510 Quantitative Determination of Fat in Milk [july 



obtained, then some of it was placed in a small Erlenmeyer flask 

 having a 5 c.c. bulb-pipette fitting snugly in its mouth. About 4 

 or 5 gm. were removed with the pipette and dropped into the center 

 of a coil of specially prepared, fat-free, absorbent paper. The 

 sample was weighed by difference. The paper coil containing the 

 milk was transferred to a hot-air oven, the temperature of which 

 was constantly below 100° C, and permitted to dry for three or 

 four hours, after which it was removed to a glass desiccator, kept 

 there at least twelve hours, over conc. sulfuric acid, and then trans- 

 ferred to a Soxhlet extraction apparatus, where it was extracted 

 for twelve to sixteen hours with absolute ethyl ether which had been 

 redistilled after Standing over metallic sodium for from five to six 

 days. After completing the extraction, the excess of ether was 

 distilled into the upper part of the apparatus and the ethereal Solu- 

 tion of fat quantitatively transferred to a weighed evaporation dish, 

 using redistilled ether as a rinsing fluid. The ether was evaporated 

 over a safety water-bath (the dish being protected from dust by 

 an inverted funnel), at a temperature below 33° C, to prevent loss 

 from ebullitlon of the ether. After the ether had been evaporated, 

 the fat was placed in a hot-air oven and dried for three hours at a 

 temperature ranging between 95°-ioo° C, then dried over sulfuric 

 acid to constant weight, which usually required about twenty-four 

 hours. The weight was then recorded and the percentage of fat 

 calculated. 



Of the above method there are many modifications, but none of 

 them are rapid methods. 



Miscellaneous methods. In the method devised by Soxhlet,^ 

 the drying of the milk is accomplished by the use of gypsum. 

 Froidevaux^ precipitates the protein and fat by means of acetic acid 

 and calcium phosphate. The precipitate is collected quantitatively 

 on a filter paper, dried and extracted in a Soxhlet apparatus with 

 absolute ether. Le Comte^ suggests the use of sodium sulphate as 

 desiccating material. In the modification suggested by Rieter,* 

 gypsum and later some Fehling Solution are used to precipitate the 



1 Soxhlet : Polytech. Jour., 1879, ccxxxii, p. 461. 



2 Froidevaux : Jour. de Pharm, et Chem., 1897 (6), vi, p. 485. 

 3Le Comte: Ibid., 1901 (6), xiii, p. 58. 



* Rieter : Schweiz. Wochschr. Pharm., 1903, xli, pp. 39 and 53. 



