68 



KEPOBT OF CHEMICAL LABORATORY 



exuded by ordinary trees, the Forestry Department was urged to furnish us with samples 

 of the two, collected at the same time, and from the same district, for purposes of 

 comparison. This req^uest has not been complied with, but a sample from a single 

 coppiced tree, kindly collected for us by Mr. E. S. Edie, was found to weigh only about 

 one-half of that exuded by an ordinary tree of about the same size. As only a single 

 tree has been tested the result must be taken merely as suggestive. The chemical 

 examination of the two gums yielded results as follows : — 



Gum from ordinary tree 



Moisture, per cent. 



Ash, per cent 



Acidity (mmtfs. KHO required to neutralise one fframme) 



Viscosity of 20% solution (degrees of retardation in torsion vis- 

 co.simeter) ... 



8-41 



•2-67 

 .3-38 



17-1 



Talk gum 



Tapping of 

 talk trees 



There is no marked difference in quality between the two gums, but both were 

 exceptionally weak as regards the viscosity of their solutions. 



As has been noted in previous Reports, hashah gum is only formed when the tree is 

 reduced in vitality, irsually as a result of the dryness of the soil. It might be expected, 

 therefore, that in the case of coppiced trees the greater root develojjment in proportion 

 to the size of the tree would result in increased vitality during the period of drought, 

 and consequently in lessened gum production. The single instance mentioned above 

 would appear to bear out this assumption, but many collections will have to be made 

 and examined before a reliable conclusion to this effect may be drawn. 



Talk gum.. This gum, which is the product of two varieties of Acacia seyal, is of 

 much less importance, commercially, than that of A. Senegal, to which it is inferior in 

 several respects ; the solution of the gum is less viscous than that of the hard variety 

 of hashdh gum, and further, on standing exposed to the air, it becomes dark in colour, 

 usually depositing a brownish-black precipitate. The gum is also more acid than is 

 hash/ih gum. 



A gum of much better quality may be had by selecting only the colourless pieces. 

 These yield a solution less acid and having little or no tendency to darken on exposure 

 to air. Colourless talk gum is found only in very small proportion in the product as 

 ordinarily collected. 



Tapping of talk trees. Talk trees are not tapped by the native gum collectors. At 

 our request an experimental tapping of these trees was carried out by Mr. S. A. Wood, 

 Inspector of the Woods and Forests Dept., with a view to determine whether the 

 quality or quantity of the gum was naturally improved. From the report made by this 

 official it ajjpeared that the quantity of gum exuded could be very considerably increased 

 in this way ; and, from the sample of such gum sent us, it appeared also that the quality 

 was even more markedly improved. In the Third Report of the Laboratories, page 436, is 

 found a comparison of the results of examination of this sample with that of ordinary 

 gum collected in the same district from untapped trees. Later investigations disclosed 

 the fact that for some unaccountable reason the sample furnished as gum from 

 tapped trees had been picked, all the darker particles being rejected. The comparison 

 of results referred to above was, therefore, rendered not only useless but misleading. 



