46 
lated. The water in this cistern is however very rarely used; 
for all domestic purposes a supply is obtained directly from the 
main ; it would therefore appear that sewer gases are slowly 
absorbed by water stored in such a cistern. That this 
absorptive action must take place slowly is evident if we 
look at the results obtained from the other waters. Although 
many of these waters were taken from badly situated 
cisterns, yet in none of them can the influence of sewer 
gases be distinctly traced. We must therefore conclude that 
the rapidity with which the water in the cistern has been 
changed has prevented any appreciable action of the gases 
upon these waters. There are, it is true, slight variations in 
the numbers obtained, but in no case do we find a notable 
increase as compared with water from the main pipe. 
The amount of ammonia, &c , obtained from a sample of the 
slimy matter found at the bottom of one of the cisterns 
(No. 11) indicates that a great part of the ammonium 
salts, &c., is concentrated therein; this matter may there- 
fore perhaps exercise a certain beneficial effect upon the 
water. 
The general conclusions which I would draw from these 
results are 
(1.) That sewer gases are absorbed by water, but that this 
absorption takes place slowly. 
(2.) That in ordinary house cisterns the water is not 
contaminated to any great extent with sewer gases, probably 
because of the short time during which this water is 
allowed to remain in the cistern, and also perhaps because of 
the deposition of part of the impurities in the muddy sub- 
stance which settles at the bottom of the cistern. 
The general problem of the influence of the means of 
supply upon potable waters is a very wide one. I offer 
these measurements as a contribution towards its solution. 
