116 MASS. EXPERIMENT STATION BULLETIN 166. 



Members of the chaulmoogric and tariric series constitute an exception to 

 the above statement. (See "Calculated Data from the Iodine Number.") 

 Unsaturated acids containing an open chain of 18 carbon atoms (oleic, 

 linolic, linolenic acids, etc.) are reduced by hydrogen in the presence of a 

 suitable catalyzer (nickel or colloidal palladium) to stearic acid. 



Dihydroxystearic and ricinoleic acids are hydroxy acids which on 

 acetylation assimilate an acetjd radical (CH3CO) in place of the hydrogen 

 in every alcoholic hydroxyl group. 



Most fats and oils contain from 93 to 96 per cent, of insoluble acids, 

 with a mean of approximately 95. Some notable exceptions, having sa- 

 ponification numbers exceeding 210 and a liigh volatile acid content, have 

 already been mentioned. The fatty acids are practically all insoluble 

 where the saponification number of an oil or fat does not exceed 195. 

 Croton oil contains about 89 per cent, of insoluble acids and unsaponifi- 

 able matter; dolphin jaw oil, 66 per cent.; porpoise jaw oil, 70 per cent.; 

 brown fish oil, 85.5 per cent.; laurel oil, 83.5 to 87 per cent.; palm nut oil, 

 87.5 to 91 per cent.; coconut oil, 88.5 to 90 per cent.; Japan wax, 90.5 per 

 cent.; and butter fat, 86.5 to 90 per cent. 



In liquid waxes the amount of insoluble fatty acids free from alcohols 

 and hydrocarbons varies from 60 to 65 per cent., and in solid waxes from 

 47 to 60 per cent. 



The acid content of palmitin is 95.29, stearin 95.73, olein 95.70, linolein 

 95.67 and linolenin 95.64 per cent.; therefore the percentage of insoluble 

 acids in most oils and fats free from appreciable amounts of the lower 

 fatty acids and of unsaponifiable matter must be in the vicinity of 95. 



Preparation of Insoluble Adds. 



The method for preparing insoluble fatty acids for analysis is the same 

 as described for the determination of "Insoluble Acids," with the ehmina- 

 tion of such features as are necessary only for quantitative work. About 

 28.5 cubic centimeters (25 grams) of the melted fat or oil are pipetted 

 into a 750 cubic centimeter Erlenmeyer flask, together with 100 cubic 

 centimeters of glycerol potash, and saponified. The resulting soap is 

 dissolved in 500 cubic centimeters of hot water, decomposed with a slight 

 excess (few drops) of suKuric acid (1 to 4), and heated on a water bath, 

 with occasional agitation, until the separated fatty acids and underlying 

 liquid become clear. Several such charges will furnish sufficient material 

 for the analysis. The fatty acids may be washed as described under "In- 

 soluble Acids," or the contents of the flasks transferred to a separatory 

 fumiel and washed bj^ shaking out with hot water, ^ until free from soluble 

 acids. The latter modification has some advantages, particularly for 

 insoluble acids of low melting point. Thorough washing may not always 



> The layer of fatty acids should be allowed to partially solidify at least, before the water is 

 drawn off, to insure conditions similar to those prevailing in the quantitative determination of 

 the insoluble acids. 



