660 
MR, H. B. DIXON' ON CONDITIONS OF CHEMICAL CHANGE 
for a. These values are given in the last column of the table. The mean of the seven 
experiments gives a=5. From this mean value the quantity of hydrogen and 
carbonic oxide burnt in any given mixture can be calculated. In the following table 
the quantities of hydrogen burnt, calculated for the mixtures employed in these 
experiments, are compared with those actually observed. 
Table XXVI.—Volume of hydrogen burnt. 
Reference 
No. 
Calculated. 
Observed. 
78 
9-7 
9'5 
77 
126 
12-4 
76 
171 
17-2 
75 
21-3 
21-3 
74 
23-5 
23-7 
73 
25-2 
25-2 
72 
26-9 
26-8 
According to this theory, the chemical changes vary as the explosion proceeds. 
The explosion starts with the direct union of oxygen and hydrogen, the change 
proceeding until all the oxygen is converted into steam, according to equation (1); as 
soon as steam is formed by this union it begins to oxidize the carbonic acid, according 
to equation (3) ; the carbonic acid so produced is in turn reduced to carbonic oxide by 
free hydrogen, according to equation (4). The heat developed by the direct union of 
the oxygen and hydrogen raises the whole body of the gases to incandescence. After 
all the oxygen is converted into steam, four gases remain at a high temperature — 
hydrogen and steam, carbonic oxide and carbonic acid. Of these four gases, one pair, 
hydrogen and carbonic acid, react at the high temperature to form the other pair, 
steam and carbonic oxide ; but steam and carbonic oxide themselves react to form the 
first pair, hydrogen and carbonic acid, so that two reverse changes take place 
simultaneously in the mixture. The quantity of each pair present at any moment 
during the reaction depends on the relative rates at which the two changes proceed. 
Possibly these rates may vary with the temperature as the whole body of gases cools 
down. The quantities actually measured are those in equilibrium at the moment the 
gases cool to the temperature at which the reaction ceases. But since in the fall from 
the highest temperature reached in any explosion to the lowest at which reaction 
occurs there is a large range of cooling common to all the experiments, the relative 
rate of the two changes observed is in all cases that which is found under similar 
conditions of temperature. 
According to Horstmann the coefficient varies with the proportion of oxygen 
employed, at first increasing with the increase of oxygen, reaching a maximum when 
from 15 to 20 volumes of oxygen are mixed with 100 of the combustible gases, and 
finally diminishing gradually as the oxygen is increased beyond this point. The 
volume of oxygen added to 100 volumes of the combustible gases was 14'2 in 
