have said that there ought to be no uncertainty when the temperature is below freezing, so long as the wet bulb has passed that point for soine hours. In the first place, of course, the differences of reading being very slight, the hygrometrical thermometers must be of the best quality, equal sized bulb, &c., and should be divided into tenths, or the observer should have had considerable practice in reading very exactly, for I am persuaded any careful observer can distinguish to the tenth of a graduated degree, even where the divisions are not large. Another important point is, the readings must be taken by the observer the instant he comes to his instruments, for the influence of the presence of his body when the temperature is low is very great. I have seen my dry bulb rise 2 Fahr. while I have been writing down my observations, although holding my breath. The next point is the one to which I wish especially to draw attention, as I consider it has been much neglected. The ice must have been allowed to freeze on the bulb several hours before the observation is taken, as it is a long time after the bulb is wetted before it arrives at the correct temperature; but in cold weather, when the evaporation is slight, it is quite often enough to obtain a fresh coat of ice every four or five days. I have found this winter, through a series of observations, that at least seven or eight hours is the time that should be allowed to elapse before the reading is taken. As an example, on December 29th I fastened a piece of muslin on my dry bulb and wetted it at 9.45 a.m., when a coat of ice formed in a few minutes; the wet bulb had been wetted a day or two before, and had a good coat of ice on the muslin. The following are the results: Bulb with fresh coat of ice, 10-15 a.m., 18° Fahr.; 10:45 a.m., 18° Fabr.; 11-15 a.m., 188 Fahr.; 11:45 a.m., 18° Fahr.; 12:20 p.m., 1999; 139 p.m., 20 Fahr.; 3-20 p.m., 20° Fahr. Wet bulb with old ice, 10-15 a.m., 16-6° Fahr.; 10:45 a.m., 179 Fahr.; 11:15 a.m., 189 Fahr.; 11:45 a.m., 17-29 Fahr.; 12.20 p.m., 189 Fahr.; 1:30 p.m., 19-89 Fahr.; 3-20 p.m., 198 Pa The next morning at 9 a.m. both stood at 10 Tak Observations with the thermometer oscillating from 7-7 Fahr. to 12.9 Fahr., and down to 1-2 Fahr., somewhat similar results. At 3-20 p.m. there a again a difference of 0.2, and both corresponded the following morning. How should the instruments be placed? After winter's experience of the climate I carefully sidered the question, and concluded, in order that the bulbs may be kept free from snow and conden moisture, or even rain freezing and so reducing fe dry bulb to the same condition as the wet, that enclosed box was the best. But there was a biched reason, not less weighty; as the ground is covered with snow all the winter, the radiation therefrom work effect thermometers exposed to this snow radiator some extent, even when placed in the shade. This! have proved to be the case by a thermometer ha outside my box, which stands in the shade. In here point out the immense power of the solar raha tion. The mean daily difference between the max mum solar radiation (registered by a black baba vacuo) and the maximum air temperaturs, November, 59-3 Fahr.; and for December, 52'6 Fair to January 21th, 53-8 Fahr. On the 25th December, the difference between the maximum solar radise and the maximum air temperature even reached 17%, the black bulb standing at 108-8. The observations taken here for the Swiss Meteor gical Society are taken from instruments in a zir: placed immediately outside a window which is free from sunshine, until a few minutes after 1 p. the hour of observation. It seems that some Germa text-books advise such a position, but I should be su under any circumstances, to be reduced to at protected situation; and surely in such a ca where all radiation ought to be avoided as mache possible, the immediate neighbourhood of a vine house must be one of the most unsatisfactory. Th box which I use is double, with a space of bin. at all round between the two, both with open Venets work, permitting free play of air; the top and b of both boxes also allowing the air to enter. It stand a little more (on account of the snow) than if fres the ground and 20ft. from any building, without any protection from wind. The last point which I will touch is the difficulty a comparison of the hygrometrical condition of the atmosphere, arising from the amount of rap required to saturate it, being at a very low tempsa ture so small. To make this clearer, I will take Davos mean temperature of last December, 17 Mar and compare it with the December mean of San Be for the last few years, i.e., 52° Fahr. Supposing the air in both cases to be saturated, we should hers have 11 grs, of vapour per cubic foot, while San Re would have 44 grs. per cubic foot; and next to pare the Davos December mean of moisture for 15, with 87 per cent. moisture, we have here 0967, p. cubic foot, while San Remo would have with 87 per 8:12 grs. of vapour. Now, while the percentage must be one of the ex important hygrometrical observations, for allposes, it is of the utmost importance in extra climates that the hygrometrical conditions shotil be compared by other means. Dr. Spengler, as pamphlet on Davos, feeling the difficulty, gives t pressure the moisture in the air exerts on the meter, but this does not at all get over the dificulta the height of the place (about 5000 English feet a difference of over 5in., there is still for compani correction of about to be made. The connderba of the meteorological in correctness of such ded from the lower stratum of air only, does not lie wa the purpose of this paper. In the snow months, in this winter residence for sumptive invalids, when with an average cold a under 20° Fahr., or 25 Fahr., the amount of m is under 80 per cent, it is perceptibly esta irritating to the patients, and with 95 per cent. at always feel very dry, and even when saturated feelings entirely mislead. In consequence, I marat that to compare the hygrometrical condition, comparison of the weight of moisture is in cold clima scarcely of less importance than that of the per The adopted height of vapour in a vertical coluna « the atmosphere is also useful, but it should beste rected to the sea level; and this seems a more re able method then calculating the amount of vap the height of a column of quicksilver. ARTHUR W. WAS Davos am Platz, Switzerland. ANALYSIS OF SILVER AND LEAD ORES [1343] WITH reference to "Un Irlandais" (let. 1220, p. 429), I hasten to redeem my war the processes for analyzing ores to be applied to th forwarding him the modifications necessary to containing copper: quires no alteration beyond the substitation of her No. 1 (p. 207, let. 798, 18th Nov., 1870). This nitrate for hydrate, and the copper remains in HS precipitate, from whence it can be dissolved potassic cyanide. No. 2 requires that the arsenic trisalphide solved out from the mixed precipitates by potat hydrate. No. 8 will need no alteration at all. Nos. 4 and 5 would require thorough reconstra to suit them for a coppery ore. P I had no leisure when I wrote last to look through the processes, and so did not notice the slight alteration they required only. I also send "Un Irlandais" a method for estimating the three elements in a complicated ore analogous to the German Fahl ore, and containing some or all of the following elements:-Silver, lead, iron, copper, zine, barium, calcium, antimony, manganese, potassiem, sodium, arsenic, sulphur, and magnesium. Boil the powdered ore with pure fuming nitric