136 EXPERIMENT STATION. [Jan. 



chloride will be taken up bv the potassium iodide. The 

 '^ bleached " condition should hold for at least five minutes, 

 though the blue color may develop again in time, due to the 

 splitting off of iodine. Several blank determinations should be 

 run with every series of tests. The difference between the titra- 

 tion of the blank and that of the excess iodine is the thiosulfate 

 equivalent of the fat, which multiplied by the factor (obtained 

 as above) and divided by the weight of fat gives the percentage 

 of iodine absorbed. 



Limit of error, .25 iodine number. 



Synopsis of Reaction. — Solution with carbon tetrachloride. 



Formation of chloro-iodo additive compounds with unsatu- 

 rated acids and their glycerides. 



Solution of the excess iodine with potassium iodide and titra- 

 tion with sodium thiosulfate, using starch paste as indicator. 



2 NajSoOg +21 = Na^406 + 2 Nal. 



10. Calculated Data from the Iodine Number. 



Theoretically the unsaturated fatty acids belonging to the 

 oleic and ricinoleic series absorb 2 atoms of the halogen, linolic 

 series 4 atoms, linolenic series 6 atoms, etc. The glycerides act 

 similarly to the free acids and absorb three times as many atoms 

 (triglycerides). In fats and nondrying oils olein is the promi- 

 nent unsaturated glyceride and linolein in drying oils. In those 

 cases where only one such acid or glyceride is present its per- 

 centage can be readily calculated from the iodine number, 

 dividing by the theoretical absorption. 



^^^'' ""^ == C^^. = "282^^72 = • ^^^^^ 



Olein = ^^ = -^^^1^ = .80098 



CsH^CCis H^ 0,)3^ 884.822 



In a similar manner linolic acid combines with 1.81220 parts 

 of iodine and linolein with 1.73380. 



Where; there are two unsaturated acids (or glycerides) pres- 

 ent (x and y) of known absor])ti()n (e and d), if the percentage 

 of the mixture (V) and the iodine niniibci- (I) of the fat have 



13(C„Il3,02) + ('3"2- 



