18 BULLETIN 1413, U. S. DEPARTMENT OF AGRICULTURE 
units per pound. Anthracite coal of ordinary good grade may be 
assumed to have an average calorific value of 7,200 Calories per 
kilogram, or nearly 13,000 British thermal units per pound; the 
corresponding values for average bituminous coal of good grade are 
7,800 Calories per kilogram, or about 14,000 British thermal units 
per pound. The average fuel value found for the cocoa cakes is 
therefore, on paper, 70 per cent of the fuel value of anthracite and 
about two-thirds that of bituminous coal. 
Volatile matter, reported in the tables, represents a value empir- 
ically determined by fuel chemists in the proximate analysis of 
coal and related products, and should not be confused with the 
" organic matter " of the general analyst. Except for the empiric 
features in its determination, volatile matter corresponds to total 
organic matter less fixed carbon. The sum of the percentages of 
moisture, volatile matter, fixed carbon, and ash equals 100. The 
volatile matter data proved to be of significance in indicating the 
degree of charring undergone by one of the samples of dried, solvent- 
extracted cocoa. 
It is evident that the calorific value of the cocoa cakes increases 
with the fat content. Investigation of this relationship has brought 
out an interesting fact. If 9,300 Calories per kilogram be accepted 
as the heat of combustion or calorific value of cacao fat (26, p. 166 ; 
21, p. 4-4-/ 4-5,) and this fuel value be assigned to the ethyl-ether 
extracts of the cocoa samples, a simple calculation serves to show 
that, on the moisture-free and ash-free basis, the nonfatty, organic 
substance of cocoa has a rather uniform heat of combustion of 
about 4,900 Calories per kilogram. With the exception of sample 
No. 107, known to have been partially charred in drying, the range 
is from 4,840 to 5,060 Calories. 24 It is therefore possible to approxi- 
mate closely the total fuel value (heat of combustion) of a partic- 
ular lot of cocoa, knowing merely its content of moisture, fat, and 
ash. It is believed that a value within a few per cent of the actual 
heat of combustion value will be given by the following formula : 
C=44 F+4,900-49 (M+A). 
C=the calorific value of the cocoa sample "as is"; that is, on 
the original moisture and ash content basis, expressed in Calories 
per kilogram. 25 M=the per cent of moisture in the sample. 
A=the per cent of ash in the sample. F=the per cent of crude fat 
or ethyl-ether extract in the sample. 
If the content of petroleum-ether extract is taken as the meas- 
ure of the fat ; that is, if F is equal to the percentage of petroleum- 
ether extract in the sample, and assuming 9,300 Calories per kilogram 
to be the calorific value of the petroleum-ether extract, recalculation 
of the data yields the following formula: 
C=43.2 F+4,980-49.8 (M+A). 
24 This calorific value might hold for the nonfatty material of other oleaginous seeds 
or fruits. As data were available for a sample of olive pomace, the test was applied to 
this material. The sample was a very thoroughly pressed residue from the manufacture 
of olive oil, containing only 5.8 per cent of ether extract, on the moisture-free and ash- 
free basis. On this basis the nonfatty substance had a calorific value of 5,025 Calories 
per kilogram. 
25 To convert this value into B. t. u. per pound, multiply the Calories per kilogram 
by 1.8. 
