IMPROVED METHODS FOR FAT ANALYSIS. 



97 



sixty minutes. The reaction is quadrimolecular with triglycerides. The 

 flask is then placed in a water bath at 60° C, and the solution, after cool- 

 ing to that temperature, titrated with N/2 hydrochloric acid, using 1 

 cubic centimeter of phenolphthalein as indicator, to the complete eUm- 

 ination of the pink color. The coohng and dilution of the solution, due 

 to the addition of the acid, occasionally give rise to small colored parti- 

 cles; this can be obviated by a shght increase in temperature. The end 

 point is particularly difficult to determine in the presence of aldehydes, 

 which impart a dark reddish-brown color to the solution. Fish oils behave 



<^:><^> c::> c:> <^ d^ 



Fig. 2. — Detailed drawing of Fig. 1. 



in a hke manner. In such cases cotton blue (1 cubic centimeter) is pref- 

 erable to phenolphthalein. The change in color is from red with alkalies 

 to blue with acids. The two indicators appear to give like results when 

 considered in connection with their respective blanks. Absorption of 

 carbonic acid from the air should be guarded against at all times. As 

 alcoholic potash gradually loses alkalinity on boiling, the operation should 

 be timed •nith reasonable care. Several blank determinations should be 

 run ^\dth every series of tests under precisely similar conditions. The 

 difference between the titration of the blank and that of the excess alkali 

 in the test is the acid equivalent of the fat taken, which should be calcu- 

 lated to miUigrams of potassium hydroxide for 1 gram of fat. 



1 cubic centimeter of N/2 acid is equivalent to 28.054 milligrams of 

 potassium hj'droxide. 



Limit of error, 0.50 milligram. 



Synopsis of Reaction. 



(RCOO)3C3H6+3 KOH =3 RCOOK+C3H6(OH)3 

 fat alkali salti glycerol 



> The term "soap" is now limited by custom to the alkali salts of insoluble fatty acids. 



