RKPOET OF CHEMICAL LABORATORY 
445 
It will be seen that the rotation of the Senegal gums is practically the same as the 
Kordofan samples, and some specimens which had been in the laboratory for two years also 
showed the same rotation. The gums mentioned differ slightly in moisture and ash, 
hut the differences would only affect the rotation to a slight extent. I attempted to 
prepare a sample of the free gum-acid from some selected strong gum from Kordofan by 
acidifying and then dialysing, but found that a trace of calcium was still left, and after 
evaporating the gum-acid solution to dryness it did not very readily dissolve, probalily 
owing to some change taking place in the drying process, which was completed at about 
105“ in an air oven. On hydrolysis of some of the acid, however, it was found to give a 
rotation of + 5-64°. There was still about 4-7 per cent, of moisture in this acid. 
The rotation of the gum after hydrolysis throws considerable light on the question of 
the constancy of different samples of Hashab gum, as shown by the ordinary methods 
of investigation. All soluble arahin gums, to which references are made in the literature 
available, have been found to be hydrolysed by dilute sulphuric acid into arabinose and 
galactose. I confirmed this in the case of a few specimens of Hashab gum by examining 
the osazones produced on precipitation with phenylhydrazine acetate, but I did not 
examine any of the series systematically in this way, thinking it unnecessary to do so. 
The rotation of a 10 per cent, solution of these series of gums after hydrolysis, however, 
taken into consideration with the proportions of pentoses and hexoses, points, I think, 
clearly to the fact that the individual pentoses and hexoses are present all through—the 
specific rotations of the different sugars varying widely. Thus, at ordinary temperatures, 
the [n]i, of arabinose is about + 104-4°; of xylose, + 18-5°; of galactose, +81-4° — these 
values varying slightly according to temperature and concentration. 
Before discussing the differences in hardness and viscosity further, it may be of 
interest to give a few determinations of the inorganic constituents of Hashab gums. The 
ash is usually stated to consist of lime, potash and magnesia, but I do not remember seeing 
the proportions in which these occur recorded. The amount of total ash varies slightly in 
different samples, owing partly to the fact that more or less of the calcium carbonate is 
decomposed by the high temperature at which the gum was incinerated. In no case did 
I find any phosphates, sulphates or chlorides in the ash. 
The figures given are grammes of the metals in 100 grammes of gum. 
Kind of Gum 
Magnesium 
Potassium 
Calcium 
Kordofan .strong glassy gum. 
0-257 
0-710 
0-773 
Kordofan “ illeached ” gum 
0-2GG 
0-596 
0-779 
Kordofan gum, giving ropy solution ... 
0-212 
0-661 
0-818 
Uopy gum from different locality 
0-198 
0-730 
0-785 
Senegal gum, f/ms\s*c 
0-18.5 
0-763 
0-70G 
From 30 middle-sized trees ... 
n-24G 
0-6.38 
0-687 
n j> 5j ••• • • • • • • • • • 
0-281 
0-614 
0-G64 
n js n • • ■ ■ • • • • • • 
0-292 
0-6G9 
()*n58 
The last three samples of gum were from the garden of .-Mi Nur-ed-Din, and re])resent 
the first tliree collections. The ash of all these gums contains a very small quantity of 
silica also. It will be seen that in spite of considerable diff’ei'ences in the source and 
Inorganic 
constituents of 
Hds/iob gums 
