IMPROVED METHODS FOR FAT ANALYSIS. 117 



insure the entire removal of caprylic and capric acids when present, but 

 the treatment should not be unduly prolonged for fear of injury to the 

 unsaturated acids. The melted fatty acids are run into a test tube, heated 

 in a water bath at 60° C. to allow any water present to settle out, filtered 

 in a jacketed funnel, and preserved in a well-stoppered bottle in a cool 

 dark place. The above process should yield fatty acids practically free 

 from decomposition. It is inadvisable to employ the I'esidue from the 

 quantitative determination of the insoluble acids for further tests. 



Neutralization Number. 



The neutralization number indicates the number of miUigrams of po- 

 tassium hydroxide required for the complete neutraUzation of 1 gram of 

 insoluble fatty acids by the saponification process. 



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 solution should be allowed to stand at least twenty-four 

 hours and filtered immediately before use. 



N/2 hydrochloric acid. 



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

 neutralized. 



Cotton blue 6B solution: 2 grams to 100 cubic centimeters of alcohol. 

 The indicator should be boiled in a flask under a reflux condenser for two 

 hours and then filtered. 



Method. — Into a 300 cubic centimeter Erlenmeyer flask are brought 5 

 grams of insoluble fatty acids, together with 50 cubic centimeters of alco- 

 holic potash accurately measured with a burette, 50 cubic centimeters of 

 alcohol and several glass beads. The flask is then connected with a spiral 

 or other form of reflux condenser and the solution boiled on a water bath 

 with occasional rotation until the reaction is complete, — about sixty 

 minutes. The flask is then placed in a water bath at 60° C, and the solu- 

 tion, after cooling to that temperature, titrated with N/2 hydrochloric 

 acid, using 1 cubic centimeter of phenolphthalein or cotton blue as indi- 

 cator. For further details see "Saponification (Koettstorfer) Number." 

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

 alkali of the test is the acid equivalent of the insoluble acids taken, which 

 should be calculated to miUigrams of potassium hydroxide for 1 gram of 

 insoluble acids. In all cases where the unsaponifiable matter constitutes 

 an appreciable amount it should be deducted in calculating the neutrali- 

 zation number of the insoluble fatty acids, and so stated. 



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

 potassium hydroxide. 



Limit of error, 0.50 milligram. 



S])noj)sis of Reaction. — See "Acid Number" with titration of excess 

 alkali, as in "Saponification Number." 



