394 THE POPULAR SCIENCE MONTHLY. 



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 sick- 

 ness and disease. 



Professor Venable has lately shown that water passed through gal- 

 vanized pipe dissolves quite an appreciable quantity of the zinc coat- 

 ing, thus making it unfit for drinking purposes. Tin-lined pipes are 

 also used, and until the introduction of the " rustless " pipe were con- 

 sidered 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. Con- 

 siderable architectural iron-work protected by the rustless process is 

 being used with very satisfactory results. It is needless to multi- 

 ply 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 pol- 

 ished. 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 oxida- 

 tion 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 ac- 

 cident happening to any such article before treatment is almost sure 

 to break it. "Whether this toughening is caused by a kind of anneal- 

 ing due to the slow cooling of the charge after coming out of the fur- 

 nace, 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 



