272 WATER HYGIENE 
organic matter in its different stages of oxidation. The chemical 
examination of water is important when a municipal supply is treated 
with alum since in this connection it is important to maintain sufficient 
alkalinity in the water to decompose all of this coagulant and not allow 
it to pass into the filtered water. Certain objectionable trade wastes 
may be detected in a water by chemical analysis. 
The bacteriological analysis is more delicate ard direct. It is easy 
to conceive that a water which, according to chemical analysis was of 
good quality, might contain many pathogenic bacteria. These, unless 
they were present in enormous numbers could not be detected chem- 
ically. In the bacterial examination the analyst is searching for the 
factors which are mostimportant. Inthe chemical analysis their pres- 
ence is inferred when other substances are present. While the isolation 
of specific pathogenic bacteria from water is not attended with much 
success, the bacterial examination yields more definite knowledge of 
their presence. In determining the efficiency of filters, this analysis is 
important. 
The purpose of water examinations are many. Mineral examina- 
tions are made by the chemist to determine the effect of any water 
on boilers, to determine the amount of pollution, presence of any of 
the heavy metals, etc. The bacteriologist is more interested in the 
number and kinds of bacteria which may be present. He has to con- 
tend with the disadvantage, unlike the chemist, that many of his con- 
clusions are drawn from circumstantial evidence. 
For our purposes, a sanitary water analysis may be regarded as 
made up as follows: 
I. Sanitary chemical examination 
A. Physical (organo leptic) tests 
a. Turbidity, b. Color, c. Odor 
B. True chemical determinations 
1. Residue 
2. Chlorine 
3. Nitrogen as 
a. Nitrates 
b. Nitrites 
ce. Free ammonia 
d. Albuminoid ammonia 
4, Alkalinity 
5. Oxygen consumed 
