Davy a few years afterwards obtained much clearer views as to the real nature of the atmosphere, and was, in fact, one of the earliest to recognise that it is merely a mixture of oxygen and nitrogen.
The third section consists of an account of observations on the action of nitrous oxide upon animals, and an investigation of the changes effected in it by respiration; whilst the fourth and last gives a history of the respirability and of the extraordinary effects of nitrous oxide, with details of experiments on its powers made by different individuals.
The last portion of the inquiry—in time of execution the first—is particularly interesting to the biographer of Davy, not only because the work in it was originated and carried out by him, but also from the light it incidentally throws on his character and genius:—
“A short time,” he says, “after I began the study of chemistry, in March 1798, my attention was directed to the dephlogisticated nitrous gas of Priestley, by Dr. Mitchell’s Theory of Contagion.” “Dr. Mitchell,” he tells us in a foot-note, “attempted to prove from some phenomenon connected with contagious diseases, that dephlogisticated nitrous gas which he called oxide of septon, was the principle of contagion, and capable of producing the most terrible effects when respired by animals in the minutest quantities, or even when applied to the skin or muscular fibre.” “The fallacy of this theory,” he continues, “was soon demonstrated by a few coarse experiments made on small quantities of the gas procured from zinc and diluted nitrous [nitric] acid. Wounds were exposed to its action, the bodies of animals were immersed in it without injury; and I breathed it mingled in small quantities with common air, without remarkable effects. An inability to procure it in sufficient quantities prevented me at this time from pursuing the experiments to any greater extent. I communicated an account of them to Dr. Beddoes.”
In the early part of April, 1799, he obtained nitrous oxide in a state of purity, and, as already stated, made the attempt to respire it.
“I was aware,” he says, “of the danger of this experiment. It certainly would never have been made if the hypothesis of Dr. Mitchell had in the least influenced my mind. I thought that the effects might be possibly depressing and painful, but there were many reasons which induced me to believe that a single inspiration of a gas apparently possessing no immediate action on the irritable fibre, could neither destroy nor immediately injure the powers of life.”
The experiment was made: the gas passed into the bronchia without stimulating the glottis, and produced no uneasy feeling in the lungs. There was a sense of fulness in the head accompanied with loss of distinct sensation and voluntary power—a feeling analogous to that produced in the first stage of intoxication, but unattended by pleasurable sensation. In company with Dr. Beddoes the experiment was repeated, with the following results:—
“Having previously closed my nostrils and exhausted my lungs, I breathed four quarts of nitrous oxide from and in to a silk bag. The first feelings were similar to those produced in the last experiment; but in less than half a minute, the respiration being continued, they diminished gradually, and were succeeded by a sensation analogous to gentle pressure on all the muscles attended by a highly pleasurable thrilling, particularly in the chest and the extremities. The objects around me became dazzling, and my hearing more acute. Towards the last inspirations, the thrilling increased, the sense of muscular power became greater, and at last an irresistible propensity to action was indulged in; I recollect but indistinctly what followed; I know that my motions were various and violent. These effects very soon ceased after respiration. In ten minutes I had recovered my natural state of mind. The thrilling in the extremities continued longer than the other sensations. This experiment was made in the morning; no langour or exhaustion was consequent, my feelings throughout the day were as usual, and I passed the night in undisturbed repose. The next morning the recollections of the effects of the gas were very indistinct, and had not remarks written immediately after the experiment recalled them to my mind I should have even doubted of their reality. I was willing indeed to attribute some of the strong emotion to the enthusiasm, which I supposed must have been necessarily connected with the perception of agreeable feelings, when I was prepared to experience painful sensations. Two experiments, however, made in the course of this day, with scepticism, convinced me that the effects were solely owing to the specific operation of the gas.”
Having thus ascertained the powers of the gas, he made many experiments to ascertain the length of time it might be breathed with safety, its action on the pulse, and its general effects on the health when often respired.
After a number of experiments made to determine its effect in allaying fatigue, in inducing sleep, or in alleviating the after-effects of vinous intoxication, he resolved