The residual gas of the lungs, after compleat expiration, equals at 55°, 32 cubic inches, and 32 cubic inches of common air contain 8.6 cubic inches of oxygene.
But in the experiments on the respiration of hydrogene, not only 5.6 cubic inches of carbonic acid were produced, but more than 4 of residual oxygene remained unabsorbed.
Hence it appears impossible that all the carbonic acid evolved from the lungs during the respiration of nitrous oxide or hydrogene could have been produced by the combination of charcoal in the venous blood with residual atmospheric oxygene: there is consequently every reason to believe that it is wholly or partially liberated from the venous blood through the moist coats of the vessels.
g. The water carried out of the lungs in solution by the expired gas of nitrous oxide, could neither have been wholly or partially formed by the decomposition of nitrous oxide. The coats of the vessels in the lungs, and indeed in the whole internal surface of the body, are always covered with moisture, and the solution of part of this moisture by the inspired heated gas, and its deposition by the expired gas, are sufficient causes for the appearance of the phænomenon.
There are no reasons for supposing that any of the residual atmospheric oxygene is immediately combined with fixed or nascent hydrogene, or hydrocarbonate, in the venous blood at 98°, by slow combustion, and consequently none for supposing that water is immediately formed in respiration.
The evolution of water from the vessels in the lungs, is almost certain from numerous analogies.
h. As from the experiments in section II. it appeared that nitrous oxide was capable of being combined with oxygenated blood, and vice versa, blood impregnated with nitrous oxide capable of oxygenation; I was curious to ascertain what changes would be effected in nitrous oxide when it was respired, mingled with atmospheric air or oxygene. For this purpose, without making a very delicate experiment, I breathed in the large mercurial airholder about 112 cubic inches of nitrous oxide, mingled with 44 of common air, for near half a minute, in the usual mode. The gas, after expiration, filled a space nearly equal to 119. I did not exactly ascertain the composition of the residual gas; it supported flame rather better than common air, and after the nitrous oxide was absorbed, gave much less diminution with nitrous gas than atmospheric air.
i. I breathed a mixture of four quarts of nitrous oxide with three quarts of hydrogene, in a dry silk bag, for near a minute; an evident diminution was produced; but on account of the mode of experimenting it was impossible to determine the quantity of nitrous oxide absorbed, or the exact nature of the products. When a taper was introduced into a little of the residual gas, it inflamed with a very feeble explosion. Now a mixture of 4 parts nitrous oxide and 3 hydrogene, detonates when inflamed with very great violence.
k. Nitrous oxide can be respired without danger by the human animal for a much longer time than that required for the death of the smaller quadrupeds in it.
I have breathed it two or three times in a considerable state of purity, in a dry silk bag, for four minutes and quarter and four minutes and half: some diseased individuals have respired it for upwards of five minutes.