100 ANIMAL CHEMISTRY LECTURE V. 



first series of experiments, as 6*85 to I in the second series, and 

 as 7 '07 to i in the mean of the two. Theoretically, then, the 

 ratio of carbon in carbonic acid to carbon in urea is as 7 to I ; 

 experimentally it is found to be as 7 '07 to i a striking mutual 

 corroboration of the two methods of calculation and research. 



(106.) With regard to the dynamic value of muscle oxidation, 

 I told you in my last lecture that, by the separation of oxygen 

 from carbon and hydrogen, a certain amount of heat-force was 

 absorbed and rendered latent in the separated bodies, which, by 

 their re-combination, was again liberated and rendered sensible. 

 Confining our attention to hydrogen, and speaking in round 

 numbers, we may say that the heat evolved by burning a cubic 

 foot of hydrogen that is, by combining a cubic foot of hydrogen 

 with half a cubic foot of oxygen will raise the temperature of 

 5 \ cubic feet of water one degree Fahrenheit ; or that the heat 

 of burning hydrogen is capable of raising the temperature of 5 \ 

 times its bulk of water one degree. But, seeing that the 

 quantity of matter in a body is proportionate to its weight, 

 we get a much better idea of the amount of heat developed, 

 by comparing the items gravimetrically instead of volumetri- 

 cally. We thus find that the combustion of one part by 

 weight of hydrogen will evolve an amount of heat sufficient 

 to raise the temperature of more than 61,000 parts of water one 

 degree Fahrenheit, or 34,000 parts of water one degree centi- 

 grade. Now, in comparing the amounts of heat given out by the 

 combustion of different substances, it is convenient to have some 

 definite standard of comparison ; and the usual continental stand- 

 ard is altogether, perhaps, the most convenient. According to 

 this standard, the amount of heat given out by one kilogramme 

 of water in cooling one degree centigrade, or, conversely, the 

 amount of heat absorbed by one kilogramme of water in rising 

 one degree centigrade, is called the unit of heat. We find, then, 

 ihat when one gramme of hydrogen gas is burned into water, it 

 gives out 34 units of heat ; or it will raise the temperature of 34 

 kilogrammes that is, 34,000 times its own weight of water 

 one degree ; while, turning our attention to carbon, we find that 



