ACACIA VERA. 
179 
cuously: gum arable, which comes from Barbary and the Levant, by 
way of the IVIediterranean, and East India gum. In Egypt and 
Arabia it was formerly the custom to pack this gum in skins, but it 
is now usually imported into England in large casks. 
The best gum arabic consists of roundish transparent tears, co- 
lourless, or of a very pale yellow, or amber colour ; it has a shining 
fracture, without smell or taste, and is perfectly soluble in water ; 
the pieces which are most transparent and colourless are sometimes 
selected from the rest, and sold for about double the price, under 
the name of picked gum. The large, rough, and reddish, or brownish 
gum, is said to be produced by a dilFerent species of tree, but the 
Arabian and Egyptian gum is commonly intermixed with pieces of 
this kind. The East India gum is darker coloured than gum 
arabic, and not so soluble in water. 
Sensible and Medical Properties. By exposure to heat, 
gum arabic softens and swells, but does not melt ; it emits air 
bubbles, blackens, and finally, when nearly reduced to charcoal, 
burns with a low blue flame. After the gum is consumed, there re- 
mains a small quantity of white ashes, composed chiefly of the car- 
bonates of lime and potash. The vegetable acids dissolve this gum 
without alteration, the strong acids decompose it. Chlorine, 
according to the experiments of Vanquelin, converts gum into nitric 
acid ; if nitric acid be slightly heated on gum till it ha^ dissolved it, 
and a little nitrous gas is exhaled, the solution, on cooling, deposits; 
saclactic acid. Malic acid is formed at the same time, and if the 
heat be continued, the gum is at last converted into oxalic acid, 
developing no less than three acids by the action of nitric acid on 
the gum. 
According to Vanquelin, gum contains traces of iron, and he con- 
jectures that the lime which it contains is usually combined with 
acetic or malic acid. Berzelius analysed it by burning it along with 
chlorate of potash, and gives the following as the result.* — 
Oxygen 51.306 
Carbon 41.906 
Hydrogen 6.788 
100. 
Gum arabic is insoluble in spirits, oil, and ether ; but readily dis- 
solves in twice its weight of boiling water, forming a simple mucilage, 
* Thomson's Chemistry, vol. iv. p. 36. 
