I9I5] Arthur W. Thomas 383 



The ordinary combustion method would fail to reveal the pres- 

 ence of one HgO-group in a molecule o£ this size. This difficulty 

 was surmounted by the oxidation of this dextrin by mercuric oxide 

 to a dextrinic acid, which, in turn, was precipitated by Hme to form 

 the calcium salt. This salt contained the theoretical amount of 

 calcium, 0.3 percent; and, upon hydrolysis, yielded the correct 

 amount of glucose. As previously mentioned, the earlier work of 

 Brown and Heron resulted in the Suggestion of the equation, 



10 C12H20O10 + 8 H2O -^ 8 CisH.aOii + 2 C12H20O10, 



Maltose Dextrin 



as a correct representation of hydrolytic changes. 



Inasmuch as this newly discovered dextrin could not be repre- 

 sented by a formula simpler than 40 CqR-^qO^ + HgO, it was neces- 

 sary to modify the above equation to allow f or it, as follows : 



I GoC 12H20O10 + 8 1 H20-^8oCi2H220ii + 



(CeHioOsjag 

 I 

 . C6H12O6 



If this equation holds, then the starch molecule must be at least five 

 times the size of the dextrin molecule. Now, the molecular weight 

 of the dextrin is 6498 or 6480 + 18; therefore, the weight of the 

 starch molecule is at least 32,400, equivalent to ( CgH 1005)200- 

 (In 1889 Brown and Morris had found that the freezing-point 

 method indicated a molecular weight, for soluble starch, of about 

 20,000 to 30,000.) 



Since starch is non-reducing it has no free carbonyl group and, 

 hence, the simplest manner, to quote- Brown and Miliar, " to ex- 

 press its constitutional form with due regard to all facts is to con- 

 sider it made up of the residues of eighty maltan and forty dextran 

 groups linked in a ring form by means of oxygen atoms. On hy- 

 drolysis the dextran complex is split off with the formation of 

 Stahle dextrin, whilst the maltan part of the ring is attacked at the 

 oxygen linkings of the Cjo groups, hydrogen ions of reacting water 

 moving in one direction and hydroxyl ions in another, thus forming 

 by successive stages of hydrolysis, maltodextrins and maitose." 



This reasoning seems to be logical and, if the experimental re- 



