=258. Removal of Dextrin by Alcohol.=—By reason of its less solubility, dextrin can be removed from a solution containing also dextrose and maltose by precipitation with alcohol. It is impracticable, however, to secure always that degree of alcoholic concentration which will cause the coagulation of all the dextrins without attacking the concomitant reducing sugars. In this laboratory it has been found impossible to prepare a dextrin by alcoholic precipitation, which did not contain bodies capable of oxidizing alkaline copper solutions. The solution containing the dextrin is brought to a sirupy consistence by evaporation and treated with about ten volumes of ninety per cent alcohol. After thorough mixing, the precipitated dextrin is collected on a filter and well washed with alcohol of the strength noted. It is then dried and weighed. If weaker solutions of dextrin are used, the alcohol must be of correspondingly greater strength. In the filtrate the residual maltose and dextrose may be separated and determined by the chemical and optical methods already described. CARBOHYDRATES IN MILK. =259. The Copper Tartrate Method.=—The lactose in milk is readily estimated by the gravimetric copper method described in paragraph =143=. Before the application of the process the casein and fat of the milk should be removed by an appropriate precipitant, and an aliquot part of the filtrate, diluted to contain about one per cent of milk sugar, used for the determination. The clarification is very conveniently secured by copper sulfate or acetic acid, as described in the next paragraph. A proper correction should be made for the volume occupied by the precipitate and, for general purposes, with whole milk of fair quality this volume may be assumed to be five per cent. One hundred grams of milk will give a precipitate occupying approximately five cubic centimeters. In the analytical process, to twenty cubic centimeters of milk, diluted with water to eighty, is added a ten per cent solution of acetic acid, until a clear whey is shown after standing a few minutes, when the volume is completed to 100 cubic centimeters with water, and the whole, after thorough shaking, thrown on a filter. An aliquot part of the filtrate is neutralized with sodium carbonate and used for the lactose determination. This solution contains approximately one per cent of lactose. In a convenient part of it the lactose is determined and the quantity calculated for the whole. This quantity represents the total lactose in the twenty cubic centimeters of milk used. The weight of the milk is found by multiplying twenty by its specific gravity. From this number the percentage of lactose is easily found. In this process the milk is clarified by the removal of its casein and fat. Other albuminoids remain in solution and while these doubtless disturb the subsequent determination of lactose, any attempt at their removal would be equally as disadvantageous.