here. The Quekett Club is unquestionably of a high class, but I think hardly embraces the features "A. A. F." desires to make characteristic of his society. The same will apply to our Manchester friends. Nothing need hinder microscopists forming local clubs. I for one should be delighted to hear of the formation of one in every hamlet, town, or city, but beyond this we need a means of intercommunication such as this journal affords. and such (or in some similar fashion) as that suggested by "A. A. F." H. P., Hull. GRANITE. [419] SIR,-An article entitled the "Story of a Piece of Granite" appeared in the ENGLISH MECHANIC of September 2nd. On this interesting subject I would like to hear more from our geological friends, as there are many things mentioned in said article that I would like an explaination of. For instance: How the pressure can be determined by microscopical examination? Also, how the presence of water in quartz crystals is taken as evidence of the agency of water in the formation of granite ? Granite readily imbibes water! Another property of granite (which, however, is not mentioned in the article referred to) is the "reed," or grain, which runs through the rock, and renders it much more easily split in one direction than another. I have never seen any article on the subject which took notice of this fact, and I would therefore feel grateful to any of your subscribers who may respond to my request. IRIOSAL. SOLUTIONS AND WEIGHTS AND MEASURES. [420] SIR," H. K.," p. 591 (338), puts forth a difficulty I have thought some of the readers of my papers on Electricity" might have, and it is one very hard to avoid when addressing so very mixed an audience as "our" readers, and attempting to go to roots of the subject dealt with and help the beginners of the study, and yet at the same time make one's work interesting and valuable to the most advanced theorist as well as the practical man. In writing on science one is compelled to take some classes of knowledge for granted. Thus, knowing from my own experience how much more valuable and available information is when classified and thrown into the tabular form, I have tried to do this as much as possible. On the other hand, such tables require some familiarity with decimal calculation, a thing which frightens many people who have not learnt that of all calculation this is the simplest and easiest. In these tables I have chosen the decimal grain system, and an explanation of the reasons of the choice will convey information to many others besides" H. K." He wants to make a "pint" of solution-pints and pounds are a perfect horror to men of science, because they know what obstacles to knowledge and progress our most barbarous weights and measures are, and what weary hours have to be wasted by our children in the effort to charge their minds with these wretched relics of our ignorant ancestors' devices before science was discovered. The only sensible system of measurement and calculation is a decimal system, not necessarily the French metric system, though this is best for the practical reason that it is already largely adopted, but any base will serve; I had then the choice of three established systems. 1. The metric; the best, but almost totally unknown in England, and rejected by me, because if I wrote about grammes and metres, I should infallibly frighten my readers, and be told that I "addressed them as if they were all philosophers." 2. Griffin's Septem system, in which seven grains is the unit, adopted in order to link together the pound weight 7,000grs. and the gallon measure 70,000grs., an ingenious fad of a clever man, but quite unneces sary. 3. The decimal grain system, which I adopted be ment would be needed for each sample; of course the "H. K." need not apologize for "asking so much." WATCH JEWELLING. SIGMA. [421] SIR,-I have read " "Nobody's" letter on watch jewelling (4128) with very great interest, and am sure many others must have done the same, and hope that he will not consider me troublesome in asking for a little more information on a subject he seems so thoroughly conversant with. The apparatus which "Nobody" describes seems somewhat different to the mandrel that we use in our shop in replacing centre or other holes. Ours is driven by a small hand-wheel, is held in the vice, and instead of the flat table mentioned, it has three clogs, made so as to hold the watch plate or other article to be operated upon, and a sliding centre to centre the work with. It may be as well to mention that we have no slide rest. The mandrel mentioned not being my own property I should not be at liberty to make any alteration in it, but I intend having one of my own shortly, and should like to know what sort of a one to buy so as to be able to set jewels. "Nobody" is no doubt aware that journeymen watchmakers are (as a rule) not troubled with much spare cash, so that I should not like to give £8 or £10 for an article which could be used for jewelling only, and could not be used for other work. Sometimes I have had a lever with a broken foot jewel hole and have replaced it in the following way: Having some foot holes set in brass I select one which fits the pivot, this I cement to piece of brass large enough to be held in the clogs of the mandrel, I then get it to run near by the sliding centre, turn it down to the required shape and size and it only remains to file the brass away to receive the jewel slip. A little further information upon the best way of fastening the article to be jewelled (in wax) would be very acceptable, and also in putting lock or foot holes, if the old settings can be used to set the new jewel in, for I find more lock and foot holes broken than any others in the watch. If our friend" Nobody" will favour me with a reply to my somewhat rambling inquiries, I shall consider it a great favour, and I doubt not his reply will be read with great interest by many others beside. RUPERT. INDUCTION COIL.-TO MR. COFFIN. [422] SIR,-I wish to ask Mr. Coffin, who states, on shortcomings of others to have endeavoured to have set them right by giving in place of an unreliable method one which is reliable, i.e., provided there be such. With respect to my answer to "Young Photo" I perhaps inferred too much, supposing that he wished to convert his silver residues into metallic silver. On the whole "Urban's" criticisms in "Various Varieties" are well founded, but I certainly don't think his manner of wording them a very happy one. AN ASSOCIATE OF THE ROYAL SCHOOL OF MINES. BOILER PRIMING. [424] SIR,-In answer to a "Working Engineer" (270, p. 543) I beg to say that the great cause of priming may be attributed to the want of water surface for the free evolution of steam. In this case 4 cabie feet of steam must be evaporated per second to supply 50 horse-power engine; and the minimum space for this purpose is 4 x 12 51 square feet, must be allowed before the steam can liberate itself from its water of formation with any kind of freedom. From the calculation of this boiler, we find the water surface is only 25 square feet, being so much deficient in this requirement; the result is wet steam and priming; and the quantity of water carried over will be in proportion to the difference between the required and given surface of the boiler in question. All the best engineers, from Watt downwards, have allowed about 5 square feet per horse-power for the tree evolution of steam, but unfortunately this boiler only gives ft., giving a ratio of 10 to 1 against the usual practice, and a ratio of 2 to 1 against that which is absolutely necessary; showing that these kind of boilers are always subject to priming when hard pressed for steam, followed, of course, by a great waste of water and fuel. a Pure water, however cold, cannot produce priming. Rapidity in the production will cause priming only with deficiency in the evaporating surface. The steam space in this case does not cause priming, as it bears a relation to the draught of steam per second of at least 20 to 1, which is sufficient in any case. The means of drawing off the steam will not cause priming, as it is sufficiently removed from the water surface that any capillary attraction that may arise from the side of the boiler is prevented. Therefore, the great cause of priming in this case may be said to be the want of evaporating surface. In order to maintain the full power of the boiler, it would be necessary to take off the steam by means of a steam chest, where the globules of water would fall to the bottom by their greater density, and thrown back to the boiler by means of a connection below the water. line of the boiler, as any attempt to throw it in above the water-line would be fruitless, as the water would always be kept in suspension by the superior force of these arising from the surface along with the steam. R. D. THE SCREW-PROPELLER. [425] SIR,-Permit me, for the sake of truth and justice, to state, through the medium of your paper. that the country owes the valuable invention of the portions or sections of the screw placed on a revolving shaft below the water-line, and at the stern of the ship, whether the section be of the hook-shaped blade, or the pear-shaped blade, or the narrow-surface blade, or the broad surface-blade, or the spoon-shaped blade, or any other configuration of a section of a true screw, to the late Mr. J. Lowe, which invention dates from March, 1838, and the novelty and validity of his invention were tried in the court at Guildhall before Lord Chief Justice Denman and a special jury; and the merits of Joseph Bramah's invention of May 9th, 1785, and that of Edward Shorter, of Feb. 4th, 1800, and Richard Freirthich, of June 6th, 1815, and Charles Cummerrow, of Dec. 10th, 1828, and B. Woodcraft, of cause it is commonly used, weights and measures gra- p. 567, No. 304, that he has found the primary current March 22nd, 1832, P. Smith, of May 31, 1836, and John duated to it being obtainable of any scientific instrument dealer, and its denominations are familiar to the ear and comprehensive, while it has this advantage, its figures are equally available for the metric system, for by putting the decimal point one figure to the left and using the gramme in place of grains, and the litre for 10,000grs. fluid, we have the metric system. Calculations made on these figures are then con vertible into any of our arbitrary measures with much less labour than by working them in those dreadful pounds and ounces, drachms, scruples, gallons, pints, and other abominations. 