_Succinic Acid._--500 c.c. of the wine are decolorised with bone-black, filtered, the filtrate evaporated over the water-bath nearly to dryness, and the residue repeatedly treated with alcohol-ether. The solution thus obtained is concentrated, carefully neutralised with lime-water, evaporated to dryness, and the glycerine present removed by washing with the alcohol-ether mixture. The remaining residue is now treated with 80 per cent. alcohol, in order to dissolve the calcium succinate contained, every 100 parts of which represent 75·64 parts of succinic acid (H_{6}C_{4}O_{4}). Thudichum and Dupré state that one litre of pure wine contains from 1 to 1·5 grammes of succinic acid. _Ethers._--The compound ethers in wine are volatile and fixed, and exist in but minute proportions. Of the former class, ethylic acetate C_{2}H_{3}(C_{2}H_{5})O_{2} is the most important. As already mentioned, the aroma of wine is largely influenced by the presence of the ethers of the fatty acids, butyric, caprylic, etc. Dupré determines the proportion of both kinds of ethers indirectly as follows:--250 c.c. of the wine are distilled until 200 c.c. have passed over. Water is then added to the distillate to a volume of 250 c.c. 100 c.c. are first titrated with 1/10th normal soda solution. Another 100 c.c. of the distillate are next heated with a known quantity of alkali (by which the ethers are decomposed into their corresponding acids and alcohol), and the titration is repeated. The amount of _volatile_ ethers is then calculated from the increased acidity shown by the second titration. In order to determine the proportion of _fixed_ ethers, 500 c.c. of the sample are evaporated over the water-bath to a small volume which is made alkaline, and then subjected to distillation. The distillate is acidulated with sulphuric acid and again distilled. The alcohol present in the second distillate is now oxidised to acetic acid by means of potassium dichromate, and the amount of this acid found estimated by titration. According to Berthelot, the proportion of ethers in genuine wine bears a fixed relation to the amounts of alcohol and acids present: he suggests the following formula for calculating the amount of alcohol contained in the compound ether of one litre of wine, when etherification is complete:-- _y_ = 1·17 A + 2·8 _x_ = (_y_ × _a_) / 100, where A is the percentage, by weight, of alcohol; _a_ the amount of alcohol equivalent to the total free acid in one litre of wine (assuming this to be acetic acid); _y_, the proportion per cent. of _a_ present as compound ether in one litre of wine, when the alcoholic strength of the wine is A; and _x_, the amount of alcohol present in the compound ether of one litre of wine.