278 ON ALOIN, THE CATHARTIC PRINCIPLE OF THE ALOES. 
was very small ; but the thick liquid which had been washed 
with the ether, after standing undisturbed for a week or two, 
was found to have yielded a crystalline crop of aloin consider- 
ably more abundant. 
The nature of the process by which the presence of aloin in 
the Socotorine aloes was tested by us was somewhat different 
from the preceding. A strong alcoholic tincture of the aloes 
having been prepared, sulphuric ether was added as long as any 
precipitate was produced. A dark-coloured compound of lime 
being thus taken out of the way, the ethero-spirituous solution, 
after becoming quite clear, was mixed with a small quantity of 
water. The result was a separation of the mixed liquids into 
two distinct portions: the one heavier, composed of most of the 
water and spirit and a little ether, forming the under portion; 
and the lighter, consisting principally of ether, but containing a 
little spirit and water, floating above it. The heavy liquid, 
having been separated, was exposed to a heat of about 130° 
Fahr. till the spirit and ether had completely evaporated. The 
watery solution now left on cooling gave crystals having the 
characteristic appearance of aloin, and a trial strengthened this 
belief of their nature. The lighter liquid, on slow evaporation, 
likewise produced similar crystals. 
The solutions of aloin are wonderfully altered by the action 
of the air. One striking experiment made by us will perhaps 
place this character of aloin in as strong a light as any that 
could be stated. Two grains of aloin having been dissolved in 
two ounces of distilled water, the solution, which was of a very 
pale yellow colour, was corked up in a phial that was nearly 
filled with it, and then set aside in a heat of about 120° Fahr. 
The colour of the solution gradually passed into a fine red, 
deepening continually in intensity, till in a few weeks the colour 
had become so deep as almost entirely to obstruct the passage 
of light. 
It may not, also, be without some interest to mention here, 
the singularly striking effect of nitric acid upon the aloin. Half 
a drachm of strong commercial nitric acid being put into a test 
tube, and fifteen grains of aloin gradually added, great heat and 
violent action are produced, with the escape of red fumes, and 
a perfect solution is the result. The syrupy liquid being now 
added to cold water, a yellow precipitate is formed, which, how- 
ever, dissolves on adding more water; and, on neutralizing the 
liquid with aqua potassee, a liquid of a splendid red colour is 
produced. The intensity of the colour is so great that, on com- 
paring it with a liquid of equal bulk, and containing the co- 
louring matter of two ounces of cochineal, that coloured by the 
aloin is of a deeper red, and even in the richness of its shade 
