About a fortnight ago, I respired, after forced voluntary exhaustion of my lungs, my nose being accurately closed, three quarts of hydrogene in a silk bag, at four intervals, for near five minutes. After this it was highly inflammable, and burnt with a greenish white flame in contact with the atmosphere; but was not so explosive as before.[237] [237] If loosely combined carbon exists in venous blood, hydrogene may probably dissolve a portion of it when respired and become slightly carbonated. At least there is as much probability in the supposition that carbon in loose affinity may combine with hydrogene at 98° as that it may combine with oxygene. _c._ From what we have lately heard of the curious experiments of Mr. Volta and Mr. Carlisle, it is very probable that the conversion of nitrous gas into nitrous oxide when exposed to wetted zinc, copper and tin, in contact with mercury, as described in Res. I. Div. V. may in some measure depend on the action of the galvanic fluid. Whilst I was engaged in the experiments on this conversion, Dr. Beddoes[238] mentioned to me some curious facts noticed by Humboldt and Ritter, relating to the oxydation of metals by the decomposition of water, which induced me to examine the phænomena with more attention than I should have otherwise done.—I recollect observing that some of the wetted zinc filings in nitrous gas on the side of the jar not in contact with the surface of mercury, were very slowly oxydated. Whilst on the surface of the mercury where small globules of that substance were mingled with the filings of zinc, the decomposition went on much more rapidly; possibly through the medium of the moisture, a series of galvanic circles were formed. [238] Dr. BEDDOES has since favoured me with the following account of these facts. “Mr. Humboldt (ueber die gereizte Faser I. 473, 1797) quotes part of a letter from Dr. Ash, in which it is said that _if two finely polished plates of homogeneous zinc be moistened and laid together, little effect follows—but if zinc and silver be tried in the same way, the whole surface of the silver will be covered with oxydated zinc. Lead and quicksilver act as powerfully on each other, and so do iron and copper._—Mr. Humboldt (p. 474) says that, in repeating this experiment, he saw air-bubbles ascend, which he supposes to have been hydrogene gas from the decomposition of water—When he placed zinc simply on moist glass, the same phænomena took place, but more slowly and later. The quantity of oxyd of zinc upon the glass alone was in 20 hours to that on the silver as one to three.