THE ANALYSIS OF BUTTER 71 



The Polenske figure varies with the Reichert-Wollny 

 figure, and the following Table shows the relation : 



TABLE VII 



Estimation of Soluble and Insoluble Fatty 

 Acids and Mean Molecular Weight. Weigh a 

 glass flask, which has been previously well boiled with 

 caustic alkali solution ; add about 4 grammes of butter 



fat, and weigh again. Run in 50 c.c. alcoholic soda 



solution (see Appendix), attach the flask to an upright 

 condenser, and boil for a quarter of an hour ; add a 

 few drops of phenolphthalein solution and titrate with 



- hydrochloric acid till the pink colour is discharged. 

 As the alcoholic soda solution alters in strength it must 

 be checked against the - hydrochloric acid, and the 



value in terms of the acid solution obtained of 50 c.c. of 



N 

 alcoholic soda ; from this subtract the volume of - 



hydrochloric acid used in titrating after saponification, 

 and multiply by 2.805 and divide by the weight of 

 butter taken ; the figure obtained will be the percentage 

 of potash required for saponification. 



