PROPERTIES OF WATER AND SOURCES OF SUPPLY. 5 



of CaCl. 2 , CaSO 4 , MgCL, MgSO 4 are not held 

 in solution by CO 2 . Lime and magnesia are the 

 most important, and exist in well water by reason 

 of the CCX,, which that class of water is known to 

 possess. They would not exist in solution in water 

 containing no CO... Being held in solution by the 

 CO 2 they are known to constitute what is known as 

 temporary hardness, but calcium sulphate and mag- 

 nesium sulphate constitute/>^r;;m;/^;// hardness, being 

 themselves soluble and difficult of eradication. For 

 a domestic supply this hardness in water is not 

 usually of any disadvantage, except that it entails 

 a waste of soap, and renders its use in some degree 

 unpleasant. Otherwise, from a dietetic point of view, 

 medical men approve of it, especially for children, 

 although to elderly people it may induce rheumatism. 

 Hence we shall not discuss methods of softening 

 which are principally applicable to water for steam 

 users and other traders. Boiling water removes the 

 temporary hardness ; very soft water, on the other 

 hand, will contain much CO 2 and dissolve lead pipes. 

 A water which is fresh, limpid, and free from smell, 

 and which will boil vegetables without discolouring 

 them, and dissolve soap without leaving curds, will 

 generally satisfy most requirements. The following 

 tests may be applied by the engineer and are very 

 useful. 



1. To test for the hardness of water, dissolve pure 

 white soap in alcohol and add the solution to hard 

 water. The result is a milky-white solution. 



2. To test for the presence of copper, add some sal 

 ammoniac and iron filings to the water, and a blue 

 colour will result. 



