EDIBLE FATS AND OILS. 139 



9. Insoluble Acids or Hehner Number. Official. 



Allow the flask containing the cake of insoluble fatty acids from the preced- 

 ing determination, and the paper through which the soluble fatty acids have 

 been filtered, to drain and dry for twelve hours. Transfer the cake, together 

 with as much of the fatty acids as can be removed from the filter paper, to a 

 weighed glass evaporating dish. Then place the funnel, with the filter, in an 

 Erlenmeyer flask and thoroughly wash the paper with absolute alcohol. Rinse 

 the flask with the washings from the filter paper, then with pure alcohol, and 

 transfer the filtrate and washings to the evaporating dish. Keep the dish on 

 the steam bath until the alcohol is evaporated, dry for two hours at 100 C., 

 cool in a desiccator, and weigh. Again place in the air bath for two hours, 

 cool as before, and weigh. If there be any considerable decrease in weight, 

 reheat for two hours and weigh again. The result obtained is the weight of 

 insoluble fatty acids, from which the percentage is easily calculated. 



10. Reichert-Meissl Number or Volatile Acids. Official, 

 (a) REICHERT-MEISSL METHOD. 



(1) PREPARATION OF REAGENTS. 



(a) Sodium hydroxid solution. Dissolve 100 grams of sodium hydroxid, as 

 free as possible from carbonates, in 100 cc of water, and preserve out of contact 

 with the air. Allow to settle and use only the clear liquid. 



(&) Potassium hydroxid. Dissolve 100 grams of the purest potassium 

 hydroxid in 58 cc of hot distilled water. Cool in a stoppered vessel, decant the 

 clear solution, and preserve out of contact with the air. 



(c) Ninety-five per cent alcohol. Distil over sodium hydroxid. 



(d) Sulphuric acid. Dilute 200 cc of the strongest acid to 1,000 cc with water. 



(e) Barium hydroxid solution. Standardize an approximately tenth-normal 

 )lution. 



(f) Indicator. Dissolve 1 gram of phenolphthalein in 100 cc of 95 per cent 

 alcohol. 



(g) Pumice stone. Heat small pieces to a white heat, plunge in water, and 

 keep under water until used. 



(2) DETERMINATION. 



Melt the butter or fat and keep at about 60 C. for two or three hours, or until 

 the water and curd have entirely separated. Pour the clear supernatant fat 

 through a dry filter, using a hot-water funnel ; if the filtered fat is not clear, 

 filter again. 



Wash the saponification flasks thoroughly with water, alcohol, and ether, 

 wipe dry on the outside, and dry for one hour at the temperature of boiling 

 water ; cool, and weigh. 



Measure 5.75 cc, equivalent to about 5 grams, of the thoroughly mixed fat 

 into the flask with a pipette that has been warmed to about 50 C., care being 

 taken to wipe off the adhering fat and to prevent any fat getting on the sides 

 of the flask. Allow to stand for fifteen to twenty minutes and weigh. 



Three methods of saponification are allowable: 



(a) Under pressure with alcohol. 



Place 10 cc of the 95 per cent alcohol in the flask containing the fat, which 

 must be made of strong, well-annealed glass, capable of resisting the tension of 



87404 Bull. 10709 11 