1lb. avoirdupois is 7,000grs., one pint is 1lb. of water (the universal agent for linking weight and measure), that is to say, 8,750grs.; and a gallon, 8 pints or 10lb., is therefore 70,000grs. To make a pint of any of the solutions in the table, p. 340, multiply the number of grains in the first division of Column V. by 8-75, that is to say, 8 and 3, and reduce, if wished, to ounces by ordinary division, and add water up to a pint in measure; then add the acid by measure, as in Col. VI., also multiplied by 8. Of course this will make the solution finally more than a pint, but as the result varies with each salt, the particulars would take both time and space needlessly. If "H. K." and others who are in the same position, will but once face the apparent difficulty of this system, they will find it is a mere bugbear, like the rustic ghost made out of a turnip. The nitric acid table is of course based on pure acid. No exact calculation is possible as to variable commercial products; thus it would not apply to "dipping aquafortis," containing sulphuric acid; special experi most suitable for medical purposes, if he will please give directions for making one such as he names, viz.: What number of wire, silk or cotton covering, quantity required, best way to insulate; what kind of contact breaker, whether it would be better with magnet or not; also what kind of battery would be best, and such other directions as he may think necessary. Being only a working-man, with limited means, I cannot afford to experiment as some of the MECHANIC readers. What little information I have has been obtained from the MECHANIC. V. W. X. TO "URBAN "-VARIOUS VARIETIES. Ericsson, of July 18th, 1836, were discussed; and I need scarcely say that all these inventions were put in to try and overthrow the novelty and validity of the late Mr. Lowe's invention; but after a 13 years' lawsuit, which he had to stand out against the combined engineers, the novelty and validity of his patent were established to describe all the above inventions, would be to take up him by the verdict of a special jury. To technically all the valuable space in your journal for three months; but I certainly do not see the utility, even if you would print it, of going through the technical terms of the screw, which was entirely eclipsed when the late Mr. Lowe's sections or portions of the screw were introduced to our Government, and foreign governments, and the merchant service at large. Mr. [423] SIR,-I have to thank "Urban" for his re- Miller, engineer in the Government dockyard at marks upon my answer concerning "Picric Acid." I Devonport, when he gave his evidence in the court at certainly ought to have pointed out the fallacies Guildhall, July 25th, 1848, said, Mr. Lowe's, in my connected with the tests which I gave; but errare est opinion, is quite a different invention to all that have humanum. I did not "exercise my ingenuity" any gone before the date of his. The whole screw was not further, as I thought the two tests which I gave were found so useful as a portion of a screw. The Archi the most simple of application and in all respects the medcans produced reverberation and a shock in the best for a non-chemical querist. motion of the vessel. That is obviated now by using "Urban" also objects to the method cited by "Crow-blades. A greater effect is also produced by blades of Trees; " is it presuming too much upon his courtesy to a similar power. Every portion of Mr. Lowe's sections ask "Urban" to give a test himself, one which he has acts as a propeller. Mr. Beale, engineer, residing at tried and proved!? I know a little of the difficulties Greenwich, who gave his evidence, said, I am not aware incidental to the detection of small quantities of picric of any invention on the same principle as Mr. Lowe's, acid (not so much by my own experience, however, as I know of nothing like Lowe's. The Rattler is worked by that of a friend's), and should be glad to see them re- with Lowe's screw-propeller. It is undoubtedly Lowe's moved. screw-propeller. All vessels that go well have Lowe's I think it would have been only good taste on the screw-propeller. A full detail of the evidence given on part of your correspondent, when he complained of the the screw-propeller trials of Lowe v. Penn can be A MEMBER OF THE INVENTORS' INSTITUTE. The seen at the Patent Office, 25, Southampton-buildings, proud of our great men, and are pleased at their laurels. [426] SIR," W. H. N." is quite correct in his description of negative slip, and I fancy, that much as we are indebted to the Rev. E. Kernan for his contributions, from which we often derive much improvement, yet that on the subject of the screw-propeller, he rather, in his communication on the subject, quoted from some popular account of its action than from knowledge derived from that study and attention which the difficulty of the subject demands. "W. H. N.," who evidently understands the subject, will forgive my supplementing his correct statement that when a ship -from strong wind or other cause-over-runs her screw, the screw exercises a "retarding influence," by adding that so strong is that influence, that cases have been known in which the screw has-from the opera. tion of the passing water-commenced to turn the engines. With regard to the train of boats, if I recollect rightly, the scheme was originally started forthe transmission of cargoes upon the Ganges for several hundred miles above Calcutta. PROPELLER. HEREPATHITE. [427] SIR,-I am sure many of your readers must be much pleased and instructed by the articles now appearing in the MECHANIC on the microscope. This week the writer has got to the polariscope; every one who possesses a microscope must desire to possess one of these most important additions to his instrument. But the price-and I fear that he would not be able to fit one to his instrument-will deter him from attempting. Now the herepathite form seems the best for your readers to try, since they will be able to fit it to their microscope without much trouble, for one erystal of herepathite goes under the object, the other over or above the eyepiece, but the Nicol prism goes inside the tube, and every microscope is not made so as to be able there to apply it; but any of your readers may apply the herepathite to his form of microscope, whatever it may be, the only difficulty being to get the herepathite large enough. I tried some years ago, but did not succeed; it can be done, and perhaps I did not have the right directions; doubtless some of your readers have, and I am sure it would be conferring a great favour on every possessor of a microscope, to put him in the way to add a polariscope to his microscope, at a little cost-a few shillings would do all, both make the herepathite and attach it properly to the microscope, whereas the Nicol prism form would cost about £1 10s. The writer of the excellent article on the microscope shows great consideration for his readers' pockets, doubtless knowing that they have a wish to get as much information as possible for their money. He cannot do better than let us know if he knows how to make the herepathite, as its fixing to the microscope is a mere trifle; it is a chemical compound, and therefore every one can make it for himself at a trifling cost. When I tried to make it I could not get it large enough, say a quarter inch diameter, although the small crystals I did obtain were beautiful objects for the microscope, and most perfect polarizers; the largest I obtained were not more than one-eighth of an inch diameter. Any of your readers would confer a great favour on many who possess a microscope, if they could give any information on the subject. EXTRACTS FROM VULPECULA. CORRESPONDENCE. WALNUT STAINS.