IN GASES: HYDROGEN, CARBONIC OXIDE, AND OXYGEN. 
621 
chemical attraction, but also on the relative quantities of them present. If a and b 
represent the masses of two bodies A and B capable of combining with C to form 
compounds AC and BC, and if x and y represent the affinities of A and B for C 
respectively, then the proportion of the compound AC formed to the compound BC 
formed will be expressed by the equation 
AC_ ax 
BC ~by 
“ It follows from this that any alteration in the mass of either A or B will cause a 
corresponding alteration in the proportion of the compounds AC and BC formed.” 
This Law of Mass, commonly attributed to Berthollet, was tested by Bunsen 
in the following way :—* 
He exploded in a eudiometer different mixtures of carbonic oxide and hydrogen 
with a quantity of oxygen insufficient to completely burn them. In the explosion a 
portion of the carbonic oxide was burnt to carbonic acid, and a portion of the 
hydrogen was burnt to steam. If the above law of mass held good, the relative 
quantities of carbonic acid and steam formed would alter in a regular manner with 
the relative quantities of carbonic oxide and hydrogen taken. Partly owing to the 
paucity of his experiments, and partly owing to an undetected source of error, 
Bunsen wrongly concluded that the law of mass was modified in a particular way by 
the tendency of the atoms to form simple hydrates of carbonic acid. “ This catalytic 
action which the excess of molecules present, taking no part in the decomposition, 
exert upon the combining molecules is seen in a most remarkable manner in the 
volumetric relation between the products formed by the combustion, and brings to 
light a singular law which appears to be of fundamental importance in the mode of 
action of affinity. If the particles a in a homogeneous gaseous mixture have the 
choice of combination between the particles b and c of two other gases present in 
excess, a certain equilibrium ensues between the attractions of all the particles, so 
that the compounds (a + b) and (a + c), formed by the union of a with b and c, 
stand in a simple relation to one another, dependent on the amount of the particles 
remaining uncombined, and undergoing discontinuous alteration on gradual increase 
of these particles.” 
Bunsen’s experiments, made by exploding electrolytic gas with varying proportions 
of carbonic oxide, gave numbers, representing the relation between the carbonic acid 
and steam formed, which almost exactly corresponded with the six most simple 
hydrates of carbonic acid. In his first paper he showed that a variation of pressure 
from 317 millims. of mercury to 726 millims. did not materially alter the proportion 
in which the oxygen divided itself, and that the same result was obtained whether 
the explosion was made in the sunlight or in the dark. In the first edition of the 
* Bunsen, ‘ Gasometry,’ 1857. 
