IMPROVED METHODS FOR FAT ANALYSIS. 135 



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 alkali should be added to the alcohol slowly, with agita- 

 tion, in order to prevent any appreciable rise in temperature. 



Methyl alcohol: redistilled, free from acids and aldehydes. The alcohol 

 is prepared from Columbian spirits by distillation over caustic lime. 



Potassium carbonate : anhydrous, free from caustic alkali. 



Ethyl ether: ^ anhydrous, free from alcohol and residue. The ether 

 should be allowed to stand over metallic sodium until evolution of gas 

 ceases, and then redistilled. 



Method. ^ — Five grams of fat are brought into a 300 cubic centimeter 

 Erlenmeyer flask, together with 75 cubic centimeters of alcoholic potash 

 and 25 cubic centimeters of alcohol. The flask is connected with a spiral 

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

 with occasional rotating of the contents until saponification is complete, 

 — about sixty minutes. The solution is transferred to a 250 cubic centi- 

 meter Griffin beaker and the flask rinsed several times with hot alcohol. 

 The alcohol is evaporated in a water bath (with the beaker immersed in 

 the water) at a gi-adually increasing temperature. Several 25 cubic centi- 

 meter portions of methyl alcohol are added and evaporated to insure 

 complete dryness. Careful heating is necessary to avoid spattering. 



The dry residue is pulverized in a mortar with 25 grams of anhydrous 

 potassium carbonate, dried two hours at 100° C, transferred to an S. & S. 

 extraction tliimble, 33 by 80 millimeters, extracted two to three hours 

 with anhydrous ether in a continuous extracter (see Fig. 4), and the ether 

 expelled as usual. Notwithstanding the precautions mentioned, mois- 

 ture may be absorbed during the process and vitiate the ether extract 

 with a small amount of water-soluble compounds. To eliminate this error 

 the air-dry extract is washed with several 25 cubic centimeter portions of 

 water at room temperature, and decanted on an ether-extracted filter 

 which is air dried, and extracted with ether, using the same flask as before. 

 The purified extract is dried from 1 to 1.5 hours in an oven at 100° C. and 

 considered unsaponifiable matter. 



In most oils and fats there is a comparatively small amount of unsa- 

 ponifiable matter, but greater accuracy is not insured by taking a larger 

 amount of material (say 10 grams), for the reason that the greater the 

 bulk of soap the more difficult the manipulation. 



Seventy-five cubic centimeters of alcoholic potash instead of 50 cubic 

 centimeters, the usual quantity, are employed to prevent any reversible 

 reaction to which there appears to be a tendency on evaporating. One 

 hundred cubic centimeters, however, destroj^ a portion of the sterols. 



Anhydrous potassium carbonate proved a more efficient dehydrating 

 agent than the corresponding sodium salt. 



> Commercial ether of the U. S. P. grade is unfit for the purpose, and the ''distilled over sodium " 

 grade is often unreliable, due to its hygroscopic properties. 

 - Not applicable for volatile hydrocarbons or ethereal oils. 



