42 THE CARBOHYDRATE ECONOMY OF CACTI. 



blood charcoal and the mixture was heated on the water-bath. After such 

 treatment the solution could be easily filtered and the filtrate was light 

 brown in color. As has been described, the disaccharides in this mixture 

 were determined by hydrolysis with hydrochloric acid and the determina- 

 tion of the cupric reducing value. The amount of maltose was exceedingly 

 small, as was indicated by the fact that the difference was very little between 

 solutions hydrolyzed with hydrochloric acid and with an invertase prepara- 

 tion. Equal amounts of the same sugar solution were treated, the one with 

 hydrochloric acid in the manner already described, the other with a solution 

 of invertase. 1 Thus 100 c. c. of the solution hydrolyzed with acid required 

 22.20 c. c. copper solution, while the same amount treated with invertase 

 took 23.30 c. c. 



The presence of glucose and fructose in the alcoholic extract was also 

 established, as in the case of the hydrolyzed portion. The mixture was 

 fermented with baker's yeast in the usual manner in order to determine the 

 nature of the pentose sugars. By treatment with phenylhydrazine-hydro- 

 chloride and sodium acetate, phenylxylosozone was obtained, which was 

 purified by recrystallization from methyl alcohol. The specific rotation of 

 the pure gum was found [a] * =-{-19.0 to -j-21.0 from several prepa- 

 rations. Here, however, a difficulty was encountered. After the aqueous 

 solution of the gum had stood for 24 hours it no longer showed the same 

 specific rotation, but had dropped considerably, and in a few cases had even 

 become levo-rotatory. In the cause of this phenomenon lay the substantia- 

 tion of the theory of pentose formation which had been previously formu- 

 lated and which is discussed in the section on the pentose sugars. This 

 reduction of the specific rotation (as was finally established) was caused by 

 glucuronic acid. The specific rotation of 1-xylose is [a]*, = +20, that of 

 glucuronic lactone is given by Fischer as [a]!) ^ -f- 19. 1 . 1 



A portion of the gum which showed this property of decreasing the 

 specific rotation on standing in water solution was thoroughly dried by 

 evaporating the water at reduced pressure from a boiling water-bath. The 

 flask containing the gum was allowed to remain open for several months 

 during the hot, dry summer. The gum was then dissolved in hot water and 

 treated for 5 minutes with blood charcoal. After filtering, the water was 

 again distilled off at reduced pressure. During this process small pure- 

 white crystals separated out from the solution, and considerably more of the 

 same substance crystallized out on cooling. This was filtered off and dried 

 in vacuum over sulphuric acid. The substance showed the following 

 properties : in water solution it reduced Fehling's solution strongly ; when 

 heated with 12 per cent sulphuric acid, furfural was liberated freely; it 

 gave the red color with 2 per cent phloroglucine and hydrochloric acid; 



1 For this purpose the best invertase preparation was obtained by the process 

 described by W. A. Davis, in The use of enzymes and special yeasts in carbo- 

 hydrate analysis. Jour. Soc. Chem. Ind., 35, 201-240, 1916. 



' FISCHEB, E., and O. PUXXTY. Reduction der Zuckersaeure. Ber. d. deut chem. Ges., 

 24, 523, 1891. 



