U5Q On the Changes produced in Atmospheric Ait 



100 parts of the mixture of expired gas gave 

 8 carbonic acid. 

 13 oxygen. 

 79 azote. 



100 



Calculation for Carhonic Acid. 

 100 : 8 : : 9872 : 789'7<3. 

 Sol that 789*76 cubic inches of carbonic acid gas were given 

 off in 24^ minutes, which gives thirty-two cubic inches per 

 minute. But here it must be noticed that the respiration 

 was more rapid than in the 11th experiment, and a larger 

 quantity of carbonic acid given off in the same time. This 

 agrees with the 12th experiment. 



We are very much inclined to think that, in ordinary re- 

 spiration, a great part of the air is returned unaltered, viz. 

 that contained in the fauces, in the trachea, and probably a 

 portion of that in the larger branches of the bronchia. If this 

 circumstance be not adverted to in experiments upon small 

 quantities of air, the results can never be correct. There is 

 even a considerable difference in the quality of the first and 

 last portions of a single inspiration. In some experiments 

 made with a view to this subject, a small quantity of the first 

 portions, given off in a common and natural expiration, was 

 received in a vessel over mercury ; on examination, it only 

 contained 3"5 per cent, carbonic acid ; in other experiments 

 the first portions contain from three to five per cent. ; while 

 the general average appears by the 11th, 12th, and 13th ex- 

 periments, to be about eight. 



The operator, after rather more than a natural inspiration 

 expired 204 cubic inches into the mercurial gasometer, 

 making his utmost efforts to press as much as possible out 

 of the lungs, this contained 9*5 per cent, of carbonic 

 acid. Here we are to recollect, that these 204 cubic inches 

 contained the first, as well as the last portions ; the first 

 portions have been proved to contain only from three to 

 five per cent. ; consequently the last portions must contain 



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