460 FOODS AXD FOOD ADULTERANTS. 



In evaporating the alcohol the residual soap sometimes froths and 

 fills the flask. This is avoided by removing the flask from the steam- 

 bath when signs of frothing are shown and rolling it in such a manner 

 as to coat the bottom and lower fourth of the flask with a film of soap. 

 The flask should also be inverted and waved to and fro towards the end 

 of the evaporation in order to remove the vapor of alcohol. 



The method proposed by Wollny* has also been used in the estima- 

 tion of volatile acids. The method is as follows : 



Five grams of the fat are weighed into an Erlenmeyer flask ; lOcc 

 of alcohol at 95 per cent, and 'Jcc of concentrated soda lye at 50 per 

 cent., which has been preserved in an atmosphere free of carbonic 

 acid, are added. The flask, furnished with a reflux condenser, is heated, 

 with occasional shaking, in a boiling water-bath for one-quarter of an 

 hour. The alcohol is then distilled off by allowing the flask to remain 

 for three-quarters of an hour in a boiling water bath. One hundred 

 cubic centimeters of recently-boiled distilled water are then added and 

 allowed to remain in the water until the soap is dissolved. The soap 

 solution is then immediately decomposed with 40cc of dilute sulphuric 

 acid (25cc sulphuric acid to 1 liter), and the flask immediately con- 

 nected with the condenser. This connection is made by means of a 

 7mm diameter glass tube, which, 1cm above the cork, is blown into a 

 bulb 2cm in diameter; the glass tube is carried obliquely upwards 

 about Gem and then beutobliquely downwards; it is connected with the 

 condenser by a not too short rubber tube. The flask is warmed by a 

 small flame until the insoluble acids arc melted to a clear transpar- 

 ent liquid. The flame is then turned on with such strength that within 

 half an hour exactly HOcc are distilled off. One hundred cubic centi- 

 meters of the distillate are filtered off, placed in a beaker glass, Ice 

 of phenolphthalein solution added and titrated with tenth normal ba- 

 rium hydrate solution when the red color is shown the contents of the 

 beaker glass are poured back into the measuring glass in which the 

 lOOcc were measured, again poured back into the beaker, and again 

 titrated with the barium solution until the red color becomes perma- 

 nent. The distillation should take place in as nearly thirty minutes as 

 possible. 



GENERAL DIRECTIONS FOR WEIGHING THE FATS FOR THE A15OVE DETERMINATION. 



The difficulty of measuring exactly 5 grams, as indicated above, is 

 considerable. Since the specific gravity of a fat at any given temper- 

 ature, say 35 or 40, is accurately known, I find it more convenient 

 to measure out into the Hask a volume of the melted fat which will 

 weigh approximately 5 grams. This can be conveniently done by a 

 graduated pipette, which should previously be warmed to a temperature 

 slightly above that of the melted fat with which it is to be used. Let 

 the specific gravity of the fat to be used at the temperature of measn i c- 

 " * Milch /.-iiiiiig, No. 25, 1888. 



