138 METHODS OF ANALYSIS. 



(2) Alcoholic potash solution. Dissolve 40 grams of chemically pure potas- 

 sium hydroxid in 1 liter of 95 per cent redistilled alcohol.** The solution must 

 be clear and the potassium hydroxid free from carbonates. 



(5) Standard acid solution. Prepare accurately a half-normal solution of 

 hydrochloric acid. 



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

 alcohol. 



(b) DETERMINATION. 



Conduct the saponification in a wide-mouth Erlenmeyer flask holding from 

 250 to 300 cc. Clean thoroughly by washing with water, alcohol, and ether, 

 wipe perfectly dry on the outside and heat for one hour at the temperature of 

 boiling water ; allow to cool and weigh. 



Run in about 5 grams of the filtered melted fat by means of a pipette, and 

 after cooling again weigh the flask and contents. Pipette 50 cc of the alcoholic 

 potash solution into a flask by allowing it to drain for a definite time. Con- 

 nect the flask with a reflux condenser and boil for 30 minutes or until the fat 

 is completely saponified. Cool and titrate with half-normal hydrochloric acid 

 using phenolphthalein as indicator. The Koettstorfer number (milligrams of 

 potassium hydroxid required to saponify 1 gram of fat) is obtained as follows : 

 Subtract the number of cubic centimeters of hydrochloric acid used to neutra- 

 lize the excess of alkali after saponification from the number of cubic centi- 

 meters necessary to neutralize the 50 cc of alkali added ; multiply the result by 

 28.06 (the number of milligrams of potassium hydroxid per cubic centimeter) 

 and divide by the number of grams of fat used. Conduct two or three blank 

 experiments, using the same pipette and draining for the same length of time. 



8. Soluble Acids. Official. 



Place the flask used in the preceding determination on a water bath and 

 evaporate the alcohol. Add such an amount of half-normal hydrochloric acid 

 that its volume plus the amount used in titrating for the saponificatio.n number 

 will be 1 cc in excess of the amount required to neutralize the 50 cc of alcoholic 

 potash added. Connect the flask with a condensing tube, 3 feet long and made of j 

 small glass tubing, and place it on the steam bath until the separated fatty acids i 

 form a clear stratum on the upper surface of the liquid. Fill to the neck with | 

 hot water and cool in ice water until the cake of fatty acids is thoroughly 

 hardened. Pour the liquid contents of the flask through a dry weighed filter 

 into a liter flask, taking care not to break the cake. Fill the flask again with 

 hot water, set on steam bath until the fatty acids collect at the surface, cool by 

 immersing in ice water, and filter the liquid again into the liter flask. Repeat j 

 this treatment with hot water three times, cooling and filtering the washings 

 into the liter flask after each treatment. Titrate with tenth-normal alkali, 

 using phenolphthalein as indicator. 



Diminish the number of cubic centimeters of tenth-normal alkali used in this 

 tltration by 5 (corresponding to the excess of 1 cc of half-normal acid) and 

 multiply by 0.0088 to obtain the weight of soluble acids as butyric in the 

 amount of fat saponified ; divide this by the amount of fat originally employed 

 to obtain the percentage of soluble acids. 



The alcohol should be redistilled from potassium hydroild on which It has been stand- 

 Ing for some time, or with which it has been boiled for some time, using a reflux 

 condenser. 



