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J. S. will find directions for making lard oil on p. 283, vol. 30.--H. C. W. should l'!lad our articles on the management of boilers on p. 293, vol. 36. As to testing boilers, see p. 246, vol. 34.--W. E. can plate brass, etc., with nickel by the process described on p. 235, vol. 33.-0. E. will find directions for making oil of peppermint on p. 219, vol. 31.--E. O. T. will find an excellent recipe for cement for mending roofs on p. 187, vol. 35.- J. B. will find a recipe for tough glue on p. 43, vol. 32.-- D. A. G. will find directions for making impression paper on p. 378, vol. 28.-T. S. L. can remove paint spots from glass by following the directions on p. 235, vol. 36. --J. T. S. will find a description of the Gatling gun on p. 143. vol. 26.--A. C. will find a description of an hydraulic press on p. 315, vol. 35.-A. H. D. will find a description of the nitrate of silver process of making mirrors on p. 267, vol. 31.--D. S. M. will find directions for kalsomining on p. 351, vol. 24.--P A. N. does not send sufficient data R. F. I. will find directions for building an ice house on p. 251, vol. 31.--E. B., C. F. Q., J. W. B. N. C., G. P, R. K. B., J. F. P., W. H., J. P., and others, who ask us to recommend books on industrial and scientific subjects, should address the booksellers who advertise in our columns, all of whom are trustworthy firms, for catalogues. (1) O. C. K., of Leipsic, Germany, says: To make lead pipes nearly hauless, as regards the poisonous properties of the lead salts soluble in water, fill the pipes for a short time with dilute sulphuric acid (SO4H2H) or 20 H.O). The pipes will become covered with a thin coating of sulphate of lead (SO4Pb), which is far more insoluble m water than the oxyhydrate of lead (pb OH.) generaUy fonned. (2) A. G. says: I have a rough chamois skin leather bag, into which, by some mistake or other, there came some English vermilion, dry. How could I clean it out? A. Vermilion is a compound of mercury with sulphur, and there is no solvent for it that would not damage the materials of the bag. Remove as much of it as you can with a stiff brush, and then cause an energetic stream of water to impinge upon the discolored surface, so as to mechanically carry off the particles of the pigment. * c (3) G. B. S. asks: 1. Will- tin (old cans, etc.), copperplated, do for the coppers in a gravity battery? A. Yes. 2. Will salt (sodium chloride) do forthe saline substance? A. Better use sulphate of zinc. 3. Will common plate (window) glass do for the plate in an electric machine? A. Yes, but it is not the very best. (4) W. M. M. says: I have a magic lantern, and want to know what kind of oil gives the best light for it. A. Kerosene gives as good a light as any, and better than most others. (5) C. M. asks : What can be appl.ied as a depilatory on horses, destroying the pi gmentary granules yet not destroying the life of the hair? 'The object in view is to brand colored horses with a white brand. A. This is not practicable. The color of the hair above the cuticle may be bleached by the application of chlorine water or nitro-muriatic acid (aqua regia). It is not probable, however, that the action of these wiU be rapid enough for your purpose. (6) C. E. H. says: Four years ago I had in a mill an upright shaft of eight inches diameter which, with attachedgearing, weighed several thousand pounds. The toe on which it turned commenced cutting badly. It was impossible to remove the toe . Washers of steel raised the shaft too high out of the step, wore out rapidly, and did not work thoroughly well. I went to a number of machine shops for advice. One told me to grind it out with emery; another said my only course was to take down the shaft and send it by rail to the shop, and none could give me any speedy and economical cure for the trouble. At length I met the rightman, who told me to raise the shaft and put under the toe (in the step) an old-fashioned large-sized copper cent. This I did, and the heating and cutting ceased at once , and the difficulty was permanently overcome. Since then I have put small cents in the steps of millstone spindles and always with good effect. The grooves filled up with the copper, and the toe looked as though it were copperplated and burnished. I even got to introducing a small copper cent under each new spindle, and think that so doing prevented cutting. (7) A. J. F. asks: How can I set the