656 
MR. H. B. DIXON OX CONDITIONS OF CHEMICAL CHANGE 
A glance at the last column in this table shows that for equal quantities of oxygen, 
Horstmann’s coefficient of affinity is fairly constant: in the third, fifth, and sixth 
sets the extreme values differ by about 20 per cent. ; the other sets show a better 
agreement. 
In a later paper Horstmann gives the following table of the coefficients of affinity 
corresponding to different percentages of the combustible gases burnt. 
Table XXIII. —Horstmann’s new table of coefficients. 
Percentage of combustible 
gases burnt. 
Coefficient of affinity. 
15 
2-68 
20 
3-8 
25 
4 83 
30 
5‘65 
35 
6T6 
40 
6-35 
45 
6-12 
50 
5 88 
55 
5'64 
60 
5-38 
6.5 
5T1 
70 
4-85 
The alteration in the coefficient of affinity, with increase of oxygen, Horstmann 
attributes (1) to the increased temperature of combustion, and (2) to the alteration 
of pressure and physical characteristics of the whole mixture produced by the combus¬ 
tion. He was led to this conclusion by the following experiments : Different mix¬ 
tures of hydrogen and carbonic oxide were exploded with air. In each experiment, 
therefore, a certain quantity of nitrogen was present. The “ coefficients of affinity ” 
were found to agree approximately with those previously obtained in explosions with 
mixtures containing the same percentage of oxygen, and not with mixtures containing 
the same relative proportion of oxygen and combustible gases. 
For instance, 100 volumes of carbonic oxide and hydrogen were mixed with 76 
volumes of air containing 16 volumes of oxygen. In the explosion, therefore, 32 per 
cent, of the combustible gases is burnt, but only 20 per cent, of the mixture of carbonic 
oxide, hydrogen, and nitrogen. From the previous experiments the coefficient of 
affinity corresponding to a combustion of 32 per cent, is 5'9, and for a combustion 
of 20 per cent, it is 4'0. The coefficient found is 3 - 7. 
