34 FATS, OILS, AND WAXES 



caustic potash which are thus utih'zcd in combining with the 

 acetyl groups to form potassium acetate. 



The number of milligrams of potash required by the acetyl 

 derivative obtained from i gram of the fat is termed the acetyl 

 value of that fat. 



Castor oil and grape-stone oil have particularly high acetyl 

 values owing to the large proportion of hydroxyacids which 

 they contain. 



The following are the acetyl values of some of the more 

 important oils, fats and waxes : — 



The following method, due to Lewkowitsch, has been 

 adopted as the standard process. 



About 10 grams of the fat are boiled in a round-bottomed 

 flask under a reflux condenser for two hours with twice their 

 weight of acetic anhydride. The mixture is then poured into 

 a litre flask and boiled for half an hour with 500-600 c.c, of 

 water, a slow stream of carbon dioxide being conducted into 

 the liquid all the while to prevent bumping. After cooling, 

 the upper layer of water is siphoned off" and the lower oily 

 layer is again boiled with water as above, the whole process 

 being repeated three times. The oil is finally filtered and 

 washed on the filter paper with boiling water until the filtrate 

 is no longer acid, whereupon it is dried in an oven and 

 weighed. 



About 5 grams of the acetylated product are next saponi- 

 fied by boiling with alcoholic potash* as described under the 

 determination of the saponification value. The alcohol is then 

 evaporated off, and the resulting soap is dissolved in water. 



Dilute sulphuric acid (1:10) is then added in excess and 

 the solution is steam distilled until 600-700 c.c. of water have 

 passed over. The distillate is titrated with N/iO caustic potash 

 using phenolphthalein as indicator ; the number of cubic centi- 



* Prepared by dissolving about 32 grams of 90 per cent stick potash in the 

 least quantity of water and diluting to i litre with 96 per cent alcohol ; the solu- 

 tion should be filtered after standing for twenty-four hours. 



