Page:Popular Science Monthly Volume 29.djvu/408

394 contain lead in solution, and the continued use of such water causes lead-poisoning, for, although the amount (of lead) dissolved may be very small, still it accumulates in the system, and finally causes sickness and disease.

Professor Venable has lately shown that water passed through galvanized pipe dissolves quite an appreciable quantity of the zinc coating, thus making it unfit for drinking purposes. Tin-lined pipes are also used, and until the introduction of the "rustless" pipe were considered the best, but were far from being all that could be desired; in many instances, after using for a time, the coating was completely destroyed. Then, again, if the pipe is to be better than lead, the tin used for the lining must be pure, because if it contains lead, which is often mixed with tin, it would be worse than the common lead pipe, the alloy dissolving much more readily than either would alone. Considerable architectural iron-work protected by the rustless process is being used with very satisfactory results. It is needless to multiply examples of its usefulness, for numberless ones will occur to the reader. Up to the present time only four furnaces have been built in this country—two in Brooklyn, one at Little Ferry, New Jersey, and one in Philadelphia. The processes by which this coating of magnetic oxide is formed differ accordingly as the iron is cast, wrought, or polished. The Bower process is the better for cast-iron, and consists in oxidizing it by means of carbonic acid and air. In the Barff method, which is the one used for wrought-iron and polished work, the oxidation is produced by means of superheated steam. This method will also give a coating of the magnetic oxide on cast-iron, but the action is very much slower than with the Bower treatment, and consequently more costly. The difference is probably due to the large amount of carbon contained in cast-iron, and which has to be oxidized as well as the iron, i. e., the carbon contained in the film of iron which is changed to oxide. It may be asked then, why, if air does the work so much quicker than steam, it can not be used for wrought-iron and polished work, as well as for cast-iron? It has been found by experience that the coating produced on the former, when air is used, is liable to scale off, which is not the case when it is treated with steam. Cast-iron after treatment seems tougher than before. I have frequently noticed, when present at the unloading of a charge of hollow-ware that had been treated, a kettle or pot fall off, and, although falling against heavy iron, it would bound off and reach the floor uninjured. The same accident happening to any such article before treatment is almost sure to break it. Whether this toughening is caused by a kind of annealing due to the slow cooling of the charge after coming out of the furnace, or whether it is that the surface of the iron becomes malleable owing to the oxidation of its contained carbon, I can not say, but think it probable that both contribute to the result. Mr. Bower, in his first experiments, treated the articles in a muffle-furnace—that is, a furnace