Researches Chemical and Philosophical; Chiefly concerning nitrous oxide / or dephlogisticated nitrous air and its respiration

by Sir Humphry Davy

In the infancy of my experiments, from general appearances, I thought that the proportion of nitrous oxide absorbed in respiration was greater in the first inspirations than the last; but this I have since found to be a mistake. In the last respirations the apparent absorption is indeed less; but this is on account of the increased evolution of nitrogene from the blood. When nitrous oxide is respired for a long time, the last inspirations are always fuller and quicker than the first; but the consumption by the same individual is nearly in the ratio of the time of respiration. Three quarts, i. e. about 174 cubic inches, are consumed so as to be unfit for respiration, by an healthy individual with lungs of moderate capacity, in about a minute and quarter; six quarts, or 348 cubic inches, last generally for two minutes and half or two minutes and three quarters; eight quarts, or 464 cubic inches, for more than three minutes and half; and twelve, or 696 cubic inches, for nearly five.

The quantities of nitrous oxide absorbed by the same individual, will, as there is every reason to suppose, be different under different circumstances, and will probably be governed in some measure by the state of the health. It is reasonable to suppose, that the velocity of the circulation must have a considerable influence on the absorption of nitrous oxide; probably in proportion as it is greater a larger quantity of gas will be consumed in equal times.

I am inclined from two or three experiments, to believe that nitrous oxide is absorbed more rapidly after hearty meals or during stimulation from wine or spirits, than at other times. As its absorption appears to depend on a simple solution in the venous blood; probably diminution of temperature will increase its capability of being absorbed.

l. The quantities of nitrous oxide absorbed by different individuals, will probably be governed in some measure by the size of their lungs and the surface of the blood vessels, all other circumstances being the same.

From the observations that I have been able to make on the absorption of nitrous oxide, as compared with the capacity of the lungs, the range of the consumption of different individuals does not extend to more than a pint, or 30 cubic inches at the maximum dose.

We may therefore conclude, that the medium consumption of nitrous oxide by the respiration of different individuals, is not far from two cubic inches, or about a grain every second, or 120 cubic inches, or 60 grains every minute.

m. When nitrous oxide is breathed in tight silk bags, towards the end of the experiment as the internal surface becomes moist, as I have before mentioned, a certain quantity of common air penetrates through it and becomes mixed with the residual gas of the experiment; but this quantity is always too small to destroy any of the effects of the nitrous oxide. The residual gas of the common air, the nitrogene and carbonic acid produced in the process, and the residuum of the admitted atmospheric air, hardly ever amount after the experiment, to one half of the volume of the nitrous oxide absorbed. There is consequently, a perfect propriety in successively inspiring and expiring the whole of a given quantity of nitrous oxide, till it is nearly consumed. In the respiration of nitrous oxide as the gas is absorbed and not decomposed, little will be gained in effect, by perpetually inspiring and expiring new portions, whilst an immense quantity of gas will be idly wasted, and this circumstance, considering the expence of the substance, is of importance.

VI. On the respiration of Atmospheric Air.

Having thus ascertained the absorption of nitrous oxide in respiration, and the evolution of nitrogene and carbonic acid from the lungs during its absorption: considering atmospheric air as a compound in which principles identical with those in nitrous oxide existed, though in different quantities and looser combination, I was anxious to compare the changes effected in this gas by respiration, with those produced in nitrous oxide and oxygene; particularly as they are connected with the health and life of animals.

The ingenious experiments of Lavoisier and Goodwyn, prove the consumption of oxygene in respiration, and the production of carbonic acid. From many experiments on the respiration of common air, Dr. Priestly suspected that a certain portion of nitrogene, as well as oxygene, was absorbed by the venous blood.