EXAINIINATION OF DRINKING-WATER. 469 



the only reliable means, in our present state of the sciences, 

 by which desirable information rei^ardins' the true character 

 of a drinking-water can be obtained. 



These tests, it must be acknowledged, although of the 

 greatest importance from a general standpoint, have their 

 limitations. They readily indicate the presence of organic 

 matters, but give no unfailing decision regarding their 

 origin, — whether animal or vegetable, — leaving thus, quite 

 frequently, the degree of their harmfulness quite undecided. 

 However, the chemical analysis may be depended upon for 

 all practical purposes, as revealing the presence of objec- 

 tionable qualities of the water. 



The harmful substances found in drinking-water are of 

 two classes, — mineral and organic. Few natural waters are 

 entirely free from mineral matters ; nearly all contain small 

 quantities of lime, soda, magnesia and iron, — substances 

 which may be considered harmless in that case. Larger 

 quantities of these elements, however, render the water ob- 

 jectionable for drinking, and also more or less unfit for 

 various applications, as washing and cooking, feeding of 

 steam apparatus, etc. 



Foremost among^ the dansjerous mineral substances which 

 have been found in drinking-water is the lead. Its pres- 

 ence is usually due to the use of lead pipes for conducting 

 the water from the well to the pump, and elsewhere. Lead 

 is a treacherous and dangerous poison. Not a ti'ace should 

 be tolerated in drinking-water. The use of lead pipes for 

 conducting the latter for either of the above stated purposes 

 should be strictly prohibited by State law. Arsenic and 

 copper are rarely met with in natural waters ; yet a careless 

 handling of paris green is at any time apt to become most 

 dangerous in this direction. 



These three metals — lead, copper and arsenic — are 

 direct poisons to the animal system, and therefore are the 

 most dangerous mineral impurities in drinking-water, though 

 ordinarily rare. 



The most frequent source of danger comes evidently from 

 the presence of organic matter, indicating contamination by 

 decaying animal or vegetable substances. Wells are not 

 infrequently found polluted by the gases and liquids emanat- 



