CONDENSED MILK 75 
difference; that is, subtracting the sum of the 
other ingredients from the total solids. 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 1% of citric acid, without heating, 
