1815.) the Gases ly different Bodies. 335 
ced in contact with the charcoal, fell 0°9°.* By a chemical 
analysis of the gas, | found that the receiver contained hydrogen 
and 4°55 volumes of oxygen gas, which, subtracted from 18°81 
volumes, leaves 14°26 volumes of hydrogen. Hence there was 
absorbed’ by the charcoal 15°6 — 14°26 = 1°34 volumes of 
hydrogen gas: and this quantity had expelled 4°55 volumes of 
oxygen gas. 
As we have seen above that charcoal free from air absorbs 9°2 
volumes of oxygen, or 1°75 of hydrogen gas, it is evident from the 
rate of absorption that 1°34 volume of hydrogen occupies the same 
space in the coal as 7°03 volumes of oxygen gas; instead of which 
only 4°55 volumes of oxygen gas were expelled by the hydrogen. 
In the present, as well as in the reverse experiment, the condensa- 
tion of the hydrogen gas was promoted by the presence of the 
oxygen. 
When the same piece of charcoal, containing 1°34 volume of 
hydrogen and 4°75 volumes of oxygen gas, was put into a receiver 
filled with mercury, and containing some water, it gave out 0°74 
volume of hydrogen and 0:23 volume of oxygen gas. But out ofa 
piece of charcoal saturated with hydrogen (1°75 volume) alone, 
water disengages 1*1 volume, and of course 0°65 volume remains 
behind. Our charcoal, on the contrary, saturated with both gases, 
left only 1-34 — 0°74 = 0°60 volume of hydrogen behind. The 
oxygen gas present in it prevented it from retaining the whole 
hydrogen, which it otherwise would have done. ‘The oxygen, 
therefore, could not be present in the state of water. 
As we have no method of separating the whole of either a single 
gas or of two gases absorbed by charcoal without destroying it, I 
cannot show decisively that a very small quantity of water is not 
formed in these cases} but all appearances, as we have seen, are 
against that supposition. 1. The absorption of the oxygen and 
hydrogen are iv quite different proportions from those that form 
water. 2. The temperature sinks when the hydrogen is absorbed 
Jast. 3. Both gases are driven off by water in very different pro- 
portions from what would be requisite to form water. 
I must now observe that the quantities of oxygen and hydrogen 
gases which a piece of charcoal absorbs, vary according to the pro- 
portions of both which remain behind in the receiver, and that both 
of these stand to each other in a determinate ratio. Thus when a 
iece of charcoal saturated with oxygen is put into 15-6 volumes of 
ydrogen gas, 4°55 volumes of oxygen are disengaged, in place of 
Which 1°34 volume of hydrogen is absorbed. But if the same 
charcoal be put into 11 volumes of hydrogen gas, only 3°12 volumes 
of oxygen is evolved, and 0°76 volume of hydrogen absorbed. The 
‘residual gas in this case contains a greater proportion of oxygen thag 
* The charcoal had nearly the same bulk as in the preceding experiment, If 
larger pieces be employed, the change of temperatare is more remarkable. But 
the experiments are made more easily, and with wore accuracy, with stall por- 
tions of gas, wad smal) pieces of charcoal, 