lenses of an eyepiece to a telescope? It Is composed of two plano-convex lenses. A. The Huyghenian eye lens is one third the focus of the field lens, and is placed its own focal length with the focus of the latter. (8) A. L. S. says: I learn from tables on the heat of water with steam, that 60 lbs. pressure equals 292'6 Fah. Is this the degree of heat under any and all circiUlDstances? A. This is for fresh water. The temperature changes, if the water contains impurities. (9) G. W. K. .says: I have tan vats which have not been used for some time. I keep them full of water to preserve them. How shall I keep mosquitoes from breeding in them? A. Cover them'tightly. (10) E. C. H. says: I wish to fill up a low place in a lot with a mixture of sand and gravel. How much will it settle after leveling it off 1 foot deep with no packing? Surface of plot is a rich loam, subsoil a clay bottom. A. From to . What is the thinnest circular saw I can nse 10dnches in diameterfor sawing 2 inch white oak, sawrIlDmng on 700 revolutions per minute with 2 horse power? A. One of No. 16 gauge, or about h of an inch thick. (11) I. says: Nearly all lugs or supports riveted to steam boilers have three on each side, one of them in the middle of the boiler; so, if either end of the support settles, the whole weight of the boiler of water is himg by the middle. This is all wrong. There should be either two or four supports on each side of the boiler, the longest space between the two inside ones. Is not this so? A. Yes. We could not tell you why the former course is pursued, except that common sense is scarce. Why is it that persons at this period of mechanical science place tightening pulleys on the load line or pulling side of a belt? A. We do not know, but we are glad to call attention to these points again, as we have frequently done before. (12) G. H. .A. says: I sometimes preserve eggs in limewater, and they keep well, but look limyaf- ter taking out of the solution, notwithstanding that I let the lime settle in the water till it looks clear, and dip it out, leaving the lime behind. Is there anything that I can put in to remove what little lime stays in the water? A. We think filtering will answer the purpose. Place a piece of filtering paper in a funnel, and pour in the liquid. (13) C. S. O. asks: 1. Has the compound engine any advantage or economy other than shortness of stroke over a single cylinder sufficiently long to secure an equal amount of expansion? A. It is claimed that the machinery can be made lighter, with the compound engine, for high grades of expansion. 2. Will highly volatile liquids give more power than water in an engine, from the same fuel? A. Not necessarily. (14) G. S. C. asks: Could not hot air balloons be used for aerial navigation, if a light furnace were constructed which would constantly run a hot current into the balloon? A. It would be difficult to carry enough fuel for an extended voyage. Fire baUoons have been used successfully for short trips. (15) A. S. E. says: The centrifugal force on the sea board and that on the top of the highest mountain is considerable. The specific gravity is the same. Let a globe be turned rapidly, and water put on; it climbs to its greatest diameter, and fiies off. Two canals are cut at the same declivity, one nortlI and the other south; the velocity is the same in both. Neither does this influence affect the wind. Please explain the law that counteracts this infiuence and produces the equilibrium? A. There is a slight difference in the effect of gravity at the different levels. (16) C. G. V. P. says: Is it practicable to heat the passenger cars with the steam from the locomotive? If so in what manner is the steam conducted from the boiler? It seems to be a failure in Europe, and some of my European friends ask me what the SCIENTIFIC AMERICAN thinks about it. A. It might be possible , but it would be necessary to increase the size and weight of locomotives. Steam pipes could be arranged in a similar manner to the air pipes used with continuous brakes. (17) M. W. H. says : How many lbs. pressure can an ordinary horse exert, when doing its best? A. Between 300 and 400. 1. What is a high pressure engine and boiler? Is it not one that condenses its steam, and uses the water over again? A. In the common acceptation of the term, a high pressure engine is non-condensing. 2. 