acid, until it is thoroughly oxydized, adding, if necessary, potassic chlorate; dilute well with water and add ammonic chloride as long as a silver chloride falls, and filter. Boil the residue with potassic carbonate and acidify with nitric acid; filter, and throw down with baric chloride the sulphuric acid; estimate this as sulphur No. 1. (To be added to sulphur No. 2.) To the first filtrate add excess of baric nitrate, heat cautiously and filter. Treat this precipitate with hot hydrochloric acid, wash well, and estimate as sulphur No 2. (A slight loss is unavoidable; if, however, antimony is not present, then by avoiding the treatment with hot HCI., this loss does not occur.) To the filtrate add ammonia until the solution is but weakly acid; boil with sulphurous acid, and pass through sulphuretted hydrogen, and filter. The precipitate is to be treated with potassic hydrate or sul phide, to dissolve out the arsenic trisulphide; and if antimony be present, separate any sulphide by reprecipitating, and dissolve out the arsenic with bisulphide of potash or carbonate of ammonia. Estimate this sulphide as arsenic. anger instead of "showing cause," and excuse one who, CRYPTOGRAM. [1846] I BEG to send IGNORAMUS. you a cryptogram or When a sentence is written, fill the open places with are the only counting letters, cancels all the other, and ongsoupe r4lan3f [5716.]-STEREOSCOPIC LENSES.-"M. P." may depend upon it I have not fallen into any error on the subject at all; and if perspective be" valuable to a portion of his profession," I would strongly advise him to apply to its simplest rudiments till he gets rid of his present delusion utterly subversive of them, that a photograph embracing The filtrate from the sulphuretted hydrogen is to be boiled to expel all traces of it, and excess of ammonia added; filter rapidly, and wash well with a solution of ammonic chloride and ammonia. If it is feared that The receiver having cancelled the filling letters there slide was taken. The moon views are taken with perhaps this treatment has not removed all traces of manganese, redissolve in acid and separate with sodic hypochlorite, re-precipitate the iron with ammonia. Estimate as Fe. In conclusion, "Un Irlandais" must accept my thanks for his kind offer, which I shall not hesitate to accept whenever I should require the assistance of his doubtlessly superior experience in various branches of assaying. URBAN. remains: D D on the upper line is e, k on the lower line is 1, of, for quantity, say about 1oz. for 5lb. brass, put brass &c., and the sentence is ENGLISH MECHANIC. Of course eight other letters can be taken instead of DECIMAL POINT. ter's letter (1258), in which, in answer I think to "Ber- in first, then borax; then cover about fin. in powdered charcoal or otherwise; without a lid the metal would oxidise and take longer to melt. It will be quite fluid enough if made hot enough. Use pair of tongs to handle crucible with; any smith would make a suitable pair if you show him the pot. Plunging the red hot castings into cold water makes them tough, or add a little copper, tin, antimony, and old bell-metal to harden the metal-GODSTONE LABORATORY. make real life-buoys and rescue the poor sailors from the [5758.]-OLD CORK-CUTTINGS.-Let T. Taylor fate of buying such deceptions, so ably exposed by the "Amateur Casual."-T. BURSTALL. ANALYSIS OF CUPRIC AMMONIA AND CLAYS. [1844] IF "Un Irlandais" (let. 1238, p. 424) will refer to Fresenius in his description of Mohr's process for estimating copper by the decoloration of an ammoniacal solution by potassic cyanide, he will find that celebrated analyst's experience is very different to his, and that he found it perfectly essential to its reliability that the same proportionate amount of ammonia should be always used. Sutton, of Norwich, found an error of 1 to 8 per cent. arise in his experiments on the same, owing to an increase in the proportionate amount of ammonia he took, a result I have had confirmed by a number of experiments, and which the theory of the process points out must be the case. However, this drawback to the process is very well known; and I can but congratulate your correspondent "Un Irlandais " on his marvellous good fortune, although he must have and some trouble in making an estimation of the cop- EXTRACTS FROM CORRESPONDENCE. moved by a square graver, it is then ready for using off per by another method to be sure he had not erred as much as two per cent. J. K. P. [5753.]-OLD CORK-CUTTINGS.-These may be emploved in the fabrication of Spanish black, or of kamp. tulicon, or of life-buoys, or in "phelloplastic "-i.e., making imitations of ruins, &c.-BERNARDIN. first shaped in a die, then legs soldered on with hard [5761.]-WATCH DIALS (U. Q.).-The copper dial is solder, then hard enamel for bottoms spread underneath) then the soft enamel is spread on the face of dial, after which it is fired on a proper ring in a muffle. It is when cool examined for specks of dirt, &c., which must be rethat is, rubbing the face on a grit stone with fine sand and water until the glaze disappears, it is then washed clean in water, the speck holes filled up with finest enamel, then placed in furnace again, very gradually rais Mr. Hicking (qy. 6293) asks a query that requires a fuller answer than at present I can spare time to give, and I must admit I do not know what is the with an Enfield rifle. I have since heard that some one ing the heat for fear of cracking until it is fused; then method generally employed, as it would vary with every sample, and usually with every analysis. Generally speaking, though as far as clays were alone concerned, the method pursued would be very analogous to the following: The determination of the organic matter, moisture and nitrogen would be done as usual, and the percentage of carbonates estimated by Mohr's method for clay, marls, chalks, &c. EDUCATING THE EYE.-The sight with cross wires (see selected article, p. 393) was used byme many years ago else tried it at Wimbledon. I cannot see how it would dispense with the necessity of having three objects in a line-namely, the intersection of the wires, the bead at the muzzle, and the object. It is certainly a great improvement."-M. PARIS The mineral constitutents analysed qualitatively as usual, being brought into solution by boiling with sul-night and morning, up to six or eight for adults. It is phuric acid. To separate for quantitative analysis, treat the clay with boiling sulphuric acid, and evaporate to near dry ness, and dissolve in hot concentrated hydrochloric acid. Boil the residue with strong potassic carbonate solution. The residue is the percentage of sand, &c. Precipitate the potassic carbonate solution with sulphuric acid; this gives the percentage of combined silica. The diluted hydrochloric acid solution is to be treated with sodic bicarbonate, filter rapidly and wash and dry the precipitate, which separate into aluminum and iron by hydrochloric acid and potassic hydrate. The manganese is thrown down from the filtrate by hypochlorite of soda, and the filtered solution treated with oxalate of scda to precipitate the calcium; and Ammonia and sodic phosphate to estimate the magnesia. The only acids then to be looked for are phosphoric and silicic acids. URBAN. NITROGEN AND HYDROGEN. (1345) I SHALL be obliged if "Sigma," "Urban," H. P. H.," or any other of my fellow-readers who are chemical experts, would say what compounds, if any, nitrogen forms with the metal titanium and with boron, also the properties of these compounds? I also wish to be informed if hydrogen forms compounds analogous to alloys with any other metal than palladium, and if so their distinguishing properties. Will any one also inform me what are the grounds of Dumas' hypothesis that chlorine, iodine, and boron are merely allotropic conditions of one substance. I sincerely trust my respected fellow-reader "H. P. CHILBLAINS.