IMPROVED METHODS FOR FAT ANALYSIS. 



107 



ficatioii is complete, — • about sixty minutes. The condenser is then re- 

 moved and the flask placed in a water bath (immersed in the water) and 

 the alcohol evaporated at a gradually increasing temperature, care being 

 taken to prevent spattering. The last traces of alcohol, occluded in the 

 soap, are expelled by breaking up the dry cake or by dissolving it in water 

 and continuing the heating. Water to a volume of 100 cubic centimeters 

 and 1 cubic centimeter of N/2 sulfuric acid in excess of that required to 

 neutralize the 50 cubic centimeters of alcoholic potash are added, and the 

 flask, connected with a spiral condenser, heated on a water bath until the 

 separated fatty acids and underlying liquid become clear. From this 

 point the process is conducted the same as for insoluble acids, using a 

 spiral condenser to prevent loss of volatile acids. The combined filtrate 

 and washings are titrated with N/2 potassium hydroxide, using phenol- 

 phthalein as indicator. The difference between the titration of the test and 

 that of the excess N/2 acid (1 cubic centimeter) is the alkali equivalent 

 of the soluble acids in the fat taken, which should be calculated to milli- 

 grams of potassium hydroxide for 1 gram of fat. 



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

 potassium hydroxide. 



Tlie percentage of soluble fatty acids (S) is calculated from the number 

 of milligrams of potassium hydroxide (k) required to neutralize the solu- 

 ble acids in 1 gram of fat and the determined (or estimated) neutraliza- 

 tion number (n) of the soluble acids by the formula — 



n 



Limit of error, 0.25 per cent. 



Supplementary Notes. — The solubility of acids of the acetic series de- 

 creases with the increase in number of carbon atoms in the molecule. 

 The so-called "soluble" acids include capric and all acids of less carbon 

 atoms. 



Acid. 



Soluble in 100 Parts of 

 Water. 



15° C. 



100° c. 



Acetic (very soluble), J 

 Butyric (very soluble), 

 Valeric (soluble), 

 Caproic (difficultly soluble), 

 Caprylic (insoluble), . 

 Capric (insoluble), 



.25 

 .10 



' Solubility based on Mulliken's classification. Identification of Pure Organic Compounds, 1, 

 p. 38 (1911): — 



in — Grams in 100 c. c. 

 20 



One Gram 



Very soluble, 5 c. c 



Easily soluble, 5- 20 c. c. 20-5 



Soluble 20- 50 c. c. 5-2 



Difficultly soluble, . 50-150 c. c. 2-. 66 



Very difficultly soluble 150-500 c. c. .C6-.2 



Insoluble 500 c. c. and over. .2and under. 



