18 T.HE ANALYST. NONTHLY RECORD OF ANALYTICAL RESEARCHES INTO FOOD. ESTIMATION OF FAT IN MILK. - MORSE, PIGGOT, AND BunToN.-This method con- sists in the dehydration of the milk by means of anhydrous sulphate of copper; the extraction of the fat by means of the.low-boiling products of petroleum ; the saponification of the butter by means of an excess of a standard solution of potassium hydrate in alcohol; and the determination of the excess of the alkali by means of a solution of hydrochloric acid. The following apparatus and reagents are required :- (1) A porcelain mortar and pestle. (2) An extraction tube, 14 or 15 mm. in diameter, 220 mm. in length, with funnel- (3) A 200 C.C. Erlenmeyer flask, strong enough t o be used with a filter pump. (4) A suitable stand for holding the flask and extraction tube.(5) Ten-cubic centimetre pipettes. ( 6 ) Weighing-glasses with ground-glass stoppers. (7) A low-boiling gasoline, distilling between 30'' and 60". (8) Dehydrated sulphate of copper. (9) Semi-normal solution of potash in 95 per cent. alcohol. ManipuZation.-Place about 30 grams. of the anhydrous copper sulphate, roughly measured in a copper spoon of the size to hold about that amount, in a porcelain mortar ; shaped top. A straight chloride of calcium tube may be used for this. (10) A semi-normal solution of hydrochloric acid.THE ANALYST. 19 make a cavity in the centre of the mass with the pestle. Allow 10 C.C. of the milk to run on to the copper sulphate, being careful that none of it touches the sides of the mortar. When the milk is nearly dry, grind the mass up with a little clean sand, transfer to the extraction tube, gently pressing it down in the tube by means of a glass rod. The lower portion of the extraction tube to be packed with clean cotton wool. The fat is extracted in the following way : 15 C.C.of benzene is poured over the material in the extraction tube and drawn down with the aid of the filter pump, until the whole of the mass to be extracted has become wet with the liquid, when the connection with the pump is closed; after about five minutes another portion of 15 C.C. of benzene is poured into the tube and the whole of the liquid slowly drawn through with aid of the pump into the flask. Usually one extraction of this kind is sufficient to withdraw the whole of the butter, but for the sake of greater accuracy the process may be repeated two or three times. Pitmtioln.-The benzene may be evaporated and the residual butter fat saponified with about 25 C.C. of the appoximately semi-normal potash. The residual alkali is determined by means of the semi-normal hydrochloric acid, using phenol-phthalein as indicator. The difference between the amount required in this process and the amount necessary to neutralise the quantity of alkali taken gives the amount of alkali required for the saponi- fication, The number of milligrams. of potash required for one gram. of the fat is taken a t 230. The fat may also be accurately titrated without evaporating the benzsne. W. H. D.