-An eminent London surgeon writes in the Lancet stating that for this prevalent and painful malady a perfectly safe and effectual remedy is obtain able in the employment of laudanum, taken internally in very small doses of from two drops for young children in such quantities perfectly harmless, and as a rule will medical man also states that he finds an excellent effect a cure in the course of four or five days. Another remedy in the new disinfectant chloralum for unbroken chilblains. It should be applied undiluted night and morning, using a moderate amount of friction.-P. F. Mr. WIT AND SCIENCE.-M. Paris thinks our scientific LOW WATER DETECTOR.-M. Paris cannot see why the piston (letter 1219, p. 420), should not be kept LOW WATER DETECTOR.-"I fail to see the prin- is made of the cannibal mode of hardening wood, i.e., HARDENING WOOD.-"M. P." wonders so little use poker. It is as hard as bone. place until well glazed. It is now ready for figuring, take out and breath on it for a few seconds and then rewhich is done with very finely ground black enamel in oil of spike lavender or oil of turpentine, generally the former, the divisions marked with a division plate and index in black pencil, the circular lines with compasses, on one leg a cone to fit the centre hole and the other a port crayon; when the painting is perfectly dry, the dial is once more fired. To make the enamel is very difficult, and most enamel makers think they have secrets better than their neighbours. They are, however, as far as my knowledge goes, made with a vitreous base, composed for the most part of silica, minium, nitre, and borax, coloured by additions of various other oxides of metals; and rendered opaque by oxide of tin or antimony and for black enamel oxides of copper, cobalt and manganese, one to two parts of each. Can be bought cheaper and better than you can make a small quantity of Lowe, in Wilderness-row, Aldersgate-street, London.-GODSTONE LABORATORY. thin steel, file the joint clean, moisten with borax and water, dust on some finest spelter, get a pair of thick tongs (blacksmith's) make white hot in fire, then pinch the steel together until the spelter runs; then cool with water before taking tongs off.-GODSTONE LABORATORY. [5775.]-BRAZING STEEL (U. Q.)-If narrow and with the method by which makers to the trade make [5798.]-VIOLIN PEGS (U. Q.).—I am not acquainted pegs. I can only state my own experience, which is as gin. in thickness; lay down a good peg for a model; follows:-Cut the material 24in. long; then into pieces draw a line up each side of it; this will make it about lin. at one end, and ĝin. at the other, which is quite large enough; cut them out in the same manner as a joiner cuts his wedges, which saves material. I then screw the square hole chuck into the lathe mandrel; this holds the smallest end of the intended peg; the poppit head point into the head or broad end; roughly shape out the head; then turn and finish off the shank to the right size and proper taper; unscrew the square hole chuck, and replace it with the face-plate; on this screw a piece of hard wood 2in. square; bore a hole up through in the centre perfectly true. I managed it thus: poppit head. This chuck holds the common centre-bit; I screwed the square hole chuck into the barrel of the it is moved forward, the lathe revolving, and the bit travelling forward. A perfectly true hole is thus made. This is widened with the taper bit, so that the shank fits nearly up to the neck; the head is then finished crown, and a piece of ornamental wood inserted, cut o Colorado (U. S.), has built 295 miles of railroad in the with a thin sharp chisel; a hole is now bored into th H.," who scolded me so heartily, will not again show last nine months. flush and turned smooth; the piece of wood on face- [5820.]-GLANDERS (U. Q.).-"Youatt" begins by [5829.]-IODINE IN MILK (U. Q.).-Why ask the question in such a stupid manner? The result would be ten drops more in the glass than before. mean its physiological effects on men or the compound Do you formed?-GODSTONE LABORATORY. [5888.]-ELEMENTARY MATHEMATICS (U. Q.).Let "T. H. S." and the others of the class, work the exercises at the end of Todhunter's, Pott's, or Green's "Euclid." snap the teeth of hard saws. Either of these can be regulated to any required set. Saws may be set with a small hammer, with chisel end, to be laid on the endwise of a hard wood or lead, to hit with a very accurate blow every alternate tooth; but the best way of setting I have experienced is with a small hand punch and a ligi.t hammer. Have the hardest piece of wood to be procured, fix it firmly in a vice or bench screw, lay the saw side on it; begin at the heel of the saw and work to point, striking the punch very nice and even. This "R. S." will find to be the simplest and most correct way of setting any kind of saw. Proved.-VELOCER. [6052.]-GUN LICENSE.-If "A Solicitor" will peruse question and answer herein with the care which we will hope that he bestows on his clients' papers, he'will see that we do not differ as he somewhat hastily concludes. The querist asks "if a gun license will authorize him to carry an air gun ?" The reply is that as any one could do this heretofore without special authority, and as the possession of a license removes the disability which the act creates, he, as the possessor of such license can do with it exactly as before the act he would have done have not by me the statute itself to refer to, but I hope without it. It is true, as "Solicitor" supposes, that I nevertheless that a re-perusal will leave him without that whether a gun license is needful for the querist it any objection either to my argument or the conclusion is also all sufficient."-J. B. PRIMUS. [6067.-AREA OF HEATING SURFACE.-On the Continent it is usual to provide in the case of vertical semiportable"Field" boilers 16 square feet per effective If any difficulty arises in the solu-horse-power, except in very large boilers (say of from 30 tion of them let it be placed among the queries in our to 80 horse power), when 18ft. to 14ft. is considered suffipaper.-C. M. H. C. cient. I have numbers of 2 to 3 horse-power boilers of this class in work in which about 48 square feet of total heating surface is provided, and I do not find them to produce too much steam for very well-constructed engines of 54in. diameter of piston, 9in. stroke, making 120 revolutions per minute under steam of 60lb. per square inch above the atmosphere. The cut-off being at five-eighths of the stroke, the quantity of steam used per hour may be roughly assumed at 1,000 cubic feet, represented by 2-6 cubic feet, or 1621b. of water evaporated per hour. This again represents an evaporation of 3lb. of water per square foot of heating surface per hour, which scarcely comes up to the power claimed for remark that the draught is not urged by turning the this class of boiler by its advocates. I should, however, the boiler is probably not worked to its full capacity. waste steam into the chimney, and that consequently Allowing 50lb. of steam per hour passing through the engine as sufficient to give off one effective horsepower, the duty performed by this boiler will be about 3 horse-power. The consumption of fuel (coal) per hour in a grate surface of 2 square feet is about 221b., evaporating, therefore, about 71b. of water per pound of coal, and consuming per effective horse-power per hour about 7lb. vertical semi-portable "Field" boiler would have 84 N.B.