THE ACTION OP CHEMICAL AFFINITY. 
181 
other. 2. If in this manner there is formed one atom of the compound A+B, and one 
atom of the compound A+B', the mass of the body B maybe increased in the presence 
of that of B' up to a certain point, without any change in that atomic proportion : but 
if a certain limit be passed, the relation of the atoms, which was that of I : 1, changes 
suddenly and becomes 1:2, 1 : 3, 2 : 3, and so on. 3. When a body A, acting on an 
excess of the compound BC, reduces it, so that AB is formed, and C is set at liberty; 
then if C can, in its turn, reduce the newly-formed compound, the final result is that 
the reduced part of B+C is in a simple atomic proportion to the unreduced part. 
4. The second observation applies also to these reductions. Debus ^ examined the 
phenomena presented in the precipitation of a mixture of the hydrates of lime and 
baryta by carbonic acid, and of the hydrochlorates of these earths by carbonate of 
soda, and arrived at results analogous to those given above. 
In each of these cases, however, the first products of the chemical combination 
have been removed at once from the field of action. In Bunsen’s experiment the 
carbonic acid and water will not react on one another ; in that of Debus the car- 
bonates separate immediately in an insoluble condition. It is evidently quite another 
case when the products themselves of the chemical action remain free to react. A 
mixture of two salts in solution, which do not produce a precipitate, affords a case 
where this requisite is fulfilled. Let AB and CD be such salts. According to the 
one view, when mixed they will either remain without mutual action, or, should the 
affinities so preponderate, they will become simply AC and BD, the excess of either 
original salt remaining inactive. According to the other view, A will divide itself in 
certain proportions between B and D, while C will do the same in the inverse ratio, 
the said proportions being determined not solely by the differences of energy in the 
affinities, but also by the differences of the quantities of the bodies. Again, sup- 
posing the latter view to be correct, another question will arise — Does the amount of 
AD or CB produced increase in a gradual manner with the relative increase of AB, 
or do sudden transitions take place under these circumstances, such as Bunsen and 
Debus observed in their experiments ? 
It was to the elucidation of these questions that I applied myself. In the majority 
of instances it is impossible to ascertain what has taken place when a mixture of the 
kind alluded to has been made; but the physical properties of salts will sometimes 
give an indication. Colour seemed to offer the best means of solving the problem ; 
yet even here a difficulty arose from the fact that many bases, such as nickel, give the 
same coloured solution when combined with different acids, and vice versa. Sesqui- 
oxide of iron, however, appeared to promise good results, since many of its salts are 
intensely coloured, while others are almost colourless. The formation of the sulpho- 
cyanide was first submitted to a full investigation ; after which other ferric salts were 
more cursorily examined ; and after them a number of other binary compounds in 
order to extend the range of observation. 
* Ann. Ch. Pharm. Ixxxv. 103; Ixxxvi. 156; Ixxxvii. 238. 
2 c 2 
