104 ANIMAL CHEMISTRY LECTUEE T. 



of water at zero one degree, and conversely, the absorption of a 

 unit of heat would lift I kilogramme weight to the height of 

 424 metres. Of course, the force necessary to lift I kilogramme 

 through 424 metres, or 10 kilogrammes through 42-4 metres, or 

 424 kilogrammes through I metre, is the same ; whence it is 

 convenient to apply the expression kilogram -metre to the product 

 of the kilogrammes lifted into the metres of height, and to say 

 that the heat evolved by the cooling of a kilogramme of water 

 one degree centigrade is equal to 424 kilogrammetres of motion, 

 and vice versa. Or we may adopt Mr. Joule's original standard, 

 and say that the heat evolved by the cooling of a pound of water 

 one degree Fahrenheit is equal to 772 foot-pounds of motion. 



(in.) The applicability of these considerations to the combus- 

 tions of hydrogen and carbon taking place in the animal body is 

 obvious. We have said that the combustion of I gramme of 

 hydrogen evolves 34 units of heat, and that a unit of heat is 

 equal to 424 kilogrammetres of motion ; so that the combustion 

 of i gramme of hydrogen will produce 34x424=14,416 kilo- 

 grammetres of motion ; or will serve to lift I kilogramme weight 

 through 14.416 metres of height, or 14,416 kilogrammes through 

 I metre of height, &c. &c. Similarly, the combustion of I 

 gramme of carbon will suffice to produce 3392 kilogrammetres 

 of motion, thus : 



One gramme Kilogrammetres 



burnt of motion 



HYDROGEN 34 x 424 = 14.416 

 CAEBON 8 x 424 = 3, 392 



In this way, then, we can form some idea of the mechanical 

 power generated, or quantity of motion producible, by the com- 

 bustion of the hydrogen and carbon of our muscles into water, 

 and carbonic acid or urea respectively.* Our knowledge of the 



* The heat produced by the conversion of carbon into urea is doubtless 

 that producible by its complete burning into carbonic anhydride C0 2 , and 

 not merely that producible by its half burning into carbonic oxide CO, as 

 sometimes represented. 