'tat steam pressure will a vat sustain, if made of 2 inch plank of oak, matched, and covered with heavy sheet iron, both out and inside? It is 3 feet to diameter and 10 feet high? A. Your data are insufficient. 1. How can phosphorus be made into solution for using on gun sights after night and other similar purposes? I dissolved some in hot olive oil, also in turpentine , but it settled and fonned a hard body as soon as cooled, in both. What is the trouble? A. Probably the ingredients were not pure. 2. What is the coldest temperature in which phosphorus will glow or show light? A. About 32 Fah. (18) F. R. H. says: I have an iron tank 4 feet in diameter by 12 feet long, in which I put dead stock to be steamed out. This tank Is supplied with steam from a portable boiler and engine. The steam dome is 1 foot high, and the pipe rises from the dome feet in three turns, and goes 6 feet down into the tank in the bottom. When I turn on the steam to the tank the water blows from the boiler faster than I can pump it into the boiler, at the same time running the steam down. It has only begun acting so lately. Can you tell me how I can overcome this difficulty? A. It is not unlikely that your pump is out of order. 'You can regulate the amount of steam let into the tank, so that the pump will supply what is taken away. (19) W. F. A. says: I have tried to bend basswood, but have failed. I gave it a long steaming, and it would break off short. Then I tried a short steaming, but it worked in the same way. Can you give me some information? A. It is very possible that the specimens you tried were not suitable. It may be that any kid of wood can be bent at pleasure, by a proper treatment, but the methods are not generaUy known. There is now for sale in this country bent-wood frci- ture, which is, we believe, manufactured abroad by a secret process. (20) A. B. says: I saw in the SCIENTIFIC AMERICAN, of January 20, an engraving of a new water velocipede. Please tell me if the two fioats would be better if they were of the shape of a triangle, and what should be the distance between the floats? How long, from end to end, and of what size should the paddle wheel be? What should be the thickness of the fioats, and what would be the best material to make them, in case of stones or rocks in the river? A. We think the cigar shape is best for the fioats. Their size depends on the load to be carried, and must be calculated for any particular case. Distance apart, 2 to 4 feet, according to capacity, wiU do. They could be made of light iron, .for clearwater, andof wood for rocky places. (21) F. W. B. asks: What power can I use to run a dental engine and a small poIishing lathe head? I have tried water motors, but they fail. A. We think there are water motors in the market that will answer. There are also small steam and electric engines suitable for the purpose. (22) S. N. M. says: 1. I read that the earth's rotation is retarded 22 seconds a centuryO'22 seconds a year. Also that two thousand million years ago, the earth was rotating twice as fast as now. I figure thus: S6164-00 Earth now rotates in 86164'09 seconds, and 2XO'S 195,327 years ago earth rotated twice as fast as now. Am 1 wrong? I also find the following: It therefore follows that she was rotating at about the same rapidity as now, when she became solid; and as the rate of rotation is certainly diminishing, the epoch of solidification cannot be more'than ten or twelve millions of years ago. How can this be? A. Your calculation does not seem to be correct. The assumption is for 0*22 seconds a year at present. We presume the article gives reasons for the second statement, which is not very alarming to the present generation, even if true. (23) W. C. W. asks: How will a cast iron vertical boiler, 3 feet high and 15 inches in diameter, shell being inch thick, with fiat heads inch thick, and firebox in base of boiler, with 15 tubes, as compared with a wrought Iron one of similarfonn? A. We think the wrought iron boiler is preferable on many accounts, and advise you not to use cast iron. (24) W. H. P. asks: Will it require less heat to boil away 100 gallons water in vacuo than under atmospheric pressure? Would there be a decided gain in the expense of fuel in thus evaporating water? A. The amount of heat required would be a few per cent less in the case of the vacun. (25) A. B. says : 1. We intend to put a siphon to draw the water from a part of mines, tlIe height to which the water has to be lifted perpendicularly is 20 feet from the summit. There is 60 feet of tunnel with a grade towards the other end of 6 inches to the 100 feet. We can extend the pipes to a depth of 35 feet, so that the discharging end will be 18 feet below the suction end. Length of pipe in all wiU be 700 feet. Will it work? A. It will be necessary to have an air valve at the highest point, which must be opened occasionally or may be made automatic. 