vm.] COMPOSITION OF NATURAL WATERS. 125 



derive their needful supply of mineral matter, directly or 

 indirectly, from the surrounding medium, and thus the 

 fresh-water shell-fish and crustaceans appropriate a large 

 quantity of carbonate of lime, to form their shells, from 

 the river m which they live. Much of this, however, must 

 be returned to the river by the decay of the shells after the 

 death of the animals. In these and other ways, it is easy 

 to account for the proportion of sahne constituents being 

 less in river than in spring-water. If the river drain a 

 country composed of hard and almost insoluble rocks, the 

 water will contain but little mineral impurity. Thus the 

 water of the Dee, of Aberdeen, which draws its supply from 

 a granite district, contains only about three grains of saline 

 matter in the gallon. It is a very different case, however, 

 with a river like the Thames, which collects its water from 

 the drainage of comparatively soft and soluble rocks. The 

 composition of the Thames water may be seen by the follow- 

 ing analysis : — ^ 



COMPOSITION OF THAMES WATER AT LONDON" 

 PER GALLON OF 70,000 GKAl 



Carbonate of Lime 

 Chloride of Calcium - 

 Chloride of Magnesium 

 Chloride of Sodium 

 Sulphate of Soda . 

 Sulphate of Potash 

 Sihca 



Insoluble Organic Matter 

 Soluble Organic Matter 



28-0385 



1 "Analysis of Thames Water." By John Ashley. Quarterly 

 Journal of the Chemical Society, vol. i'. p. 74- 



2 Probably the calcium exists rather as sulphate of lime, and the 

 chlorine as chloride of sodium. 



