578 



unsnbstitiited sugars, but also for the glucosides, the acetates, the 

 hydi-azons, and the compound sugars, so that this gives a verv 

 weighty support to the validity of the assumed structure for the 

 a- and i:?-modifications. 



Hudson, however, has overlooked a very important point as far 

 as the structure of the sugar mono-hydrates is concerned. 



In this he has not been very consistent, as he assumes e.g. for 

 the sugars lactose, glucose, arabinose, and galactose as rotation for 

 the «-modification (a rotation which is not directly to be determined 

 because the «-modification of those sugars passes into hydrate on 

 contact with water), that calculated from the rotation of the hydrate, 

 for which he gives the structure as follows e.g. for glucose: 



CH.OH. OHOH.CHOH.CHOH. CHOH. CH(OH),. 



This formula cannot be correct, as in this way the asymmetric 

 final carbon atom of Tollens's formula disappears, which means 

 that the rotation of this hydrate will no longer be A -{- B, but 

 only B' , which quantity is equal to the algebraic sum of the rotations 

 of the asymmetric carbon atoms indicated by X : 



CH,OH . CHOH . CHOH . CHOH . CHOH . CH(OH,) 

 Ö y ^ a 



and this sum is no longer equal to B, because the asymmetric 

 carbon atom has changed now too. 



The observed regularities for the aldoses are, therefore, no longer 

 to be explained in this way. We should e.g. have for glucose: 



«-hydrate: B' \ sum 



i?-anhydride : — A -[- B \ — A -\- B -\- B' 



On the other hand we have e.g. for the ethylglucosides « and i? 

 (both anhydrides) 



«-ethyiglucoside : -\- A' -\- B j sura 

 ^-ethylglucoside : — A' + B \ 2B 



Hence the sum of the molecular rotations of the « and ^ glucose 

 cannot be equal to that of the a and the /? ethyl glucoside, 23200 

 and 25230 being found, hence a pretty good agreement. The same 

 thing holds for galactose and ethyl galactoside, for which is found 

 34700 and 36400. 



For other glucosides e.g. meth} i-d-glucoside, raethyl-d-galactoside, 

 and methyl-d-xyloside, of which the t?-modifications of the two first 

 contain resp. { H^O and 1 H,0, and of the third the a and ^ 

 modifications are anhydrous, Hudson's law holds good in spite of 