2. We intend to use 3 inch gas pipe for tlIe siphon, but the present supply of water will probably run through a inch pipe, and the water will increase in quantity. Can we regulate the siphon so that the present supply of water will run in a continual stream through the 3 inch pipe by putting a stopcock on the discharging end and keeping it open or i of the time--as the supply of water varies? A. Yes. (26) A. A. H. asks: How can I remove ink stams from fabrics, fingers, and paper without Injuring the article stained? A. To remove ordinary ink (tanno-gallate of iron) stains, the following treatment is recommended: In many cases lemon juice will often prove efficacious. If this fails, try an aqueous solution of oxalic acid (1 part to 2 parts water) and rub well with a soft cloth. Or use a solution of chloride of tin (1 part to 3 parts water, or pure dilute muriatic acid (1 part to 10 parts water). Apply with a camel's hair brush, and then wash in cold water. Where the colors of the fabric are affected by the above treatment, moisten the spots ith fresh milk and cover with fine salt. This should be done before washing. If the fabric is fine and delicate, the stained portions may be dipped in melted tallow and then pressed for some time between layers of wann pipeclay. Stains of indelible ink (made from nitrate of silver) may be removed by moistening them with a brush dipped in a strong aqueous solution of cyanide of potassium, and then well washing the fabric in water. The cyanide solution Is very poisonous. How can I gild book covers, picture frames, etc.? A. Fine gold leaf is used for ornamenting books. It is stamped in the covers by a press. On gilt picture frames gold leaf is also used, but in many instances the gold-like finish on these frames is produced by laying on first silver leaf, and then lacquering this with an alcoholic solution of orange shellac, to which is often added gum sandarac and dragon's blood, saffron, gamboge, etc. (27) J. W. S. says: Can you give me a goodfonnula for making a fiuid extract of annotto? A. Annotto is often adulterated with fiour, soap, Venetian red, and red lead. Macerate it witli twice its weight of alcohol for several hours and filter. Please tell me how to make a good stencil ink, which contains no oily matter and will quickly? A. Rub up a quantity of lampblack in II mortar with enough of a strong, hot solution of dextrin in water to fonn a paste, and add a little alum water. Solution of soap is sometimes used in place of the dextrin and water. (28) J. R. K. asks: By what process can I remove the silver from old mirror backs, so that it can be used again? A. If it is silvered, use nitric acid, ane! crystallize from the solution by evaporation in a ;ma'l porcelain vessel. If the coating is an amalgam of tin and mercury, use mercury, and loosen the film by rubbing with a cloth. I have some walnut furniture finished in shellac. It got wet in moving; and wherever the water touched it, it left a white spot. How can I remedy this? A. Rub the spots with a little oil mixed with Venice turpentine. Is arsenite of copper called Paris green? A. No. Ar- senite of copper is known as Scheele's green; Paris green is an aceto-arsenite of copper. (29) G. J. H. asks: Is there any way to separate tin and copper which have been melted together, so that the copper can be used again? A. Most of the tin may be bed out by prolonged exposure to the air at a high temperature. This is the onlypractical method we know of. Small quantities of the alloy may be dissevered by dissolving It in a slight excess of strong nitric acid. The insoluble oxide of tin will then settle to bottom of the vessel, when the copper solution may be decanted and the copper precipitated out as oxide with.an excess of potassa, soda, or lime. This precipitate may be reconverted into metallic copper by first drying it thoroughly, and then mixing It in a crucible with powdered .charcoal, and exposing to a high temperature. The tin may be recovered in a similar way . (30) W. B. M. says: I want to build a tank 48 inches deep by 48 inches wide