CHEMICAL EXAMINATION OF THE WATEK SUPPLY. 291 
drinking water, it is generally admitted that an excess of these sub- 
stances must be looked on as an unfavorable indication with respect 
to the purity of the water and its potability. According to Frank- 
land, ® While the oxidation of animal matters in solution in water 
yields an abundance ot nitrites and nitrates, vegetable matters furnish 
under like circumstances none or mere traces of these compounds,’’ and 
according to Ekin, ^ the presence of nitrates in large amounts points to 
sewage contamination. Stoddart^ also states that Natural waters 
can, at most, contain but from 1.43 to 2.86 parts per million of nitrogen 
as nitrates from sources other than animal matter, and that practi- 
cally the whole of the nitrogen of sewage may be oxidized to nitric 
acid without diminishing the risk involved in drinking it.” He re- 
gards the proposal to regard a water as safe as soon as the nitrogen has 
been oxidized to nitrates, irrespective of the quantity present, as 
entirely irrational. Mallet is also inclined to lay great stress on the 
determination of nitrates in drinking water, with the view of obtain- 
ing a correct notion of the extent of sewage pollution. 
In Table 13 are given the shallow wells which, according to the 
chemical analyses, show: (1) Immediate sewage pollution; (2) re- 
mote pollution; (3) no pollution at all. In Table 14 are given the 
shallow wells which, according to the results of the bacteriological 
examination, have been classified as being: (1) Polluted by sewage 
or surface contamination; (2) fair; (3) good. In Table 15 is to be 
found a list of the shallow wells which, on account of insanitary 
environment and the unfavorable results of the bacteriological and 
chemical examinations, are regarded by this board as unfit for drink- 
ing purposes. It will be seen from a comparison of Tables 13 and 14 
that of the 31 shallow wells regarded by us as unfit for drinking pur- 
poses 18 were condemned independently by both the bacteriological 
and chemical examinations, and of the remaining 13, 12 showed bac- 
teriological evidence of immediate sewage pollution and 1 was good; 
II gave chemical evidences of remote sewage pollution, 1 of immediate 
sewage contamination, and 1 showed no pollution at all. 
O' Rivers Pollution Commission, Report VI, 1874, p. 13. 
^ Potable Water, Ekin (1890), p. 11. 
c Analyst, XVIII, p. 293. See also Mason, Examination of Water (1901), pp. 41-42. 
^ Report of National Board of Health, 1882. See also Mason, “ Interpretation of a 
Water Examination,” Science, N. S., Vol. XXI, No. 539, pp. 650-651. 
