1867.] 



and the Cholera. 



325 



recently made I find that 2 volumes of carbonic acid dissolved in 

 100 volumes of water completely protect even distilled water from 

 such contamination. Bain water as it descends to the earth dissolves 

 atmospheric gases, and this solution is afterwards continued in 

 brooks and rivers. Of the chief atmospheric gases, carbonic acid is 

 by far the most soluble, 100 volumes of pure water can dissolve 100 

 volumes of this gas ; oxygen, on the other hand, only dissolves to 

 the extent of 3 volumes in 100 volumes of water. Nevertheless, 

 owing to the much larger proportion of oxygen than of carbonic 

 acid in atmospheric air ( 500 : 1), water takes up oxygen more rapidly 

 than carbonic acid, and hence freshly fallen rain-water acts upon 

 lead ; but when the water flows a great distance through an open 

 conduit, the carbonic acid absorbed finally reaches the protecting 

 proportion, and the action upon lead ceases, although the water 

 retains its original softness. Hence there is no necessary connection 

 between soft water and lead corrosion. Even distilled water left in 

 contact with the air for some time loses its property of acting upon 

 lead. 



The hardness of a water is expressed in parts of carbonate of 

 lime, or of its equivalent of other hardening salts, contained in 

 100,000 parts of the water, and each part of carbonate of lime con- 

 tained in this quantity of water is generally termed a degree of 

 hardness. This quality of the water may also be more popularly 

 though less accurately expressed by the number of parts of soap 

 destroyed or wasted by 100,000 parts of the water when used for 

 washing purposes. Each degree of hardness indicates the destruc- 

 tion of 12 parts of the best hard soap by 100,000 parts of water. 

 The following table shows the hardness of the London and Loch 

 Katrine waters, according to both these methods of expression : — 



Names of Companies. 



Hardness. 





February. 



April. 



February. 



April. 



Thames. 











Chelsea .... 

 West Middlesex . . 

 Southwark & Vauxhall 

 Grand Junction 

 Lambeth .... 



16-2 

 16-2 

 16-8 

 17-1 

 16-0 



17-7 



16-3 

 17-7 

 17*7 

 17-7 



194-4 

 194-4 

 201-6 

 205-2 

 192-0 



212-4 

 195-6 

 212-4 

 212-4 

 212-4 



Other Sources. 











New River .... 

 East London . 



Kent 



South Essex 



18-5 



18-8 

 23-1 

 211 



16-3 

 16-0 

 21-1 



222-0 

 225-6 

 277-2 

 253-2 



195-6 

 192 

 253-2 



Water from Loch j 

 Katrine as supplied in> 

 Glasgow 



l 



•3 



— 



3-6 



— 



Soap Destroyed. 



