ADULTERATION OF CHILE SALTPETER 299 



To recapitulate: The chief functions of sodium nitrate are to 

 give to the plant a supply of oxidized nitrogen ready for absorp- 

 tion into its tissues and incidentally to aid, by the residual soda, 

 in the decomposition of silt particles containing potash or phos- 

 phoric acid and in supplying to the soil salts of a more or less 

 deliquescent nature. 



261. Commercial Forms of Chile Saltpeter. The Chile salt- 

 peter of commerce may reach the farmer or analyst in the lumpy 

 state in which it is shipped, or as finely ground and ready for 

 application to the fields. Unless the farmer is provided with 

 means for grinding, the latter condition is much to be preferred. 

 It permits of a more even distribution of the salt, and thus en- 

 courages economy in its use. For the chemist also it is advan- 

 tageous to have the finely ground material, which condition per- 

 mits more easily a perfect sampling, a process which, with the 

 unground salt, is attended with no little difficulty. 



262. Percentage of Nitrogen in Chile Saltpeter. Chemically 

 pure sodium nitrate contains 16.49 P er cent, of nitrogen. The 

 salt of commerce is never pure. It contains moisture, potash, 

 magnesia, lime, sulfur, chlorin, iodin, silica and insoluble mate- 

 rials, and traces of other bodies. The value of the salt depends, 

 therefore, not only on the market value of nitrogen at the time 

 of sale, but also on its content of nitrogen. The nitrate of com- 

 merce varies greatly in its nitrogen content and is sold on a 

 guaranty of its purity. The best grades range in nitrogen from 

 15 to 1 6 per cent. The content of nitrogen has long been esti- 

 mated in the trade by determining the other constituents and 

 counting the rest as nitrogen. This practice arose in former 

 times when no convenient method was at hand for determining 

 nitric nitrogen. The process is tiresome and unreliable, because 

 all errors of every kind are accumulated in the nitrogen content, 

 1)ut inasmuch as the method is still required by many merchants, 

 the analyst should be acquainted with it, and it is therefore given 

 further along. The usual methods for determining nitric nitro- 

 gen may be applied in all cases where samples of sodium nitrate 

 are under examination, but some special processes are described 

 further on for convenience. 



263. Adulteration of Chile Saltpeter. The analyst, aside from 



