90 PUBLIC HEALTH CHEMISTRY 



Wollny of 7, palm-nut fat of 5, and certain fish oils are 

 said to give values above 40. In the case of coco-nut oil, 

 the figure is due to the presence of the glyceride of caprylic 

 acid, with a little caproic, but no butyric glyceride. To 

 meet this difficulty, several tests have been devised. Here 

 we describe that of Polenske, which is the most generally 

 adopted one. 



Polenske Method. Is based on a determination of the 

 insoluble volatile fatty acids, which are distilled over in 

 the Reichert-Wollny process. Certain arbitrary condi- 

 tions must be observed to get results which will be compar- 

 able with those of Polenske and others. 



PROCESS. Five grm. of the fat, 20 grm. of glycerol, 

 and 2 c.c. of 50 per cent NaOH (an alcoholic solution of 

 soda must not be used) are taken in a 300 c.c. boiling-flask, 

 and heated over a naked flame, with constant shaking, until 

 a clear solution is obtained. The soap formed is dissolved 

 carefully in 90 c.c. of hot water ; 50 c.c. of N/i sulphuric 

 acid are added ; and o-i grm. of pumice, which has been 

 powdered and then sifted through muslin. The flask is 

 quickly connected to the top of an upright Liebig con- 

 denser, by means of a glass tube with a bulb just above 

 the cork, and the tube thereafter bent, first at an obtuse, 

 and then at an acute, angle. Distillation is commenced, 

 and the flame so regulated that no c.c. are distilled over in 

 nineteen to twenty-one minutes. When no c.c. have been 

 received into a small flask, the latter is replaced by a 25 c.c. 

 cylinder, and the flame withdrawn. The cylinder receives 

 the drainings. The flask containing the no c.c. of 

 distillate is, without shaking the contents, put into a 

 bath of water at 10 C. for ten minutes, the level of the 

 water outside being just above that of the distillate inside 

 the flask. (At this stage, it may be noted that the insoluble 

 fatty acids are almost invariably opaque and white in the 

 case of butter, while 10 per cent or more of coco-nut oil 

 gives clear oily globules.) The distillate flask is now 

 shaken, and the contents are filtered. The Reichert figure 

 may be obtained on 100 c.c. of the filtrate. The filter- 

 paper is kept ; and the distillate flask, the condenser, and 

 the cylinder are washed out with 18 c.c. of distilled water, 

 which is then poured on to the filter-paper. This paper 



