_Analysis of Wine._--The analysis of wine comprises the following estimations:--Specific gravity, alcohol, extract, sugar, polarisation, glycerine, total free acids, volatile acids, free tartaric acid, potassium bitartrate, malic acid, succinic acid, tannin, ethers, ash, chlorine, sulphuric and phosphoric acids, and colouring matters. _Specific gravity._--The density is determined by means of the gravity bottle, at a temperature of 15°. _Alcohol._--The proportion of alcohol is ascertained by the distillation of 50 or 100 c.c. of the wine in a suitable flask, which is connected with a Liebig’s condenser, until about half of the liquid has passed over. The distillate is made up to the original volume with water, and its specific gravity taken, from which the amount of alcohol (by weight) present is calculated by aid of the usual alcohol-metric tables (see p. 196). The result (as well as the proportions of the other constituents) is preferably stated in grammes per 100 c.c. of wine. The determination may also be made by first removing the alcohol by evaporation, adding distilled water to restore the original volume, and then estimating the density of the liquid (see under Beer, p. 142). In unfortified wines the alcoholic strength ranges from 6 to 12 per cent., and in wines which have received an addition of spirit, it may vary from 12 to 22 per cent. _Extract._--The extract is conveniently determined by evaporating 50 c.c. (measured at 15°), in a platinum dish over the water-bath, the residue being dried for 2½ hours in the steam-oven. In case a wine rich in sugar (containing, say, over 0·5 grammes per 100 c.c.) is under examination, 20 c.c. will suffice for the determination. The indirect method used in the estimation of the malt extract in beer may also be employed. According to Girardin and Pressier, it is possible to detect the watering of certain wines, the average composition of which is known, by means of the proportions of extract and alcohol present. For example, in genuine Bordeaux wines the proportion of extract ranges from 20 to 20·8 grammes per 1000 c.c., and the amount of alcohol is also very constant, it being a mean of 100 grammes per 1000 c.c. Should a sample of Bordeaux wine show an extract of 14·5 grammes per litre, the proportion of genuine wine present would be 72·5 per cent., for (1000 × 14·5)/20 = 725·00, the remainder being water and alcohol. In order to estimate the amount of spirits artificially added, the alcohol contained in 72·5 parts of the wine is determined. If, for instance, it is found to be 11 parts, then, (11 - 7·25 = ) 3·75 parts of alcohol have been added.[101] The quantity of extract in pure natural wine varies from 1·5 to 3 per cent., but in sweet and fortified wines, it may reach 10 per cent. or more.