CONDENSED MILK. 61 



sugar-containing liquid is calculated by allowing for 

 the precipitated proteids and fat, as described under 

 the determination of milk sugar. 



SO c. c. of the filtrate are placed in a flask marked 

 at 55 c. c, apiece of litmus paper dropped in and the 

 excess of nitric acid cautiously neutralized by sodium 

 hydroxid solution. The liquid is then faintly acidified 

 by a single drop of acetic acid, (it must not be alkaline) 

 a few drops of an alcoholic solution of thymol added, 

 and then 2 c. c. of a solution of invertase, prepared 

 by grinding half a cake of ordinary compressed yeast 

 with 10 c. c. of water and filtering. The flask is 

 corked and allowed to remain at a temperature of 

 100° to iio°F. for 24 hours. The cane sugar will be 

 inverted while the milk sugar will be unaffected. The 

 flask is filled to the mark (55 c. c.) with washed 

 aluminum hydroxid and water, mixed, filtered and the 

 polarimetric reading taken. 



The rototary powers of cane sugar and dextrose 

 are not appreciably affected by temperature within 

 the limits of ordinary experiments. The same may 

 be said of milk sugar (see page 40). Invert sugar, by 

 reason of the levulose present, is materially affected 

 by the temperature. Thus, a solution of cane sugar, 

 which, before inversion, causes a rotation of + lOO an- 

 gular degrees, has after inversion, if observed at 32°F., 

 a rotation of — 44 degrees, a total change of 144; but 

 at70°F. the reading will be only — 33 angular degrees. 