-In England a 6 horse-power square feet of total heating surface, and cost about £100. On the Continent it would have 94 square feet, and cost about £85.-E. W. A. [5852.]-SKATES (U, Q.).-Plates of iron or brass are fastened on the iron instead of clogs. Holes are bored through the plates, by which they are fastened with short wood screws to the boot; this is the most practicable method that I know of. Most of the others are patented.-EKLOM. [5901.]-MEDALLET.-I have unaccountably overlooked this query until the present moment. The medallet inscribed The haughty queen humbled by the King of Prussia, 1757," must refer to the victory of the Prussians under Frederick II. (the great) over the French at Rosbach and at Lissa, 1757. most likely means France.-HENRY W. HENFREY, The haughty queen M. N. S., &c. [5922.]-CEMENT FOR LEAD FLATS AND GUTTERS.-I can fully sympathize with "Meunier " on the annoyance he has experienced with his gutters, having gone through all the same troubles myself. I cannot give him the reference he requires, my Vols. being at the binder's, but I will give him my experience. Take gutta-percha, one part, best pitch, two parts, melt them thoroughly, and stir well until perfectly fluid, and well mixed. Clean the gutter, especially about the crack, and warm it slightly, pour on the gutta-percha and pitch, and spread over the crack. When nearly set, take a warm soldering iron and smooth over the edges. He will find this a most valuable recipe for the purpose, and worth to me all I have paid for the MECHANIC, and I am an old subscriber.-T. BURSTALL. [5992.]-PROBLEM.-To find an oval of given surface is there not a condition left out? Thence the area of an ellipse being ab. m, there are two undetermininated quantities in the problem.-X. Y. [6029.]-ANIMAL CHARCOAL AND FILTER.Animal charcoal, or bone-black, is made by calcining bones in closed vessels. Two methods are adopted, in one of which the bones are calcined in retorts similar to those used in the production of gas; and in the other, the bones are placed in iron pots, two of which are placed together imouth to mouth, and luted with loam. A number of these are placed in a kiln! somewhat similar to that used in the manufacture of pottery, and submitted at first to a gentle heat, which is gradually raised and maintained at a high temperature for about eight hours, after which the fire is allowed to slacken for about six hours, and the doors of the ash-pit and furnace are then opened, and the kiln permitted to cool. The pots are taken out, and their contents emptied into the magazine, when pots are ready to repeat the process. If calcining in retorts is adopted, the bones, after the application of heat, are thrown into an air-tight receiver, where they remain till cool, After calcination, the bones are broken up by means of grooved rollers, and sifted to separate the dust. Bone-black is employed to clarify sugar, and is "restored " over and over again by washing and re-baking. It can be bought of the makers (see "Post-office Directory," Charcoal-makers), and also of some seedsmen and nurserymen in London, who use it mixed with cocoa-nut fibre for growing tulips and hyacinths, and other plants. I believe it is an excellent manure for all kinds of plants, whether in pots or the open ground. The latter part of the query I cannot answer.-H. U. [6034.]-BILLIARD BALLS.-If "Ben. G." has not yet succeeded in colouring billiard balls red, perhaps the following recipe may be of use to him :-Take grms. of picric acid, and dissolve in 250 grms. of boiling water; add, after cooling, 8 grms. of liquid ammonia. Dissolve also 2 grms. of crystallized fuchsine (magenta) in 45 grms. of alcohol, dilute with 373 grms. of hot water, and next add 50 grms. of ammonia. As soon as the red colour of the magenta solution has disappeared, the two solutions are mixed together, making a bulk of liquid amounting to about litre, which is a sufficient quantity for dyeing from four to six sheep's skins. Ivory and bone should be placed in very weak nitric or hydrochloric acid first, before immersion in the ammoniacal liquid; wood cannot be dyed by this liquid unless it has been previously painted over with paste made from flour. When to the ammoniacal liquid some gelatine solution be added, it may serve as a red ink, which does not attack steel pens. By varying the proportions of the magenta and picric acid the tints obtained may be varied from a bluish red to a bright orange-red. The desired colours do not appear until the ammonia is evaporated. This solution may be used for either ivory, bone, or horn.-H. U. [6047.]-SETTING SAWS.-If "R. S." will ask at any respectable tool shop for a 38. 6d. spring punch sawset, he will get a tool that will do him justice. It is rather tedious at the first, but patience will master. There is another patent set, about the same price, used instead of a punch with a lever, but this is liable to [6071.]-BULLET-PROOF CLOAK.-The only thing I can say about the bullet-proof cloak is to repeat a story told of the Iron Duke. A person called upon him requesting his patronage for an invention of his of a ballet-proof jacket. The Duke made no reply, but ordered up a file of soldiers and told them to load with ball cartridge. He then told the inventor to stand at the end of the room, and the men to take good aim. The poor fellow turned pale, and "skedadaled" at his greatest speed. The Duke was never more troubled about such inventions.-T. BURSTALL. [6079.]-THE AURORA.-" Aroma " (p. 405) remarks: "An Aurora is seldom seen in the morning." His reChristmas Day, 1860, at about half-past one p.m., from mark reminded me of one observed in full sunshine, on the Derby road, on the way from Osmaston to Ashbourne. The sketch which I send shows its position in clouds, mostly in pairs of linear form. radiated t N.E. to S.W., while the centre point of the radiati the Aurora was N.W. I lost sight of the phenome upon entering a house in Ashbourne, facing the S REV. GERARD SMITH. [6093.] STRAIGHTENING SAW.-If "Baiker" has not tried "Jack of all Trades" remedy, let first try this. I think the fault of the crook is n buckle in the plate of the saw. Let "Builder" take blade and back out of the handle, and ease the lane where the back fits close beneath it in the handle, r he has done this put the parts together, and he lightly tap the back at both ends (not in the mid until the teeth are straight. Too often the cripple a saws is because the back fits hard against the at the underneath edge. If this remedy does no g "Builder" could do no better than try "Jack of Trades'" directions. Proved.-VELOCER [6122.]-POULTRY BREEDING.-As Mr. Wher to examine two authorities on the point as to whe challenged my reply on this subject I took the tro Brahma Pootres are a distinct breed or not. This the in fact grey Cochins, crossed with the Buff Shangh result. One says:-" The fowls known by this na have before stated, and I now repeat, that fats certainty of origin seems to be here demonstr purposes they are worthless." The other says:-"To by great uncertainty of both plumage and featur the birds erroneously, as we most assuredly th denominated Brahma Pootras- understanding th term to depend on their specific distinction from Shanghae-there are two sorts.... Combs mest bes be described as various, running from the single mation through gradations of a Malay character to triple-folded or pea-comb." Now if Brahmas distinct breed what is their origin? I do not they come from the jungle-fowl, of India or from a banks of the Brahmapootra.