If cane sugar, containing grape sugar, is boiled with water, to which about 2 per cent. of potassium hydroxide has been added, the solution acquires a brown colour. Upon mixing a solution of pure cane sugar with a solution of cupric sulphate, adding an excess of potassium hydroxide, and boiling, only a slight precipitation of red cupric oxide takes place. Under the same conditions, grape sugar at once produces a copious green precipitate, which ultimately changes to red, the supernatant fluid becoming nearly or quite colourless. A very good method for the quantitative estimation of grape sugar when mechanically mixed with cane sugar, is that of P. Casamajor. It is executed by first preparing a saturated solution of grape sugar in methylic alcohol. The sample to be tested is thoroughly dried, and then well agitated with the methylic alcohol solution, in which all cane sugar will dissolve; any grape sugar present remains behind, and upon allowing the mixture to remain at rest for a short time, forms a deposit which is again treated with the grape sugar solution, and then collected upon a tared filter, washed with absolute methylic alcohol, and weighed. Glucose and invert sugar are usually quantitatively determined by means of Fehling’s solution. As this preparation is liable to decompose upon keeping, it is advisable to first prepare cupric sulphate solution by dissolving exactly 34,640 grammes of the salt in 500 c.c. of distilled water, and then make up the Rochelle salt solution by dissolving 68 grammes of sodium hydroxide, and 173 grammes of Rochelle salt in 500 c.c. of water, the solutions being kept separate. When required for use, 5 c.c. each of the copper and Rochelle solutions (corresponding to 10 c.c. of Fehling’s solution) are introduced into a narrow beaker, or a porcelain evaporating dish, a little water is added, and the liquid brought to the boiling point. The sugar solution under examination should not contain over 0·5 per cent. of glucose. It is cautiously added to the hot Fehling’s solution from a burette until the fluid loses its blue colour (see p. 37). The number of c.c. required to completely reduce 10 c.c. of Fehling’s solution, represents 0·05 gramme of grape sugar. The foregoing volumetric method is sometimes applied gravimetrically by adding a slight excess of Fehling’s solution to the sugar solution, collecting the precipitated cupric oxide upon a filter and weighing, after oxidation with a few drops of nitric acid; or, it may be dissolved, and the copper contained deposited by electrolysis, in which case the weight of copper obtained, multiplied by 0·538, gives the equivalent amount of glucose. The proportion of cane sugar in a sample of raw sugar can be determined by first directly estimating the proportion of invert sugar contained by means of Fehling’s solution, as just described. The cane sugar present is then inverted by dissolving one gramme of the sample in about 100 c.c. of water, adding 1 c.c.