238 



rion of 13 to 10.3*. Although, therefore, the re- 

 sults, obtained by these philosophers, do not com- 

 pletely coincide, yet in experiments of so much dif- 

 ficulty and delicacy, the small difference that ex- 

 ists is not sufficient to invalidate the general con- 

 clusion, That, " when equal quantities of oxygen 

 gas are converted into carbonic acid by animal re- 

 spiration, and by the combustion of carbon, nearly 

 equal quantities of caloric are set free f." 



193. But farther, as the quantity of heat produ- 

 ced, when a given bulk of carbonic acid is formed by 

 the combustion of charcoal, has been demonstrated 

 by Lavoisier J ; and as the quantity of air usually 

 respired (85.) has been ascertained, it is evident, 

 that the quantity of heat liberated in the lungs, in 

 any given time, could also be found out, were we 

 able to estimate the quantity of carbonic acid contain- 

 ed in air which has beon once breathed. Thus, says 

 Dr Menzies, if the bulk of air commonly inspired be 

 estimated at 40 cubic inches, and the number of 

 respirations at 1 8 in a minute, the volume of air in- 

 spired every minute will be 72O cubic inches ; of 



which ~, or 158.4 cubic inches, consist of oxygen 



gas, the only part of the air changed by respiration. 

 But of the air thus inspired, only, or two cubic 

 inches, are changed in each respiration, which gives 

 for the amount of carbonic acid, formed every mi- 



* Mem. de 1'Acad. dcs Scicn. 1783. 



f Crawford on Animal Heat, p. 353. 



J Kcrr's Lavoisier's Elements of Chemistry, 4th edit, p. 113, 



