52 AGRICULTURAL ANALYSIS 



prepared in some of the ways described is placed in the flask and 

 a measured quantity of the acid mixture, from five to 

 10 cubic centimeters, poured over it and warmed with a 

 moderate flame. As soon as the evolution of brown 

 nitroso-vapors becomes slow a further addition of the 

 acid mixture, drop by drop, from the funnel furnished with 

 a stop-cock, is added and this addition continued until the re- 

 action ceases and the intensity of the brown vapors evolved is 

 diminished. In order to determine whether the destruction of 

 the material has been completed, the addition of the acid mixture 

 is discontinued for a short time and the mass further heated until 

 the brown vapors formed disappear and it is noticed whether 

 the liquid in the flask is still dark or black. If this is the case 

 the acid mixture is again added and the test above 

 described, after a few minutes, is repeated. If on standing 

 and after the expulsion of the brown vapors the bright 

 yellow or colorless liquid is not again darkened by further heat- 

 ing, and also no evolution of gas is observed, the incineration may 

 be regarded as complete. If the liquid is colored slightly yellow 

 it generally becomes completely clear on cooling. Three times 

 as much water is now added as the quantity of acid mixture 

 which has been used, the mixture heated and boiled from five to 

 10 minutes. By this process brown vapors are evolved which 

 are derived from the decomposition of the nitrosyl sulfuric acid 

 which has been formed. 



It must be remembered that in the above operation the nitro- 

 gen of the protein matter is not converted into ammonia. In 

 fact, no trace of ammonia can be found in the resulting liquid. 

 The ash constituents, however, of the organic matter are found 

 in a completely inorganic state dissolved in the mixture, and this 

 mixture can be used for the determination of these constituents 

 in the ordinary way. 



The above method for freeing the phosphorus and converting 

 it into inorganic forms has given good results in the laboratory 

 of the Bureau of Chemistry. 



60. Loss of Phosphoric Acid by Incineration. It is well known 

 that in certain substances used for fertilizing purposes, such as 



