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POPULAR SCIENCE REVIEW. 
matter and tannin is thrown down. The formation of com- 
pound ethers by the mutual action of the different acids and 
alcohols present goes on, and at the same time some of the 
compound ethers of the higher fatty acids at first formed, are 
gradually decomposed and converted into ethers of the lower 
acids : as a consequence the wine increases in bouquet. This 
formation of compound ethers, however, ceases long before all 
the acids present have been converted into ethers ; the necessary 
conditions for such complete conversion being, that the acids 
should be dissolved in absolute alcohol, and that the water 
produced during the formation of the ethers should be removed. 
The presence of water prevents the complete etherification of 
the acids, even when mixed with a large excess of alcohol ; the 
greater the proportion of water, the less complete the etherifi- 
cation. After the lapse of from three to six years, according to 
the nature of the wine and the temperature at which it is kept, 
this formation of compound etherswill thus arrive at a maximum, 
beyond which it cannot go except there be some alteration in 
the amount of alcohol or acid present, when the process will 
start again, so as to arrive once more at an equilibrium. 
Professor Berthelot, the celebrated French chemist, has given a 
formula, by means of which we may calculate what amount of 
compound ether may be formed in a wine containing a given 
proportion of alcohol, acid, and water. If, therefore, we pos- 
sess the means of accurately estimating the amount of compound 
ethers present in a wine, we obtain thereby a guide to judge to 
a certain extent of its age. Berthelot himself has given a 
process for estimating these ethers applicable to certain classes 
of wines; and the author has, more recently, published a 
method by means of which the amount of compound ethers in 
all classes can be estimated. 
The latter process also enables us to gain some insight into 
the nature of the compound ethers present; the complete 
separation and estimation of the different compound ethers 
present have, however, still to be accomplished. This may be 
less a matter of surprise, if it be borne in mind, firstly, that a 
wine containing, say, 5 different acids, and 5 alcohols (and 
wine contains often more than that number), may contain 
25 different kinds of ethers ; and, secondly, that even of such 
compound ethers as are found in greatest abundance in the wine 
— namely, malic, tartaric, and acetic ethers— there is rarely 
more than 1 part present in 2,000 parts ; whilst of some there is 
certainly less than 1 part in 100,000 parts. But, as stated 
above, a certain amount of insight may nevertheless be 
obtained. 
The acids present in the wine may be conveniently divided 
into two classes : first, such as are volatile without decom- 
