150 MILK AND DAIRY PRODUCTS PART 



evaporates, and it is not long before frothing of the contents of 

 the flask is noticed. In a few minutes (generally about seven) 

 the saponification is finished. To get rid of the last traces of 

 alcohol a current of air is blown in from the bellows and the 

 flask moved from side to side. The blowing in of air is repeated 

 each half-minute, after which the flask is again returned to the 

 water-bath. 



The alcohol may also be got rid of by fitting a rubber stopper 

 with two glass tubes into the flask and then attaching one of the 

 tubes to the water-pump so that a stream of air is drawn through, 

 the flask being kept in the water-bath. Air is drawn through 

 the flask until all the soap has become solid and does not swell 

 up when one of the glass tubes is closed and the pump makes a 

 vacuum in the flask. The soap which has been freed from 

 alcohol in the above manner is dissolved in 100 c.c. of distilled 

 water, and ought to give a perfectly clear solution. If this is not 

 so it is a sign of imperfect saponification, and the operation must 

 be repeated. After the addition of the water several pieces of 

 pumice stone, about the size of peas, are put into the flask and 

 40 cc. of dilute sulphuric acid (1 in 10), and it is attached to a 

 condenser of not less than 50 cm. in length. Exactly 110 c.c. 

 of liquid are distilled over into a flask provided with a mark at 

 this level ; the distillation should be completed within thirty 

 minutes. 



In this way the volatile soluble acids from the butter are 

 distilled over, and along with them are also some volatile acids 

 which are insoluble in water. To separate these the distillate 

 is shaken up and poured through a dry filter, and 100 c.c. of 

 the filtrate titrated with N/W caustic soda, a few drops of 

 alcoholic phenolphthalein being used as indicator. By adding 

 one-tenth to the number of cubic centimetres of caustic soda 

 which have been used, the amount required for the whole distillate 

 is obtained. The number of cubic centimetres of JV/10 caustic 

 soda is known as the Reichert-Meissl number. 



Leffmann and Beam l have worked out a modification of the 

 method, arid at the present time this is used more extensively 

 than the original. In carrying out this modification, 5 g. of fat 

 are weighed out as before in a 300 c.c. round-bottomed flask of 

 Jena glass, and then 20 c.c. of pure glycerine and 2 c.c. of caustic 



1 Chemiker-Zeitung, No. 62, p. 607. 



