472 
TI1E CONSTITUTION OF MATTETt. 
chemically combined with the carbon therein. But the proportion of carbon 
and hydrogen can never be expressed by a probable atomic formula. 
2. There are numerous compounds, some of which are connected with the 
living animal or plant organism, either as products of secretion or excretion, 
the constitution of which we believe we understand perfectly, not only be¬ 
cause they exhibit definite properties, but also because many of them can 
be artificially produced by processes of synthesis ; but there are others from 
which these are products of disintegration, which have never been formed 
synthetically, nor is there any probability of their being so, and which, whilst 
presenting tolerably definite external characteristics, are so complex in com¬ 
position, that in order to express the atomic proportion of their constituents, 
we are obliged to represent their molecules as built up of hundreds of atoms. 
When we come to such formulae as C 116 H 240 N 4 PO 22 , or C 72 H 113 !NaN ls S0 22 , 
would it not be more candid to give up definite proportions, and admit that 
these may be examples which do not fit the rule ? 
3. The phenomena of solution can be explained only upon the assumption 
that some modified form of chemical affinity is the disposing influence in such 
cases. That attractions related to those commonly called chemical are exerted 
is probable, from the well-known fact that there is a sort of “ elective 
affinity” exhibited in the action of different solvent liquids upon solid and 
other substances, and also that some of the solutions produced exhibit a sta¬ 
bility, uniformity, and definiteness of character, rivalled only by those of true 
and undoubted chemical compounds. Examples of the latter condition are 
met with in the combinations of hydriodic and hydrochloric acids with 
water: at a certain stage of concentration, and under uniform barometric 
pressure, these liquids have a constant boiling-point and specific gravity. 
Examples of the selective power of solvents are so familiar and numerous 
that one will suffice here. 
Water, HHO, dissolves 
nearly all salts ; no fatty 
substances; few organic 
principles, except those 
of saline constitution. 
Alcohol, EtHO, dissolves 
few salts; some fatty 
bodies ; but chiefly crys- 
tallizable organic sub¬ 
stances. 
Ether, EtEtO, dissolves 
scarcely any salts; but 
chiefly fatty and highly 
carbonaceous substances. 
Here are three liquids, usually regarded as possessing analogous chemical 
constitution ; alcohol being formed from water, and ether from alcohol, by 
the successive replacement of the atoms of hydrogen by a hydrocarbon radicle. 
In proportion as the carbon increases in the solvent, so its affinity for car¬ 
bonaceous substances increases ; whilst, on the other hand, as the saline cha¬ 
racter of the solvent is lost (water being usually regarded as a kind of salt), 
so its action upon saline bodies decreases. Solutions can, of course, be pre¬ 
pared of any degree of dilution at pleasure. 
Further illustrations of the chemical nature of the attractions which give 
rise to solution may be found in such simple and familiar experiments as the 
following :—If some resin be dissolved in rectified spirit, and water be then 
added, the whole of the resin is redeposited in the form of a precipitate. The 
spirit has an affinity for the resin, but a greater affinity for the water; it 
therefore parts from the former in favour of the latter, and the resin being 
insoluble in the new compound, is thrown down again. 
If alcohol is mixed with water, the resulting compound possesses a density 
greater than the mean of the densities of the two liquids; this shows that 
contraction of volume has taken place ; consequently there must be a bond 
betw T een them more intimate than that of mere mechanical mixture. 
4. There are a few very interesting bodies, among the best known of them 
being the graphitic acid discovered by Brodie, the constitution of which 
