529 



a 

 mination of the initial and the final rotation the ratio was found. ) 



In the determination of the final rotation use was made of the 

 positive catalytic influence of a drop of a solution of ammoniac. 



Is is clear that when the ratio - is given, it is not stated that the 



molecules of the two modifications « and ^ really occur in perfectly 

 unhydrated condition in the solution; it only expresses what the ratio 

 is between the concentration of « and /?, leaving it quite an open 

 question in how far these molecules are hydrated. 



Thus also the point D was determined, which is the point of 

 intersection of the isotherms of the (i,^^ and of the (^^-modification. 



It has already been ascertained by Hudson whether the situation 

 of the equilibrium between a and /? in solutions of ditFerent total 

 concentration shifts with the concentration. The result was that the 

 equilibrium a"^^ does not change on dilution of the solution, as 

 was indeed to be expected in dilute solutions, as we have there to 

 do with isomers. We can, therefore, represent these equilibria in our 

 triangle by a straight line starting from the point H^O. 



As it had appeared that «„^ below 93°, 5 is the stable solid phase 

 in the system water-milksugar, it was certain that the said line for 

 the homogeneous equilibrium would have to intersect the isotherms 



of aaq. 



This point of intersection is now determined by shaking aaq with 

 water for 2 or 3 days at 0° with the aqueous solution. On analysis 

 of this solution in the same way as this had been done with the 

 liquid D the point L was fourtd lying on the isotherm of «o^. Hence 

 the phases ««^ and L and the homogeneous equilibrium line H,0 — E 

 denote the binary equilibrium system water-milksugar at the existing 

 temperature. 



Now it is clear that the observations must show that at 93°, 5 

 the equilibrium line H,0 — E must pass through the three-phase 

 point D as Fig. 5 expresses, so that then ftay -{- [i ± L can coexist 

 in the binary equilibrium system. 



1) The ratio between initial rotation ry and final rotation r» was determined 

 at 0° for hydrate and jj-anhydride mixtures of different concentration. The gra- 

 phical representation of this gave a straight line, which enabled us, not only to 



. ^ ^'o 



determine the ratio — from — , but also to find the accurate value of the equi 

 a r 



librium-constant K' at 0, because K' = — , when — = 1 . 



« roo 



K' = 1,65 was found. 



