NATURE OF SOLUTION. 099 
This extremely lucid explanation of the phenomena of solution evidently 
is based on the assumption that solution in general is a species of chemical 
action, and in Turner’s Elements of Chemistry (1842) the same assumption 
is made. At p. 139, in discussing “affinity,” he says :-— 
“The most simple instance of the exercise of chemical attraction is afforded by the admix- 
ture of two substances. Water and sulphuric acid, or water and alcohol, combine readily. On 
the contrary, water shows little disposition to unite with ether, still less with oil. .... Sugar 
dissolves very sparingly in alcohol, to any extent in water; while camphor is dissolved in a 
very small degree by water, and abundantly by alcohol. It appears from these examples that 
chemical attraction is exerted between different bodies with different degrees of force... .. 
Simple combination of two substances is a common occurrence, of which the solution of salts 
in water, the combustion of phosphorus in oxygen gas, and the neutralisation of a pure alkali 
by an acid, are instances.” 
The opinion at present generally held is thus formulated in Roscoe and 
Schorlemmer’s Treatise on Chemistry (vol. i. p. 232) :— 
“Concerning the nature of solution, whether of solids, liquids, or gases, we know at present 
but little. The phenomena of solution differ, however, essentially from those of chemical com- 
bination, inasmuch as in the former we have to do with gradual increase up to a given limit, 
termed the pnint of saturation, whereas in the latter we observe the occurrence of constant 
definite proportions in which, and in no others, combination occurs. Solution obeys a law of 
continuity, chemical combination one of sudden change or discontinuity.” 
But on closer examination this distinction disappears. A mixture of 
chlorine gas with excess of hydrogen would be a precise analogue of a solution 
of a salt in excess of water. The chlorine would combine with its equivalent 
of hydrogen, and then the hydrochloric acid so formed would mix with the 
excess of hydrogen. Similarly, the salt would dissolve in its “ equivalent” of 
water, and then the saturated solution would mix with the excess of water. 
This would go on in the one case till a// the hydrogen had combined with its 
equivalent of chlorine, when any excess of chlorine added would remain uncom- 
bined and show its presence as free chlorine by its colour, &c.; in the other 
case, till all the water had united with as much salt as it could take up, after 
which any excess of salt added would remain undissolved. The same con- 
tinuity appears in the one case as in the other. In one case, excess of gas 
mixes with combined gases; in the other, excess of salt is visibly separate 
from the combined salt and liquid, and this constitutes an apparent difference, 
but that it is apparent only is seen in the fact that solids can be so finely 
divided as to remain mixed with liquids for an almost indefinite period. And 
the analogy holds when we compare a compound such as peroxide of hydrogen 
with a supersaturated solution of a salt. A change of conditions interferes 
with the stability in both cases. Pickerine has lately shown that basic 
