579 



this, though the rotations of these substances are faken as if they 

 were really anhydrous. 



It is therefore evident that the optical superposition takes place 

 here whether these substances contain water or not, and that for 

 all the" asymmetric final carbon atom with the lacton ring occurs. 



Accordingly we arrive at the result in this way that for the 

 unsubstituted aldoses e.g. glucose, galactose, milksugar etc. the presence 

 of H^O does not change amy thing at all in the structure of the 

 asymmetric final carbon atom. 



No more, therefore, than for methyl glucoside will the water be 

 bound to the tinal carbon atom in glucose itself. We may now 

 question how it is that Hudson notwithstanding this inconsistency, 

 has arrived at satisfactory results. The answer to this question is 

 very simple. In his calculations for the rotation of the anhydride 

 Hudson has namely taken the rotation of the hydrate, which is 

 only allowed when the water is bound in such a way that it 

 cannot influence the rotation of the final carbon atom. 



If e.g. milk sugar hydrate is a molecular compound of C,, H,, On 

 with one mol. of water, and quite to be compared with CuSO^H,0, 

 tlien it is clear that the water bound to the sugar molecule does 

 not affect its rotation or only very slightly. If we, therefore, know 

 the rotation of c^-milksugar hydrate, this rotation is the same as 

 that of milksugar anhydride, as nothing has been changed in the 

 grouping of the active carbon atoms, and thus it may be understood 

 that though Hudson has executed his calculations with the rotations 

 of hydrates, they have yet led to good results; but in this way it 

 has been proved very convincingly that the hydrates do not contain 



the group — C jj 



SUMMARY. 



The results of this research may be summarized as follows: 



1. The final solubility curve was determined between 89° and 

 200°, starting both from /^-anhydride and from «-anhydride, and 

 this curve, in connection with Hudson's determinations, proved the 

 existence of a break at 93°. 5. 



2. From the fact that «-anhydride is always converted into 

 /i-anhydride above 93°. 5, and also from the melting-points of «-anhy- 

 dride (222°. 8) and of ^-anhydride (252°.2) determined for the first 

 time follows with certainty that above 93°. 5 the «-modification is 

 metastable. 



