WATER ANALYSIS 35 



or palmitate of sodium or potassium. Hard soap has 

 soda for its base, and soft soap has potash for its base. 

 These soaps are soluble in water and form a lather there- 

 with on shaking. When soap is used with a water in 

 which lime, magnesia, baryta, iron, alumina, or other such 

 substances are present, oleates, etc., of these bases are 

 formed, which being insoluble are precipitated, and no 

 lather can be produced until an excess of soap is present. 

 A certain amount of the hardness is removable by boiling, 

 and this is called temporary hardness, and is chiefly due 

 to the carbonates of lime and magnesia held in solution 

 by carbonic acid gas, and by sulphates of these, with salts 

 of silica, alumina, and iron when present. The permanent 

 hardness, or what still remains in solution after boiling, 

 consists mainly of some sulphates, chlorides, and nitrates 

 of calcium and magnesium, with a little iron and alumina. 

 Free carbonic acid gas in water also consumes soap, two 

 equivalents uniting with one of soap as ordinarily estimated. 

 Amount of hardness is expressed as grains per gallon 

 (Clark's degrees), or parts per 100,000 (metrical degrees) 

 in terms of calcium carbonate. In Germany the hardness 

 is expressed as metrical degrees of CaO per 100,000. 



The total hardness of a water should not exceed 30 parts 

 per 100,000, if for domestic purposes. Hard waters vary 

 from 20 to 30 degrees on the metrical scale ; a soft water 

 from 8 to 15 ; and a very soft water from 8 downwards. 

 The greater the permanent hardness, the more objectionable 

 is the water ; and of a good water it should not exceed 5 

 metrical, or 3 to 4 Clark. 



Determination of Hardness. 



i. BY STANDARD SOAP SOLUTION METHOD. 



Dissolve 10 grm. of castile or soft soap in i litre of a 

 mixture of equal parts of distilled water and methylated 

 spirit. Standardize the solution so that i c.c. completely 

 precipitates i mgr. of calcium carbonate or an equivalent 

 salt. The CaCO 3 may be dissolved in the least possible 

 quantity of HC1, then evaporated to dryness twice, to get 

 rid of the HC1, and then the resulting CaCLj dissolved in 

 the proper amount of distilled water ; that is, i grm. 

 of the carbonate is treated as above, and the resulting 



