CONDENSED MILK 75 



difference; that is, subtracting the sum of the 

 other ingredients from the total soUds. This will 

 serve for ordinary inspection purposes, since 

 the amount present is almost always large, gener- 

 ally more than the total of milk-solids, and a 

 slight error does not affect the judgment as to 

 the wholesomeness of the sample. Exact work 

 requires, however, that the sucrose be de- 

 termined directly. Several processes have been 

 devised for the purpose. Sucrose exerts but 

 little action on Fehling's solution, but invert- 

 sugar acts powerfully, and some processes depend 

 on determining the reducing power before and 

 after inversion. Since the polarimetric reading is 

 also markedly changed by the inversion, the 

 difference in polarization may be employed. 

 Fermentation may be so conducted as to re- 

 move the sucrose (also any form of glucose) while 

 the lactose is unaffected. This method is chiefly 

 valuable for recognizing invert-sugar or either of 

 its constituents. 



Inversion Methods. — These must be such as to 

 secure prompt inversion of the sucrose without 

 affecting the lactose. Experiment shows that 

 citric acid and invertase are the most suitable 

 agents. Stokes & Bodmer have worked out the 

 citric acid method substantially as follows: 



25 c.c. of the diluted sample are coagulated by 

 addition of i% of citric acid, without heating, 



