88 METHODS OF DETERMINING ALKALI 



In the work at California no distinction has been made 

 between the carbonate and the bicarbonate of soda. Their 

 method of first evaporating the solution, then igniting 

 the residue, and finally redissolving the salts before 

 titrating with sulphuric acid, using methyl orange as the 

 indicator, eliminates most of the calcium and magnesium. 

 After this the solution is titrated with sulphuric acid, and 

 the difference between the sodium carbonate added and 

 that indicated by the titration shows the sodium carbon- 

 ate present originally. If there is a deficit, the quantity 

 of calcium and magnesium carbonate in excess is shown. 



Acting on the assumption that all carbonates and bi- 

 carbonates were combined with sodium when in the soil, 

 the Utah Station titrates the original solution with sul- 

 phuric acid and states the results as sodium carbonate. 

 Where the solution remains in contact with the soil but 

 a few minutes, it is assumed that the less soluble lime and 

 magnesium salts will be present to only a slight extent, 

 but where the agitation is continued for Jong the results 

 are high compared with other methods on account of the 

 presence of carbonate other than those of sodium. 



Chloride Determination. -- The method used in prac- 

 tically all places for determining chloride is to titrate 10 

 to 50 cc. of the original solution with standard silver 

 nitrate solution, using potassium chromate as the indicator. 

 The results are expressed as the sodium salt. As shown 

 in Table XI, the results by the different methods are 

 fairly uniform, although by heating to get the solution, 

 as is done by the Arizona method, the results are some- 

 what higher in most cases than with the other methods. 

 An excess of silver nitrate titrated back with ammonium 

 sulfocyanide is sometimes used, but it is rather hard to 

 read in brown solutions. The turbidity method for 

 chlorides is little used. 



