On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Hints to Correspondents Name and Address must accompany all lette, or no attention will be paid thereto. This is for our information and not for publication. Reference to former articles or answer should give date of paper and page or number of question. Inquires not answered in reasonable time should be repeated; correspondents will bear in mind that some answe require not a little research, and though we endeavor to reply to all either by letter or in this department. Each must take his turn. Buye wishing to purchase any article not advertised In our columns will be furnished with addresses of houses manufacturing or carrying the same. Special written information on matte of peonal rather than general interest cannot bee expected without remuneration. Books referred to promptly supplied on receipt of price Minerals sent for examination should be distinctly marked or labeled. (5151) C. W. S.-The care of a gravity cell is very simple. Two things are necessary; one is to keep the zincs clean, the other is to keep the line of de-markation of the copper solution and the zinc sulphate abont half way between the zinc and copper solutions of the battery. This you can do hyregulating the resistance of the circuit. If yon find your cells running down to rapidly, connect them up in series of two or three in parallel; if on the other hand, level of the blue liquid rises into close proximity with the zinc, it indicates too much resistance in the circuit, the remedy for which is obvious --to decrease the resistance of the external circuit. (5152) J. J. M. says : Some time ago I saw 1.1. man who made it his bnsiness writing names and designs on glassware. I am acquainted with the process using the vapo of fluoric acid, but this man used a fluid with pen and brush. Would you kindly let me know under queries of your valuable paper whatkind of a solution he probably used? A. 1. The pieparation may be made by mixing sulphate of barium and fluoride of ammonium in the proportion of three parte of the former to one part of the latter, with sufficient sulphuric acid to decompose the ammoninm and bring the mixture to the consistency of rich milk. The mixture should be made in a receptacle of lead, and kept in a bottle of the same material, or of gutta percha. 2. Since fuoric preparations have been produced at reasonable prices the deco-tipnof glass by their means has steadily made its way. Etched glass is now to be found everywhere, and glass etching runs glass cutting very hard. It is very . easy to undetand that well etched objects appear actually more beautiful than those which have been cut, The cost of production is cheaper. and since M. Hock, a Viennese chemist, has given us an elaborate work upon the technics of glass etching, the difficulties attending this kind of work have ben reduced to 1.1. minimum, As is well known, fluoric acid usually etches smooth, while other fluoric preparations yield a matt surface. The most beautiful ornamentation is obtained when certain parts of the glass surface are rendered matt by means of Ilouride of ammonium which baa been slightly acidified hy means of acetic acid. The matt appearance is not always the same with different kinds of glass, but varies much in beauty. This effect is governed by the composltion of the glass, lead glasses being easily acted upon and furnishing a very flne matt surface. 3. Where it is desired to have the surface of the glass not altogether matt, but shining like ice, as in the case of window glass, this may be attained in a simple manner by placing the glass plate in a perfectly horizontal position and covering it with fine groats. Then very dilute fluoric acid is poured upon it. The groats act as a shield and produce upon the glass raised points.--"Cyclopedia of Receipts, Notes and Queries." (515)3) J. M. says: Will you please advise a sucriber how to finish an oak front to a dwelling that is exposed to the weather, where the finish will stand any reasonable length of time and notcome off, bleach out and fade? All fronts to dwellings and stores in this part of the State that i have noticed do not stand the weather. Also please advise how tomake a glue that will hold a joint that is exposed to the weather. A. An oak front should be thoroughly oiled with raw linseed oil as soon as finished, andrubbed down with woolen cloths. In a few days, or as soon as the raw oil has struck in and dry enough, apply 1.1. coat of boiled linseed oil, and when dry a second coat. A good weather glue is made by boiling the glue with skimmed milk, in the proportion of half a pound of dry glue to 1.1. quart of skimmed milk. Swell the glue in the milk before boiling. (5154) P. McL. writes: I am about to erect two batteries of boile, four boile ineachbattery. Size of fit battery 26 feet long by 88 inches