There is scarcely to be found a more striking illustration of chemical genius, than that afforded by his chapter on the "Absorption of Nitrous Gas by solutions of green Sulphate of Iron."
The address with which he gradually disentangles the subject of its difficulties, and catches at every opening to truth, affords a study which may be safely recommended to the attention of every young experimentalist, as being no less instructive than it is beautiful.
The phenomena attending the absorption of nitrous gas by solutions of sulphate of iron had been examined by Vauquelin and by Berthollet, but the conclusions of these chemical philosophers were fatally infected by errors, arising from the neglected action of the atmosphere. Davy, by conducting his experiments over mercury, proved that, in the absence of air, the absorption was simply owing to a combination between the gas and the fluid; but that, on admitting air, the nitrous gas became nitrous acid, a portion of which, together with a part of the water, subsequently underwent decomposition, and gave origin to ammonia, and ultimately to nitrate of ammonia, while the iron passed into the state of a peroxide.
We have also to admire in this work an ardour for investigation, which even the most imminent personal danger could not repress. He may truly be said to have sought the bubble reputation in the very jaws of Death. What shall we say of that spirit which led him to inspire nitrous gas, at the hazard of filling his lungs with the vapour of aqua fortis! or what, of that intrepid coolness which enabled him to breathe a deadly gas, and to watch the advances of its chilling power in the ebbing pulsations at the wrist!
These experiments, however, are far too interesting and important to be related in any other than the author's own words; but it is first necessary that his trials with the nitrous oxide should be considered.
He found that this gas might be most conveniently, as well as most economically, prepared by the decomposition of a salt known by the name of nitrate of ammonia, by the application of a regulated heat; but, as the researches by which he arrived at this conclusion are recorded at length in his work, and as the most important of them are now embodied in every elementary system of chemistry, it would not only be tedious but useless, to enter into a detail of them upon this occasion.
"In April," he says, "I obtained nitrous oxide in a state of purity, and ascertained many of its chemical properties. Reflections upon these properties, and upon former trials, made me resolve to inspire it in its pure form, for I saw no other way in which its respirability, or powers, could be determined.
"I was aware of the danger of the 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, possibly, be 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 materially injure, the powers of life.
"On April 11th, I made the first inspiration of pure nitrous oxide. It passed through the bronchiæ without stimulating the glottis, and produced no uneasy sensations in the lungs.
"The result of this experiment proved that the gas was respirable, and induced me to believe that a farther trial of its effects might be made without danger.