[(19) J. H. S.,] writes: I have three drawings each 21 x 30 inches, which I wish to mount upon cloth like a map, placing them end to end so as to make one whole sheet 90 inches long. The drawings are upon heavy Whatman paper. A. You should stretch wet canvas or factory cloth upon a frame, and while it is still damp apply paste to the backs of the drawings and lay them smoothly on the stretched cloth. When the paste becomes thoroughly dry cut the cloth from the stretching frame and paste a tape binding around the edges.
(20) P. M. asks: What is the difference between the inner and outer rails of a 10° curve 100 yards in length, gauge 4 feet 8 inches? A. If this 100 yards is measured on the center of the curve, whose radius in feet is R, the length of the inner rail is
R - 2-1/3
———— x 100,
R
and of the outer rail
R + 2-1/3
———— x 100.
R
[(21) W. B. K.] asks how to make a shoe dressing for ladies' shoes. A. Soft water, 1 gallon; extract of logwood, 6 ozs.; dissolve at a temperature of about 120° Fah. Soft water, 1 gallon; borax, 6 ozs.; shellac, 1-1/2 oz.; boil until dissolved. Potassium dichromate, 3/8 oz.; hot water, 1/2 pint; dissolve, and add all together. It is preferred to add 3 ozs. of strong aqua ammonia to the liquid before bottling.
[(22) J. D.] asks: What chemicals can be put into water to increase its efficiency in extinguishing fire? A. Carbonic acid; sodium carbonate.
(23) H. P. writes: Please give me the advantages and disadvantages of substituting a galvanized iron tube 18 inches in diameter and 20 feet high for a wood tank, 5 feet wide and 6 deep, as a container of water in a dwelling house in the country. Would the narrower body of water keep fresh or sweet longer, etc.? Also the thickness of iron necessary to safety, and the number of gallons of water this tube would hold. A. The advantages are in favor of the wooden tank; zinc lined vessels (galvanized) are unsuitable for reservoirs for potable water. See p. 369, vol. 36, Scientific American. 0.3 inch iron would be stout enough. A pipe of the dimensions specified would contain about 327 gallons when full.
[(24) F. L. M.] asks: 1. What is the process by which wire is given a copper finish? A. Clean the wire by pickling it for a short time in very dilute sulphuric acid and scouring with sand if necessary. Then pass the clean wire through a strong bath of copper sulphate dissolved in water. 2. Can wire be thus finished and also annealed? If so, how? A. The wire should be annealed first. 3. What other finish can be put on iron wire (annealed), and by what process? A. Zinc—by passing the clean wire through molten zinc covered with sal ammoniac; tin—by drawing the wire through a bath of molten tin covered with tallow.
Minerals, Etc.—Specimens have been received from the following correspondents, and examined, with the results stated: