ON ALOINE. 
289 
water-bath. I was quite unsuccessful in every instance. The 
impurities 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 injuriously upon it, the aloine may be quite readily crystal¬ 
lized 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 chry- 
s'ammic acid, together with much oxalic and some nitropicric 
acids. There appears, therefore, great reason to believe that 
all the three kinds of aloes contain aloine. 
Since the above was written, I have learned from Mr. Smith 
that he has not succeeded in obtaining crystallized aloine from 
either Cape or Socotrine aloes. Mr. Smith does not doubt that 
both of these species of aloes also contain aloine, though most 
probably contaminated with so much resin, or some other sub¬ 
stances, as prevents it from crystallizing. What tends to con¬ 
firm Mr. Smith in this opinion is the observation he has made, 
that, when the crude crystals of aloine are allowed to remain in 
contact with the mother-liquor of the Barbadoes aloes, they dis¬ 
appear and become uncrystallizable. I have also observed a 
similar occurrence in the mother-liquors of tolerably pure aloine. 
These become always darkerand darker; so that if we continue 
to dissolve new quantities of aloine in them, at length scarcely 
any of it crystallizes out, and the whole becomes changed into 
a dark-coloured magma. 
In the year 1846, M. E. Robiquet published an account of an 
examination he had made of Socotrine aloes. By treating the 
concentrated aqueous solution of this species of aloes with basic 
acetate of lead, he obtained a brownish yellow precipitate, which 
was collected on a filter and washed with hot water. On de¬ 
composing this lead compound with sulphuretted hydrogen and 
