=166. Optical Test for Sucrose.=—The simplest test for the presence of sucrose is made with the polariscope. A small quantity of the sample under examination is dissolved in water, clarified by any of the usual methods, best with alumina cream, and polarized. A portion of the liquor is diluted with one-tenth its volume of strong hydrochloric acid and heated to just 68°, consuming about fifteen minutes time in the operation. The mixture is quickly cooled and again polarized in a tube one-tenth longer than before used; or the same tube may be used and the observed reading of the scale increased by one-tenth. If sucrose be present the second reading will be much lower than the first, or may even be to the left. =167. Cobaltous Nitrate Test for Sucrose.=—Sucrose in solution may be distinguished from other sugars by the amethyst violet color which it imparts to a solution of cobaltous nitrate. This reaction was first described by Reich, in 1856, but has only lately been worked out in detail. The test is applied as follows: To about fifteen cubic centimeters of the sugar solution add five cubic centimeters of a five per cent solution of cobaltous nitrate. After thoroughly mixing the two solutions, add two cubic centimeters of a fifty per cent solution of sodium hydroxid. Pure sucrose gives by this treatment an amethyst violet color, which is permanent. Pure dextrose gives a turquoise blue color which soon passes into a light green. When the two sugars are mixed the coloration produced by the sucrose is the predominant one, and one part of sucrose in nine parts of dextrose can be distinguished. If the sucrose be mixed with impurities such as gum arabic or dextrin, they should be precipitated by alcohol or basic lead acetate, before the application of the test. Dextrin may be thrown out by treatment of the solution with barium hydroxid and ammoniacal lead acetate. The reaction may also be applied to the detection of cane sugar in wines, after they are thoroughly decolorized by means of lead acetate and bone-black. The presence of added sucrose to milk, either in the fresh or condensed state, may also be detected after the disturbing matters are thrown out with lead acetate. The presence of sucrose in honey may also be detected by this process. The reaction has been tried in this laboratory with very satisfactory results. The amethyst violet coloration with sucrose is practically permanent. On boiling the color is made slightly bluish, but is restored to the original tint on cooling. Dextrose gives at first a fine blue color which in the course of two hours passes into a pale green. A slight flocculent precipitate is noticed in the tube containing the dextrose. Maltose and lactose act very much as dextrose, but in the end do not give so fine a green color. If the solutions containing dextrose, lactose and maltose be boiled, the original color is destroyed and a yellow-green color takes its place. The reaction is one which promises