26 



FATS, OILS. AND WAXES 



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■7.5 



The following method which is due to Liebermann and 

 Szekely * has the advantage of giving in a short time a re- 

 liable value for the percentage of fat in almost any substance, 

 and is specially convenient for the estimation of fat in fodder, 

 meat, f?eces, and physiological work in general. Five grams 

 of the sample are placed in a flask (of the 

 dimensions given in Fig. 2) with 30 c.c. of 

 50 per cent caustic potash (sp. gr, i"54). 

 The mixture is boiled over a wire gauge for 

 half an hour and frequently shaken. After 

 cooling 30 c.c, of 90-94 per cent alcohol are 

 added and the heating is continued for an- 

 other ten minutes ; the mixture is then cooled 

 again and carefully mixed with 100 c.c. of 

 20 per cent sulphuric acid (sp. gr. ri45) 

 and thoroughly shaken after each addition ; 

 the temperature must be kept low so as to 

 avoid any loss of volatile fatty acids. When 

 quite cold 50 c.c. of light petroleum (sp. gr. 

 0'6-07 ; b.p. about 60° C.) are added, and 

 the flask is then closed with a tightly fitting 

 rubber stopper and is thoroughly shaken for 

 about ten seconds ; the shaking is repeated 

 ^'°- -' about thirty times at intervals of one or two 



minutes without removing the stopper. Saturated salt solution 

 is then added until the lower aqueous layer reaches up to the 

 240 c.c. graduation which is marked on the neck. After shak- 

 ing again a few times the flask is set aside in a vessel of cold 

 water. When the petroleum containing the fatty acids in solu- 

 tion has separated, 20 c.c. are withdrawn by means of a pipette 

 and are placed in a wide-mouthed 150 c.c. flask ; 40 c.c. of 96 

 per cent alcohol, free from acid, are now added, together with 

 I c.c. of a solution of phenol phthalein (made by dissolving i 

 gram of accurately weighed phenolphthalein in 100 c.c. of 

 96 per cent alcohol) and the solution is titrated with N/io 

 alcoholic potash. 



The titrated liquid is then carefully transferred in small 

 portions at a time to a tared weighing bottle of about 80 c.c. 



* Lieberrnann and Szekely : " Pliiger's Archiv," 1898, 72, 360, 



