IN GASES: HYDROGEN, CARBONIC OXIDE, AND OXYGEN. 
619 
equalled by the rate of decomposition of the other pair. Were it possible to measure 
accurately the quantities of four reacting bodies which preserve such an equilibrium, 
the precise relative rate of the two changes would be obtained. But in most cases it 
is impossible to make accurate measurements of one of the constituents of a mixture 
without separating it from the others, and tints disturbing the equilibrium ; so that 
some indirect method of measurement becomes necessary in experiments of this nature. 
Changes of colour, of temperature, of volume, of magnetic and optical properties, have 
afforded indirect methods of measuring the amount of particular bodies present in such 
a mixture without separating the constituents. By these means measurements of 
the rate of chemical change have been made by Gladstone, Thomsen, Ostwald, 
Guldberg and Waage, and other chemists. 
Again, when one body is presented to two others which are in excess, with each of 
which it is capable of uniting to form a stable compound, it divides itself between the 
two in proportions depending upon the relative rates at which the two reactions take 
place. Measurements of the masses of the reacting substances present at the begin¬ 
ning of the experiment and of the products finally formed give data for calculating the 
relative rates of the two changes. The incomplete combustion of a mixture of 
hydrogen and carbonic oxide by a small quantity of oxygen seemed to present a case 
of this kind suitable for investigation. The gases could easily be prepared in a pure 
state ; the measurement, explosion, and subsequent analysis could be readily performed 
in a eudiometer. By the study of this reaction, Bunsen, with the refined apparatus 
devised by himself for the manipulation of gases, made the first attempt to elucidate 
the laws of chemical change. His experiments form the starting-point of several long 
series of observations by E. von Meyer, Horstmann, and other chemists, and led me 
to make a careful investigation of the conditions which affect the chemical changes 
occurring during the explosion of these gases. An account of this investigation, 
carried on during several years, I venture to bring before the Royal Society, in the 
belief that the results obtained clear up some discrepancies between the observations 
of previous workers, and prove that, under the simplest conditions, the division of the 
oxygen is determined by the reciprocal reaction of two pairs of gaseous bodies, forming 
a system in mobile equilibrium capable of exact expression by a simple formula. 
Henry’s experiments . 
The first experiments on the incomplete combustion of hydrogen and carbonic oxide 
were made by Henry. In a memoir printed in these Transactions (1824), Henry 
compared the action of the electric spark and of platinum sponge on mixtures 
of carbonic oxide and electrolytic gas. He discovered the fact that the lower the 
temperature at which the reaction occurs the greater is the proportion of carbonic acid 
produced. 
He writes: “ I made numerous experiments to ascertain whether the oxygen, under 
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