diameter, two 15 inch flues in each boiler. Size of second battery 32 feet long by 42 inches diameter, two 15 inch flues in each boiler. Will you please through your Notes and Queries inform me the distance grate bare should be below shell of boiler, also distance from bridge wallto shell of boile, depth of combustion chamber, and style of back wail, whether staight wall or should it be racked off in front ? Boile to bum Pittahnrg coal and can use all steam they can make. Also please give me beight and diameter for iron smoke stack for each battery ? A. The grate for soft coal should be 3 feet below boile in both batteries. Bridge wall, one foot below the boile. Size of grate for each boiler of the fit battery should be 40 inches wide,4J.i feet long. Size of grate for each boiler of second battery should be 44 inches wide, 5 feet long. Bridge wall should be vertical for 9 inches above the grate, then racked off or beveled to the top at about 45. Iron smoke stack of fit battery 88 inches diameter by 60 feet in height, For second battery 44 inches diameter by 60 feet high. (5155) F. W. M. asks : Is there any need of a flux in casting brass ? If there is, what is the best to nse ? A. No flux is used in casting brass. A little powdered charcoal is put on the surface in the crucible to prevent oxidizing. (5156) J. J. P.-We wo not chink a fan blower is adapted to organ blowing, on account of the vibration of the column of air, which would affect the sounds produced by the pipes. (5157) C. H. asks : 1. I have just made two storage batteries, 4 plates, each 4X5 inches, coated with red lead mixed with sulphuric acid and water. i want to charge them from a 50 volt, 16 candle power socket. Is the voltage too high? A. By introducing your battery, together with some resistance, into your 50 volt circuit, youcancharge it. 2. How can i rednce the voltage from the socket low enough to charge the cells to the best advantage ? A. Use a wire rheostat ora bank of lamps for resistance. 8. How many gravity batteries will it take to charge the storage batteries so as to bum 1.1. 1 candle power lamp 15;to20 mlnntes each evening, using the gravity cells during the day time to charge them ? A. Four gravity batteries to each cell of sto age battery. llie proposed lamp is rather urn ail; you might use 2 or 8 cells with 1.1. larger lamp and run it for 1.1. much longer time. (5.158) W. M. writes : I have constructed a pair of receive of the Bell telephone pattern, merely as an experiment. When I tried them I found that the sounds were very low and indistinct. Can yon tell me what the cause of this is? A. Possibly you may have placed the diaphragm at too great a distance from the pole of the magnet, or you may have used 1.1. weak magnet, Possibly you have not sufficient length of wire on yonr spools, or the wire may be short-circuited. (5159) B. M. C. V. asks: 1. What is the rule to know the charging time of a given accumulator ? Has the number of plates anything to do with it, or the surface of the plates 1.1.8 represented by square inches ? A. Charge your batteries until the positive plates look like wet slate nearly black; when partly discharged they become dark red, chocolate or plum color. It requires about 7 or 8 hou to charge a battery. 2. i have an accumulator for medical usee, composed of four separate accumulato to be charged, connected in parallel with 2 Bnnsens 20 cells for 8 hou. i want to know how many hou it will take to charge them with 4 telegraph cells ? A. Four gravity cells to each cell of storage battery will charge storage cells in about the same time, 7 to 8 hou. 3. I have two large Bunsens (2 gallons) with two zinc plates each; one of the plates in each cell is nearly destroyed by llttle use. The connections are properly made, the 2 zincs in each cell and one of them with the carbon of the neighboring cell; the plates are thoroughly amalgamated, screws firmly attached, nevertheless the browsing is very strong in both the mentioned plates, Can you help 'me with your advice in preventing such a trouble? i use for charging 1 part strong sulphuric acid 'to 12 of water by volume. A. The only way to prevent the destruction of the zincs is to remove them from the cell when the batteiy is not in use. 4. How can I know the amperage andampere hou of a given accumulator ? A. You can determine this only by trial,. or addressing the maker, if it is one which is on the market. RepUel! to Enquiries. The following replies relate to enquiries published in the SCIENTIFIC AsrEBtcAN, and to the numbe therein given. Boring GLAss.-In the May 6. 1893. number of the Scientific American, a correspondent, M., tells of a very good way to drill glass plate. His methodiB a good one, but if 1.1. saturated solution of camphor in turpentine be used 88 a lubricant, the drill will cutmore rapidly.--C. R. JOHNS, M.D.
