ON ALOINE* THE CATHARTIC PRINCIPLE OF THE ALOES. 281 
matter. When aloine is heated on platinum foil it melts, and 
then catches fire, burning with a bright yellow flame, and emit- 
ting much smoke. It leaves a somewhat difficultly combustible 
charcoal, which, when strongly heated, entirely disappears, not 
a trace of ashes being left. 
***** 
It has long been known to medical practitioners, that the 
aqueous extract of aloes is by far the most active preparation 
of that drug. The reason of this is now very plain, ^s the con- 
centrated extract of aloes obtained by exhausting aloes with 
cold water consists chiefly of aloine, by much the larger portion 
of the resin being left undissolved. Mr. Smith informs me, 
that, from a series of pretty extensive trials, from 2 to 4 grs. of 
aloine have been found more effective than from 10 to 15 grs. of 
ordinary aloes. Aloine is, I should think, therefore likely ere 
long to supersede, at least to a considerable extent, the ad- 
ministration of crude aloes. 
I endeavoured to obtain aloine by operating on considerable 
quantities of Barbadoes, Cape, and Socotrine aloes. These were 
macerated in cold water, and the aqueous solutions obtained 
were concentrated to the state of thin extracts on the water- 
bath. I was quite unsuccessful in every instance. The im- 
purities contained in the extracts in these different kinds of 
aloes appear, when in contact with the oxygen of the air, to act 
upon the aloine so as effectually to prevent it from crystallizing. 
Aloine can only, therefore, be obtained in a crystalline state by 
concentrating the cold aqueous solution of aloes in vacuo; 
though, after the aloine has once been crystallized, and it is freed 
from the presence of those impurities which appear to act so in- 
juriously upon it, the aloine may be quite readily crystallized 
out of its aqueous solutions in the open air. 
Though aloine has as yet only been obtained from Barbadoes 
aloes, I have scarcely any doubt that it also exists both in Cape 
and Socotrine aloes. The amount of aloine in Cape aloes is, 
however, in all probability, much smaller than in either of the 
other two species ; for Cape aloes is well known to be a much 
feebler cathartic, and to contain a mass of impurities. In cor- 
roboration of this opinion, I would refer to the fact already 
mentioned in a previous part of this paper, viz. that when aloine 
is digested with nitric acid, it is converted into Dr. Schunck’s 
chrysammic acid. Now, it has been satisfactorily ascertained 
that all the three species of aloes yield chrysammic acid, of 
which, in fact, they are the only known sources. Cape aloes, as 
might have been expected, yields by far the smallest amount of 
chrysammic acid, together with much oxalic and some nitro- 
VOL. XXIV. Q q 
