_Sugar._--The sugar in wine consists of a mixture of fruit and grape sugar, usually in the proportion of 3 parts of the former to 1 part of the latter. The amount of sugar is best estimated by Fehling’s solution (see p. 111). In the case of white wines, it is advisable to employ 100 c.c. for the determination; with sweet rich wines 25 c.c. are sufficient. The alcohol is first removed by evaporation over the water-bath, and the diluted liquid is next decolorised by means of bone-black or plumbic acetate, filtered, and made alkaline by addition of sodium carbonate. It is then made up to a volume of 200 c.c. and gradually added to 10 c.c. of Fehling’s solution. It is always well to test the wine by the polariscope, and, whenever the presence of cane sugar is indicated, to invert 100 c.c. of the sample by heating with a few drops of hydrochloric acid, and again make a sugar determination with Fehling’s reagent after neutralisation with sodium carbonate. _Polarisation._--The optical examination of wine is conducted by adding 20 c.c. of plumbic acetate solution to 100 c.c. of the sample, shaking the mixture, allowing it to stand for a short time, and passing it through a filter. If necessary the filtrate is further decolorised with animal charcoal and again filtered. The polariscope tube is then filled with the clear solution and the reading made. The majority of wines exhibit a left-handed polarisation, which is due to the fact that, as a rule, the proportion of fruit sugar present predominates over that of grape sugar; moreover, ½ part of fruit sugar will neutralise the dextro-rotary action of 1 part of grape sugar. In case the presence of an excess of grape sugar is indicated by the polariscopic examination, it is often assumed that this body has been directly added to the wine. It sometimes occurs, however, that, in the fermentation process, more grape sugar remains undecomposed than fruit sugar, under which circumstances the preponderance of the former body in the resulting wine would not prove sophistication; but, under ordinary conditions, the presence of an excessive proportion of grape sugar may safely be regarded as strongly pointing to the artificial addition of must syrup.