430 
KKPOKT OF CHEMICAL LAHOUATOIiA' 
Of the ganlens selected for experiments, tliat of Ali Nnr-ed-Din furnished the most 
complete series of results, since it was possible in it to secure suflicient of each grouji — 
small, medium and large—for the purpose. 
The following tables give the averages of results from the three classes of trees, and 
what may he taken roughly as a general average of the garden as a whole : — 
Large 
trees 
Medium 
trees 
Small 
trees 
Average yield of gum per tree ... 
l-OO 
1-3:! 
O.7.') 
Average acidity (milligrams potassium hydroxide) ... 
2-4.0 
2-74 
2-(11 
Average ash 
2.')(> 
2-'tl) 
2-‘J(l 
Average viscosity C Degrees of retardation iu torsion viscosimeter 
34-7' 
30-2" 
27-9' 
of 1 , 
20 per cunt. "l Qramaies of sug.ar, per 100 c.c. of solution, re(phrudi 
solution 1, to produce the same viscosity .1 
G2-3 
Gl-,') 
Gl-ii 
Average op ale trees in garden of Ali Nur-ed-Dis 
Yield ... ... ... . 
1-.33 
Acidity ... . ... . 
2-GO 
Ash ... . 
2-‘J4 
Viscosity of f Degrees of ret.Trd.atioii . 
30-9 
20 per oeiit. -1 
solution [ Sugar ctpiivaleut 
Gl-G 
Normal and 
abnormal 
viscosity 
Alteration on 
storage 
From the above results it will he seen that the proportion of harder glass-like gum 
varied considerably as the season advanced, and increased markedly towards the end. 
It is to he noted, however, that the harder gum was not the hard, strong gum, of high 
“ viscosity strength,” whicli was formerly found in Sudan mixed gum, and picked from 
it under the name of ‘‘Khartoum gum”; hut that the solution yielded by it was even 
weaker in viscosity than that of the softer gum. It is also evident that Sudan (and, 
as will he seen below, Senegal) gums exhibit in tlieir solutions two kinds of viscosity, 
one of them lieing false or abnormal. The latter is the form exhibited by certain samples 
which appear to dissolve completely in weaker solutions (5 to 10 per cent.), but in higher 
concentration yielding, especially on standing, a glairy mucus-like liquid, from which 
tliere separates a greater or less amount of true solution of lower viscosity. This behaviour 
ajipears to characterise the gum of early collections, more especially the harder tears, 
since when these were separated from the softer, and tested, the condition of comparative 
insolubility was found to persist in some cases up to the third collection, whereas the 
mixed gum is completely soluble, at least to all apjioarance, in 20 per cent, solution. 
The above facts point to the necessity of testing the solulhlity and viscosity of a 
gum in solutions of not less than 20 per cent. 
It was found that if the abnormal gums just mentioned are kept for a certain time 
they become perfectly soluble in solutions even of the highest concentration. In some 
cases (e.fj. that of a sample of Senegal gum) the alteration was found to have taken 
place at the end of about two months, hut more usually they require to be kept for 
three or four months. One sample required nearly two years, hut this was exceptional. 
The alteration, on storage, in the behaviour of the gum a^ipears to be due to molecular 
re-arrangement. This view is borne out by the results of Mr. Edie’s researches (ji-v.). 
The following results would appear to indicate that the behaviour just mentioned 
is a characteristic rather of the gum exuding as the result of tapping than of the 