by 96 inches long, for boiling linseed oil with steam. What- amount of pipe will be Tequired to dissoive the manganese used in boiling that amount of oil? A. This can best be determined by experiment. It may require 150 to 20 feet of inch pipe, but this, of course, Is dependent on the temperature attained and the length of time allowed for the operation. There are no accurate data on the subject. (31) W. B. asks: Is there any possible way to get the turpentine taste out of rosin? A. Pulverize the rosin and boil it for some time with a quantity of water; then dry, and fuee it. (32) O. E. says: I will advise R. L. D., who asks how to harden an eggshell, to lay the egg in vine- garfor two weeks. The shell becomes soft, and you can stretch it like a piece of rubber. Lay it in a strong solution of saltpeter for two weeks, and then you cannot strike it to pieces with a hammer. (33) A. J. J. asks: How can I make an indelible mixture of nitrate of silver, using oil? A. Yon may make an emulsion of the nitrate in the oil by rubbing them up together in a mortar. It is better to use glycerin instead of oil. Mordant with a strong solution of carbonate of soda. (34) H. E. W. asks: 1 In the manufacture of electric annunciators, will malleable iron castings answer as well for frames for the magnets, etc., as brass castings? A. Yes. 2. H the magnet cQl'es are screwed 1877 SCIENTIFIC AMERICAN, INC. 316 J titutifit Smtritan. [MAY 19, 1877. directly to the malleable iron frame, without a connecting piece of iron, will it answer as well, the malleable iron acting as the connecting piece? A. Yes. Which is cheaper, to cast small articles in brass, or to cut them with dies? A. Castings will probably be found cheaper. (35) W- P- E. asks: 1. Have you any knowledge of a speed of 25,tt)0 revolutions per minute having been obtained by a single motion, without gear- ingof any kind? A. We do not remember having seen or heard of such a device. 2. Could such a speed be advantageously applied, for instance in blowing a steam fog horn for the Signal Service , or for other purposes, provided the machine giving the motion was not too expensive? A. It might be usefully applied to numerous cases, if cheap, simple, and powerful. (36) A. M. W. says, in reply to D. W.'s query as to his singular phenomenon: This does not appear to me at all singular. It is very evident that the bearing, or step, had become dry. It is a common occurrence , where steel runs in or on steel , that the bearing will, it allowed to get dry, become heated to such a degree that the temper is lost, and the surfaces get to cutting and almost weld together. The statement that the plate was bent by the hammer shows that the plate was soft then, even if it had once been hardened. D. W. says that sufficient oil was found above the plate collar, but he does not say that there was oil on the plate where it was most needed. In my experience, I have never known hardened steel to cut or grind together when properly lubricated, and I think it impossible to produce that effect except by a pressure that would expel every particle of the lubricant. Two hardened steel surfaces may be ground together when dry without losing the temper; butthey would not adherewith the tenacity that D. W. describes. It is possible that the time taken to raise both stones gave the spindle and plate opportuni ty to give off the heat to the cast foot and bed. In my opinion, the construction of the oval end spindle would have a tendency to run dry even under common lubrication, as it would only bear on a small part of the end, which might, with the weight of the stone, force it dry. Hardened steel bearings do not oftel;l,.give any- notice of being dry, except by refusing to do duty, a very few revolutions being sufficient to announce the fact and ruin the bearing. I would suggest to D. W. that he make his spindle so that its epd rests its whole surface on the step with a hole in the latter opposite the center of the spindle. The spindle should be made like a cup, so as to form a reservoir for the oil, and so deep that the end of the spindle shall be immersed. (37) J. R B. says: I have found a specimen of tantalite. Can you tell me anything about this rare mineral? It is said to cone ist of tantalic acid and iron, and is valuable, especially when found in crystallized forms. May we expect to find it in veins or beds, or on high or low lands? A. Tantalite is Fe O, Mn 0, TaO5, with sometimes oxide