140 



METHODS OF ANALYSIS. 



alcoholic vapor at 100 C., and add 2 cc of the sodium hydroxid solution. 

 Insert a soft cork stopper in the flask, tie down with a piece of twine, and 

 place on a water or steam bath for at least one hour (fig. 7). Gently rotate 

 the flask from time to time, being careful that the fat does not rise on the 

 sides of the flask to a point where it can not be reached by the alkali. Cool 

 to room temperature before opening. 



(6) Under pressure without the use of alcohol. 



Place 2 cc of the potassium hydroxid in the flask containing the fat, which 

 must be round bottomed and made of well-annealed glass to resist the pressure, 

 cork, and heat as in the previous method. Rotate the flask very gently during 

 the saponification, taking great care that none of the fat rises on the sides of 



the flask out of reach of the alkali. 

 Potash makes a softer soap than 

 soda and thus allows a complete 

 saponification without the use of 

 alcohol. This method avoids the 

 danger of formation of esters and 

 the trouble of removing the alcohol 

 after saponification. 



(c) With a reflux condenser and the 

 use of alcohol. 



Place 10 cc of the 95 per cent 

 alcohol in the flask containing the 

 fat, add 2 cc of the sodium hydroxid 

 solution with a reflux condenser (a 

 glass tube not less than 1 meter in j 

 length is allowable), and heat on 

 the steam bath until- the saponifica- 

 tion is complete. 



After the saponification, in case 

 alcohol was used, remove this by 

 dipping the flasks in a steam bath | 

 up to their necks. When the alco- 

 hol is nearly gone frothing may 

 occur. Avoid any loss from this 

 cause or from creeping of the soap 

 up the sides of the flask by removing from the bath and shaking to and fro. 

 Remove the last traces of alcohol by waving the flask briskly, mouth down, to 

 and fro, or, better, by a current of carbon dioxid free air. 



Dissolve the soap by adding 135 cc of recently boiled water (or 132 cc if 

 potassium hydroxid was used in the saponiflcation) and warm on the water 

 bath, with occasional shakings, until the solution is clear. Cool to from 60 to 

 70 C., throw in a few pieces of pumice stone, add 5 cc of the dilute sulphuric 

 acid (or 8 cc if potassium hydroxid was used in the saponification), stopper 

 as in the method of saponification, and heat on the water bath until the fatty 

 acids form a clear, transparent layer on top of the water. This may take sev- 

 eral hours. Cool to room temperature, add a few pieces of pumice stone, and 

 connect with a glass condenser as in fig. 8. 



Heat slowly with a naked flame until ebullition begins and distil, regulating 



FIG. 7. Saponiflcation flask. 



