Air, water, and food from a sanitary standpoint . limb of the T tube slides a bent glass tube,which is turned up at the lower end. The tubeis adjusted by sliding it through the rubbercollar (C) so that the lower end rests just abovethe junction of the two layers. On then blow-ing gently in the side arm (5), the upper layeris forced out into the flask. Repeat the extrac-tion once, using 10 each of ether and pe-troleum ether and blowing it off into the off the solvent and dry the residual fatto constant weight in the water oven. Notes.—It is almost useless to try to extractthe
Air, water, and food from a sanitary standpoint . limb of the T tube slides a bent glass tube,which is turned up at the lower end. The tubeis adjusted by sliding it through the rubbercollar (C) so that the lower end rests just abovethe junction of the two layers. On then blow-ing gently in the side arm (5), the upper layeris forced out into the flask. Repeat the extrac-tion once, using 10 each of ether and pe-troleum ether and blowing it off into the off the solvent and dry the residual fatto constant weight in the water oven. Notes.—It is almost useless to try to extractthe fat from milk by shaking it directly solvent. An emulsion is formed with the other constituentsof the milk, and it is impossible to get a good separation ofthe solvent even with the centrifugal machine. This is prob-ably due to the action of the colloidal casein, because it isfound that when a complete or partial solution of the caseinis effected it is comparatively easy to extract and separatethe fat by a solvent immiscible with food: analytical methods: milk. 179 The method is applicable to whole milk but is especiallyvaluable in determining fat in such products as skim milk orbutter milk, which are low in fat. It is also of value in theanalysis of sweetened condensed milk. Relation between Specific Gravity, Fat, and Solidsin Milk.—As has been stated already, the specific gravityof milk is, in the main, a function of two factors, namely,the percentage of solids not fat and that of the fat. The formerraises it, the latter lowers it. Taken by itself it affords verylittle indication of the composition, but if any other item beknown, it should be possible to find, by calculation, the otherquantities, provided the assumption is true. The solids notfat are made up of several fluctuating constituents, but nor-mal milk seems to contain them in such a constant ratiothat a calculation serves at least to detect an abnormal sam-ple. For example, given the specific grav
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