COMPOSITION AND TESTING OF WELL WATERS 165 



The examination of the water will, therefore, usually consist of a 

 determination of the chlorine (for comparison with unpolluted 

 waters of the same locality), tests for nitrites and nitrates (indic- 

 ative respectively of present and past organic decay) and bac- 

 teriological examinations. 



The tests involved in the sanitary analyses and bacteriological 

 examinations are quite delicate and to be wholly reliable must be 

 made by competent specialists. 



Almost every state has a laboratory for testing waters at the 

 office of the state board of health, at the agricultural college or 

 at the state university. Some private commercial laboratories 

 also undertake the sanitary analysis of water, but, unless such a 

 laboratory makes a speciality of water analysis, the results are 

 likely to be of doubtful value. Many of the state laboratories, as 

 well as the laboratories of the health boards of the cities, make 

 no charge for the examinations, and, even when charges are 

 made, the fees are usually moderate, seldom exceeding $5 per 

 sample. 



Simple Sanitary Tests. Although the sanitary examina- 

 tion of water should, whenever possible, be left to the trained 

 analyst, there are a number of relatively simple tests affording 

 some indication of the presence of pollution that may be made by 

 the well-owner himself. 



In the test for chlorine, the significance of which has been 

 pointed out, a glass tumbler, previously thoroughly washed and 

 rinsed in the water to be examined, is filled half full of the same. 

 To this are added six drops of a solution (obtained from the drug- 

 gist) made by dissolving five grains of nitrate of silver in an 

 ounce of distilled water. If chlorine is present in appreciable 

 amounts, a cloudiness or milkiness, which may be detected by 

 holding against a dark surface, will be produced. Since, how- 

 ever, chlorine is an ingredient of common salt, which is normally 

 present in slight amounts in most waters, a parallel test should 

 be made with a near-by well or stream of known purity for 

 comparison. 



