CONDENSED MILK 719 
the reducing methods, and if the sum of it and 
the amount of sucrose obtained by inversion is 
equal to that obtained by the direct reading of 
both sugars before inversion, no invert-sugar is 
present. If the amount of reducing sugar seems 
to be too great, the lactose must be re-determined 
as follows: 250 grams of the condensed milk are 
dissolved in water, the solution boiled, cooled to 
80°, a solution of about 4 grams of glacial phos- 
phoric acid added, the mixture kept at 80° for 
a few minutes, then cooled to room temperature, 
made up to mark, shaken, and filtered. It may 
be assumed that the volume of the precipitate 
is equal to that obtained by mercuric iodid solu- 
tion. Enough sodium hydroxid is then added to 
not quite neutralize the free acid, and sufficient 
water to make up for the volume of the solids 
precipitated by the phosphoricacid. The mixture 
is then filtered and the filtrate is measured in 
portions of 100 c.c. into 200-c.c. flasks. A 
solution containing 20 milligrams of potassium 
fluorid and half a cake of compressed yeast is 
added to each flask, and the mixture allowed to 
stand for ten days at a temperature between 25° 
and 30°. Invert-sugar and sucrose are fermented 
and removed by the yeast in the presence of a 
fluorid; lactose is unaffected. The flasks are filled 
to the mark and the lactose determined either 
by reducing or by the polariscope. The amount 
