22 BULLETIN 1413, U. S. DEPARTMENT OF AGRICULTURE 
"Ammonia*' designates the amount of ammonia (NH 3 ) equiva- 
]ent to the total nitrogen present, and its percentage is obtained by 
multiplying the percentage of total nitrogen by 1.2159. Crude pro- 
tein (sometimes stated merely as protein), of significance in the 
animal-feeding world, also is a concept related to the nitrogen 
content. The percentage of crude protein is obtained by multiply- 
ing the percentage of total organic and ammoniacal nitrogen by 
the arbitrary factor 6.25. The crude protein content of the cocoa 
cakes, omitting samples 109 and 114, therefore varies from 22.38 to 
27.94 per cent and averages 24.8 per cent, or 31.1 per cent on the 
dry, ether-extract-free basis. 
In order properly to understand and interpret the data contained 
in Table 3, on the solubility and quality of the nitrogen of the 
cocoa samples, it is necessary to know just what the neutral and 
alkaline permanganate tests are intended to show. These tests are 
based on two independent purely chemical methods of procedure 
designed to distinguish fertilizer materials whose water-insoluble 
" organic nitrogen " is relatively inert or resistant to decomposition in 
the soil and slowly becomes available to growing plants, from ma- 
terials whose water-insoluble " organic nitrogen " quickly decomposes 
in the soil, yielding compounds that are readily assimilated by 
plants. The two methods have been developed by different groups 
of chemists of the State experiment stations, and it happens that 
the alkaline permanganate test is more generally used in New 
England and the Middle Atlantic States, while the neutral per- 
manganate method is the one in vogue in the South. 
It is no longer claimed by their respective proponents that either 
method is quantitative in the sense of determining the actual per- 
centage of the insoluble nitrogen that is available to plants (23, 
4.6). The tests are credited, however, with being means of dis- 
tinguishing in a qualitative way between good and poor sources of 
water-insoluble organic nitrogen by showing the relative lability of 
the nitrogenous compounds, or the so-called activity of such 
nitrogen. 
For mixed fertilizers, by common consent, arbitrary limits have 
been established for the percentage activity of the water-insoluble 
nitrogen below which this insoluble nitrogen is held to be of in- 
ferior quality. By percentage activity is meant the percentage of 
the water-insoluble nitrogen shown to be active by the particular 
permanganate test being used. The limit is different for each of 
the two tests. At its 1924 convention, the Association of Official 
Agricultural Chemists (20) adopted the following as tentatively 
official : 
The water-insoluble nitrogen in mixed fertilizers showing activity below 
50 per cent by the alkaline method and below 80 per cent by the neutral 
method shall be classed as inferior. 
Such official limits have not been fixed for defining an acceptable 
activity for water-insoluble nitrogen in the crude or unmixed 
fertilizer materials furnishing organic nitrogen. An activity of 50 
or 55 per cent by the alkaline method is commonly considered to 
be the passing mark, however, for the insoluble nitrogen of unmixed 
materials, furnishing organic nitrogen; whereas, in the neutral per- 
manganate test, if any dividing line were generally adopted, it 