of tin replacing part of the ferrous oxide. Some specimens are nearly destitute of manganese and some contain oxide of copper and lime. Its luster isneariypure metallic, somewhat adamantine; its color is iron black, and streak reddish brown to black. It is opaque and brittle, and its hardness varies from 6 to 6'5. Its specific gravity is from 7 to 8. It is confined mostly to albite or oligoclase granite, and is usually associated with beryl. it is also found associated with gigantolite in albitic granite, and with lepido- lite, black tourmaline, and colorless beryl. The name is usually extended to the American mineral columbite, the average analysis of which gives Si O2 (SO'6O), Fe 0 (15'57), Mn 0 (5'0), Sn O. (a trace). (38) T. McC. says : 1. I am building a small horizontal steam engine, with 2 inches bore and 4 inches stroke. What size of boiler would I need for it, and what should be the thickness of the iron ? A. Make it 15 inches in diameter, 24 inches high, of inch iron, for 60 lbs. pressure. 2. What would be the best speed to run it at in order to get the most power? A. You may run it at revolutions a minute. 3. Could I make a cylinder of an engine with 2 inches bore and 4 inches stroke with Babbitt metal, that would stand the steam pressure as well as brass or iron? A. No. (39) H. P. S. says, in reply to A. B.'s questions as to the violin: There are two or three different tools with which the grooves are cut. One of the best I ever used or saw, I constructed myself; but it cannot well be described in a limited space or without illustrations. With it a perfect groove can be cut around a violin plate inhalf an hour. A perfect groove cannot be made without a tool well adapted to the purpose. The threads mentioned by A. B. are known as purfling, and consist of a thin slip of .white holly wood between two similar slips of ebony, and are glued into the groove before the plate receives its final finish. Staining is, in most cases, done upon the wood, with thin, transparent dyes of different composition, and varnish laid on over that in the ordinary manner; but' the technicalities of this portion of the subject are too numerous for treatment in brief space. See Business and Personal column of this issue. (40) D. H. M. says, in reply to D. W.'s query as to the welding of his mill spindle: I suggest that the mill had been in use long enough to wear the lower end of the spindle to such a nice fit on the step that no oil could get under it, which caused friction sufficient to produce heat enough to weld it, and as it was done suddenly, the heat did not extend far in either direction, and the cold metal in connection with it soon cooled it down again. While the oil that it was covered with answered in the place of borax or other welding preparation, and at the same time excluded the atmosphere so that no change of color of the heated parts took place: I have seen a hardened steel gudgeon that was in the lower end of a water wheel shaft welded to the step when it was three feet under water. The force of the wheel twisted it off a little above where it was welde(l; and when it was taken out the piece could not be knocked off the step with a sledge hammer. (41) R. L. C. says, in reply to D. W.'s query as to the millstone spindle and step: I have repaired two mill spindles that have had their points ground or welded to the steel plates npon which they ran. In one case the steel point was inches in diameter, andprojectedfrom the spindle (which was 4 inches in diameter) about 3 inches. It was twisted off about inches from the end, and the parts were to all appearance thoroughly welded together. In the second case, the point was of about the same dimensions as thefirst; but instead of twisting the point off, it med in the spindle (which of course cut it badly), where it stuck to the plate. After considerable hammering, they were broken apart, but not where they were welded, as part of the plate came away with the point when they separated. I account for it in this way: As long as two metal surfaces that areintended to run together are properly lubricated , we have no grinding or welding if they ' are proportioned! to the work they have to do. In the above cases, the person in charge of them said there was j plenty of oil in the pots. It often happens that the pas! sage ways get stopped up and the oil fails to reach the | parts, and the result is that they grind together almost ' instantly. | (42) M. D. L. says: