24 A'ETEEINAEY HYGIENE 



carbonic acid ; if it is alkaline and remains so after boiling, 

 it is due to carbonate of soda. 



In forming an opinion as to the quality of a water, 

 it is most essential that the collective tests, and not a 

 single one, should be our guide. As an example of this 

 the subjoined table from Parkes (see p. 25) will be found 

 useful. 



It would be beyond the scope of this work to describe 

 the quantitative analysis of water, nor is it possible for any- 

 one to undertake this with exactitude unless in constant 

 practice. 



In order, however, to appreciate the results of a quantita- 

 tive examination, it is necessary to understand the propor- 

 tion in which the various substances in water may exist 

 compatible with purity. 



The following are dealt with in a quantitative analysis : — 



Solids : a, total ; h, fixed ; c, volatile. 



Chlorine. 



Hardness : a, total ; h, fixed ; c, removable. 



Free ammonia. 



Albuminoid ammonia. 



Oxygen required for total oxidizable matter. 



Nitrous acid. 



Nitric ,, 



The analyst shows his results either as grains per gallon, 

 equivalent to parts per 70,000, or he expresses them in the 

 metrical system, and describes them as parts per 100,000 

 or parts per 1,000,000.* 



So many conditions influence the quantity of each of the 

 substances found in good drinking-water, that no hard and 

 fast rule can be drawn in the case of any but one substance, 

 and that is nitrous acid. 



* Parts per 100,000 are converted into grains per gaUon by multi- 

 plying by 7 and dividing by 10. Conversely, grains per gaUon are 

 converted into 'parts per 100,000 by multiplying by 10 and dividing 



Digitized by Microsoft® 



