440 ORD. XXV. Lomentacce. MIMOSA NILOTICAs 
those trees, which are situated near the equatorial regions; and 
we are told that in Lower Egypt the solar heat is never sufficiently 
intense for this purpose. The gum exudes in a liquid state from 
the bark of thé trunk and branches of the tree, in a similar man- 
ner to the gum which is often produced upon the cherry trees, 
&c. in this country; and by exposure to the air it soon acquires 
solidity and hardness. In Senegal the gum begins to flow when 
the tree first opens its flowers,* and continues during the rainy 
season till the month of December, when it is collected for the first 
time. Another collection of the gum is made in the month of 
March, from incisions in the bark, which the extreme dryness of 
the air at that time is said to render necessary.‘ 
Gum arabic is now usually imported into England from Barbary, 
not packed up in skins, which was the practice in Egypt and_ 
Arabia, but in large casks or hogsheads. The common appearance 
of this gum is so well known as not to require any description of 
it here; and the vartous figures which it assumes seem to depend 
upon a variety of accidental circumstances attending its transuda- 
tion and concretion. 
Gum Arabic of.a pale yellowish colour is most esteemed; on 
- the contrary, those pieces which are large, rough, of a roundish 
figure, and of a brownish or reddish hue, are found to be less 
pure, and are said to be produced from a different species of ' 
Mimosa: (M. Senegal) but the Arabian and Egyptian gum is 
commonly intermixed with pieces of this kind, similar to that 
which comes from the coast of Africa, near the river Senegal. 
Gum Arabic does not admit of solution by spirit or oil, but in 
twice its quantity of water it dissolves into a mucilaginous fluid, 
of the consistence ofa thick syrup, and in this state answers many 
useful pharmaceutical purposes, by rendering oily, resinous, and 
pinguious substances, miscible with water. 
4 Niebuhr Reisebesch. Arab. 1. B. p. 143. 
¢ Adanson Mem. de l’Ac. d Sc. d. Paris, 177. 3. p. 8. 
* Demanet Nouvelle Hist. de Afrique Francoise, t. 1. p. 56. 
* See Mr. French’s Experiments in Lond. Med. Observ. vol. 1. p. 413, &c. 
