I breathed three quarts of Nitrogene mingled with a very small portion of carbonic acid, for near a minute. It produced no alteration in my sensations for the first twenty seconds; then the painful sense of suffocation gradually came on, and increased rapidly in the last quarter of the minute, so as to oblige me to desist from the experiment. My pulse was rendered feebler and quicker. I felt no affection whatever in the head. Mr. Watt’s observations on the respiration of diluted Hydrocarbonate by men, and Dr. Beddoes’s experiments on the destruction of animals by pure hydrocarbonate, proved that its effects were highly deleterious. As it destroyed life apparently by rendering the muscular fibre inirritable without producing any previous excitement, I was anxious to compare its sensible effects with those of nitrous oxide, which at this time I believed to destroy life by producing the highest possible excitement, ending in læsion of organisation. In the first experiment, I breathed for near a minute, three quarts of hydrocarbonate mingled with nearly two quarts of atmospheric air.[209] It produced a slight giddiness and pain in the head, and a momentary loss of voluntary power: my pulse was rendered much quicker and feebler. These effects however, went off in five minutes, and I had no return of giddiness. [209] I believe it had never been breathed before by any individual, in a state so little diluted. Emboldened by this trial, in which the feelings were not unlike those I experienced in the first experiments on nitrous oxide, I resolved to breathe pure hydrocarbonate. For this purpose, I introduced into a silk bag, four quarts of gas nearly pure, which was carefully produced from the decomposition of water by charcoal an hour before, and which had a very strong and disagreeable smell. My friend, Mr. James Tobin, Junr. being present, after a forced exhaustion of my lungs, the nose being accurately closed, I made three inspirations and expirations of the hydrocarbonate. The first inspiration produced a sort of numbness and loss of feeling in the chest and about the pectoral muscles. After the second inspiration, I lost all power of perceiving external things, and had no distinct sensation except a terrible oppression on the chest. During the third expiration, this feeling disappeared, I seemed sinking into annihilation, and had just power enough to drop the mouth-piece from my unclosed lips. A short interval must have passed during which I respired common air, before the objects about me were distinguishable. On recollecting myself, I faintly articulated, “_I do not think I shall die_.” Putting my finger on the wrist, I found my pulse thread-like and beating with excessive quickness. In less than a minute, I was able to walk, and the painful oppression on the chest directed me to the open air.