determined, i c. c. of the soap represents -48 parts of 

 CaCO 3 in 100,000; 5 c, c., 6 parts; 10 c. c., 13*31 parts; 

 15 c. c., 21*19 parts, and so on, as per Table. 



(2) Permanent Hardness indicates ihe amount of Cal- 

 cic and magnesic salts in a state other than carbonate. The 

 Calcic and magnesic carbonates are held in solution in water 

 by the carbonic anhydride dissolved in the water. On boiling, 

 this gas passes off and the carbonates are precipitated, while 

 all other salts remain unaffected. A high degree of 

 permanent hardness indicates sewage contamination, showing 

 the presence of sulphates and chlorides, both of which might 

 be derived from sewage matter. Moreover, it is impossible 

 to render such water portable by boiling. In estimating 

 permanent hardness, the soap-test is applied after boiling 

 the water, and the result noted as "permanent hardness." 



(3) Chlorine as chlorides also indicates sewage conta- 

 mination, though sea-breeze also accounts for some of the 

 chlorine in water. 70 c. c. of the water to be tested are 

 placed in a beaker over a sheet of white paper and brought 

 under a 10 c. c. burette charged with the standard solution 

 of silver nitrate. Two drops of the solution of Potassium 

 Chromate are then added, and the silver solution carefully 

 run in with constant stirring, until the solution in the beaker 

 just changes from yellow to red. This indicates that all 

 the Chlorides have been precipitated as Silver Chloride. The 

 red coloured Argentic Chromate will not form until all the 

 chlorides have been removed, but whenever this is attained, 

 the least excess of silver solution, turns the Chromate red. 

 Each c. c. of silver solution will indicate '00355 grammes of 

 chlorine per litre. The Silver Nitrate and Potassium Chro- 

 mate solutions must be both perfectly neutral. 



(4) Nitrates and Nitrites. The sample of water is 

 treated with a hydrate and a piece of sheet-albuminium drop- 

 ped in. The nitrates and nitrites are reduced to ammonia in 

 contact with nascent hydrogen and then Nessler's test ap- 



