From the increase of volume, it would appear that a minute quantity of gas had been generated during the respiration, and this was, as we shall see hereafter, most probably carbonic acid.[196] Likewise there is reason to suppose, that a little of the residual oxygene must have been absorbed. Making allowances for those circumstances, it would follow, that the 37,5 cubic inches of gas remaining in my lungs, after a compleat expiration of atmospheric air at animal heat 98°, equal to 31,8 cubic inches at 59°, were composed of Nitrogene 21,9 Carbonic acid 4,9 Oxygene 5,0 ———— 31,8 [194] Annales de Chimie, vol. 1, page 279. [195] This is only an imperfect approximation; the ratio of the increase of expansibility of gases to the increase of temperature, has not yet been ascertained. It is probable that the expansibility of gases is altered by their mixture. [196] For there is no reason to suppose the production of nitrogene. E. 2. I respired for near a half a minute in the mercurial airholder at 61°, 182 cubic inches of hydrogene; having made during this time, six long inspirations. After the last expiration, the gas filled a space nearly equal to 184 cubic inches, and analised, was found to consist of Carbonic acid 4,8 Oxygene 4,6 Nitrogene 21,0 Hydrogene 153,6 ————— 184,0 Now in this experiment, reasoning in the same manner as before, 28,4 cubic inches of hydrogene must have remained in the lungs, and likewise 5,5 of the atmospheric residual gas. Consequently, the whole residual gas was nearly equal to 34 cubic inches at 61°, which at 98° would become about 40,4 cubic inches. And reasoning as before, it would appear from this experiment, that the quantity of gas remaining in my lungs after a compleat voluntary respiration, equalled at 98, about 40 cubic inches, and at 61°, 34 nearly: making the necessary corrections; that after common air had been breathed, these 34 cubic inches consisted of Carbonic acid 4,1 Oxygene 5,5 Nitrogene 24,4 _b._ It would have been possible to prove the truth of the postulate on which the experiments were founded, by respiring common air or oxygene after the compleat expiration of the hydrogene, for the same time as the hydrogene was respired and in equal quantities. For if portions of hydrogene were found in the airholder equal to those of the residual gases in the two experiments, it would prove that a _uniform_ mixture of residual gas with the gas inspired, was produced by the respiration. That this mixture must have taken place, appeared, however, so evident from analogous facts, that I judged the experimental proof unnecessary.