512 Quantitative Determination of Fat in Milk [july 



Richmond and Rosier^ advise treatment of milk with definite 

 proportions of 90-91 per cent. sulfuric acid sol. and amyl alcohol, 

 and, after cooling to about 25° C, extracting with 20 c.c. of 

 petroleum ether. This method is not very accurate because of the 

 fact that petroleum ether itself frequently leaves an evaporation- 

 residue, probably an isomeric substance, hence the percentage by 

 this method is likely to be too great. 



Utilizing the tragacanth process devised by Rusting,^° Bon- 

 nema^^ describes an ether-extraction method, — following prelimi- 

 nary treatment with potassium hydroxid sol. Tragacanth is added 

 to facilitate the Separation of the water and the ethereal Solutions, 

 The results are fairly good but not as accurate as those obtained 

 with the paper-coil method. 



In the Ram-Fouard^2 method, milk is treated with a special 

 reagent containing potassium hydroxid, ethyl alcohol, amyl alcohol 

 and ammonium hydroxid. The milk is placed in a special 50-60 c.c. 

 flask with 10 c.c. of this reagent, the flask is immersed in boiling 

 water for ten minutes, then removed, and enough distilled water 

 added to carry the liquid into the neck of the flask, when the flask 

 is placed in water at 40° C, and the fat allowed to separate. The 

 average milk fat has a specific gravity of about 0.90 at 40° C. ; 

 hence, one-quarter the amount of fat recorded volumetrically gives 

 the number of grams of fat per liter of milk. 



Hanget and Marion^ ^ speak favorably of a method in which 

 they use a special reagent consisting of 100 c.c. of n/6 ammonium 

 hydroxid sol. neutralized to litmus by the addition of lactic acid 

 and made up to 150 c.c. with distilled water, and 435 c.c. of absolute 

 ether, 420 c.c. of absolute alcohol and 40 c.c. of a Solution of i gm. 

 of methyl violet (5B) in 1,000 c.c. of absolute ether. After con- 

 traction has occurred, the volume is measured and 38.9 c.c. of abso- 

 lute ether are added per liter. A special apparatus is used, by the 

 aid of which the percentage of fat is read off on the scale at 2)7° C. 



ö Richmond and Rosier : Analyst, 1899, xxiv, p. 172. 



lORusting: Chem. Centr., 1898 (ii), p. 393 {Nederl. Tijdschr. v. Pharm., 

 Chem. en Tox., 1899, x, p. 163). 



11 Bonnema : Chem-Ztg., 1899, xxiii, p. 541. 



i2Leze (Ram-Fouard method) : Ann. de Chim. anal. appL, 1899, iv, p. 371. 



13 Hanget and Marion : Ibid., 1902, vii, p. 297. 



