CONDENSED MILK 79 



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 phosphoric acid. 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 2 5° 

 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 



