16 



jjurities, it is Ly the introduction of newage matter ; and tliere is 

 practically no room for doubt that the noxious matter in most, if not 

 in all cases, consists of living micro-organisms — so-called bacteria. 

 It cannot be too clearly understood tliat the chemist is unable 

 in the great majority of cases, to say whether a water be or not 

 ))m'e and fit for use for dietetic purposes : he is rarely able to say 

 more than that tlie evidence points to the water being contaminated 

 with sewage-matter, and to recommend its disuse, since experience 

 sliows that the use of water thus contaminated is attended with 

 danger. The evidence on which the chemist cliieflj' relies in 

 proof of sewage contamination is the presence in unusual amount 

 of substances such as ammonia, nitrates and chlorides, which, 

 although normally present in all waters, are yet, as a rule, met 

 with in only small quantities. 



Judged of from the point of view of freedom from sewage 

 contamination, the water sujjplied to our district from deep wells 

 in the chalk by the Kent Company is on all hands admitted to be 

 a water of great purity : the presence of a large quantity of lime 

 salts is sometimes popularly supposed to favour the development 

 of a certain class of disease, but there appears to be no satisfactory 

 scientific evidence in support of this view; so that for dietetic 

 purposes we may regard our water supply as entirely satisfactory, 

 and if it could only be made compulsory upon the Company to 

 supply (on fair and reasonable terms), and householders to accept, 

 a constant service, all such abominations as tanks being of 

 necessity abolished, the district might contemplate its lot with 

 a fair sense of security. 



But, unfortunately, the Kent ^water is not nearly so well 

 suited for other domestic purposes — for cooking, for cleaning 

 purposes, and in lioilers. As the rain which has fallen upon the 

 lanil penetrates into the earth it becomes saturated with carbonic 

 acid ; and as the water thus charged percolates through the chalk 

 this acid acts upon tlie chalk or calcium carbonate, forming "acid 

 calcium carbonate," a substance which is much more soluble than 

 clialk itself. When the water is boiled, this acid carbonate decom- 

 poses into carbonic acid, which escapes, and chalk which separates 

 in a more or less crystallized state, and chiefly on the surfaces of 



