Chemistry. — "On Milk-Sugar'. I. By Prof. A. Smits and J. 

 Gillis. (Communicated by Prof. S. Hoogewerff). 



(Communicated in tiie meeting of Jnne 30, 1917). 



1. Introduction. 



When in 1880 Schmoeger ^) and Erdmann *) began their investigations 

 about milk sugar, besides the iiydrate, an anhydride was known, which 

 was obtained by heating the hydrate in a drying stove at J 25°. 

 Later on this anhydride, in contradistinction to another anhydrous 

 modification, was called the «-form. This other anhydrous modifi- 

 cation, the ^?-form, was obtained by Schmoeger and Erdmann by 

 evaporation of a saturate solution of milk sugar at the boiling 

 temperature (± 108°). 



That this was another anhydrous modification than the «-form 

 followed from this that while the «-modification is very hygroscopic, 

 gives a clear generation of heat when brought into water, and 

 yields a solution, the optic rotatory power of which decreases with 

 the time, the ^-modification on the contrary is not hygroscopic, 

 dissolves under heat-absorption and yields a solution, the rotation of 

 which decreases with the time. 



Hudson *) was the first to consider the problem offered by the 

 milksugar, from a physico-chemical point of view. He demonstrated 

 that whatever form of the milk-sugar is dissolved in water, the 

 final condition is always the same, and represents an equilibrium. 



Hudson showed furtlier that the muta-rotation has the same course 

 as a mono-molecular reaction - he determined on one side k^ -f k^, 

 on the other side k,, and thus found k^ indirectly ; in this way lie 



k 

 got K' =^ — \,Q for the constant of equilibrium at 11°,2. 



Hudson started from the supposition that the hydrate possessed a 

 high rotation, and the /^anhydride a low rotation, and he was of 

 opinion therefore that the said equilibrium was to be represented by 

 the equation : 



1) Berichte 13 1915 (1880). 



2) Berichte 18 2180. 



») Zeitschr. Phys.-Ghem. 44 487 (1903). 



