672 
MR, H. B. DIXON ON CONDITIONS OF CHEMICAL CHANGE 
For instance, in the last three experiments of Table XL., where 17 5 parts of oxygen 
were exploded with 73’3 of carbonic oxide, and 26’7 of hydrogen, there was only sufficient 
hydrogen to burn at once 13*3 parts of oxygen ; now, supposing the hydrogen to have 
been all burnt at once, then the other 4”2 parts of oxygen had to wait until the corres¬ 
ponding quantity of steam, formed at first, had been decomposed by the carbonic oxide. 
Of course the steam produced at first immediately began to react with the carbonic 
oxide, but owing to the deficiency of hydrogen, the rate of formation of steam was 
limited, during a considerable portion of the reaction, by the rate of formation of 
carbonic acid through the double decomposition of steam and carbonic oxide. The 
intensity of the reaction was thus diminished. 
Now the presence of an inert gas, such as nitrogen, is found to affect the coefficient 
a in the same way. To a mixture containing about three times as much hydrogen as 
carbonic oxide and some 14 per cent, of oxygen, was added about two-thirds its volume 
of nitrogen. When this mixture was exploded under 1000 millims. pressure at 100° C., 
the coefficient was found to be 3'2. A similar mixture without the addition of nitrogen 
gave 4 for the coefficient under the same conditions. 
Table XLY.— Pressure = 1000 millims. 
Reference 
No. 
Before the explosion. 
After the explosion. 
Tempera¬ 
ture. 
Oxygen. 
Carbonic 
oxide. 
Hydrogen 
Nitrogen. 
Carbonic 
oxide. 
Carbonic 
acid. 
Hydrogen. 
Steam. 
a. 
°c 
104 
Mixture without 
nitrogen . . . 
15-9 
245 
75'5 
• • 
21-2 
3-3 
47-0 
28-5 
100 
4.0 
140 
Mixture with 
nitrogen . . . 
16’5 
24-5 
k r, r 
75 j 
72-0 
20-5 
4-0 
46-3 
29-2 
100 
32 
The diminution in intensity produced by the presence of the inert nitrogen favours 
the formation of carbonic acid in preference to steam in the explosion. 
If the fall of the coefficient from 4 to 3‘7 is due to the presence of inert oxygen 
during a portion of the reaction, it will follow that, so long as the oxygen employed is 
not more than half the hydrogen, the coefficient will remain normal whatever be the 
proportions of carbonic oxide and hydrogen present ; but whenever the oxygen is more 
than half the hydrogen the coefficient will fall. The change of the coefficient will not 
be abrupt, but the chief gradient will occur at the point when the hydrogen is double 
the oxygen. 
This explanation can therefore be readily tested experimentally. Two mixtures were 
made ; one of carbonic oxide and oxygen, the other of hydrogen and oxygen—both con¬ 
taining the same percentage of ox} 7 gen. Varying proportions of these two mixtures 
were brought together in the eudiometer and exploded at a high temperature, and at 
a pressure greater than the critical pressure. It was found that when the hydrogen 
