240 GAMBOGE. GUM- ARABIC. 



kinds of trees, growing in Ceylon, Siam, and Cochin China. It 

 flows out in a liquid form, when incisions are made in the bark, 

 and is afterwards made solid by the heat of the sun ; but it also 

 occasionally exudes from the surface in tears. When rubbed 

 with water, it forms a bright yellow fluid, which is much em- 

 ployed in water-colour drawing ; the water dissolves the gum, 

 whilst the resin remains suspended in the form of very minute 

 particles, which may be seen with the microscope. The whole 

 is dissolved in spirit of wine ; and this solution is used as a lac- 

 quer, to heighten the colour of brass- work, by its golden hue. 

 Gamboge is also a powerful medicine, having a violent purgative 

 effect ; and with aloes it is the principal active ingredient, in the 

 nostrum known under the name of M orison's Pills.* 



379. The true Gums may next be noticed; these are distin- 

 guished from the previous substances, by their being entirely 

 soluble in water, whilst spirit of wine does not act upon them. 

 Their solution in water is a thick adhesive fluid, which is used 

 for many purposes in the arts. It serves to unite substances 

 together, in the same manner as glue ; and may be used in cases 

 where heat is undesirable. Its chief employment, however, is in 

 calico-printing, being used to stiffen the cloth before the colours 

 are applied, so that they are prevented from running into each 

 other and becoming indistinct. As all trees contain gum in their 

 sap (. 328), it might be obtained in some degree from any ; but 

 it naturally exudes in large amount from some kinds, which, 

 therefore, yield it most readily when incisions are made in the 

 bark. The kind of gum termed Gum Arabic, which is the one 

 most valued, is obtained from a species of Acacia, which flourishes 

 in almost every part of Arabia and Middle Africa ; but it is only 

 in the hottest regions, that the gum is produced in much abund- 

 ance. "When the tree first opens its flowers, the gum begins to 

 exude spontaneously from the bark of the trunk and branches ; 

 in the same manner as it is often seen to do from the cherry-tree 



* Tt is probably to the bad mixture of the ingredients, by which an undue pro- 

 portion of this active substance has been contained in a particular batch of pills, 

 that some of the deaths which have occurred from their use, are to be attributed ; 

 and in other instances they have resulted from the enormous number of pills taken. 



