| Carbonic acid | 5,25 |
| Nitrous oxide | 88,75 |
| Oxygene | 5,00 |
| Nitrogene | 29,00 |
Consequently, in this experiment, 93,25 cubic inches of nitrous oxide had disappeared.
In each of these experiments, the cylinder was covered with condensed watry vapor exactly in the same manner as if common air had been breathed in it. It ought to be observed that, E. 1. was made in the morning, four hours and half after a moderate breakfast; whereas, E. 2. was made but an hour and quarter after a plentiful dinner; at which near three fourths of a pint of table-beer had been drank.
From these experiments we learn, that nitrous oxide is rapidly absorbed by the venous blood, through the moist coats of the pulmonary veins. But as after a compleat voluntary exhaustion of the lungs, much residual air must remain in the bronchial vessels and fauces, as appears from their incapability of compleatly collapsing, it is evident that the gas expired after every inspiration of nitrous oxide mast be mingled with different quantities of the residual gas of the lungs;[192] whilst after a complete expiration, much of the unabsorbed nitrous oxide must remain as residual gas in the lungs. Now when a complete expiration is made after the breathing of atmospheric air, it is evident that the residual gas of the lungs consists of nitrogene,[193] mingled with small portions of oxygene and carbonic acid. And these are the only products found after the respiration of nitrous oxide.
To ascertain whether these products were partially produced, during the process of respiration, as I was inclined to believe from the experiments in the last section, or whether they were wholly the residual gases of the lungs, I found extremely difficult.
I at first thought of breathing nitrous oxide immediately after my lungs had been filled with oxygene; and to compare the products remaining after the full expiration, with those produced after a full expiration of pure oxygene; but on the supposition that oxygene and nitrous oxide, when applied together to the venous blood, must effect changes in it different from either of them separately, the idea was relinquished.
I attempted to inspire nitrous oxide, after having made two inspirations and a complete expiration of hydrogene; but in this experiment the effects of the hydrogene were so debilitating, and the consequent stimulation by the nitrous oxide so great, as to deprive me of sense. After the first three inspirations, I lost all power of standing, and fell on my back, carrying in my lips the mouth-piece separated from the cylinder, to the great alarm of Mr. Patrick Dwyer, who was noting the periods of inspiration.
Though experiments on successive inspirations of pure nitrous oxide might go far to determine whether or no any nitrogene, carbonic acid and oxygene were products of respiration, yet I distinctly saw that it was impossible in this way to ascertain their quantities, supposing them produced, unless I could first determine the capacity of my lungs; and the different proportions of the gases remaining in the bronchial vessels after a compleat expiration, when atmospheric air had been respired.
In some experiments (that I made on the respiration of hydrogene, with a view to determine whether carbonic acid was produced by the combination of carbon loosely combined in the venous blood, with the oxygene respired, or whether it was simply given out as excrementitious by this blood) I found, without however being able to solve the problem I had proposed to myself, that in the respiration of pure hydrogene, little or no alteration of volume took place; and that the residual gas was mingled with some nitrogene, and a little oxygene and carbonic acid.
From the comparison of these facts with those noticed in the last section and in R. III. Div. I. there was every reason to suppose that hydrogene was not absorbed or altered when respired: but only mingled with the residual gases of the lungs. Hence, by making a full expiration of atmospheric air, and afterwards taking six or seven respirations of hydrogene in the mercurial airholder, and then making a compleat expiration, I conjectured that the residual gas and the hydrogene would be so mingled, as that nearly the same proportions should remain in the bronchial vessels, as in the airholder. By ascertaining these proportions and calculating from them, I hoped to be able to ascertain with tolerable exactness, the capacity of my fauces and bronchia, as well as the composition of the gas remaining in them, after a complete expiration of common air.