(4) W. H. G. S. writes: I wish to give a blue color to screw heads, wire and steel. What shall I use? A. Heat them in a sand bath, or apply shellac or copal varnish, to which a little Prussian blue has been added.
(5) T. McW. asks (1) for a good recipe for making Babbitt metal. A. By weight, 4 parts copper, 8 parts antimony, 96 parts tin. 2. What is meant by heating surface in boilers, and how is it computed? A. The term heating surface, as ordinarily used, refers to the surface which has water on one side, and flame or the products of combustion on the other. 3. I have a peculiar kind of steel which I cannot harden by fire and water, neither will it caseharden by prussiate of potash. What can I do with it to harden it? A. Assuming your account to be correct, we judge that you cannot harden it.
(6) A. Van B. writes: A correspondent in your last issue asks how to keep rubber belts from slipping. Mine slipped considerably, but I checked it by throwing powdered rosin in between the belt and pulley while running. The pulley soon becomes covered with a tough black coating, very much like leather, and there is no more slip. [This expedient can be used to advantage in certain cases, but it is better to have a belt large enough to drive without using any preparation.—Ed.]
(7) E. B. C. asks: 1. Does a more powerful battery produce better results in telephone or microphone? A. A powerful battery is not required for either. 2. Can you give me a short description of the principle and construction of the aerophone? A. We think it has not been perfected.
(8) A. T. L. asks for a recipe for a liquid boot or shoe polish. A. Clausen's ink is made as follows: Nutgalls, 8 parts; logwood extract, 10 parts; boil together in water, q. s., and add Castile soap, 4 parts; glycerin, trace. Crocker's—Logwood extract, 6 ozs.; water, 1 gallon; ivory black, 1.5 oz.; glycerin, 1 oz.; bichromate of potassa, 0.125 oz.; copperas, 0.125 oz.; boil together. Sefton's—Orange shellac, 64 ozs.; alcohol, 4 gallons; pure asphaltum, 60 ozs.; neat's foot oil, 1 pint; lampblack, q. s. Ovington's—Water, 1 gallon; logwood extract, 6 ozs.; water, 1 gallon; borax, 6 ozs.; shellac, 1.5 oz.; water, 0.5 pint; bichromate of potassa, 0.375 oz. Mix the solutions, and add 3 ozs. ammonia. Shaw's—Borax, 3 ozs.; orange shellac, 5 ozs.; water, q. s.; boil and add soluble aniline black or nigrosine, q. s. Rub the spots with strong aqueous solution of ferric chloride, and dry before applying the dressing.
(9) J. S. & R. M. write: 1. We propose putting in a steam engine of 20 horse power, and we are informed there is an engine that weighs 2,700 lbs., that has a balance wheel weighing 500 lbs., cylinder 10 x 10 inches; cutting off at ¾ stroke, running at 180 to 200 revolutions a minute, and they say that it is 20 horse at 70 lbs. steam. Will such an engine develop 20 horse power? A. The engine would develop 20 horse power under the above conditions, if well constructed. 2. How can we calculate the power of an engine? A. To determine the power of an engine, multiply the mean pressure on the piston in lbs., by the piston speed in feet per minute, and divide the product by 33,000.
(10) A. L. G. asks: 1. With a boiler 15 inches in diameter by 30 inches in height, with five 1½ inch tubes 18 inches long, firebox 12 x 12, and all made of iron plates ¼ inch thick. What is the greatest number of pounds of steam to the square inch it will hold, and what fraction of a horse power will it give to an engine having a cylinder 2 x 4 inches, situated 2 feet from the boiler, and connected by 40 inches of steam pipe? A. You can carry 150 lbs. of steam, and might develop 1 horse power. 2. What is meant by the pitch of a wheel in a propeller, and what is the inclination of a cylinder? A. The pitch of a propeller is the distance it would advance in the direction of its axis at each revolution, if it worked without slip. The inclination of a cylinder refers to the angle made by its axis with a horizontal or vertical line.