-B. E. Loddy says:-"As walnut season is now coming on, I beg to submit to you a simple plan to take the stains of the nuts off your hands:Take a ripe pear and cut it in slices; then rub the hands with it, and it will render them quite clean and soft.-Proved." OUR PAPER.-"Mr. Editor,-I am glad to know that our paper goes on swimmingly. We ought all try to extend it. Perhaps, quoth Mr. Somebody, "very fine talking; why don't you do something?" Well, I have tried, but have not done much. "Fact is," as Jonathan says, "I wan't our publisher to help me." My letters every week are no trifle in number, and in pennies. Now, if I had a prospectus sort of paper of our MECHANIC, about the size of a quarter of a sheet of notemy letters. paper, I would stick one in as outside folder in most of BICYCLE RIDING." Senex," in a letter says:On my way to town, a few days ago, I passed a man on a bicycle with his wife behind him on a pillion! This is enough; let no one henceforth say it cannot be made of real service." MR. PROCTOR. "I am gratified to see in the graceful publication, The Graphic, of Sept. 10, an article entitled Life in Mars,' being a highly appreciative critique on a part of Mr. Proctor's book. We, mechanics, feel REPLIES TO QUERIES. In their answers, Correspondents are respectfully requested to mention in each instance the title and number of the query asked. [2756.]-LAMENESS IN HORSES.-My best thanks to T. D. Broad for the manner in which he explained the treatment, and the method of shoeing in cases of laminitis or fever in the feet. I have of late years adopted the same plan, in making the shoes without seating and fitting them to the foot so that the sole can take part of the bearing as well as the crust. I have also brought the frog in contact with the ground, so that it may also take part of the bearing, and have applied blisters around the coronet, and have given ordinary physic balls and a run at grass. But as regards the cure, the horse has all the appearance of going sound for a short time, but almost as soon as he is put to his ordinary work the lameness returns and he is quite unable for fast road work.-J. O. DYFFRYN. [4281.]-FORCE-PUMP.-The best force-pump which I know and have tested is the "Californian," either for "hand" or "power; it can readily be made "portable" at moderate cost, is not liable to get out of order, and the hose may be canvas with or without india rubber, as the height to which the water has to be forced is great or otherwise.-J. B. PRIMUS. [4332.]-BLACK GLASS OF ANTIMONY (Unnoticed [4361.]-METHYLATED SPIRIT.-Henry James pro- cuts the diagonals, as at m n o p, draw lines parallel to the sides of the exterior square, forming a square, of which the sides, o m and m n, are only given in the diagram. Construct the horizontal plane of a cube, b c d e, Fig. 2, of which the line b c is nine-elevenths of bc, Fig. 1. Draw the diagonals bdec, bisect be and c d in the points h and f, and through these draw lines, hag and fal, parallel to c d and c b. With a m from Fig. 1, set off on bd Fig. 2, to the points n and o; from these points draw liues to m and p, parallel to the sides of the horizontal plane. Through the series of points thus obtained, draw by hand a curve. This (the outline of an ellipse or oval) is the isometrical projection of the circle in Fig. 1. The horizontal plane Fig 2, is constructed with a T square, and a template cut to the angles of 30°, 60°, and 90°, the angle de H being always 30. Fig. 3 is a right hand isometrical plane, it being constructed to the right of the line S T; when constructed to the left of it, it is termed a left hand isometrical plane. A circle is constructed, in a right or left hand isometrical plane, in the same manner as already explained. Mr. Carl J. H. Cotthesson must not think that this question was not answered before, I sent a similar answer some weeks back to Mr. Editor, so it either went astray in the office, or else never came to hand, and since that, I had not time to write another.-THOMAS J. O'CONNOR. [4415.] CURIOUS PROBLEM. — I admire "Saul Rymea's" ingenious method of solving his own difficulty, and also getting a laugh at his answerers. His cool assumption that those who assert that "immovable and "irresistible" bodies cannot exist together, necessarily hold that the words "irresistible" and "immovable" are obsolete, or ought to be crossed out of the Dictionary, is also pretty good. Did it strike him, however, that an "irresistible" body which "makes a hole" in an "immovable" one, and, I suppose, passes through, must necessarily be smaller than it? Will he kindly tell us what would be the consequence if the than the "immoveable" one?-IGNORANT IRISHMAN. "irresistible" body happened to be as large as or larger [4489.] TURNING COPPER.-T. W. Boord has not hit the mark in his reply to 4489. For turning copper, keep the edge of the tool wet with milk. For iron or steel, use soap-suds or saliva. For lead or other soft metal, oil. Each will give a clean cut.-J. B. PRIMUS. [4546.]-DIVISION PLATE.-Now that "Wahsrof" has explained what he means by "dividing into differences," which seems to me to convey no meaning, I wish to point out to him that with a circle of 720 holes you can get divisions of 16, 48, 80, 144, 240, 720, none of which is to be got with a circle of 360 holes, and, therefore, he is, on p. 618, very unfair towards the larger numsmaller has. I make the larger to contain 29 different numbers against 23, which is the proper way to estimate the working value of a plate. Counting his way, too, he has no right to put 20 and 36 both down as divisions of 720. He ought to stop at 24 by 30. I flatter myself that he will be prepared to rescind the first clause of his letter on p. 618, when he has perused the list of plates I sent him, and acknowledge that I have paid very coning to admit that I never do fine drilling, or fluting, or siderable attention to the subject, while I am quite willornamental work of any kind. I see that "G. C. C." agrees with me as to the value of the two rows of figures that I found fault with, viz., 209 and 221, which, I repeat, would never come in for fine fluting, &c., and are only intended to give the numbers 11, 18, 17, 19, and nothing else.-J. K. P. [4862.]--CONDENSING WATER (Unnoticed Query.)—ber, when he ascribes to it one more divisor only than the The method of distilling water for the use of passengers on board ship would take up too much of your valuable space, to fully describe and illustrate it. I will therefore explain the matter as simply as possible. The apparatus used consists of three principal parts, an evaporator, a condenser, and a refrigerator, all of which must be made steam-tight, and be screwed and bolted together without soldering or brazing of any kind. The evaporator is made in the form of a cylinder, partly filled with seawater, through which a coil or sheaf of pipes passes. On admitting steam through these pipes it is condensed into fresh water, and at the same time evaporates a portion of the sea-water by which the pipes are surrounded. The steam is obtained either from the ordinary boilers, or, as in sailing vessels, from a special boiler fitted up for the purpose. The steam produced by the sea-water in the evaporator passes through a sheaf of [4588.]-BLACKENING INSIDE OF TELESCOPE. pipes in the condenser, where it is condensed by the-If Mr. Hill wishes to blacken his telescope well, he cold water surrounding the pipes, and joins the fresh must not apply the liquid with a brush or any instruwater produced by the condensation of the steam in the ment, as in such a case light streaks will be left all over evaporator, in circulating through pipes placed in a refrigerator, which are surrounded by water flowing in into the tube, and then turn it round until every part the surface. He must pour a good quantity of the liquid from the sea. By this means the steam is condensed has been covered. Then he may pour off the refuse. He and gradually cooled, and at the same time the sea- must be careful not to put too little liquid in, as if it water is raised in temperature, passing from the reruns round anywhere in streamlets instead of in one frigerator to the condenser, and thence to the evaporator. flood (magnis componere parva !), shiny lines, like those The fresh water in a non-aerated condition, after made of a snail-track, will be left. He must also not be running from the refrigerator is passed through a afraid of putting lamp-black into his liquid, as it is imquantity of charcoal, placed in a filter so constructed possible to add it after the latter has dried, but any exthat the water enters at the top and passing under a cess will then readily fall off if the tube be well patted diaphragm flows out at the top. There are several and shaken. The more the lamp-black the rougher and little matters connected with the apparatus, such as a deader the surface. Opticians' recipes do not recommend feed and priming box, steam-trap, &c., which would take too long to thoroughly explain; but I think I have given enough either of this or of spirits of wine.-B. A. sufficient for the querist's purpose. There were some [4596.]-JAPAN ISINGLASS.-I extract the followcondensing and distilling machines used in "Waste Products and Undeveloped ing note from the Abyssinian campaign, but whether they were different to Substances," by P. L. Simmonds (London: Robert the one I describe, which is known as Dr. Normandy's, I Hardwicke, 1862), a book full of useful information. cannot say. This apparatus is, or was, in use, on nearly "Under the incorrect name of Japanese isinglass, there all of the ships chartered by the Government Emigration has been of late years imported into London from Japan Board, and was found very successful.-H. U. a quantity of prepared sea-weed of two kinds; the first having the form of compressed irregularly four-sided [4372.]-THE HAUTBOY.-The information "Anon" requires, as to how to blow the hautboy, could not be parent, yellowish white membrane; they are 1lin. long sticks, apparently composed of shrivelled, semi-transcompressed into a single column of "ours," much less a by from 1 to 1in. broad, full of cavities, very light (each short paragraph. In selecting a reed, care should be weighing about 3 drachms), rather flexible, but easily taken to see that the grain is straight, that the cane is broken, and devoid of taste and smell. Treated with of uniform colour and not too dark. Reeds that are cold water a stick increases greatly in volume, becomdark at one end or much mottled are nearly sure to being a quadrangular spongy bar with somewhat concave unserviceable. The price varies from 1s. 6d. to 2s. 6d. sides, 1 in. wide. Though not soluble in cold water to One costing 2s. ought to last a long time with care. It any important extent, the substance dissolves, for the is advisable to have two or three, so that when one gets most part, when boiled for some time, and the solution, too soft to use it may be put away and another used in its place. In fact, one to take care of the other. If second kind resembles the preceding in all its properties, even though dilute, gelatinizes upon cooling. The "Anon" will publish his address in the Sale Column under but its form is very different, it being in long shrivelled the heading "Hautboy," I shall have great pleasure in strips about in. in diameter; these strips when imsending him all the information I can.-R. A. M. [4411.] ISOMETRICAL DRAWING (Unnoticed Query). In reply to this query (p. 501), the method of mersed in water speedily increase in volume, and are then seen to be irregularly rectangular. This substance in colour is usually whiter than the preceding; it is also more readily soluble, clearer, and altogether a more carefully manufactured article. The substance under notice, in all its forms, is used by the Europeans in China as a substitute for true isinglass, for which many of its properties render it highly efficient. That which is, perhaps, most distinctive is its power of combining with very large proportions of water to form a jelly. This property is due to the principle named by Mr. Payen gelose, of which the Japanese sea-weed product mainly consists; the jelly formed by boiling this senweed product, or crude gelose, in water, and allowing the solution to cool, requires a high temperature for fusion, differing in this respect from a jelly made of isinglass, which readily fuses and dissolves in warm water. This character occasions a peculiarity in the taste of culinary jellies made of the new material, inasmuch as they do not dissolve in the mouth as ordinary animal jelly. The jelly of gelose is but little prone to undergo change; so little, indeed, that sometimes, under the name of sea-weed jelly, it is imported to this country from Singapore, sweetened, flavoured, and ready for use; and in this state it may be kept for years without deterioration. Gelose differs from animal gelatine in not precipitating tannic acid; from starchjelly, in not being rendered blue by iodine; from gum, by its insolubility in cold water, and its great gelatinizing power. From the mucilage of Chondrus crispus, named by Pereira carrageenin, it appears to differ chiefly in its power of combining with a greater quantity of water to form a jelly, which is not the case with carrageenine. Of the botanical origin of crude gelose, or Japanese isinglass, and the mode of its preparation in Japan and China, we are not yet well informed. Mr. Payen finds it may be extracted from many species of sea-weed, but especially from Gelidium corneum, Lamouroux, and Gracilaria lichenoides, Greville; the former of which yielded in his experiments to the extent of 27 per cent. One part of gelose dissolved in 500 parts of boiling water will afford, upon cooling, a colourless, transparent jelly, thus forming ten times more jelly than a like weight of the best animal gelatine. In order therefore to produce a jelly of equal consistence, it would be only necessary to employ the tenth part of what is necessary when isinglass is used. Jellies prepared from species of gelidium, laurencia, &c., are much employed for food in China, Japan, &c." Particulars about the industrial employ of the Japan isinglass I could not find.-BERNARDIN. [4597.]-INDIAN COIN-I thank Mr. H. Henfrey for his kindness in describing my coin; but I am living too far from Brighton to profit by his offer. Let him permit me a slight remark. My coin bears clearly the date 1229 (in Indian characters). Might this, perhaps, be a fault? From its dimensions I think it is the double peisah.-I. N. D. C. [4602.]-MELTING GLUE.-I was very much surprised in reading "Vulpecula's" letter at his ridiculing the answer sent by me to the above query. Perhaps he partly misunderstood me, or I did not carry my answer far enough. The answer I sent is perfectly practical and correct as followed by me, and I might say by almost every other cabinetmaker. The glue certainly requires occasionally stirring when nearing boiling point, to prevent its burning; strain into an earthenware vessel. If wanted immediately put some into the inner pot of a proper glue kettle, with the outer one contain: ing water. If not wanted immediately, let it stand until cool, when it can easily be turned out or allowed to remain in the vessel at pleasure. A portion can then be eut out with a wet knife and put into the proper gluepot as directed. I should not think of adding water after use, as directed by "Vulpecula," but after frequent heatings it gradually thickens, I then add a little water to bring it to its proper consistence for my use, as it is not always required of one thickness. If "Vulpecula's" plan were followed, of putting water to it until too thin for use when put away, it would still be too thin for use after re-melting, unless allowed to stand a considerable time on the fire to evaporate the extra amount of water.-CABINETMAKER AND FURNITURE MANUFACTURER. [4634.]-ELECTRIC CLOCK.-As my friend, Dr. W H. Stone, mentions my name in connection with his electric clock, will you kindly allow me, in justice to the maker, to correct a slight inaccuracy in his remarks? I believe that the English patent has expired, and that it was never purchased by Mosely & Co. I have obtained a number of these clocks direct from Switzerland for my friends and have several varieties now in my possession. One of them has gone for more than two years with four sulphate of lead cells. The battery power is economized to the utmost extent by the clocks. If desired, I shall be happy to explain in what manner this result is obtained.-G. W. GRABHAM, M.D. to the pressure per square inch. Example: Height of 34:12:14:75: 5:20 in it just sufficient to allow the pivots to pass through, and as you revolve them with your bow, you will be able to file them to the required length and to round them .. 52 pressure per square inch. off and burnish them. If the watch bauks on the And if it is required to find the pressure on the whole potence you may now rivet your balance on, and then surface multiply the total surface of bottom in square narrow your pallets. If it does not you had better juinches by the pressure per squre inch.-ASSISTANCE. put it on slightly, so as to narrow your pallets and cet your bankings right before you rivet it, otherwise you [4664.]-PRESSURE OF WATER.-The vertical pres- may find your banking pin in the wrong place. The sure of a fluid on the bottom of an inclosing vessel is theo- pallets are narrowed by placing the pallet in a slip en retically exactly equal to the weight of the column whose in a piece of boxwood, and with a good hard file they cross sectional area equals the area of the bottom, and are easily filed away. If you attempt to file them withwhose height equals the vertical distance between the out this precaution you will in all probability break your bottom of vessel and the surface of the fluid. This is verge. If the watch you are putting a verge to is jenquite independent in the sense of the inquiry of any elled, you may see if the pivots are small enough by change of cross sectional enlargement or contraction in putting the jewel upon the pivot, and trying if it drops the upper portions of the inclosing vessel. If, for in- off freely. Of course, both the pivot and jewel-Luls stance, a funnel were filled with water, the pressure per must be thoroughly cleaned, or they will stick together. unit of surface at the spout on being closed by the "Scrape" must use a light cane or whalebone bow, and finger would only correspond to the depth of the fluid a horse-hair or cow-hair line upon it. I prefer cane to and have no reference to the conical enlargement. The whalebone, for I think it is lighter; and cow-hair to pressure at the bottom, in the case submitted by "Hol- horse-hair, for I think it is stronger. In putting new beck," is in both pipes equal, both per square inch, and pinions in, they are turned, not filed, or they would be per total surface, viz., when filled with water to 12ft. of out of truth. If Scrape" requires any further as height, in each case, respectively, 5·1931b., and 65-26021b.sistance in the matter of turning in his verge, I shall At 4ft. from bottom, however, whilst the pressure per be most happy to give him any information I cansquare inch would be in both pipes relatively the same, RUPERT. the total pressure would be in the one case 43-5081b. and in the other 17403361b.