106 MASS. EXPERIMENT STATION BULLETIN 166. 



factor .0001 of the molecular weight of the acid (monobasic) for an N/10 

 solution, or .001 for N. 



The percentage of acidity (A) can also be calculated from the acid 

 number (a) and the neutralization number (n) of the total fatty acids. ^ 



A = ^ (16) 



n 



The percentage of free fatty acids can be estimated approximately from 

 the acid number (a) and saponification number (s) : — 



Neutral Fat and Unsapoiiifiable Matter. — The percentage of neutral 

 fat and unsaponifiable matter can be determined by difference, — 1 .00 

 minus per cent, of free fatty acids. 



Neutral Fat and Free Fatty Acids. — The percentage of neutral fat (N) 



and free fatty acids (A) can be estimated from the ether number (e) by 



assuming an average saponification number (k) for the neutral product 



as basis for the calculation. 



N = « 

 k 



A= 1.00 -N 



Soluble Fatty Acids. 



The soluble fatty acids in an oil, fat or wax indicate the percentage of 

 fatty acids that is soluble in water. ^ 



The percentage of soluble fattj^ acids can be readily calculated by 

 difference, — total fatty acids less the insoluble. It is unnecessary to 

 make the actual determination in most instances. When desired for 

 some particular purpose, however, the test may be carried out as follows: — 



Reagents. — Alcohol: redistilled, free from acids and aldehydes. 



Alcoholic potash solution: 50 cubic centimeters of a saturated solution 

 of potassium hydroxide, free from carbonate, to 1,000 cubic centimeters 

 of alcohol. The alkali should be added to the alcohol slowly, with agita- 

 tion, in order to prevent any appreciable rise in temperature. The solu- 

 tion should be allowed to stand at least twenty-four hours and filtered 

 immediately before use. 



N/2 sulfuric acid. 



N/2 potassium (or sodium) hydroxide. 



Phenolphthalein solution: 1 gram to 100 cubic centimeters of alcohol, 

 neutralized. 



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

 Erlenmeyer flask, together with 50 cubic centimeters of alcoholic potash, 

 accurately measured with a burette, and 50 cubic centimeters of alcohol. 

 The flask is connected with a spiral or other form of reflux condenser and 

 the solution boiled on a water bath with occasional rotation until saponi- 



' Strictly it should be the neutralization number of the free fatty acids. The number of cubic 

 centimeters of N alkali required can be substituted in place of the values a and n. 

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



