WATEE 11 



nesia are dissolved and taken up by the water in the 

 manner previously described. Such water can only with 

 difficulty form a lather with soap, and imparts a feeling to 

 the fingers known as ' hard.' Hardness in water may be 

 due to calcium carbonate, sulphate, or chloride, or to mag- 

 nesium carbonate ; that which is due to calcium carbonate 

 can readily be removed and is spoken of as temporary 

 hardness, but the other salts, generally speaking, are not 

 capable of being removed and produce permanent hard- 

 ness. 



When water is boiled its carbonic acid gas is driven off, 

 and the chalk no longer being kept in solution is deposited. 

 Such deposits are familiar in vessels used for boiling water. 

 As the result of the deposition of chalk the water becomes 

 much softer ; the same result can be obtained in another 

 way, which will be alluded to presently. 



No lather can be formed with soap so long as salts of lime 

 or magnesia remain in solution, for these combine with the 

 fatty acids of the soap and form a curd. It is not until the 

 salts are entirely precipitated that a lather can be formed, 

 so that much waste of soap occurs, in fact one grain of 

 lime wastes eight grains of soap. Advantage is taken of 

 the action of soap on lime and magaesia, to use it as a test 

 of the amount of hardness in water. 



Eain-water contains less than half a grain of lime per 

 gallon ; a water containing more than ten grains of lime or 

 its equivalent per gallon, is described as ' hard.' 



Action of Water on Metal Pipes.— head pipes are largely 

 used for the conveyance of water, and depending upon the 

 character of the water, the metal is more or less attacked 

 and enters into solution. In this way many cases of lead- 

 poisoning have occurred in man. Soft water is particularly 

 liable to act on lead and dissolve it. Certain soft waters 

 do this with greater facility than others ; for example, the 

 waters of Huddersfield and Sheffield have a marked effect 

 on new lead. Several theories have been propounded to 

 explain why one soft water should, and another should not, 

 act on lead. The presence of a small amount of silica in 



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