278 



acid is formed by the spontaneous decomposition of the sulphates, is 

 shown by the presence of this noxious compound in the water taken 

 from the logs. 



3rd. The analysis of number one, from the iron pipe, shows it to be 

 water superior to that of most other cities. Thus, an examination of 

 the annexed table, will show that it contains less solid matter in the gal- 

 lon, than either the Croton or Cincinnati water, but more than the 

 Fairmount or Long Pond water. In estimating the value of your city 

 water, as compared with the water of other cities, due allowance must 

 be made for the fact, that the total solid matter is materially increased 

 by the presence of silica, allumina and iron, elements that can produce 

 little or no injury, whUe the chlorides, much the most injurious com- 

 pounds, are entirely absent. The presence of such large quantities of 

 silica and iron, is accounted for, by the fact that Lakes Superior and 

 Huron are formed, for the most part, in a basin of ferruginous sand- 

 stone and igneous rock. It will also be observed that the carbonate of 

 hme is more abundant, in the water collected in February, than Octo- 

 ber. This arises, doubtless, from the change of temperature, the cold 

 water holding much more lime in solution, than when warm. 



35 



