132 EXPERIMENT STATION. [Jan. 



absorption of the insoluble acids. Drying in a vacuum oven 

 below 70° C, in a current of carbonic acid gas or in a vacuum 

 desiccator will i:>ractically prevent oxidization as well as volatil- 

 ization. 



Limit of error, .25 per cent, insoluble acids. 



8y7iopsis of Reaction. — Similar to those of the Reichert- 

 Meissl number. 



Supplementary Notes. — Most fats and oils contain from 05 

 to 97 per cent, of insoluble acids. Some notable excej)tions are 

 stated under the Reichert-Meissl number. 



(a) Neutralization Number. 



The neutralization number indicates the milligrams of po- 

 tassium hydrate required to saturate 1 gram of insoluble fatty 

 acids. 



Reagents. — Ninety-five per cent, alcohol, free from acid and 

 aldehyde. 



N/2 potassium (or sodium) hydrate solution. 



Phenolphthalein solution, 1 gram to 100 cubic centimeters of 

 alcohol, neutralized. 



Method. — The dried insoluble fatty acids resulting from the 

 determination of the Hehner number are treated with 100 cubic 

 centimeters of alcohol, connected with a condensing tube and 

 heated on asbestos board at low ebullition until the solution 

 is complete, about five minutes. When cool the solution is 

 titrated with N/2 alkali, using a few drops of phenolphthal- 

 ein as indicator. The temperature during titration should 

 be sufficient to retain the fatty acids in solution but not greatly 

 in excess. Blank determinations should be run on the alcohol 

 with every series of tests and deducted. If preferred, the al- 

 cohol can be neutralized previous to its use. 



One cubic centimeter N/2 alkali is equivalent to 28.079 milli- 

 grams of potassium hydrate. 



Limit of error, 1 neutralization number. 



Synopsis of Reaction. — See Acid number. 



