122 MASS. EXPERIMENT STATION BULLETIN 166. • 



alcohol^ of about 95.25 per cent., heated sufficiently to give a clear solu- 

 tion. 



Ethyl ether: free from residue. 



Apparatus. — Eight-ounce sterilizer bottles " of narrow cj^lindrical 

 form (6f by 2 inches). 



Small thistle tubes (i-inch bulb) with a felt of absorbent cotton, weigh- 

 ing .02 gram, supported by a glass bead and covered by a piece of cheese- 

 cloth. 



Ice tank of |-inch material (approximately 20 inches long, 10 inches 

 wide and 20 inches deep), lined with galvanized iron, provided with a 

 tight cover, and supported by legs to a convenient worldng height. 



For icing, a basket (ISJ by 6 by 18 inches) of galvanized screening of 

 y^g-inch mesh. 



Pockets of galvanized screening to support the bottles so that only a 

 small portion of the neck projects out of the ice water. 



A pump or agitator run by motor to keep the water in continuous 

 circulation. 



Method. — Five-tenths of a gram of melted insoluble acids are brought 

 into an 8-ounce steriUzer bottle, and 150 cubic centimeters of an alcoholic- 

 stearic solution, accurately measured with a pipette at 30° C, added. 

 The bottle is sealed with a soUd rubber stopper, shaken at a gradually 

 increasing temperature until a clear solution is obtained, immediately 

 placed in a pocket of the ice tank and allowed to stand overnight. The 

 following morning the solution is gently agitated by inverting the bottle 

 several times, and in the afternoon is siphoned off as thoroughly as possi- 

 ble by means of a small thistle tube' and a perforated rubber stopper, 

 using suction. The residue is dissolved in ethyl ether, transferred to a 

 tared 140 cubic centimeter wide-mouthed Erlenmeyer flask, the ether 

 carefully distilled off, dried at 100° C, and weighed. As saturation may 

 vary somewhat with the amount of stearic acid present, and as the quan- 

 tity of solution retained by the precipitate depends in a measure on the 

 amount of precipitate, blanks are run on a weight of stearic acid equivalent 

 to that expected in the test. By deducting the additional stearic acid 

 taken, from the weight recovered, the true blank for the alcoholic-stearic 

 solution is obtained. 



The molecular weights of the precipitates should be determined occa- 

 sionally to check the operation. In the presence of palmitic acid it has 

 been found necessary to increase the amount of stearic acid in solution in 

 order to counteract the solvent action of the former acid. 



Limit of error, from 0.50 to 0.75 per cent. 



Synopsis of Reaction. — Solution of insoluble fatty acids in alcoholic- 

 stearic solution. 



Crystallization of stearic acid under control conditions. 



Filtration. 



Recovery and weight of precipitate. 



» See "Reagents," under "Saponification Number." 



' Manufactured by Whitall Tatum Companj', Philadelphia, Pa. 



s The size of the tube and preparation of the felt have already been described. 



