

9 





I )RIN KING WA TER. X^tT^^^'^^^x.^ 



i-N^^A^t;^ * 



WITH SPF.CIAl, RKFEKENCK TO THE OTTAWA CITY SUPPLY. 



A Lecture by A. McGill, }'>.A., 15. St., A^^ibtaiU Analyst to the 

 Inland Revenue Department. 



A very little thought given to the subject will convince us of the 

 hopelessness of seeking for absolutely pure water as a natural product. 

 The great solvent power of water, together with the universal presence 

 of substances, gaseous liquid or solid, which it can take into solution, 

 are conditions which amply suffice to explain the contamination of all 

 natural sources of supply. The whole of the fresh water on the face of 

 the earth has fallen as rain on field, forest, city, street, swamp, or other 

 more or less similar gathering-ground, except such insignificant fraction 

 as falls directly into river or lake. The soluble impurities jjresent in 

 such gathering grounds are conveyed to the storage centres in river, 

 lake or well, and it is fortunate for us that nature has provided, in the 

 course of natural filtration to which such supplies are necessarily sub- 

 jected, a means of reducing in a great degree the pollution due to 

 organic matter, as will be hereafter explained more fully. The mineral 

 content remains to give so-called " hardness," or other specific character 

 to the supply of each locality. Even before the rain has reached the 

 surface of the earth, however, it is far from pure, since there are always 

 present in the atmosphere particles of organic and inorganic dust, ill- 

 smelling and often poisonous gases, the products of decay, microscopic 

 germs, and other impurities which are washed out of the air by the rain, 

 and make it, — especially the first portion of each shower, — decidedly 

 polluted and unfit, without filtration, to be used as a food supply. The 

 conditions which influence the solubility of solids in water are essen- 

 tially three, namely, the specific nature of the substance, the tempera- 

 ture of the water, and the presence of other bodies in solution. Even 

 among quite soluble substances very marked and interesting specific 

 differences may be observed. In the six flasks before you I have sus- 

 pended, in muslin bags, equal quantities (i ounce) of six different salts, 

 themselves having important relations in the subsequent treatment of 

 this subject, all of them decidedly soluble, and powdered to an approxi- 