-E. W. A. [4674.]-PROBLEMS.-Remembering that there is always the same ratio between two parts of any line cut in extreme and mean ratio, I may write the problem as follows:A point O being given in a circle, to draw a line which will be cut by the circle in the ratio of m n. I have then MO: 0 N:: m : n, but I have also, drawing any line through O (Euc. III. 35) MO. ON AO.OB = a square K2 (Euc. VI. 13); the first proportion givesON MO. " hence M O2 = K, and M 03: K2 :: m:n, and I find MO by the well-known problem to construct a square which will be to a given square in a given ratio. 2nd problem. An angle being substituted for the circle, draw O D parallel to B A, take D E, a fourth proportional to m: n and A D (Euc. VI., 12), draw E O F, hence, F 0:0 E::m:n, analogous construction if the point be exterior to the angle. - BERNARDIN. M B N B m A 0 E m [4684.]-TYPE.-The difference between "genuine" and "pirated" type is readily seen in the "depth" of the cut of the face. Genuine type has a clean, deep cut, whereas the pirated has only a "surface" face. The reason of this is obvious. The genuine type is cast in a matrix that has received its "die" from the original steel punch; but the "pirated" is cast in a matrix produced by the electrotype process; i.e., a mould is taken of the genuine type bought from the original maker, and the matrix is deposited on this mould. Even in equal qualities of metal the "genuine" lasts longer than the "pirated." Type is now cast by machine; therefore no difference in quality can be made by the mere manner of casting.-SAUL RYMEA. [4691.]-POWER OF ENGINE.-See "E. W. AR letter. [4692.]-SCREW-PROPELLER.-To find the pitch of propeller, from the square of the extremity of the blade subtract the square of the length in the direction of the keel, the square root of this difference gives tan arc; then as the arc is to the circumference so is the length of screw to the pitch. Ex. 6ft. Oin.2-1ft. 10in.3 57, and 12 x 31416 = circumference, .. 57: 877 :: 1·3: 12, .. 12ft. = PitchASSISTANCE. [4694.]-HOROLOGICAL.-B. E. Loddy wishes to know what sizes of watches are made use of and recognized by the trade. Also what difference there is betweens watch 15-10in. and another 19-10in, diameter. Wate makers of England recognize eight sizes-namely 6, 8,1), 12, 14, 16, 18, 20; but then, although every maker does not have the exact same size of his watch as his neighbour ing fellow manufacturers, it is nevertheless called the sizes, smaller and larger. The 6 size has a diameter across the face 1 7-16in; the 8 size in.; and for ever following size, about 1-16in. additional. The dial measuring 1 5-10in. would be termed an 8 size; that of 1 9-10in. would be recognized as an 18 size by some makers, and a 16 size by some others. Pinions o watches differ in number of their leaves by different makers. The ordinary lever watch has third pinion of, fourth do. 8, escape pinion 7. Then in better-clas watches the two first-named have 10 leaves, and the latter 8, and sometimes it is 7. These are the pinions. The teeth of the wheels also differ when the number of the pinion leaves are altered and stand thus:-The centre wheel 64; third do. 60; fourth 60; escape 15; for pinions of 8; and 1 of seven. Pinions of 10 and 1. Seven have centre wheel 80; third 75; fourth 70; escape 13 Some makers will make a difference in the velocity of the train by adding or lessening the number of teeth in the fourth wheel.-SECONDS' PRACTICAL WATCHMAKER. same size if the diameter of the face be between the two inquires the way to turn a verge in, and he must not be [4690.]-TURNING IN VERGES.-Our friend "Scrape" offended at the advice I am about to give him, as it is given with the very best of intentions. It is this: that before he attempts to turn in a verge he must make himself thoroughly master of the bow and graver, and to do this he must have plenty of practice. The work that I should recommend him to begin with is making small drill stocks for watches. For this he will require a whalebone bow, with a catgut line, and with perseverance he will no doubt acquire the delicacy of touch so much needed for turning in verges and other fine work. When he can use his graver with confidence and precision, let him proceed in the following inanner to turn in his verge:-First, try it in his callipers to ascertain that it is true, for it is sad waste of time to work upon a bent verge; then see that its pallets are of the proper angles-that is, a little wider than right angles. The height of the verge may be determined by measur ing it across the diameter of the scape wheel, so that when the collet of the verge rests upon one side of the wheel the foot pallet extends just beyond the other. Having attended to these points, let him fasten his ferule upon the verge and run the pivots to a conical point by filing them as they revolve in his turns. The holes in the centres of his turns should be made close to the edge to admit of the pivots being turned easily, for if the verge is far from the edge of the centres it will be impossible to get the graver to work at it. Fasten the verge in the turns so as to revolve easily; place your rest about half-way up the collet, or about on a level with the pivots of the verge; then pass the hair of your bow round the ferule so that it crosses at the top; sharp your graver to a good point, and as you draw your bow towards you hold the point of your graver against the work, which you will be able to cut away in nice little shavings: begin by turning the collet so as to receive the hair-spring collet, turn it away with the point of Bateman has estimated the cost of laying lead and your graver, and cut it smooth with the edge. Next, labour, trenching, and carting as follows:turn the collet to a shoulder so as to receive the balance, which, by the way, must fit very tightly; the shoulder for it to rest on must be turned perfectly flat, otherwise the balance will not be level. A good rule for ascertainIing if the balance is let on the proper distance is to screw the slide and potence on the plate. Let the balance rest upon the slide, and if it is the proper height the lower pallet will touch the foot of the potence; of After the balance is fitted turn the collet away so as to course, this, like other rules, has numerous exceptions. form a hollow, leaving just enough to rivet the balances on with. The next operation is turning the pivot; the most likely to be broken, had better be turned first. foot pivot being the most troublesome, or rather the one "Scrape" must keep a good point on his graver, and not want to cut too much at one time, or he may break his pivots off: he must turn them down till they are but a trifle larger than what he requires, then take all the graver marks out with powdered oilstone applied with a steel polisher; clean all the oilstone off, and polish with crocus. If he does not like this plan (which is the best one), he may take his graver marks out with a fine file and then burnish them. This task accomplished the pivots must be passed through a centre, with fiue holes [4651]-POWER OF WATER WHEEL.-The following rule is derived from Dr. Gregory's formula :-Raise the radius of the wheel to the third power, and extract the square root of that power. Multiply this root by the area of the transverse section of the stream that supplies the buckets; divide the product by 6, and the quotient will equal the horse power. Required, the horse-power of wheel 16ft. diameter, and (suppose) section of 8ft., radius = 8ft. and 83 == then /512 22.62. 22.62 x 8 And 6.5 stream = = 512, 27 horse-power nearly. It would be a disadvantage to fix a penstock.-P. S. should be happy to work out the actual horse-power if "Miller" could give the velocity of stream per minute and section of ditto.-ASSISTANCE. [4656.]-GOLD COIN.-Mr. V. Gaillard, in the preface of his work, "Monnaies des Comtes de Flandre" (Ghent, 1852), gives exactly the figure of the same gold coin, and attributes it to the Morini, the Atrebati, other neighbouring people of Gallo-Belgian origin. BERNARDIN. or [4664.]