NOTE ON HEATS OF COMBUSTION*. 



169 



A COMPARISON OF DETERMINED AND CALCU- 

 LATED HEATS OF COMBUSTION". 

 L. H. Merrill. 

 It has been frequently observed in this laboratory and else- 

 where that the heats of combustion of vegetable foods as deter- 

 mined are higher than the results obtained by calculation when 

 the usual factors are employed. This fact is illustrated by the 

 wheat products in the following table in which it will be seen 

 that the differences range from .026 to. 430 calories, or from nearly 

 one to ten percent of the determined value. The wheat products 

 were chosen because they contain nutrients of precisely the same 

 character and origin, but in varying proportions. The milling 

 products are placed in the table below the wheats from which 

 they were derived. The caluculated results are obtained by the 

 use of Rubner's factors, viz.: for 1 gram protein, 5.5 calories; 

 for fat, 9.3 calories; for carbohydrates, 4.1 calories. 



HEATS OF COMBUSTION OF WHEATS AND THEIR MILLING PRODUCTS 



DETERMINED COMPARED WITH THE CALCULATED VALUES. 





Material. 



Heats 



OF CUMBUSTION. 



■ 













O 





<0 



O 









p 



si 



O 















C3 





fi 



S 



Q 



6301 

 6302 



0303 

 0304 



0305 



0290 

 6297 

 0299 

 629S 



6270 

 6273 



6279 

 0280 

 02S1 



Wheat 



Flour, first grade... 

 Flour, second grade 



Middlings 



Bran 



Wheat 



Flour, first grade- . 

 Flour, second grade 



Middlings 



Bran 



Wheat 



Flour, high grade .. 

 Flour, low grade .. 



Middlings 



Bran 



Calories 



Calories. 



Calories. 



3.918 



3.849 



.069 



3.S39 



3.S13 



.026 



3.892 



3.S43 



.049 



4.169 



4.023 



.146 



4.163 



3.933 



.430 



3.922 



3.833 



.089 



3.768 



3.679 



.089 



3. 780 



3.701 



.079 



4.115 



4.005 



.110 



4.142 



3.946 



.196 



3.987 



3.S92 



.095 



3.942 



3.S64 



.078 



4.365 



4.218 



.147 



4.350 



4.075 



.275 



4.196 



3.900 



.296 



% 



2.00 

 .23 

 .29 



4. SO 

 7.32 



2.54 

 .16 



3! 20 

 7.18 



1.96 

 .33 



2.47 



9.02 

 10.07 



A very brief inspection of the table will show that the differ- 

 ences noted stand in very intimate relation to the amount of 

 crude fiber present, and leads to a suspicion that the fiber is the 



12 



