i8 



FATS, OILS, AND WAXES 





kl 



I 



*3-6 Cm/.-' 



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, faeces, 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. 1*54). 

 The mixture is boiled over a wire gauze 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 another 

 ten minutes ; the mixture is then cooled again and carefully 

 mixed with 100 c.c. of 20 per cent sulphuric 

 acid (sp. gr. 1-145) ^^'^ 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. 0-6-0-7 ; 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 solu- 

 tion is then added until the lower aqueous 

 layer reaches up to the 240 c.c. graduation 

 which is marked on the neck. After shaking 

 again a few times the flask is set aside in a 

 vessel of cold water. When the petroleum 

 containing the fatty acids in solution 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 separated, 20 c.c. are withdrawn by means of a pipette and 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 phenolphthalein (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. 



* Liebermann and Szdkely : " Pfliiger's Archiv," 189S, 72, 360. 



2,^0 



■15 



c<*»/.- 



FlG. 2. 