-PRESSURE OF WATER. -"Holbeck" will find there is no difference in the pressure of water on the bottom of the two pipes per square inch if the height of water is the same in both pipes, as the pressure per square inch is governed by the height of water only, irrespective of diameter of pipe. And since a column of water, 34ft. high, equals 147lb. pressure per square inch, therefore to find the pressure for any other height per square inch, as 34ft. is to the given height, so is 14.75 Note that the first is the actual cost, the second the esti mated, the latter including carting. As to the second part of the query, there is no pressure in the pipes beyond that due to the head of water, but there is the friction caused by bends, outlets, valves, and inequali resistance to be overcome-first from air, secondly froua ties in the pipes. The pressure of the atmosphere is, as we know, 15lb. per square inch. The friction is so vari"T. W. C." may find tables in all books treating of byable that an empirical rule cannot be given, bat draulics. I will just give him the particulars of a test I have been favoured with, the result of which was that on a length of 7:69 miles there was a loss of head from friction of 19ft. per mile. On a length of 6-96 miles the loss was 12ft. per mile. The pressure due to a head of water is equal to the weight of a square inch of water lit. long multiplied by the head and the area of the pipe. For instance, take a head of 200ft., weight of inch of water 1ft. long 4341b. x 200 86-800lb. pressure per square inch. Say a pipe 2ft. diameter = 452 square inches x 86-8002240 17.5 tons pressure due to head of 2001t.-ESPERANCE. [4700.]-ELECTROTYPES.- Electrotype copies of coins may be easily aud cheaply made as follows:-Procure a common white preserve jar, some brown paper, sealing-wax, copper wire (that used for bell-hanging will do), 1lb. sulphate of copper, and some slips of sheet zine. Now take a rather large round ruler and wind round it a strip of the brown paper 4in. in width, five or six times; the end must be made to lie down on the roll and be well cemented with the sealing-wax; now take the roll off the ruler and you will have a brown paper tube. Take a card or thin piece of wood, and with the assistance of sealing-wax make an end to one side of the tube. Stand the tube on its closed end and fill it with water, if none runs out this part of your apparatus is complete, if it does the holes must be stopped up with sealing. wax. Next take a strip of zinc and see that it will fit the paper tube: it must be a little higher than the tube. To one end attach about Sin. of copper wire; this may be done by making a hole in the zinc and twisting the wire round it; to the other end of the wire attach the coin you wish to copy, this must be perfectly clean and the side which is not wanted to be copied must be coated with sealing-wax. Bend the wire down so that the coin has its face towards the zinc, and is parallel to it. Every thing is now ready for use. Place your paper tube to stand up in the jar, fill the jar outside the tube with a saturated solution of sulphate of copper, fill the tube with a week solution of salt and water, insert the strip of zinc in the tube so that the coin is in the solution of sulphate of copper opposite the zinc and as near the tube as possible without touching. Place the whole apparatus in a quiet place, and in twelve or fourteen hours you will have the coin covered with a thin coating of pure copper, which can be easily removed. This will form the foundation for another copy, which will then be exactly like the original.-CLEFOR. [4725.]-SHORT SIGHT.-The general tendency of a normal sight is to become longer as we increase in years. Therefore, as in my own case, a person who is shortsighted at (say) 15, may expect at 30 to possess a good average range of vision. But there are exceptions, as in the case of a sister of mine who suffers similarly to your correspondent. In such cases advice should be taken of an eminent oculist. At the same time I may say, from my own experience, that no injury can possibly be done by wearing spectacles suited to correct the optical defect in the eyes. Concave glasses of no greater power than is just sufficient to correct the error of focus, may be not only safely but advantageously used; they should be of such power as scarcely or not at all to diminish the apparent size of objects. I used a pair for some years, when requiring to see minute detail at a distance-.g., the faces of performers at the theatre. My sight has gradually become longer, and I now need no glasses, although for a distant landscape they still help me somewhat.-G. R. FITT. able, sitting under the organ at the west end of the [4725.]-SHORT SIGHT.-At ten years of age I was parish church, to read distinctly the Creed and Commandments painted over the altar at the east end of the church. By degrees the range of vision contracted, until at 16, when I left the school, I was unable to distinguish the clergyman standing at the communion table except for his white surplice. My sight then required concave glasses No. 8. Several of my young friends wore spectacles, but observing their helplessness when any accident occurred to the glasses I determined to do without, wearing an eyeglass, which I made use of as little as possible, and applied to either eye. I also endeavoured to lengthen my sight if practicable, by looking at distant objects. Ten business compelled me to use spectacles, and I found years after my that No. 6 was sufficient. Now after thirty years my sight is much improved, and those friends who took to glasses early have gone on increasing the power until they now find great difficulty in getting suited. A similar experience to mine may, I think, be found mentioned in a work by Dr. Kitchener. My own son has injured his sight by sticking a glass always in the same eye, and is now obliged to wear spectacles of different foci, made expressly for him at 21s. the pair. His sight was much improved after leaving school by two or three long voyages until he adopted the foolish habit alluded to.-PATERFAMILIAS. " [4707.)-STEAM.-Mr. Jackson does not mention the length of the conducting pipe; nor does he say if the steam pressure (40lb.) is in excess of the atmospheric pressure, or from zero. There are rules for estimates of this kind given in Spons' "Dictionary of Engineering," from which I select one application, as I think, to this case-not so much with the view of giving information about which I personally know but little, as rather of eliciting it from others of far greater capacities, and of directing their attention to these probably very useful rules. To permit of being treated by these formulas, the data given by Mr. Jackson must first be reduced into [4733.]-BRONCHITIS.-" Omega should have admetrical equivalents thus:-Uniform diameter of pipe vice from a physician. It is a very delicate matter to 2ɣin. = 0·06985 metres, steam pressure 40lb. per square become one's own doctor; many fatal cases have inch in excess of atinospheric resistance = 2-660 atmo-occurred by taking medicine injudiciously. In all cases spheres 202616 metres of mercurial column too much care cannot be taken by obtaining proper 00019385 density of the steam. The length of the pipe advice at once.-HARRY G. NEWTON. equal (say) 25 metres. Then for mean velocity of flow through the pipe as also of escape per second:266.76 x 202616 × 0·06985 (0-0238 × 25+ 0·06985) x 0-0019385 metres, or 170-9 x 8-281 x 60 33643-374 feet per minute. Area of pipe = 0.03765 square feet x 33643-374 = 1266-673 cubic feet of steam of 40lb. pressure, or of original density passed per minute. Mr. Jackson can try this rule for any length of pipe he may require by reducing its length to metres and inserting it in the place 25 occupies in the above calculation. I trust other and more able correspondents will have given this query their attention, and that we shall thereby arrive at its complete and satisfactory solution. Some years ago a very similar question appeared in a contemporary journal, but the replies elicited thereby were utterly unsatisfactory and inexhaustive. I trust that in this instance it will find a complete solution; the more so as it touches, in the case of short lengths of pipes, upon the x= minimum E. W. A. areas = = 170-9 [4734.]-REMOVING WRINKLES FROM PRINTS. -If anything will remove the wrinkles, it will be moist ening by steam, and carefully pressing them down whilst moist and hot, when perchance they may adhere to the old gum. But the best and only certain remedy is to remove the print entirely when so moistened and remount whilst moist.-J. B. PRIMUS. [4784.] REMOVING WRINKLES FROM PRINTS. The only thing that "Winner" can do is to soak his print in hot water by a brush (very light), and that will take it off the frame, then when it is dry stick it on with paste or gum.