NITRATE DETERMINATION 89 



Sulphate Determination. - The most common method 

 in use for determining sulphates is to acidify the solution 

 with a few drops of hydrochloric acid and after bringing 

 the solution to boiling, . to add a few cubic centimeters of 

 boiling standard barium chloride. The solution is kept 

 boiling for about an hour and then filtered through an 

 ordinary filter paper and the precipitate thoroughly washed 

 with hot water. The precipitate and the filter paper are 

 then placed in a weighed crucible which is heated until 

 all volatile matter is driven off. After this the crucible is 

 reweighed and the difference as barium sulphate calculated 

 first to calcium and magnesium and the remainder to 

 sodium, if the former bases have been determined, but 

 otherwise the sulphates are all expressed as sodium 

 sulphate. 



Turbidity and colorimetric methods for sulphate de- 

 termination have been employed to a slight extent, but 

 they are not in common use. In certain places, notably 

 at the California Station, the difference between the total 

 solids and the sum of the carbonates and the chlorides 

 has been expressed as sodium sulphate. As the sulphates 

 are least harmful, and in certain localities seldom present 

 in injurious quantities, they are frequently omitted from 

 analyses of alkali. 



Nitrate Determination. Nitrates are seldom deter- 

 mined in alkali investigations, but under a few conditions 

 such as prevail in parts of Colorado and Utah, they reach 

 toxic concentrations, and it is therefore desirable that the 

 quantity present be known. The method for nitrate de- 

 termination, which has been most extensively used in the 

 past, is discussed by Schreiner and Failyer (9) as follows: 



"The nitrates are best determined by means of the 

 color produced by the action of phenoldisulphonic acid 



