350-353] A nalysis of Water for Drinking Purposes 209 



boiled distilled water until the volume is again 250 c.c, measure 

 out 70 c.c. into the stoppered bottle, and estimate the hardness 

 as before. 



350. Temporary Hardness is obtained by subtracting 

 the ' permanent ' from the total hardness. 



HEHNER'S METHOD FOR ESTIMATION OF 

 HARDNESS 



351. By this process the carbonates of calcium and mag- 

 nesium, which have an alkaline reaction on methyl orange, are 

 estimated by titrating with decinormal sulphuric acid in the 

 presence of that indicator. Since the temporary hardness is 

 due to these carbonates, it may be directly calculated from the 

 titration of 350 c.c. of water. 



To estimate the total hardness, add to 350 c.c. of the 

 water 50 c.c. of decinormal sodium carbonate solution, and 

 boil for half-an-hour. Filter, dilute to the original bulk, add 

 a drop of methyl orange, and titrate with decinormal sulphuric 

 acid. Thus the number of c.c. of sodium carbonate solution 

 used to precipitate the sulphates of calcium and magnesium 

 may be estimated. Each c.c. corresponds to 1 grain CaC0 3 

 per gallon. 



352. Nitrates. — The nitrates in water are estimated by 

 dissolving the ' total solid ' matter (see paragraph 339) in 2 c.c. 

 of dilute HC1, and placing in the nitrometer, together with 

 5 c.c. strong sulphuric acid, as described in paragraph 114. 



REMARKS ON ANALYSIS OF DRINKING WATER 



353. From the results of each of the determinations which 

 have been described certain deductions may be made. 



Total Solids. For drinking purposes the quality of the 

 solid matters is of far more importance than their quantity. But 



p 



