WHAT TO USE FOR WATER-PIPES. 143 



derstood. Zinc is a coarse, cheap metal, easily- 

 oxidized or corroded by weak acids, and when thus 

 acted upon forms salts which are harmful to the 

 economy. Who ever heard of zinc being recom- 

 mended by a reputable chemist as a suitable metal 

 from which to construct water-pipes ? And yet 

 pipes composed entirely of zinc would be less readily 

 acted upon by water than the coating of the metal 

 when deposited upon iron. The thicker this coat- 

 ing, the more dangerous it becomes, as the longer 

 time is consumed in removing it, and the larger the 

 quantity of salts produced. It may be further ob- 

 served, that if the salts of zinc were not injurious, 

 galvanized iron pipe should not be used for water 

 from economical considerations. It costs more than 

 plain iron pipe, oxidizes more readily so long as a 

 trace of the zinc remains, and therefore has a less 

 money value. Used for dry gas, above ground, 

 iron pipes coated with zinc may have some advan- 

 tage over the uncoated, but they are, after all, 

 insignificant. We now pass to the consideration 

 of plain 



IRON PIPE. 



Water, when it is brought in contact with the 

 metal iron, oxidizes or rusts it more or less rapidly ; 

 but it is not rendered poisonous thereby. Neither 

 the oxide, nor any of the salts of iron liable to be 

 formed from water contact, are in the least degree 



