1813,] Philosophical Transactions, PartlJ. 1812. '21S 



niit of precision. But it is not the experiments on arterial blood, 

 though these are the only ones alluded to by Mr. Brodie ; it is 

 the experiments on the specific heat of the aerial bodies con- 

 nected with respiration that constitute by far the most difficult 

 part of the investigation. If Dr. Crawford's statements respect- 

 ing the specific heats of oxygen gas, atmospherical air, and car- 

 bonic acid gas, be admitted, we do not see how it is possible to re- 

 ject the conclusions to which he has come. Let us take his 

 statements for granted, and see what will follow. According to 

 him the specific heats of these gases are as follow : 



Oxygen gas 4''^40 



Air 1790 



Carbonic acid gas 1-0454 



Now let us take any one of Mr. Brodie's experiments, as, for 

 example, the second. The rabbit converted -yV^h of the bulk of 

 the air into carbonic acid gas ; otr which is the same thing, —th 

 of the oxy2;en was changed into carbonic acid. Of course, its 

 specifit heat was sunk from to 1*0454. To get a base of 



calculation, let us suppose the absolute quantity of heat in bodies 

 at the temperature of 65"^ to be 1500 degrees. In that case, no 

 less than 11 70 degrees of heat will be disengaged merely by the 

 change of the oxygen into carbonic acid gas. 1 his quantity lias 

 to be divided over 18 parts of an air consisting of a mixture of 



79 azotic gas 

 15*5 oxygen gas 

 5*5 carbonic acid gas 



lOO'O ♦ 



Now the specific heat of this mixture will be obtained bv 

 multiplying these numbers respectively into tlie specific he;^t of 

 each of these gases, adding the products together, and dividing 

 the sum by 100. This operation gives us the specific heat of the 

 residual mixture, after respiration, 1-420. The 1 IJO degrees of 

 heat divided into 18 parts gives 65 degrees for each part ; but as 

 the specific heat of the residual gas is 1-42, these 65 are only 

 capable of producing an increase of temperature equivalent to 

 45*7 degrees. The air, when drawn in, was 6d° ; it oughtj 

 therefore, when thrown out, to be of the temperature of 1 10°'7 ; 

 but as its temperature is only about 100^, there are 10-7 degrees 

 of heat to be accounted for. and which can only be accovmred 

 for bv supposing it to be absorbed i)y the body„ If we were to 

 suppose, with Mr. Dalton, that the absolute heat of bodies 

 amounts to 6000 degrees, in that case no less than 46/9 degrees 

 would be disengaged from the oxygen by its change into carbonic 

 acid. This ought to heat the. residual air up to the temperature 



