522 



The following results refer to 1 gram of anhydrous milk sugar 

 and to the temperature of 20°. 



aaq (solid) -^ a„,i (dissolved) — 12,6 cal. (initial heat of solution). (1) 



i? ( „ ). ^? ( „ )- 2,3 „ „ . (2) 



a { „ ) -^ ct^„i ( „ ) + 7,3 „ (hydration heat + inital 



heat of solution of Uaq)- (3) 

 «„,/ (dissolved) -^i? ( „. ) + 1,05 „ (heat of transformation 



in solution ^). (4) 



From these data the following calculation can be made; 



from (1), (2), (4) : a„^ (solid) -^ /? (solid) + H,0 - 9,25 cal. . (5) 

 from (1), (3) : (I (solid) + H,0 -^ «„,, (solid) + 19,9 cal. . (6) 

 from (5), (6): « (solid) -^ ^ (solid) + 10,75 cal (7) 



In these determinations Hudson found also that the difference 

 between initial and final heat of solution, both starting from 

 «-anhydride and from hydrate, had exactly the same value, from 

 which, therefore, follows that «-anhydride in contact with water 

 hydrates immediately, and that then the following slow conversion 

 takes place : 



Hydrate -^ ^-Anhydride + H,0. 



We also come to the same conclusion when we consider that 

 «-anhydride and hydrate show the same initial rotation. 



Hudson has also determined the temperature where the trans- 

 formation of hydrate to /i-anhydrate takes place, i.e. he determined 

 ihe temperature at which the coexistence Sh -\- S^ -\- L occurs. 



From the final solubility of the hydrate between 0° and 89° and 

 from two final solubilities (0° and 100°) of the /^-anhydride followed 

 92° as transformation temperature. *) 



He further determined this point from the intersection of the 

 three-phase lines of Sh -\- L -\- G and Sh -\- S^-\- G, and then 

 the temperature of the quadruple point Sh + S^i -\- L -\- G was 

 found at 94°. 



Attempts to determine the transformation point thermically and 

 dilatometrically proved unavailing, because of the exceedingly small 

 velocity of conversion. 



On the ground of these data Hudson in 1910 drew up a general 

 theory of muta-rotation ^), which for all sugars can be given 

 schematically as follows : 



') in this the situation of the equilibrium at 20° has been taken into account. 

 2) J. Amer. Chem. Soc. 30 1775 (1908). 

 S) J. Amer. Chem. Soc. 33 893 (1910). 



