TRANSACTIONS OF SECTION B. 495 
Behaviour of Liquids when Mixed together. 
There are three points to consider when two liquids are brought together— 
(1) their miscibility, whether infinite, partial, or inappreciable; (2) the relative 
volumes of the mixture and of the components ; (8) the heat evolved or absorbed. 
Liquids which are classed as non-miscible rarely, if ever, bear any close 
chemical relationship. Thus water is practically non-miscible with all hydro- 
carbons and with their halogen and many other derivatives; again, mercury, so 
far as I mow, is not miscible with any liquid compound, organic or inorganic. 
It is true that the higher aliphatic alcohols are almost insoluble in water, although 
there may be said to be some chemical relationship between them, inasmuch as 
an alcohol may be regarded as an alkyl derivative of water. But the alcohols 
may also be looked upon as hydroxyl derivatives of the hydrocarbons, and, the 
higher the formula weight of the alkyl group, the greater is its influence, rela- 
tively to that of the hydroxyl, on the properties of the alcohol. Thus, while the 
lower alcohols show considerable resemblance to water—for example, in their 
behaviour with dehydrating agents, such as sodium, phosphoric anhydride, or 
lime, and in their power of uniting with metallic salts to form crystalline alco- 
holates corresponding to the hydrates—this resemblance diminishes as we ascend 
the series, and is generally not observable with the higher members. 
On the other hand, the higher the molecular weight of the alcohol the closer is 
its resemblance to the hydrocarbon from which it is derived. This, as already 
mentioned, is well shown by the diminishing difference between the boiling-points 
of the aleohol and paraffin as the series is ascended; it may also be noted that 
methane was long classed as a permanent gas, while methyl alcohol is a liquid ; 
whereas both hexdecane (C,,H;,) and cetyl alcohol (C,,H,,0H) are solids, the 
former melting at 18° and the latter at 50°, 
It may, in fact, I think, be stated that the chemical relationship between water 
and methyl alcohol is fairly close, while that between water and cetyl alcohol is 
very distant. So, also, two adjacent members of a homologous series, such as 
methyl and ethyl alcohol, are more closely related than two members of widely 
different molecular weight, such as methyl and cetyl alcohol. 
Adopting this view, it is, I believe, safe to state that liquids which are 
chemically closely related to each other are invariably miscible in all proportions. 
As regards the relative volumes of a mixture and of its components at the 
same temperature, it is well known that inequality is the rule and equality the 
exception; and, further, that contraction is more frequently observed than 
expansion on admixture. So far, however, as experimental evidence is available, 
it appears that when the liquids are very closely related to each other the change 
of volume is exceedingly small. For example, with ethyl acetate and propionate 
in equimolecular proportions, + 0-015 per cent.; toluene and ethyl benzene, 
— 0-034 per cent.; 2-hexane and n-octane, — 0:053 per cent.; methyl and ethyl 
alcohol, + 0:004 per cent.; chlorobenzene and bromobenzene, no change. 
When the relationship is less close the changes are usually, but not invariably, 
larger, and are in some cases positive, in others negative ; and it is rarely possible, 
in the present state of our knowledge, to predict from the nature of the sub- 
stances—unless one is basic and the other acidic in character—whether contraction 
or expansion is to be expected. Thus, when methyl alcohol is mixed with water 
considerable contraction occurs, although the relationship is less close than 
between methyl and ethyl alcohol, which expand to a minute extent on mixing. 
All we can say with regard to the alcohols is that, the higher the molecular 
weight—or, if isomeric alcohols are included, the higher the boiling-point—the 
smaller, as a rule, is the contraction on mixing with water. 
Very similar remarks apply to the heat changes which occur on mixing liquids. 
It appears that in the case of very closely related substances these changes are 
exceedingly small, or negligible, as is indicated by the very minute change of 
temperature which has been observed, thus: ethyl acetate and propionate, — 0°-02; 
toluene and ethyl benzene, + 0°05; n-hexane and n-octane, + 0°06; methyl 
and ethyl alcohol, — 0°:10; chlorobenzene and bromobenzene, 0°00, 
