Air, water, and food from a sanitary standpoint . void the vicinity of free flames. Dry the flask with theextracted fat in the water oven to constant weight. Avoid pro-tracted heating, which would cause partial oxidation of the fat. Notes.—Absorbent paper exercises a selective action onthe constituents of milk so that the fat is left on the surface ofthe paper, mixed with only about one-third of the non-fattysolids, and hence it is more easily extracted; further, owingto the greatly increased surface exposed, the extraction of thefat is practically complete. 176 AIR, WATER, AND FOOD. Ethyl eth
Air, water, and food from a sanitary standpoint . void the vicinity of free flames. Dry the flask with theextracted fat in the water oven to constant weight. Avoid pro-tracted heating, which would cause partial oxidation of the fat. Notes.—Absorbent paper exercises a selective action onthe constituents of milk so that the fat is left on the surface ofthe paper, mixed with only about one-third of the non-fattysolids, and hence it is more easily extracted; further, owingto the greatly increased surface exposed, the extraction of thefat is practically complete. 176 AIR, WATER, AND FOOD. Ethyl ether may be used instead of petroleum ether, but careshould be taken that the ether is perfectly dry, otherwise othersubstances than fat, principally milk-sugar, will be the other hand, substituted glycerides may not be dissolvedout by ether. For these reasons the petroleum ether is to bepreferred as a solvent, although its action is considerablyslower than that of the other. Owing to the inflammable nature of the solvents employed,. Fig. 12.—Apparatus for Fat Extraction. it is best not to use a flame as the source of heat, but to heatthe flask by means of a steam- or water-bath. In this labora-tory small electric heaters about 4 inches in diameter are usedand have been found safe and convenient. The completeapparatus is shown in Fig. 12. In using these it should beborne in mind that considerable quantities of ether or petroleumether in contact with the heatea surface may ignite, and cautionshould be taken not to evaporate any quantity of these solventsfrom an open vessel. (2) Babcock Method.—Directions.—Measure ex. ofthe milk from a pipette into the long-necked, graduated whirling- food: analytical methods. 177 bottle. Measure out of sulphuric acid 1^0, gr. )rand add it gradually to the milk, mixing the t\*-« thoroughlyafter each addition. Take care that none of the liquid spurtsinto the neck of the bottle. After mixing the milk and acid,
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