STATICS 121 



contain a large amount of starch, e.g. potatoes, barley, etc., 

 it is safer to take 3*9 kt. for the former and 4*2 kt. for the 

 latter. 



These conclusions may be briefly summarised as follows : 



Heat of Combustion. 



Mean 

 *' kt. 



(Of oily seeds and animal fats . . 9*4 

 Of cereals and other seeds ... 9-0 9 - o 

 Of hay, straw, and coarse fodders . 8*5 

 Proteins, except peptones ........ 5'^ 5*8 



Carbohydra.es \ 4' 



The heat of combustion of any food as a whole is often 

 called the total fuel value of the food. It can be determined 

 by burning the substance in the calorimeter as described 

 above. For a sample of meadow hay it was found to be 

 3*65 kt. per Ib. But it is not necessary to make a separate 

 determination for each specimen. When the composition is 

 known, the fuel value can be calculated by means of^the 

 factors given above. Thus the heat of combustion of pro- 

 tein is 5*8 kt. per Ib., and meadow hay contains 10 per cent. 

 of that ingredient; so we have 10 x 5 '8 = 58 kt. as the fuel 

 value of the protein in 100 Ibs. of meadow hay. The values 

 for the other ingredients may be found in a similar manner 

 and the whole calculation set down as follows : 



TOTAL FUEL VALUE OF MEADOW HAY. 



Constituents. Per cent. Factor. Fuel value kt. 



Oil ........ 2-45 X 8-5 = 20-82 



" Albuminoids " (proteins) . IQ'O X 5*8 = 58*00 



Carbohydrates 4 2 'o\ 



Crude fibre 26'OJ 



4-2 = 285-60 



Total fuel value . . . 364-43 



The T.F.V. of meadow hay is, therefore, 3*6443 kt. per Ib., 

 i.e. when i Ib. of this hay is burned in a calorimeter it gives 

 out enough heat to raise the temperature of 3644*3 Ibs. of 

 water i C. 



Available Energy. The T.F.V., however, is not the true 

 measure of the nutritive value of the food. It is obvious that 

 any substance that is not oxidised gives out no heat at all ; and 



