54 PUBLIC HEALTH CHEMISTRY 



3. Chemical analysis made as soon after collection as 

 possible. 



It is rare for a sample of water to yield results under the 

 second and third headings, where careful local inspection 

 has failed to suggest danger of pollution. It should, there- 

 fore, be thoroughly carried out. 



Bacteriological examination absolutely condemns a water 

 for domestic use when pathogenic organisms are found in 

 it. Unfortunately the detection of these is not always 

 an easy matter, and so their presence or absence is 

 inferred from the abundance or scarcity of associated 

 forms which are more readily found and identified. The 

 result of this is that the bacteriological examination mostly 

 furnishes evidence confirmatory to that derived from 

 other sources. 



Chemical analysis is more rapidly accomplished than 

 the other procedures, and was formerly regarded as a 

 sufficient basis for diagnosis of a water sample, in regard 

 to its wholesomeness or otherwise for domestic purposes. 

 This is so no longer, because it is recognized that the consti- 

 tuents sought for and actually found in a particular water 

 sample, for the most part are of themselves non-deleterious, 

 and by their excess or deficiency simply suggest the pre- 

 sence or absence of the actual materies morbi. Chemical 

 evidence, therefore, must be used in conjunction with all 

 the other evidence before a definite opinion is formed, and 

 even then the judgment may be wholly based on negative 

 findings, which here, as elsewhere, may at any time not 

 bear the interpretation put upon them. Nevertheless, 

 the following statements, when cautiously used, are helpful 

 in interpreting results. 



High chlorine and oxidized nitrogen, associated with 

 marked free and albuminoid ammonia, suggest present or 

 recent animal pollution. 



High chlorine and oxidized nitrogen (not from strata), 

 with little free and albuminoid ammonia, suggest past or 

 remote animal pollution. 



Low chlorine and oxidized nitrogen, and very low free 

 and saline ammonia with high albuminoid ammonia, suggest 

 pollution of vegetable origin. 



Deep wells often show a large amount of chlorides and 