-A VOLUNTEER. blowpipe is a proper one (a gasfitter's pipe is too small articles), then see that the flame is full and large,one from in the hole to command a flame for soldering large a gaspipe with the nose screwed off is the best; in absence of that, make a flame with tallow melted in a large iron spoon or ladle with rag, lint, or cotton; moderate the flame by spreading the wick. Provide a piece of rough of safety-valve connections, &c. clean slate and a small camel-hair pencil; rub up a piece of borax thereon with clean water; cut the silver solder in small even pieces, paint the joint with the borax liquid, lay on solder. Now warm the article carefully, blow continually, increasing heat. Draw in supply of breath through your nose; this will keep your blast continuous until the solder is satisfactorily melted. Beware of the presence of lead about the article. "Cheek 14737.1-BLOWPIPE.-Let "Cheekache" see that his [4708.]-LOSS OF VOICE.-I have suffered for a long time in the same way as "Forester." Having tried a great many remedies, sometimes two or more simultaneously, I cannot say to which of them I am indebted for my cure. I put flowers of sulphur on hot coals and inhaled the fumes twice or thrice a day. I also used a similar remedy in a more costly form, inhaling sul-ache's" failure was want of suflicient flame.-T. C. phurous acid spray by means of a spray tube. I had solution of nitrate of silver injected into the larynx causing horrid pain, and I think little permanent benefit. What I have the most faith in, is, however, the cold douche to the throat, if patiently persisted in; I used it for some months, and I think it was that which cured me; I had a gin. tap, and held the throat under it, as long as I could possibly bear it, every morning. "Forester" may like to know that there is an instrument used by surgeons called a larnygoscope; by this ingenious combination of mirrors the interior of the larynx can be viewed, and probably the nature of the complaint detected, as was my case.-ARGENT SABLE. [4710.]-FASTENING BRASS TAP IN KITCHEN BOILER." Inquirer" should cut out a washer of the softest sheet lead (about 6lb. to the foot), and put it on to the screwed part of tap, between the back nut and the inside of boiler, and screw up tight. I did mine so three years ago, and it is all right now.-ARGENT SABLE. [4713.]-BEES.-I remember an instance of a hive kept in a garret to which the bees had access through a tiny hole drilled through the wall. Syrup is the best food.-ARGENT SABLE. [4737]-BLOWPIPE.-Use a larger lamp with a thick wick and increase the size of the hole in the blowpipe point. With a large flame and large hole in the blowpipe I can easily melt 4oz. of silver, or 8lb or 10lb. of lead. T. FLETCHER. can [4714.]-HOT OR COLD BATH.-"Handy Man have a pump for hot liquids. If he wishes to alter a common pump for that use, Warner, of Cripplegate, supplies buckets and valves (for any size barrel from gin. to 5in.) made without any leather about them, but a stuff called "quilting." I advise him to have nothing to do with either india-rubber or gutta-percha, but to ase iron barrel, black or galvanized, putting bends instead of elbows; in. would do; but pumping through it is slow work; lin. would cost more, but the friction would be less and the suction faster. By using a tee piece, the suction pipe could branch off to the butt and Copper; but this would involve having two cocks, one to each branch; these are rather expensive in the large sizes. lin. about 75. each; in. not much more than If there are a great many angles and turns between the bath room and wash-house, perhaps lead pipe would come cheaper, but I do not think it stands extremes of heat and cold very well.-ARGENT half as much. SABLE. [4788.]-GEOLOGICAL.-There have been, since the creation, changes in the texture of certain rocks, the result of which is the deposit of mud or sand, which after time changes by the chemical action into sandstones, clays, limestones, &c.-A MANXMAN. [4738.]-GEOLOGICAL.-The beds of sandstone land whereon the forests grew; the submerged forest thus occuring in the coal series are due to the sinking of the became the bed of a sca or estuary, and the sand was deposited upon it. In course of time the land again became elevated, another forest grew, and was in its turn submerged, and so on.-F.R.G.S.I. [4789.] -COLOURING SIZE.-John Bury should obtain some granular aniline blue, soluble in water. The price is high, but he will find it as enconomical as indigo, with a much better result. The way of using it is to disolve about an ounce in three gallons of water, then add sufficient to make the size the desired tint.-FACTORY LAD. [4741.] DISSOLVING INDIA-RUBBER. -Indiarubber can be dissolved in turpentine, oil, ether, or any other solvent, by introducing the solvent in the form of vapour. into a vessel containing the india-rubber in small pieces; tho vessel being then exhausted of air, and kept at the required temperature by means of steam.-HARRY G. NEWTON. [4741.] - DISSOLVING INDIA-RUBBER. - Indiarubber may be dissolved in coal naphtha, the quantity depending on the consistency required.-AUGUSTINE. [4741.] DISSOLVING INDIA-RUBBER. - India rubber is readily dissolved by chloroform or benzole; but I am unable to give any opinion as to the solution mixing with oil and turpentine.-UNIT. [4741.]-DISSOLVING INDIA-RUBBER.-The best solvent for india-rubber is benzole, or coal-tar naphtha may be used.-G. R. FITT. [4744.]-GUN COTTON.-To prepare gun cotton, make a mixture of three parts sulphuric acid, and one part nitric acid; when this has cooled (for it becomes hot on mixing), put into it some cotton wool, and let it be stirred about with a glass rod, then taken out, and all superfluous acid strained from it; it is then to be covered up for an hour or so. It should now be thoroughly washed in cold water, so that all the acid be removed; to ensure this completely, let it be afterwards washed in a very weak solution of potash, and then dried by a very gentle heat, produced either by steam or hot water; when dry, soak it in a solution of nitre and dry it again. It is now so explosive that great care is required in its management, being about three times as explosive as gunpowder.-CUTHBERT. of [4744.]—GUN-COTTON.-There are several varieties "gun-cotton,"-first, the explosive, soluble only in ether and alcohol, which is the basis of collodion, and acetic ether; second, pyroxiline, soluble in sulphuric to the existence of which the perfection of photography action of nitric acid on cotton or lignine in some form. is dae; third, xyloidine. All these are formed by the The difference between them consists mainly in the strength and temperature of the acids employed in pared with the strong acids (sulphuric and nitric) mixed. their preparation. The most explosive (No. 1) is prethe object of the sulphuric being to take water from the nitric, and so leave the latter in its full strength to combine with the lignine (or cotton). Any work on photography-e.g., Hardwicke's "Photographic Chemistry," treats of the preparation of photographic pyroxoline (No. 2). The following has been given for preparing the explosive compound (No. 1):- Dried and pounded nitrate of potass, 5 parts, sulphuric acid, s. g. 1845, 8 parts. Mix quickly in a Wedgewood mortar. more cotton than can be well covered, steep it four minutes, then quickly remove it and wash in a large quantity of water, which change frequently. The cotton should be scarcely altered in texture, and the last water should not redden blue litmus paper. The cotton must then be removed, pulled out, and dried at a very gentle heat. If put in Mrs. Smith's kitchen oven and over heated it will very likely cause an explosion which may render the services of the bricklayer, &c., not to say the doctor, requisite. "Experimentalist" used acids too weak, hence the gelatinizing. They should be first mixed, and then the cotton added. His product would be more like xyloidine. The process I give is best, as the nitric acid is liberated in a nascent form, and acts on the cotton in its strongest state.-G. R. FITT. Use no [4744.]-GUN COTTON.-The first thing to be done is to thoroughly cleanse the raw material. This is effected by boiling it in an alkaline solution, then drying it in a current of air, and then again boiling it in clean water. After the second boiling it must be very thoroughly dried at about 120. The cotton must be very thoroughly dried, as any moisture which might remain in it would, by combining with the acid, generate heat and set up a destructive action. The cotton, in charges of 1lb., is placed separately in a bath containing the mixed acids, the mixture in which the cotton is submerged consisting of 3 parts by weight of Nordhausen sulphuric acid (s. g. 184) and 1 part of nitric acid (s.g. 15), this mixture allowed to cool down-a process which occupies two or three days-before the cotton is placed in it. After immersion, the charges of cotton are strained until each contains only about ten times its weight of jar and covered down. In order to prevent any heating acids, and each charge is then placed in an earthenware current of cold water. The action which takes place from taking place, the jars should be placed in a when the cotton is immersed is as follows:-Cotton, when pure, is one form of cellulose, and is an organic compound consisting of six equivalents of carbon and ten equivalents of hydrogen-both combustible or oxidizable elements-together with five equivalents of oxygen, its composition being thus expressed, Ce H10 05 (by old notation C36 H30 Oso). Nitric acid, on the other hand, is a powerful oxidizer, and if added to cotton and its action assisted by heat, it will rapidly oxidize not only the H but a portion of the C which the cotton contains. In the manufacture of gun-cotton, however, instead of the action being assisted by heat, care is taken to abstract any heat as soon as it may arise, and the action of the acid thus moderated, only a certain proportion of the H being oxidized, and the C being unaffected. The nitric acid is, as I have said, mixed with three times its own weight of sulphuric asid, and the purpose fulfilled by the latter is that of intensifying the action of the nitric acid by absorbing the water with which even the strongest nitric acid is diluted, and also the water set free by the action of the nitric acid upon the cotton. The hydrogen removed from the cotton is replaced by an equivalent quantity of nitric acid, which has lost a portion of oxygen, and has thus become peroxide of nitrogen, and this makes the cotton explosive. C123N3 04 H14 Trinitro cellulose. (Gun-cotton.) 