-SAUL RYME [6127.]-CEMENT FOR INDIA RUBBER TIRE FIG.IFIC.2 FIC.3 My method is to t annular iron plates wheels, turning u side edge as the 3 sketch, Fig. 1; R, rim of weed.. iron side-piece fa india-rubber tire les laid in the grow formed, the ira pare are pinched toget shown in Fig. 2. 'Here T is the tire; this secures tire in its place. The pincers or nippers I use are stor in Fig. 8; they are provided with long handles, and jo large enough to embrace the tire.-B. C. E. B [6170.]-VALUE OF COINS.-No. 2 a satirical struck in 1545, I think, in Germany or in HallastBERNARDIN. Correspondent" and "Sigma" for their replies to [6180.] CONSTANT BATTERY. A "New Ba The battery will neesm time to time the addition of sufficient water to com sate for evaporation. Six cells will do a great deal work. B. A. [6187.]-SCRAPING SLIDE-VALVE FACE-I used several kinds of scraping tools, but find a cut flat file, cut off about 6in. long, flattened out an about 1 in. wide, and sharpened on oil-stone, to be Sa cheapest, and answer the purpose as well as any use it almost the same as a chisel, holding the farther from the work; it should be flat at the end, that you will have two edges to work with.-J. W.A [6192.] VARIATIONS OF CURVES-Whats "W. W." might mean, there is not the least used trigonometrical tables, or any calculation beyond "rule of three," in the case of circular ares as l those he names, or indeed any under a degree. Pa tically, the versed sine is to the sine, as the latter is the diameter of circle. Thus, the distance of the of his first arc from its chord is the same pert half-chord, 6in., that 6in. is of 2 miles. The corr ing distance in his second are is the same part of that 4in. is of 4 miles. For proof, see "Euclid," 1II. 31, and VI. 8.-E. L. G. [6198.]-EQUAL BALANCING.-T. B." is right in saying that the engine should lever (when a bar is applied to the fly-wheel) as casy 7 as going down. To give "T. B." a more explicit ing of the answer, I will put it in the general way a by engineers and valve improvers. When they start new job, the first thing they do after indicating, take all the packings out of the different parts of at the entrance to Dovedale, may be seen in the sketch. the spring-ring out and drop the punch-ring in its the N. W. Beneath it, Thorpe Wood, a cone-faced hill, engine. If the piston has metallic packing, ther one of this generation can forget that Christmas Day, and lower it in the cylinder; when the piston The country at the time was covered with snow. No again, and put the spring-ring on the top of puas but I have not met with one person who saw this re- supposed (in this state) to be without friction. If the markable Aurora. While it was under observation, for is an air-pump bucket, serve that the same, and fully twenty minutes, the longer ray of the silvery white thing else that is packed. This done, they at an crown elongated itself, so as nearly to stretch across the to and make all the valve-levers to angle equal, space of clear sky above it. The air was very still. The they balance the engine with dead weights, and where It is found wanting in this respect they add to more metal in some convenient part of the fly-wheel to compensate the loss of balance. If I understand right T. B.'s" engine is a vertical one. In his case he must lake all the packing out and test it by dead weights at Bach end of the fly-wheel. In the way of illustration, when you have put the piston in the middle of its traverse, ascertain how much more dead weight it takes on one side than the other to move the engine from This position; when you have found this out, it is an asy matter to devise means to add as much metal to some convenient part of the wheel that will make up he balance. It is a matter of impossibility to get equal teaming and steady running in the engine and nachinery without equal balancing. We might as well ry to make the engine go without steam.-EDWARD MALBON. [6201.]-PUNCHES.-For a "Blacksmith's" informadon I wish to inform him that they are made by the proess of heating red-hot, and forging into the required hape. The cutting of the letters is done by a tool alled a counter, which fits inside the letter, and is track into the punch; the rest is taken away with hisel, file, and graver.-EKLOM. [6201.]-PUNCHES.-"A Blacksmith" surely does hot want to know how punches are made to stamp the igures, &c., on iron; if he does, get a hammer and hit he head of the punch while holding the face of it in ontact with the article to be marked. But to make the vanches or dies requires patience and time, with a good tock of small punches, with round, square, and any haped face that requires making on the punch wanted. do not think any information can be given which Tould enable "A Blacksmith" to make one. Get a piece f steel, soften it, and try a simple cross or star first. set of figures or letters can be bought cheaper than A Blacksmith" could make them.-W. FRED. ROE. [6210.] PREVENTING SPINDLE HEATING. Perhaps "Guillaume" will find, if he examines his earing, that it requires re-adjusting and cleansing. apposing it heats, then apply a little brimstone.W. B. (6215.)-RIPPLES AND WAVES.-"M. P." desires to e favoured with "what is new" on a subject of great athematical difficulty, on which elaborate treatises ave been published, the last and most profound being your present Astronomer Royal. What he means by de waves from a stone in a pool increasing "in ampliide and altitude" I cannot tell. I always see them derease in every dimension except ring-like extent, and ever knew that waves increased in altitude of themalves, except in passing from deeper water into shalwer. As for " amplitude," if it means breadth from the rest of one wave to the crest of the next, this increases decreases as their rate of progress does, and the veloity always increases with the depth of water. The only ew remark I can make is that miniature waves of slow rogress can be very prettily seen in a shallow liquid overed by a deeper one of only slightly less density, as ethylic spirit and benzole.-E. L. G. [6222.]-DRAUGHT IN ENGINES.-I think "Marn" has not been explicit enough to enable one to anver his query. I have found portable engines by some akers very deficient in not having any hood on chimay, which will sometimes make great difference, allow g the wind to blow down. But if made by a good aker, I should say if tubes are clean, fire bars in rder and clean, and having exhaust steam in chimney, would certainly draw; but if not, I should advise a eam jet discharged in chimney from a jin. tube, leadig from top of boiler.-J. W. B. kindly publish. 1st. Take a piece of flat brass, about 4in. long, and 24in. wide, and draw a line up the centre of it. 2nd. Near to one end strike a circle A, the exact diameter of the escape-wheel, then with the same radius strike the circle B, so that it will cut through the centre of A; then, still keeping the same radius, strike the circle C, so that it will cut through the centre of B. The three circles will be all of the same diameter, and their centres will all be in the same line. The centre of A will be the axis of the escape wheel, and the centre C will be the axis of the pallets. 