The volume of the precipitate formed by good, whole milk when the process is conducted as above described, is about one cubic centimeter, for which a corresponding correction is readily made. =260. The Official Method.=—The alkaline copper method of determining lactose, adopted by the Association of Official Agricultural Chemists, is essentially the procedure proposed by Soxhlet.[215] Dilute twenty-five cubic centimeters of the milk, held in a half liter flask, with 400 cubic centimeters of water and add ten cubic centimeters of a solution of copper sulfate of the strength given for Soxhlet’s modification of Fehling’s solution, page 129; add about seven and a half cubic centimeters of a solution of potassium hydroxid of such strength that one volume of it is just sufficient to completely precipitate the copper as hydroxid from one volume of the solution of copper sulfate. In place of a solution of potassium hydroxid of this strength eight and a half cubic centimeters of a half normal solution of sodium hydroxid may be used. After the addition of the alkali solution the mixture must still have an acid reaction and contain copper in solution. Fill the flask to the mark, shake and filter through a dry filter. Place fifty cubic centimeters of the mixed copper reagent in a beaker and heat to the boiling point. While boiling briskly, add 100 cubic centimeters of the lactose solution, prepared as directed above, and boil for six minutes. Filter immediately and determine the amount of copper reduced by one of the methods already given, pages 149-155. Obtain the weight of lactose equivalent to the weight of copper found from the table on page 163. =261. The Copper Cyanid Process.=—It has been found by Blyth that the copper cyanid process of Gerrard gives practically the same results in the determination of sugar in milk as are obtained by optical methods.[216] The milk for this purpose is clarified, by precipitating the casein with acetic acid in the following manner: