G18 
mi, H. B. DIXON ON CONDITIONS OF CHEMICAL CHANGE 
Page. 
Horstmann’s conclusions. 657 
Author’s experiments with dry gases above critical pressure... 658 
Equation representing the rate of chemical change in the combustion of carbonic oxide 
and hydrogen . 659 
Effect of an increase of oxygen on the rate of chemical change. 660 
Experiments on the influence of initial temperature . 662 
Explanation of the effect of initial temperature. 665 
Experiments on the critical pressure at high temperatures . 667 
Experiments on the effect of varying the proportion of hydrogen to oxygen in the explosive 
mixture ... 672 
General conclusions. 674 
References. 676 
Appendix . 676 
Note by Mr. Essox. 682 
INTRODUCTION, 
The influence of physical forces, of modes of aggregation and of mass, not only on the 
result, but on the manner of the transformation of one kind of matter into another 
kind—in brief, the conditions of chemical change —present a problem to the chemist 
which only of late years has been submitted to experimental investigation. The 
difficulties besetting this line of inquiry are many, but the greatest of them is the 
difficulty of finding a reaction that is simple in kind, that takes place between bodies 
which can be prepared in great purity, and that yields products which can be exactly 
measured. Several methods of investigation have been pursued. The course of a gradual 
change between two bodies has been followed step by step, either by measuring 
the amount of residue still remaining undecomposed after successive equal inter¬ 
vals of time, or by measuring the time required for the successive formation of equal 
quantities of one of the products of the reaction. Such was the method employed by 
Berthelot, who measured the rate of etherification of an alcohol by an acid, and 
by Harcourt and Esson, who measured the rate of decomposition of hydric 
peroxide by hydric iodide. Unluckily but few of the reactions, which occur slowly 
enough for such investigation, appear to be of a simple nature; examination reveals 
the fact that, in most cases, the change from the initial substances to the Anal product 
does not take place in one stage, but is a complex reaction brought about by the 
successive formation and decomposition of intermediate compounds at rates which 
severally vary with the conditions of the experiment. 
Another method of investigation is that of comparing the rates of two opposite 
changes taking place simultaneously in a homogeneous mixture. When two bodies 
enter into double decomposition to form two new bodies which are themselves capable, 
under the conditions of the experiment, of re-forming the original substances by a 
reverse change, a mixture of the four bodies is produced, and an equilibrium is finally 
established when the rate of decomposition of one pair of the reacting bodies is exactly 
