of Barbadoes Aloes. 485 



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, as the 

 concentrated 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 in- 

 forms 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 consider- 

 able extent, the administration 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 ob- 

 tained were concentrated to the state of thin extracts on the 

 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 crystal- 

 lizing. 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 crystallized out of its aqueous solutions in the open 

 air. 



Though aloine has as yet only been obtained from Barba- 

 does 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 im- 

 purities. In corroboration 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 con- 

 verted 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 nitropicric acids. There appears there- 

 fore 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 



