114 MASS. EXPERIMENT STATION BULLETIN 166. 



centimeter flask and filter are dissolved in alcohol and titrated with N/10 

 alkali, using 1 cubic centimeter of phenolphthalein as indicator. The 

 titration reading minus the blank, reduced to a 5-gram basis, is the Po- 

 lenske number. 



Limit of error, 0.10 cubic centimeter. 



Synopsis of Reaction. — Solution of insoluble volatile acids in alcohol. 

 Titration. 



Supplementary Notes. — The Polenske number for most oils and fats 

 having a saponification number of about 195 rarely exceeds .65, unless 

 the product is excessively acid or rancid. ^ The Polenske number of butter 

 fat is about 2 to 3, of palm kernel oil, 10 to 12, and of coconut oil, 15 to 20. 



Insoluble Fatty Acids and Unsaponifiable Matter (Hehner 



Number). 2 



The insoluble fatty acids in an oil, fat or wax indicate (unless otherwise 

 stated) the percentage of fattj' acids and unsaponifiable matter that is 

 insoluble in water.' 



Reagents. ■ — Glycerol potash solution: 120 grams of potassium hydroxide, 

 free from carbonate, to 1,000 cubic centimeters of pure glycerol, heated 

 sufficiently to dissolve the alkali (about 115° C.)- 



Sulfuric acid: 1 to 4. 



Ceresine: pure white, filtered. 



Ethyl ether: anhydrous and free from alcohol and residue. 



Method. — Five grams of fat are brought into a 300 cubic centimeter 

 Erlenmeyer flask, together with 20 cubic centimeters of glycerol potash, 

 and heated over a small naked flame, rotating continuously until the sa- 

 ponification is complete, as shown by the solution becoming perfectly 

 clear. Care should be taken not to overheat and discolor the material. 

 The resulting soap, absolutely free from globules of fat, is dissolved in 

 150 cubic centimeters of hot water and decomposed with a sUght (few 

 drops) excess of sulfuric acid (1 to 4).'* The flask is heated on a water 

 bath with occasional agitation, until the separated fatty acids and under- 

 lying Hquid become clear. This requires a number of hours, generally 

 overnight, and must not be sUghted. The flask is immersed in cold water ^ 

 to solidify the fatty acids, after which the solution is decanted through a 

 dense, ether-extracted filter, ^ care being taken not to break the insoluble 

 cake. One hundi'ed and fifty cubic centimeters of boiling water are added, 

 thorouglily agitated, heated as above, cooled and decanted, the process 

 being repeated imtil the washings are free from acid. Litmus paper is 

 not sufficiently sensitive for this purpose. The final 150 cubic centi- 



' Lewkowitsch, Analysis of Oils, Fats and Waxes, 1, p. 426 (1913). 

 2 Angell and Hehner, Butter: Its Analysis and Adulteration (1874). 



* This may mean either hot or cold water, according to the method employed. 



* About 5 cubic centimeters are required. 



' A flat-bottomed "plug" sink with the outlet closed with a perforated cork, carrying a piece of 

 glass tubing to regulate the height of the water, serves quite satisfactorily as a chilling bath. 



* Baker & Adamson Chemical Company, 12.5 centimeters washed filter paper, "B" dense. 



