386 Chemical Constitution of Starch [June-September 



To use Johnson's own words, — "As is seen, two dextrose 



molecules condense in a secondary group (HC. OH HO .CH) 



whilst the maitose molecules condense in the primary group 



(H2C.O IH HOI .CH2), the former becoming HC.O — CH and 



the latter HgC.O — CH2. The two aldehyde groups of the original 

 dextrose molecules condense in the amylin groups as is shown above. 

 This explains the non-reducing character of the starch." 



The suggested condensation of "primary" and "secondary" 

 OH groups in each sugar molecule has no experimental justifica- 

 tion. In my opinion it does not seem necessary to assume poly- 

 merization of the aldehyde groups to explain the non-reducing 

 character of starch. The disaccharide sucrose is not a reducing 

 sugar, yet we do not assume that the aldehyde groups of the con- 

 stituent monoses polymerize with one another. 



The latest attempt to construct a starch molecule, and probably 

 the most painstaking of any previous hypothesis, was brought out 

 by Synkiewski^'^ in 1902. His work consisted in studying the 

 products of hydrolysis of starch by infusions of malt, with exhaust- 

 ive investigation of the properties of the several dextrins isolated 

 therefrom. The starting point in his work was the isolation of 

 two dextrins, one called by him "protodextrin I" which was formed 

 by hydrolyzing starch at ordinary temperature ; and another, called 

 " protodextrin H," which was formed by the hydrolysis of starch 

 at 78° C. 



The preparation of protodextrin H was accomplished by allow- 

 ing malt extract to act on starch at about 78° C. until all starch was 

 hydrolyzed. The dextrin was then separated by evaporation of 

 the water, extraction with dilute alcohol to remove soluble carbo- 

 hydrate, and final precipitation with strong alcohol. The product 

 was a white amorphous powder which, after ultimate analysis and 

 by determination of the depression of the freezing point of water, 

 showed a molecular weight and structure equivalent to CgeHgaOsi 

 or (C6Hio05)6 + H20. This is similar to the formula for the 



1^ S3mkiewski : Ann. Chem., 1902, cccxxiv, p. 212. 