8rd. Draw a line 4, 4, through the points where the 4th. circles A and C cut B. Draw a line through the points 1, 2, 3. th. From the centre C, with the distance to the point where the circle B cuts A, strike short arcs, which will represent the inside of the pallets, the outside (which of course will be struck from the same centre) must be just so much larger as to allow the pallets to go easily between the teeth of the escape wheel. The inside points of the pallets will just touch where the circle B cuts A. The pallet d must now be filed away until it lays against the line 4, 4, and the pallet E must be filed away until it lays on the piece of brass, drill holes in the centres of the ciragainst the line 1, 2, 3 at 1. When the diagram is drawn cles A and C, and put studs in them, one for the wheel and the other for the pallets to work on, and after having roughed out the pallets to something like the size, drill the hole in them to fit the stud C. Of course the [6230.]-MAKING BREAD.-"M. B." is quite right in ttributing her difficulty in making bread in a "new amp draughty house" to that cause, for only washing ae brick floor in my bake-office in cold weather has aused as the greatest trouble; and on a Monday when he office is cold from not being used on the Sunday, ur bread has generally been an hour or two later than sual, and we have been obliged to put a bottle of hot water in the sponge to make it rise (or lay a hot brick or Professor Leslie's treatise on "Climate," I find the fol- actual pallets must be hardened and polished, and if Would "M. B." kindly publish the recipe for making east in the ENGLISH MECHANIC? for proved, useful, ractical information is much better than so much alge ra, the usefulness of which was sometime since chalenged in a very sensible letter.-R. R. S. [6244.]-DEEP-SEA TEMPERATURE.-The temperature of the sea at different depths is ascertained by means of Johnson's "Deep-Sea Thermometer," which is upon "Borguet's" principle, and contains both maximum and minimum thermometers. For a description, see Brooke's "Natural Philosophy," p. 766. In lowing (p. 282):-"The instrument he employed for exploring the temperature at different depths was free from the ordinary objections, being a registering thermometer, let down in a horizontal position, which could acquire the impression in not many seconds, and might be drawn up leisurely, without risk of subsequent alteration."-C. M. H. C. From (1) ... from (2) (1) (2) (a) [6233.]-THE EFFECT OF METAL ON ICE.-AS [6245.]-EQUATION.-This equation, which is ap right metals, and especially silver, are the worst radia-parently a quadratic, is really a biquadratic, of which ora of heat, a coin left as "Outside Edge" describes, only one pair of roots can be evolved. inder a clear starlight sky, would have the effect of conx2 + y2 = 11 ining in the ice under it some heat that the bare ice y2 + x = 7 radiates off into space; and thus there might be a local haw under the metal while elsewhere the ice was thicky = 11-22 ning. If this be the true account, the exact opposite should result under sunshine, the metal reflecting rays of heat that the bare ice absorbs. Thus it should become raised on a pedestal, as large stones become on the surface of a glacier, while small ones eat their way down and disappear. But under an overcast sky neither effect is perhaps to be expected.-E. L. G. [6294.]-WATER SUPPLY.-No tap is required for Put one at the lowest level for the purpose of drawing off the water.-Fux CHOO. air. [6235.]-CARPET AND SURFACE DESIGNING.-I presume that "Wood Carver" wishes to produce an even dead appearance; let him mix his own colours from the powders, with the addition of a little gum water weak), he will succeed after a few attempts.-B. C. E. BRODIE. time. [6236.]-SOLDER FOR GOLD.-Solder of two carats less than the gold ought to dissolve without injury to it, but it requires great practice to solder gold at any The gold should be brought to a red heat before melting the solder.-A DENTIST. [6239.]-DISSOLVING SOLDER.-Sal enixum is-at east, I suppose I must say was-used some years ago for the removing the surplus and stains of soft solder; it is likewise used for a purging flux for brass. I am not aware that they have found anything to supersede it. Perhaps our chemical friends will give us the proper name of it, and what it is composed off. Fownes spoke of it in his "Manual of Chemistry" as being a name used of old for something, but does not explain what. I have used it, and found it effectual.-JACK OF ALL TRADES. ог 121-22x+x+x=7 The three other pairs of roots can only be obtained by solving the cubic equation, 23+3x2-13-880.-PI. to act, and the beat will be quite dead. I would strongly advise all querists to consider well the question they save themselves much disappointment and prevent wish to ask before they ask it, for by doing so they would much of your valuable space and time being wasted.HENRY CHAPMAN. [6256.]-DISSOLVING GUTTA-PERCHA.-I have used turpentine with success for years.-B. C. E. BRODIE. [6256.]-DISSOLVING GUTTA-PERCHA.-For cement for straps and shoe repairs, I have never fonnd anything better than spirits of turpentine. I have done some work with it, and always given satisfaction for waterproofing coats, repairing hose-pipes, straps, pumps, buckets, whips, boots and shoes, &c., used it instead of glue for tanks and lining the same for salts, water, &c.-JACK OF ALL TRADES. [6262.] BREWER'S QUESTIONS. - "A Young Brewer" should allow his ale to ferment for two or three days, or until it has ceased to throw up any more yeast. He should then put three or four handfuls of spent hops, [6245.]-EQUATION.-" T. F.'s" question gives r = 3 free from seeds and stalks into each cask, then run the y=2 [6246.]-GEOLOGY.-It is certain that ships now pass beer in so as to fill the cask to within 3in. of the bunghole. Then bung tight down and place the cask on gauntry so that the front end of cask is the highest, and it ought to be clear in a week without isinglass.-EAST YORKSHIRE. [6268.]-GLYCERINE v. COD-LIVER OIL.-Glycerine is not an oil, and what is worse, contains no iodine, which is the most peculiar, and regarded, I believe, as the active constituent of the fish oil.-E. L. G. [6264.]-PROTECTING ELM.-Equal parts of crude petroleum oil made warm, and the timbers dressed with it two or three times. The next, for timbers upon dock, is 1 oz. common brimstone, such as you buy in rolls, 1 pint of linseed oil; put the oil in an iron ladle or pipkin and boil until it ceases spitting and spluttering, then cast in your brimstone; stir until dissolved with a stick of wood, take off, and when very nearly cold mix either with 1 pint of turps or crystal oil, and it is a preservative for wood or stone out of doors.-JACK OF ALL TRADES. [6265.] LATHE (Errata).-On p. 453 in my answer' for cheek-nuts read check-nuts; and for capped, read lapped. The engraver has shown the plan and elevation only half size; and in the end view of mandrel head has shown it as it was on my drawing-viz., turned over to get it into a sinall piece of paper; and the arm for back spindle should be represented as flat, not rounded. The poppet is shown with a fillet round the opening, whereas the double line was only drawn to indicate that the inside of the opening is rounded, i.e. thicker in the middle than at the edges. The heads are shown about 1-6th, and the mandrel about 1-3rd full size. The nose of mandrel is 1-4 diameter, with Whitworth's thread 7 to an inch, and barrel of poppet 18 diameter.-J. K. P. [6267.]-GONGS.