1909.] PUBLIC DOCUMENT — No. 31. 137 



been determined, the per cent, of each acid (or glycerides) can 

 be calculated by formula : — 



x + y = P 



ex + dy =.011' 



.01 I — dP 

 "= c-d 



11. Neuteal Fat asb Unsaponifiable Matter. 



The neutral fat and nnsaponifiable matter indicates the per- 

 centage of these substances in an oil, fat or wax. 



Reagents. — Sodium carbonate, anhydrous powder, free from 

 caustic alkali. 



Ethyl ether, anhydrous and free from alcohol. 



Method. — Into a 3-inch porcelain dish are brought 2 grams 

 of fat together with 1 gram of sodium carbonate and 5 cubic 

 centimeters of alcohol, and the contents stirred thoroughly. 

 After evaporation of the alcohol 25 grams of quartz sand are 

 added, and the mixture transferred to a S. & S. capsule and 

 extracted with ether in a continuous extractor. The extract is 

 dried for one hour in an air bath at 100° C, and considered 

 neutral fat and nnsaponifiable matter. Drying^ in a vacuum 

 oven below 70° C. is preferable. Unnecessary heating should 

 be avoided, as it causes oxidization and sometimes volatilization. 



Limit of error, .15 per cent. 



8y7iopsis of Reaction. — Neutralization of free fatty acids 

 with sodium carbonate. 



Extraction of neutral fat and unsaponiiiable matter with 

 ether. 



Free Fatty Acids. — Free fatty acids can be determined by 

 diiference, — 100 less per cent, of neutral fat and nnsaponifi- 

 able matter. 



12. Unsaponifiable Matter. 



The nnsaponifiable matter of an oil, fat or wax is that por- 

 tion which does not combine with caustic alkali to form soap, 

 thereby insoluble in water l)ut soluble in ether. 



Reagents. — Glycerol-soda solution, 100 cubic centimeters of 



' See " method " under Insoluble Acids for suggestions on drying. 



- The factor .01 converts the iodine nniiiher to the same basis as the figures for theoret- 

 ical absorption stated on previous page. 



