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The estimation of fat in dry milks

 

作者: H. Droop-Richmond,  

 

期刊: Analyst  (RSC Available online 1908)
卷期: Volume 33, issue 391  

页码: 389-390

 

ISSN:0003-2654

 

年代: 1908

 

DOI:10.1039/AN9083300389

 

出版商: RSC

 

数据来源: RSC

 

摘要:

THE ANALYST 389 PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS AND OTHER ANALYTICAL CHEMISTS. THE ESTIMATION OF FAT IN DRY MILKS. BY H. DROOP-RICHMOND, F.I.C. THE recent paper on this subject by Mr. B. G. McLellan (ANALYST, 1908, 353) renders it desirable to call attention to the conditions which must be observed in working the Riise-Gottlieb method for the estimation of fat. While I agree with the author of this paper that the Werner-Schmid method (provided, however, that the fat,” after being weighed, is extracted with petroleum ether, and the weight of the small undissolved residue subtracted from the total weight) gives satisfactory results, and while I am also prepared to admit that he has established the accuracy of long-continued direct extraction with ethylic ether (specific gravity 0.720) as a method for fat estimation, I entirely dissent from his con- clusion that the Rose-Gottlieb method, which he has roughly described under the title of No.1, is useless. By following the details which I describe below not only do duplicates agree very closely (proving the absence of adventitious errors), but the results are prac- tically identical with those furnished by the Werner-Schmid method. The essential points of the Rose-Gottlieb method are strict adherence to the proportions of water to the reagents, and thorough mixing of each reagent before the others are added; neglect of these precautions may cause enormous errors, and I have little doubt that Mr. McLellan, in his experiments, did not appreciate the importance of the mixing. I prefer to modify this method, as also the Werner-Schmid, by extracting the whole of the fat by successive treatment with solvents, rather than to measure the total volume of the mixed ether and petroleum ether, and to take an aliquot portion for evaporation and weighing, as this avoids one source of error.I have, however, obtained good results by taking aliquot quantities. 0.5 to 0.7 gram of the dry milk is weighed into a narrow stoppered cylinder holding about 50 c.c., and sufticient water is added to make up a weight of 515 grams; 0-5 C.C. of ammonia solution (0.88 ammonia diluted with an equal bulk of water) is measured in, and the dry milk dissolved by shaking, and, if necessary, slight warming ; 5 C.C. of alcohol are added (methylated spirit, if free from petroleum, will serve), and the mixture shaken till homogeneous.12.5 C.C. (circa) of ether (methylated, specific gravity 0.720, preferably freshly distilled, to remove the acrid substance formed on standing) are poured in, and the contents of the tube well mixed, the thorough mixing at this stage being, perhaps, the most important detail. Finally, 12.5 C.C. of petroleum ether (boiling-point below 60” C.) are added, and the contents of the tube again thoroughly mixed two or three times ; separation of the ethereal layer takes place rapidly, and -when globules can no longer be detected390 THE ANALYSTo in the lower layer, the upper layer is drawn off with wash-bottle tubes ; by the addi- tion of successive quantities of a mixture of ether and petroleum ether (the recovered solvent serves admirably) the whole of the fat is extracted. The solvent is removed by distillation and the fat dried and weighed. The fat is dissolved in petroleum ether, and the solution decanted from the minute residue, and after three or four washings with petroleum ether the residue is dried and weighed. If desired, the quantities given may be doubled, or increased in any other ratio, provided that the relative proportions are strictly adhered to. The method is so convenient, accurate, and rapid that I now use it in preference to all others for the analysis of milk (of which 5 C.C. are taken and no water added), and all milk products; it is also applicable to the analysis of eggs, egg-yolk, and dried egg preparations, provided the quantities taken are not too large.

 

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