-Gongs are generally made of a hard alloy, very similar to bell metal, and hammered. The best way of heating these is in the midst of a fire of wood shavings, or straw, that they may expand equally. There is a great risk of their breaking even then, if that precaution is not taken with some brass, and I have even seen copper go the same way, after being planished, if the fire catches it too fiercely in annealing in any one After the metal is very much spot more then another. condensed with the bammer, it is the unequal expansion that rends these alloys, especially as they all become crystalline in heating, especially the lower order. The gong ought to have been annealed before the experi ment was tried. If you had succeeded, it would have to be hammered or planished to have restored its tone, and you would have stood a chance of a few fractures. So, taking all things into consideration, you were perfectly right in advising the piece to be taken out. JACK OF ALL TRADES. [6271.]-PAINT SPOTS ON GLASS.-Caustic soda or caustic potash will remove the same. Take a lb. of pearlash, dissolve it in a quart or three pints of water; take a knob of unslacked lime and place in it. After the lime has slacked, take a stick, or, I use a piece of stout cane, and hammer the end of it to make a brush, for it will destroy a hair brush very soon. Mix 2oz. of soft soap, and stir it all up and apply it like paint, but do not touch the wood work, or you will have it take the paint all off that. Do not dabble in it with your hands, or they will be very sore, and it will destroy your finger-nails. Clean off with a dry duster, cotton, not leather.-JACK OF ALL TRADES. [6271.]-PAINT SPOTS ON GLASS.-I never met with matter so adhering to glass as not to be readily scraped off, and should be glad to hear more of the paint having so remarkable an adhesion.-E. L. G. [6271.]-PAINT SPOTS ON GLASS.-Take caustic, or soda dissolved with just sufficient water; apply two or three times, to remain a few hours; rinse the whole with water, rub the glass with a small piece of smooth wood and rinse again.-FANCY. [6272.] - ELLIPTICAL CUTTING FRAME. TO TOMETER.-I am very sorry that I am not able to supply the information that "Tometer" requires concerning this instrument. I prefaced the description of it with a few remarks (which, for some reason best known to the editor, did not appear in my communication), to the effect that I was not an ornamental man, and simply gave the description as I found it in Holtzappfel's catalogue. Nevertheless, I can tell him that the band does not run upon the edge of the disc, but upon one or other of the groves of a two-speed pulley immediately behind it. Perhaps T. W. Boord or "Wahsrof" can oblige you with details.-G. W. A. [6274.]-WEIGHT OF CUBIC INCH OF MERCURY.-The "Engineer's Pocket Book" gives this as 04904lb., which, as 7000 grains make 1lb avoirdupoise, will be equivalent to 3388 grains.-J. B. PRIMUS. [6274.]-MERCURY.-" J. K." is referred to Brooke's "Natural Philosophy," p. 228 (Art. 421), where he will find that "a cubic inch of mercury at 169 C. weighs 3429 grains nearly."-C. M. H. C. [6283.]-COLOURLESS VARNISH.- Spirit varnish, turpentine ditte, and Canada balsam ditto, are used for it. You can purchase either of them cheaper than you can make them, and it is very difficult to get the pale resin to make it yourself, as it is a thing very much in request for varnishes, sealing wax, fancy and bright, for carved work, as well as for the various fiddlers and violinists; the former I have seen use it to an alarming extent, but make very little progress.-JACK OF ALL TRADES. to [6283.]-COLOURLESS VARNISH.-In answer "Dixi" and "Plymouth" (queries 6283 and 6292), I think the following varnish will answer their purpose:Spirit of wine pint; sandarac 2oz.; mastic joz.; Venice turpentine loz.-FRANK CHESSELL. [6284.] TAKING PLASTER CASTS.-Use with a shaving brush a lather of curd soap, as you would for shaving. It can be removed with a stronger soap and olive oil afterwards.-JACK OF ALL TRADES. [6285.]-GLASS PRISMS-Are cast and polished at a glass-polisher's wheel and finished by a leather disc and putty-powder.-B. C. E. BRODIE. [6287.]-PAINTING NEW IRON.-" Veloce" had best use gold size in addition to dryers, if he wishes for a very neat appearance; he will find the tube colours come expensive, unless for model work, when of course the extra expense will not matter much; if the iron is greasy dip for a few moments in dilute sulphuric acid. -B. C. E. BRODIE. [6287.]-PAINTING NEW IRON.-Use only a small portion of copal varnish, and plenty of turps, that your paint may dry dead-flatting. After you have well scraped and cleaned with turps to remove grease, apply two or three coats and varnish with copal, and your paint will never blister.-JACK OF ALL TRADES. [6292.]--VARNISH.-White shellac is the ingredient, if any of our readers can find a solvent for it. I have wanted the same myself, and have lb. I purchased some years ago for purpose in a country town and lb. I purchased in London, but cannot find a solvent for it. It is beautiful looking stuff, very much resembling the best class of pulled sugar you see in the confectioners' shops. I have tried spirits of wine and pure alcohol, ether, naphtha, strorg ammonis, turps, &c., and have forwarded a sample and chloroform to some friends to try, but to no purpose; it swells to about four times its original size, and insists upon settling at the bottom, like so much mealy otato.-JACK IN A FIX. [6297.]-ENGINE. " G. B. W." should be very careful with his fast running condensing engine. The cause of the knock (so far as one can judge from his description) is the want of cushion. The shifting of the eccentric only partly effects this. He should indicate his engine at once, and a little attention to the diagrams will most likely show the cause. If he would send his diagrams for insertion to the Editor of the ENGLISH MECHANIC, he would be sure to get some useful hints. Valuable as such information would be to him, and a host of others who look eagerly for such cases as this, he must (if an engi. neer) work out the greater part of his difficulty himself. He will value experience thus got more than all the theory he can buy. I enclose diagrams (which I hope you will find space for in your valuable MECHANIC) of an engine under my care, which formerly had the same vice. The causes were, first, bad valve setting; second, the working parts unequally tightened. This engine has a description of valve gear similar to that recommended by "Leh Teb." Those enclosed are taken with a Richard's indicator, 1-16in. scale.-DOWNSHIKE. [6298.]