1813.] Memoirs of the Manchester Society, 



461 



and valuable experiments of Allan and Pepys on the subject. 

 The phenomena of respiration as described by Dalton in x\\u 

 paper, and as generally admitted, are as follows: — A portion of 

 the oxygen of the air inspired disappears, and is replaced by an 

 equal bulk of carbonic acid gas. The air expired is saturated 

 with moisture, and its temperature is raised to about 98°. Mr. 

 Dalton adopts the theory of Crawford, that respiration is the 

 source of animal heat; and in his second appendix he endea- 

 vours to refute the objections to this theory brought by Mr. 

 Brodie. Crawford's theory depends upon the two following 

 propositions : 1. The speciric heat of oxygen gas is greater than 

 that of carbonic acid. 2. The specific heat of arterial blood is 

 greater than that of venous blood. If these propositions be 

 inaccurate, Crawford's theory falls to the ground. Now in the 

 last number of the jinnals of Philosophy (p. 3S9) there is a 

 table of the specific heat of the gases from the experiments of 

 Delaroche and Berard, from which it appears that the specific 

 heat of oxygen gas is to that of carbonic acid gas as the numbers 

 0-2361 : 0-221 0. Now if these numbers be correct^ the first of 

 Crawford's propositions falls to the ground. Suppose 20 cubic 

 inches of air to be drawn into the lungs by one inspiration, and 

 that one cubic inch of oxygen gas is converted into carbonic acid 

 gas; from the above numbers we see that -'-^-th of the heat of 

 the oxygen gas would be disengaged. Let us suppose the tem- 

 perature of the air inspired to be 60^, and that of the air expired 

 to be 98°. The whole 20 cubic inches of the air will have been 

 heated 38°. Now let us suppose the absolute quantity of heat 

 in the oxygen to be 10000°; the quantity of heat thus disen- 

 gaged would be 6o6°. This being divided into 20 portions 

 would heat the whole air only 33°, or from 60° to 93° ; so that 

 the whole heat evolved would not be sufficient to raise the air 

 inspired to the temperature of the body. In fact, it would not 

 produce so great an effect as I have supposed; for, according to 

 the table of Delaroche and Berard, the specific heat of azote is 

 0*2754 ; so that a degree of heat from oxygen gas would not 

 heat azotic gas quite a degree. It follows from this, that if ihe 

 table of Delaroche and Berard be correct, Crawford's theory of 

 animal heat must be given up. 1 do not know how the experi- 

 ments of the French Gentlemen were n»ade, and therefore 

 cannot say what confidence may be placed in them ; but I have 

 seen a letter by BerthoUet, in which he declares that he has the 

 most perfect confidence in their accuracy. Now Mr. Daltoo will 

 acknowledge, I think, that BerthoUet is not very apt to adopt 

 the opinions of others without pretty strong evidence. I think, 

 therefore, we are warranted at present in rejecting Crawford's 

 theory altogether, till new and indisputable evidence be pro- 

 duced of the truth of liis fundamental principles, which are. 



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