We desire to manu- ' facture for our own use in large quantities, carbon plates I for batteries, and carbons for electric lamps, of larger size and greater length than we can find in the market. What mixture of materials secures best results? What degree of compression is required? How is compression applied ? Should the mixture be heated while under compression? What kind of mould is used? How can we prevent the carbon from adhering to sides of mould? A. In his work on Electricity and the Electric Telegraph, Prescott says: The fine dust of coke and cok- 1 ing coal is first put into a close iron mould of the shape ' required for the carbon and exposed to the heat of the furnace. When taken out, the burned mass is porous and unfit for use, but b,.;repe'btedly soaking it in thick , syrup of gas tar and reheating it, it at length acquires the necessary solidity and conducting power. (43) R. J. J. asks: How can I make a galvanic machine for giving shocks from the wire of the telegraph sounder? A. You can get a pretty strong shock from an ordinary telegraph relay, if you have one, and do not want to i. cur the expense of a special apparatus. The connections are made in the following manner: The relay is joined up in circuit with a battery and mechanical vibrator for interrupting the circuit, and two wires with handles, to be held when taking the shock, are connected to the binding screws of the relay's helices , one wire to each screw. (44) H. A. H. says: I have a glass jar, about two feet of insulated wire, some blue vitriol and some sulphate of zinc. Please tell me what more I want to make a battery with? A. Get a copper plate, attach the wire to it, and place it on the bottom of the J ar with the wire sticking out. Fill the jar about two thirds full with a weak solution of sulphate of zinc and water, and suspend a zinc casting, provided with a terminal wire, from the top of the jar; let the zinc just dip below the surface of the solution. Now drop a few crystals of blue vitriol on the copper plate and join the wires for a short time, when the battery witi be ready for action. MINERALS, ETC.--Specimens have been received from the following correspondents, and examined, with the result stated : WillJ. M. P. send us a specimen of the residue from his limestone water ?-G. S. A.--The piece of rock contains titaniferous iron . It would require a quantitative analysis to determine all of the other constituents. It also contains a little arkansite--titanic acid . The pieces of metal consist apparently of the iron from your ladle, together with some titanic acid.--J. Z.--So far as we can discover, the segar contains only very strong tobacco. The odor is due to certain essential oils peculiar to tobacco, and canno; well be imitated.-- G. H. P.--Itis a variety of mica called muscovite, consisting of potash, alumina, and silicic acid. It is not valuable.--B. F. C.-It consists principally of carbonate of soda. We do not see that it would be likely to prove very efficacious as a scale preventive. It will not injure the iron.--We have received some minerals in a small pasteboard box without a name on it. No. 1 is chlorite, composed of oxide of iron, magnesia, alumina, and silica. No. 2 is chondrodite--a silicate and fluoride of magnesium. No. 3 is spinel--magnesia and alumina. OFFICIAL. INDEX OF INVENTIONS 1I'0R WHICH Letters Patent of the United States were Granted in the Week Ending April 10. 1877, AND EACH BEARING THAT DATE. [Those marked (r) are reissued patents.] A complete copy of any patent in the annexed list, including both the specifications and drawings, will be furnished from this office for one dollar. In ordering, please state the number and date of the patent desired, and remit to Munn&Co., 3? Park Row, New York City. Amalgamating ores, Laflin&Elliott. .. Animal trap. M. Early. Anti-friction bearing, O. R. Chaplin ... Anvil, blacksmith's, H. B. Sevey Axle box, D. Dalzell Bale band tightener, J. L. Sheppard ... Bale ties, etc., cutting, J. R. Tobin Barrels, etc., lining, M. Laflin Barrels compressing, O. D. Goodell ... Bed bottom, spring, F. B. Franklin (r).. Bed bottom, spring, J. H. Palmer Bedstead, wardrobe, M. cfosby D. F. H. asks: How is the tubing of brass band instruments formed, and how are the dents removed from the same?--D. S. says: I have made a few wooden organ pipes, but they do not give more than a whistling sound. Can any one give me the proportions for a middle C ?
