NoTKS on TIIK ClIKMISTUY OF SuDAN (rUMS 
jn- 
K. S. Kdie, M.A., JJ.Sc. 
(Jurnegie Researcli Fellow 
On iny arrival in Khartoum, I found that the principal prohleni in connection with 
the chemistry of Sudan “Gum Arabic” was to discover the cause of the marked differences 
noticed hy Dr. Beam in certain physical properties of the gum, sucli as hardness and 
viscosity. These differences are discussed fully in Dr. Beam’s report. A second point 
of interest was to discover some sirecifio properties of each kind of gum, so that it would 
be possible, for example, easily to distinguish “ Hashab ” from “Talh,” “Sunt,” or any 
of the other gums occurring in the Sudan. This cannot be always done hy physical 
tests, such as viscosity. The literature on gums is comparatively scanty, and few observers 
mention more than the acidity, total ash, and optical activity of the gum. O. Fromnd 
goes into the question of the valuation of gum-arabic, giving special attention to the 
colour, viscosity, optical activity, and volume of insoluble matter. He found that some 
of the properties, such as viscosity of solution and acidity, decreased on keeping the gum 
for some time. Unfortunately, no mention appears to be made of the actual source of his 
samples, which are described chiefly by the commercial names, such as “ Kordofan ” or 
“Senegal” gum. 
Dr. Beam has mentioned that at the time when Fromm conducted his experiments 
there would be very little Hashab gum from Kordofan in the market, and some of the 
latter’s figures, for example, of optical activity, vary widely from those obtained hy me 
with gums of known origin. These differences will be referred to later. 
E. HefelmaniF determined the amount of pentoses in 25 samples of commercial Pentoses in 
gum-arabic, but not all from the same species of tree. He found no relation between 
the amount of pentoses and the trade value of the gum, and he also remarks on the 
fact that the viscosity is the best guide to the value of any particular sample. A few 
other observers have given figures with regard to isolated specimens of particular gums, 
mentioning acidity and optical activity, but there appears to have been little or no 
attempt to study the gum of any particular species of tree under varying conditions, 
such as soil, age of trees, or season of collection of the gum. Since, from the commercial 
point of view, the viscosity is the most important character of a gum, it is of great interest 
to iirvestigate the changes of viscosity, noting carefully differences in conditions as Changes in 
mentioned above, and to attempt to correlate these differences with variations in other 
physical and chemical properties of the gum. 
Dr. Beam has investigated the effect of the age of the trees, and the season of 
collection, in causing variations in viscosity and acidity in Hashab gum from the Sudan 
as completely as the samples obtainable would allow. 
Prom a chemical point of view, it seems at first sight probable that these variations 
in viscosity would be accompanied by corresponding variations in the various constituents 
of the gum molecule. The simplest way to test this seemed to be to estimate the 
proportions of pentoses and hexoses produced on hydrolysis of the gum by dilute acid. 
In gum-arabic arabinose is the pentose produced, and galactose the principal or only 
hexose. 
‘ Zeits. /. AnaL Chemic-t 1901, XL., p. 143. 
Zeits, f. offcutl. VhcmiCi VII., p. 195. 
