IDOi).] PUBLIC DOCUMENT — No. 31. 123 



higher will bo the sapoiiilicatiou miniber. I'ats aud oils con- 

 taining a considerable amount of the glycerides of the lower 

 (volatile) fatty acids arc characterized by a saponification 

 number exceeding 200. 



2. Acid Number. 



The acid number indicates the milligrams of potassium hy- 

 drate recjuired to neutralize the free fatty acids in 1 gram of 

 an oil, fat or wax. 



Keagenls. — A^inety-five per cent, alcohol, free from acid and 

 aldehyde. 



N/10 ]wtassium (or sodium) hydrate solution. 



Phenolphthaloin solution, 1 gram to 100 cubic centimeters of 

 alcohol, u(Mitralized. 



Method. — Ten grams of fat are brought into a 300 cubic 

 centimeter Erlenmeyer flask together with 100 cubic centimeters 

 of alcohol. The flask is connected with a condensing tube and 

 heated on asbestos board at low ebullition for five minutes to 

 insure solution of the free fatty acids. When cool the solution 

 is titrated^ with N/lO alkali, using a few drops of phenol- 

 phthalein as indicator. The pink coloration will not remain 

 permanent because of the saponification of neutral esters and 

 the decolorizing action of the carbonic acid absorbed from 

 the air on shaking. Allowing the solution to cool, however, 

 previous to titration will practically prevent saponification. The 

 indicator also appears more sensitive to cool than to hot solu- 

 tions. Undue shaking should be avoided. Several blank de- 

 terminations should be run on the alcohol with every series 

 of tests and deducted. A purified alcohol should lie nearly 

 neutral, or it can be readily made so, if desired, before being 

 used. 



One cubic centimeter of N/lO alkali is equivalent to 5.6158 

 milligrams of potassium hydrate. 



Limit of error, .10 acid number. 



Synopsis of Reaction. — Solution of free fatty acids in 

 alcohol. 



3 RO.H -\- 3 KOH = 3 ROoK + 3 H2O 



> Note directions rel.-itive to titrating saponification nunilKT of fat and neutralization 

 number of insolulile acids. 



