548 Mr Robinson, The Adsorption 



The Adsorption of Acids by Carbohydrates. By F. Robinson, 

 B.A. (Communicated by Dr Fenton.) 



[Read 23 May, 1910.] 



The action of acids, especially hydrogen chloride and hydrogen 

 bromide, on carbohydrates has been studied by many chemists 

 and it now appeared desirable to investigate the nature of the 

 reaction of the various carbohydrates with the above-mentioned 

 acids, in order to determine whether the initial phenomenon was 

 one of adsorption, or chemical action, or both, and if possible to 

 devise a method of characterising the various carbohydrates with 

 reference to the capacity of each for absorbing the acid in 

 question. 



In 1809, Bouillon-Lagrange and Vogel (Ann. de Chim. 70, p. 91) 

 showed that cane sugar, when boiled with aqueous hydrogen 

 chloride, became coloured and that only a small percentage of the 

 acid remained combined. 



Similar experiments were conducted by Vogel (Ann. de Chim. 

 82, p. 158) with starch, milk-sugar and hj^drogen chloride, but the 

 product did not contain acid in combination. 



Afterwards, Emil Fischer investigated the action of hydrogen 

 chloride at low temperatures on various sugars, and isolated the 

 substances known as 'chlorhydroses.' 



In 1898, Fenton and Gostling (Journ. Chem. Society, 1898, 

 p. 554) observed that levulose with ether and dry hydrogen 

 bromide almost immediately gave an intense purple colour: further 

 investigation showed that the ether had nothing to do with the 

 formation of the colour, since the dry solid absorbed the gas to 

 give the same purple colour. This reaction, with ether and hydro- 

 gen bromide, was repeated with various carbohydrates, which were 

 found to fall into four distinct groups. 



(a) With ketohexoses, such as fructose, sorbose, a purple 

 colour appeared after a few minutes and became very intense in 

 about one hour: and substances which, by hydrolysis, are capable 

 of giving rise to these compounds [cane sugar, inulin] gave a 

 similar effect but rather more slowly, the maximum intensity of 

 colour being attained in about two hours. 



(b) Hexaldoses (dextrose, galactose) and substances capable of 

 giving rise to them (maltose, lactose, dextrin) showed in the first 

 instance various shades of yellow, brown, or red and it was only 

 after long standing that the purple colour was apparent. 



The colour never approached that of the first group either in 

 brilliance or intensity. 



