Twenty-five cubic centimeters of milk are diluted with an equal volume of distilled water, and strong acetic acid added until the casein begins to separate. The liquid is heated to boiling and, while hot, centrifugated in any convenient machine. The supernatant liquid obtained is separated by filtration and the solid matter thrown upon the filter and well washed with hot water. The filtrate and washings are cooled and completed to a volume of 100 cubic centimeters. This liquid is of about the proper dilution for use with the copper cyanid reagent. The percentage of sugar determined by this reagent agrees well with that obtained by the optical method, when no other sugars than lactose are present. If there be a notable difference in the results of the two methods other sugars must be looked for. The presence of dextrin may be determined by testing a few drops of the clear liquor with iodin, which, in the presence of dextrin, gives a reddish color. Other sugars are determined by obtaining their osazones. For this purpose the filtrate obtained as above should be concentrated until the volume is about thirty cubic centimeters. Any solid matter which separates during the evaporation is removed by filtration. The osazones are precipitated in the manner described in paragraph =147=. On cooling, the almost solid crystalline mass obtained is placed on a filter, washed with a little cold water, the crystals then pressed between blotting paper and dried at a temperature of 100°. The dry osazones obtained are dissolved in boiling absolute alcohol, of which just sufficient is used to obtain complete solution. The alcoholic solution is set aside for twelve hours and the separation of a crystalline product after that time shows that dextrose or invert sugar is present. Milk sugar alone gives no precipitate but only a slight amorphous deposit. The lactosazone is precipitated by adding a little water to the hot alcoholic solution and the crystals thus obtained should be dissolved in boiling absolute alcohol and reprecipitated by the addition of water at least three times in order to secure them pure. The osazones are identified by their melting points, paragraph =172=. The first part of this method does not appear to have any advantage over the optical process by double dilution (p. 278), and requires more time.