575 



It should be pointed out here that the shape of the surface of 

 equilibrium could be derived from the una! solubility of Sx and *S^3 



from 0° to 170°, and further from the projection of this line on 

 the ground plane over the temperature range 0° to 100°. 



Theory of the inutarotation. 



On the ground of the new views to which we were led by our 

 experimental investigation, we now arrive at a theory on muta- 

 rotation which is essentially ditFerent from that drawn up by 

 Hudson. 



As follows from the here given explanation of the behaviour of 

 the system water-milksugar, this system must be considered to be 

 pseudo ternary, in which water is then a component and a and /? 

 milksugar are the pseudo components. From this it follows imme- 

 diately that it must be assumed that these different sorts of molecules 

 occur side by side in the liquid [)hase, in which the phenomenon 

 of the mutarotation takes place. We know further that for 'milk- 

 sugar a hydrate ctaq is known in solid state. This alone would 

 already point to the presence of this hydrate also in the solution, 

 for which, as we have seen, other phenomena plead too. 



Now it is evident that when the «-anhydride can combine with 

 water to a hydrate, this will also be the case with the /?-modifica- 

 tion. That we do not know this hydrate in solid state, does not 

 plead at all against this assumption, for this tells us only in this 

 connection, that the solubility of the {-iaq must be greater than that 

 of ^?-anhydride, which is just the reverse for the other pseudo- 

 component. 



In favour of the assumption of /i^,, in the solution pleads further 

 that for maltose, a substance which also presents mutarotation, the 

 ^nq is known in solid state ^), but the Haq is not, and also that here, 

 therefore, we find exactly what is still wanting for the milk sugar. 



We assume, therefore, that in the aqueous solution the following 

 equilibrium sets in : 



« + H,0 ^ «ay 

 it It 



/? + H,0 :;^ ^.aq. 



In this symbol there are two conversions of which we can say 

 that they take place with great velocity. 

 First the reaction 



1) J. Amer. Soc. 31 76 (1909) en 32 p. 894 (1910). 



42^ 



