RESPIRATION. 635 



3f cubic inches of oxygen gas, when converted into carbonic acid 

 gas, give out 1 of heat. 



(4.) From the experiments of Despretz, it farther appears, that 

 when a pound of hydrogen is burnt, a quantity of heat is evolv- 

 ed, capable of melting 315-2 Ibs. of ice, or the heat evolved 

 would heat one pound of water 44,128 degrees. But for this 

 combustion eight pounds of oxygen gas are required. Now eight 

 pounds of oxygen gas are equivalent to 165,246 cubic inches. 

 Hence every 3 J cubic inches of oxygen gas, when they combine 

 with hydrogen, evolve 1 of heat. It would appear from this 

 that the heat evolved during the combustion of carbon and hy- 

 drogen, is proportional to the quantity of oxygen gas consumed. 



These preliminary observations were necessary to enable us to 

 understand the experiments of Despretz. 



(1.) A rabbit was made to breathe during an hour and thirty- 

 six minutes inclosed in a copper vessel, air-tight, but connected 

 with two air-holders, by means of which a regular current of air 

 was made to pass through the vessel. This air, after respiration, 

 passed through a serpentine worm twelve feet long and surround- 

 ed with water, which cooled it to the same degree as when ad- 

 mitted to the vessel containing the animal. The volume of air 

 respired was 2929 cubic inches. It was reduced by the breath- 

 ing to 2919-5 cubic inches. The loss of volume was 9-5 cubic 

 inches, or about s^yth of the original volume. The proportion 

 of azotic gas was increased by 51*2 cubic inches, The elevation 

 of temperature of the water gave the quantity of heat withdrawn 

 from the animal by respiration, &c. 66 Ibs. avoirdupois of water 

 were heated P.26, or the quantity of heat given out by the ani- 

 mal in one hour and thirty-five minutes would have elevated the 

 temperature of one pound of water 70. 84. The quantity of oxy- 

 gen gas consumed was 247*5 cubic inches. Of these 187*7 cubic 

 inches were converted into carbonic acid,* and Despretz supposes 

 that the other 59-8 cubic inches combined with hydrogen, and 

 were converted into water. 



Now we have stated above that 3 j cubic inches of oxygen 

 when combined by combustion with carbon or hydrogen would 

 evolve 1 of heat Hence 247 '5 cubic inches would evolve 66. 

 The heat actually given out by the animal was 70 -84, or 4.& 



* This is more than double the quantity of carbonic acid obtained by Sir B, 

 Brodie in his experiments. 