-BRAZIL. My experience may be useful, having resided there some five years, and travelled some thousands of leagues during my stay there. I have no wish to damp "O. F. W.'s" desire to go to Brazil, but emigrants are as a rule much disappointed in their selection of a new home, owing to the ignorance they are in as to the country customs and manners of its inhabitants. We hear of a rich fertile land and think that if two crops a year can readily be raised that there is nothing to do but select a spot and sow our seeds or till our ground. This is perhaps one of the greatest fallacies that can be entertained. With these few remarks I premise my own experience, although not having gone out there as an emigrant, but acting as representative for a large engineering firm, principally engaged in sugar (plant) machinery, I soon found that unless my principals altered their terms I should not earn my bread, for the simple reason that I could get there than I was authorized to accept. longer credit from the small founders and machine shops Corn is not grown generally in Brazil, except in the province of Minas Geraes, which is some hundreds of miles from the coast. The north of the empire is too hot and swampy, the tropical district is too woody, and I doubt the southern part being adapted. However, all the flour required in the large seaconst cities and towns in the empire is imported. I was myself travelling some few hundred of miles in the interior, and for three years never saw or heard of bread. Indian corn, or, as it is called there, "milho," is grown generally on estates, but not in large quantities, and when reduced to flour is done in a very primitive way by slaves in a wooden mortar, by means of a long wooden pestle. The only substitute I found for bread and potatoes was "farinha," made from a root called mandioca, resembling an overgrown parsnip. From this is made also tapioca. To explain the modus operandi would entail more space than I am entitled to. The only seeds requiring grinding that I am aware of are castor-oil nuts or seeds; these are reduced also in a primitive manner into oil for household purposes, not medicinal.-J. G. [6299.]-FRENCH BRONZING.-You want nothing but sulphate of copper and water. Treat after with carbonate of soda; afterwards well wash with water and lacquer with pale lacquer. I have marbled and bronzed the clasps of travelling companions and guns the same way, and they look better than rusty.-JACK OF ALL TRADES. [6300.]—QUININE.-Sulphate of quinine is prepared from yellow bark, coarsely pulverized and boiled in water acidulated with sulphuric or hydrochloric acids. The decoction is poured off, and it is repeated four times. Filter and add finely powdered lime when it is cold, until it assumes a dark colour. The precipitate is collected and pressed'; then when dry, powdered and digested in rectified spirit. Filter and distil until the residue assumes a brown viseid Fappearance. The residue to be dissolved in sulphuric dilated acid. The solution filtered and set aside to crystalize. It is then drained, pressed, and dried, when it assumes a yellowish brown colour. Dissolve in water, decolourize in animal charcoal, recrystallize and dry. This last part must be done carefuly, to prevent eillorescence. Taken from have chosen it as the simplest.-FUM CHOO. Pereria's Materia Medica," Dublin College formula. I [6301.)-RECOVERING CYANIDE OF SILVER.-I burn the sawdust; then pour boiling water upon the ashes, filter, and precipitate with sulphuric acid. Mine is only in a small way; try it.-JACK OF ALL TRADES. [6301]-ANEMOMETER.-If "Der Sunthal's" cups be fixed upon a vertical revolving shaft terminated by an endless screw, which actuates the clockwork, he will require no chains.-C. M. H. C. [6305.]-MOULDINGS.-To work any kind of wood mouldings, first gauge the stuff up to the required width and thickness you wish to have the mouldings : then mark with pencil on both ends of the piece, the exact pattern it is to be; set a plough and work down the moulding work first that is farthest on the e The accompanying sketch will give an idea; te lines are the plough grooves. Proved.-z [6306.]—GALVANIZING BOAT NAILS.-Tak of sulphuric acid and 1 gallons of water; to nails into an old pan or dish, and cover the v acid and water mixed. After they have been for a while take some of them out and see whack are clean. Take them out and shake them in t of burnt straw and clean water; then get fl. 4 acid, and add pieces of zinc until it will hur more. Then take lb. sal ammoniac, and pow a portion of the powder, mix with the red t paste, put into the dry nails and well turn them to. put them into a pot or ladle with some zinc, ar zine; well stir them about until they are covered 12 will be very soon after the metal is melted; the% out into a cinder sieve and well shake aboat, er. done. I prefer a mixture of tin with it.-Jac TRADES. [6307]-SHOWING OPAQUE OBJECTS OY DEL Top view of the Aphengescope: A A, two blah to the lanterns; B, door on which to place. A B opaque object; C, second door for changes; De and focal arrangements. If J. Wade can call uyna HUNTLEY. I shall be happy to allow him to inspect me-l [6308.]-GLOBES.-A spherical block of wood less than the intended size of the globe, is cove pieces of paper laid over each other with paste 27 L (taking care not to touch the ball with it) till about in. thick. This is allowed to become qu when it is cut through the middle with a knife equal hemispheres or halves; the block is täst and a piece of wood is put in to form the sain ul A globe. Into this axis a piece of stout wire is dre form the poles. The two paper hemispheres als k... on this axis, so that their cut edges may be s gether. Then a semicircle of brass is made, edge of which is exactly the size of the globe se finished (12in.); there is a hole at each extremt semicircle to receive the poles of the axis. Ap then made with whitening and very thin glue. T spread upon the paper, and the brass rim di over the surface in an equal manner. To cracking, successive layers are spread on, and a to dry between each time, until the globe is rendered large as just to pass below the rim, and the wh face is perfectly smooth and even. It is now allow dry and harden, and then touched up with de paper, and also to get it nicely balanced on its a is now ready to receive the paper map. These majes engraved on gores or segments of the sphere, wa being applied from pole to pole, and their edges adjusted to one another, inay cover the whole se of the globe. I understand that these gores are di to be got. Would W. P. B." be so kind as to t where they are to be had, and their cost 7-VALVE. [6308.]-GLOBES.-See reply 5426, No. 205, and b diagram. The second, if wanted at all, must be cal by No. 296.-E. L. G. [6308.)-GLOBES.-Material: a gauge struck 1. ' half circle made of wood; one brick and three h one brick in the middle, a half brick upon each s the other upon the top in the centre, a sixpenny bar plaster of Paris, half gallon of floor eand, and to build upon, or upon the head of a half butter is Build up your mould; after dry, make a template tre the diameter you require; get some sugar-paper, of that will not cost much, blue or white will do, we and pull into pieces about the size of a halfpenny, stick them all over with nothing but water a after you have laid the foundation, wet your pap tolerably thin flour and water paste; thus ved build and trim your two halves, and all you will Late do is to trim them true to the half hemisphere, join.-JACK OF ALL TRADES. [6310.] ELECTRICAL (ERRATUM.)-In my reg p. 455, by some extraordianry process, probably oversight, I am made to speak of the electro-mag machine, instead of the "frictional electric machine. SIGMA. [6314]-BOILER VALVE.-The only one whic know answering to the description given by "Valv that patented by Mr. Robert Crickmer for the p vention of priming in steam boilers, No. 28, 186) M A. C. F. Franklin, of 18, Abingdon-street, Westmins doubt, answer any inquiries Valve" insy is pu Mr. Crickmer's sole London agent, will, I have a make. I may add that it answers admiraly the p pose for which it is designed.-B. C. E. BRDE [6315.]-MISTLETOE.-Place the berries in dry: 15 serted in small holes made in the bark of an a until the early part of May, when they should b gauze from birds. pear, lime, or thorn tree, protected by a little nest done, ani in few cases will the seeds be found is ja This is all that is necessary to b There is no difference in the seeds. Perhaps Ami would oblige me with a few seeds if he has any Florist to spa e.-P. SKINNER. |