ON SOCOTRINE ALOE JUICE. 
233 
are moderately large and regular, become small and pulverulent 
when dry. Like the aloin crystals of Messrs. Smith, the aloin 
crystals of Socotrine aloes strongly doubly refract and depolarize 
light, and are, therefore, beautiful objects when viewed by the 
polarizing microscope. 
The crystals of aloin contained in Socotrine aloe juice cannot 
be confounded with the crystals of oxalate and phosphate of lime 
found in the juices of various plants, and which are called by 
botanists raphides. The appearance under the microscope of 
the former is very different from that of the latter. Moreover, 
the ready fusibility, solubility, and complete combustibility of 
aloin crystals easily distinguish them from the calcareous salts 
just referred to. On platinum foil the aloin burns without leav- 
ing any residue, except such as may arise from the presence of 
traces of some foreign matter. 
Aloin may be readily obtained from the juice by mixing the 
latter with spirit (either reotified or proof,) and collecting and 
drying the precipitate. When procured in this way it appears to 
the naked eye like a yellow powder ; but when examined by the 
microscope it is found to consist of minute fragments of crystals. 
The tincture from which the aloin has been separated, yields 
by distillation a spirit having the fragrant odor of the juice ; 
showing that the latter contains some volatile odorous principle. 
By evaporation the tincture yields a resiniform extract. 
In the first edition of my Elements of Materia Medica, pub- 
lished in 1840, I have stated, that by digesting hepatic aloes in 
rectified spirit of wine, a yellowish granular powder is obtained, 
which is insoluble in [cold] water, alcohol, ether, and dilute sul- 
phuric acid, but is readily soluble in a solution of caustic potash, 
forming a red colored liquid. The powder-like residue here re- 
ferred to, is identical with the aloin of Socotrine aloes. When 
examined by the microscope, it is perceived to consist of very 
minute prismatic crystals, which depolarize polarized light like 
the larger crystals of aloin above referred to. I think, therefore, 
that it may be safely inferred that hepatic aloes has been prepar- 
ed without the employment of artificial heat, and that its opacity 
is due to the presence of minute crystals of aloin. 
When Socotrine aloes is digested in rectified spirit an insolu- 
ble portion is also obtained ; but its color, instead of being yellow, 
