164 



On the Liquid Gim 



[March^. 



Nolliing is known, to me at least, respecting its history^ 

 except what the ticket attached to it conveyed The term guiUj 

 whicii is applied to it, seems to indicate that it has exuded 

 sportaneoiisiy from some tree or shrub ; but the properties of it 

 imnfiediately to be described. Fender this origin CKtremeiy pro- 

 blem ari<;al. it is an intermediate substance between the two 

 vegetable princij:;]es called exti'active and tannin by chemists. 

 Now no iosrance, so far as I know, of any species of extractive 

 or lannin having exuded spontaneously from plants can be pro- 

 duce? i. indeed^ they have all such a tendency to enter into 

 combination, and to form solid conipounds with other vegetable 

 principles, that the ^ plant from which any of them could exude 

 spontaneously in a state of purity must be of a very peculiar 

 nature. 



llie resemb\ oce between this liquid gum and kino was so 

 striking as tc induce rae to examine this last substance. The 

 portion of this drug which is soluble in alcohol is absolutely 

 identical with the solid matter of the liquid gum; but kino 

 contains several substances which are not to be found in our 

 gum. The most remarkable of these is a red substance, whicli 

 gives a red colour to water, and a still deeper tint to alkaline 

 leys, and which possesses the smell and taste of logwood. It is 

 well known that a part of the kino of the shops comes from 

 Botany Bay, as well as our gum ; arM from the striking similarity 

 between them, I think there is every reason to believe that both 

 of them are obtained from the same vegetable. 



The liquid gwn (for I shall employ that term, though by no 

 means proper, till v/e have ascertained its properties) has a red 

 colour, approaching to crimson, but considerably darker, it is 

 opake. It has a peculiar smell, and an astringent taste, without 

 the disagreeable intensity of the infusion of nutgalls. Its specific 

 gravity at 60° was only 1'196, Its consistence in the ordinary 

 temperature of the air is nearly the same with that of turpentine. 

 Like that substance, it is very tenacious, and may be drawn out 

 into very long threads. Vv^hen exposed to cold it becomes 

 harder; and when heated it becomes more and more liquid, till, 

 at the temperature of about 180°, it may be poured from one 

 vessel to another nearly as easily as water. If the phial containing 

 Jt be plunged into hot water, and kept corked, the v. hole gum 

 collects at the bottom, without leaving any stain upon the sides 

 of the phial ; but in the open air a solid skin almost immediately 

 collects on its surface. On allowing the gum to cool it becomes 

 as thick as at first. 



\¥hen a portion of the gum is exposed upon a plate of glass to 

 the open air, it gradually becomes solid, contracts in its dimen- 

 sions, and splits mto very regular fragments. The surface of the 

 gum, thus dried, is as smooth as that of sealing-wax; the 