2 C6 H10 Os + 6 HNO3 = Cellulose. Nitric acid. } O10 + CH. O Water. The cotton after being exposed to the action of the acid for 48 hours, in order to ensure its thorough conversion, is removed from the jars and squeezed nearly dry. It is then to be suddenly plunged into a strong fall of cold water, and left for a short time. The object of placing the gun-cotton in the fall of water is to ensure the sudden and complete submersion of the material, and thus avoid the heating and decomposition of the cotton, which would take place at the surface of the water if the cotton were immersed gradually. On its removal from the fall of water, the gun-cotton is wrung dry and placed in a stream of water for 48 hours. After being should be thoroughly dried at the temperature of no washed and partly dried several times more, the cotton more than 140°.-A. E. [4746.]-SCREW CUTTING.-In answer to Joseph Moseley, it is a pity his screw has a square thread as that is not suitable for a split nut, unless a great deal of the thread is filed away towards both sides of each half of the nut. In Whitworth's lathes, which have a square thread rounded on the top, the nut only touches about of the circumference of the screw on each side or one half altogether, and the nut would not open or close without it. "W. H. N.," on p. 331, Vol. X., gives a drawing of his clasp nut, on which I think mine, that I send herewith, is a great improvement. First, the square plate that carries the nut is held on by two screws and can be detached easily for cleaning, which should often be done. Next the cam, of which a front view is shown on Fig. A, instead of being outside the square plate with the pegs that actuate the half nuts coming through slots in the plate, is countersunk into the thickness of the plate on the inside, and the pegs are reduced in length. The nut is first made in one piece, and fitted into chamfer slides on the plate, one side being cast in the solid and planed out, and the other formed by a strip or wedge piece of wrought-iron, which is held on by two small screws, and bears on one side on the chamfer of nut, and is supported behind by an upright fillet also cast on the plate, as shown at A, Fig. 2. The nut is afterwards sawn in two. The cam is forged as a round plate, with a stalk to it like a mushroom-headed bolt, and is squared for the lever handle, and screwed on the end for a nut, by means of which it can be made to work as tight as may be desirable. The pins that work in the grooves of the cam are indicated in Figs. 2 and 3. I have shown the left-hand end of leading screw fitted into a socket with a bearing close to it, as recommended in my answer, (4631, p. 573), by which means it can be reversed so as to distribute wear. The section of bed shows the way I have fitted my slide-rest to a bed of ordinary section the strips being of wrought-iron, about lin. broad x 5-16th thick, and about 14 or 15 inches long, the one over the clasp nut being forced up to its place by a wedge piece against a solid fillet B, Fig. 8, similar to the one in the nut. The other is set up by set screws C, as they can easily be got at on that side. There is also shown a stay bar that I put just under the end of mandrel head as there was no stay cast into the bed as there should have been. The slide-rest side view shows the one I use, except that I have added a fillet where the word is printed on the drawing, in order to enable the plate of slide to bear on its outside edges, as shown in the back view, Fig. 1, and not on the top where the double line is drawn, as I find this plan makes the slide-rest double as strong. I have shown the slide 10 long, and it would be all the better if it were 12in., the additional length being put on the right hand end. As to advice I think he would do best to put a clasp nut even on the square threaded screw, as the bevel wheels and clutch are troublesome to fit. It would be better to have the sides of his square thread sloped a trifle-but under any circumstances, to make quite sure first that the screw is exactly 48 to a foot, as screws are very often 893 or 48 to a foot, and with them you cannot cut screws to fit Whitworth's screw tackle. And if it proved not to be quite true, I should have it cut over again with a V thread which would probably involve reducing the diameter of the screw by 1-16in. You can cut your own nut, if you make a temporary one first by casting some Babbit's metal on to part of the screw which should first be well smoked over a paraffine lamp. Two or three threads quite enough.-J. K. P. [4748.]-ELECTRO-MAGNETIC BATTERY.-I must apologize to "Beriro" for not having answered his query before, but I am afraid neither I nor any one else can efficiently aid him until he acquires a knowledge of the subject far greater than can be imparted in a short letter. The principle of magneto-electric machines may be thus illustrated:-Take a long insulated copper wire, say 200ft., and coil it upon a bar of soft round iron, say lin. diameter and 8in. long. Let the ends of the wire be connected with the binding screws of a galvanometer. SCREW CUTTING. Now take a strong bar-magnet and quickly approach one of its poles to within an eighth of an inch of one end of the soft iron, the needles of the galvanometer will move, indicating a current in a certain direction through the coil of wire: the needles will, however, again resume their original position, as the current is but momentary. Now take away the magnet, and the galvanometer will again indicate a current in the opposite direction to the first. The longer and thinner the wire the more powerful the magnet, and the more rapid its motion the more intense will be these induced currents. In most machines it is not the magnet which moves, but the coil of wire and its soft iron core. There are usually two coils and cores, which revolve rapidly in front of the poles of a horse-shoe magnet. It is evident that the current obtained is not continuous, but consists of a rapid succession of currents in opposite directions; if currents in one direction only are required, one set of currents are taken out of the circuit by a commutator arrangement. "Beriro" cannot, of course, make a machine from this description. I cannot give him details sufficient to do so without occupying too much space, and he will find them in most books on the subject, but I would not advise him to attempt it, as he is pretty certain to fail without full knowledge of the subject and considerable skill in construction of such instruments. Far better buy one if it will answer his purpose, but this I doubt, as for most uses of a galvanic battery a magneto-electric machine, unless very powerful and expensive, would be an inefficient substitute. If "Beriro" will say for what purpose he wants a battery I shall be happy to give him my opinion as to what will best suit him.-IGNORANT IRISHMAN. [4750.]-CARBOLINE.-In reply to Mr. Jarman regarding the price, &c., of "carboline," I beg to refer him to my letter, No. 141 (page 448), in answer to the same question of "cheap gas" (page 383). Messrs. Woodward's price is 4s. 6d. per gallon.-C. D. C. [4751].-TAPS AND DIES.-I thought "Semper Para- hope just to strike the thread, which must be finished [4758.]-GERANIUM PROPAGATION.-Take your cuttings and level them just under a joint (about four joints in the cutting are best, though you may strike with only two), then having filled some 6in. pots with light soil put your cuttings in close to the side, all round about 3in. apart, two joints in and two out, and keep damp. You will know when they are rooted by their beginning to grow, then pot off in thumb pots, or let them remain and pot at spring.-WELBY. [4757.]-GAS PRESSURE GAUGE.-I send a rough sketch and description of the simplest form of a gas pressure gauge. They are made in various shapes and ס'יינייינייידיי'דיי sizes to suit requirements, but nearly all depend on the same principle as that I am going to describe-viz., displacing a column of water. A is a strong glass tube |