IN GASES: HYDROGEN, CARBONIC OXIDE, AND OXYGEN. 
G51 
Table XYI.—Pressures from 75 millims. to 1000 millims. 
Reference 
No. 
Pressure. 
T1 . CO., 
Eafio 
Temperature. ; 
milliins. 
° C. 
75 
mean 1*395 
100 
mean 1*403 
125 
mean 1*17 
43 
150 
1*07 
15 1 
44 
175 
1*03 
15-2 
45 
200 
*99 
151 
46 
25' > 
*94 
150 
47 
300 
*92 
11-7 
48 
400 
*91 
15-3 
49 
700 
*90 
14-9 
50 
1000 
*90 
157 
Under very small pressures considerable differences were found in the ratio C0 2 : hhO, 
in several experiments repeated under the same conditions. Thus under 75 millims. 
pressure this ratio was found to vary from 1*35 to U46 in eight experiments. These 
discrepancies may partly be accounted for by errors of manipulation, for on the very 
small masses of gases employed at this pressure, the error of experiment becomes 
serious. If the mean value of the ratios found in the several experiments made at 
the lower pressures he taken as correct, we see that the ratio rises very slightly as the 
pressure is increased from 75 millims. to J 00 millims., and then falls abruptly as the 
pressure is increased to 150 millims., after which the fall is more gradual, until at about 
400 millims. the ratio becomes constant. This result entirely confirms the previous 
series of experiments, and proves that for a mixture of carbonic oxide and electrolytic 
gas containing 12 per cent, of oxygen, there is a “ critical pressure ; ” below this critical 
pressure alterations of pressure affect the division of the oxygen, above it alterations of 
pressure have no effect. 
In working at low pressures, therefore, there are two sources of variation to be taken 
into account: one springing from changes of pressure, the other from changes in the 
length of the column of gases exploded. 
We have seen above that changes in the length of the column cease to have any 
effect on the ratio of the products of combustion, when a mixture containing 19 per 
cent, of oxygen is exploded under a pressure only as high as 250 millims. The 
question arises, what is the “ critical pressure ” for such a mixture? To determine this 
point a series of experiments was made at different pressures with a mixture of the 
following composition. 
Composition of Mixture. 
Carbonic oxide.58*47 
Hydrogen.22*54 
Oxygen.18*99 
4 o 
o 
100*00 
