WHAT IS WINE? 
41 
on until either the whole of the acid or the whole of the alcohol 
has been converted into compound ether. The presence of 
water, however, prevents this complete etherification ; the more 
water present, the smaller the proportion of ether formed from 
a given quantity of alcohol and acid. Under these circum- 
stances, then, the amount of alcohol converted finally into com- 
pound ether depends upon the proportion of alcohol, acid, and 
water present, but is independent of the nature of the alcohol 
and acid. 
Whatever be the proportion in which these three substances 
are mixed, after the lapse of a longer or shorter time there 
will have been produced a certain amount of compound 
ethers, the rest of the alcohols and acids remaining free ; 
beyond this no more ether will be found, however long the 
mixture may be kept. If, after this stage of equilibrium has 
been reached, the relative proportion of the different substances 
is altered — if, for example, alcohol be added, or the acid be 
increased — more ether will begin to be formed ; if, on the other 
hand, alcohol or acid is removed, or water is added, some of the 
compound ether already formed will begin to be decomposed, 
until, in either case, equilibrium is once more established. 
By means of a formula given by Berthelot, the amount of 
alcohol contained in the compound ethers of any mixture of 
alcohols, acids, and water, when etherification is complete, can 
be calculated, whilst, by a process elsewhere described by the 
author, the amount actually so present at any time can be 
estimated. As long, then, as the amount found falls below the 
amount calculated, etherification is not yet completed ; when 
both agree, equilibrium has been established. 
As regards the formation of compound ethers, wine may be 
looked upon as a mixture of several alcohols and acids with 
water, and all the foregoing rules will be applicable to it. The 
estimation of the alcohol contained in the compound ethers of a 
wine, coupled with the calculated amount, will thus, among 
other things, give us some information as to the age of the 
wine. In young wines the amount found will fall below, in 
older or old wines it will agree with, the calculated amount. 
Wines of no very great alcoholic strength have generally 
arrived at the stage of equilibrium, as regards the formation of 
compound ethers, in from four to six years ; in the case of 
strong wines, ten years and upwards are required. The con- 
ditions under which the wine is kept will, however, greatly 
influence this time; thus a high temperature promotes, a low 
temperature checks, the production of ethers. 
As previously explained, wine contains both fixed and volatile 
acids, and these give rise to fixed and volatile compound ethers 
respectively; that is, such as cannot, and such as can, be dis- 
