184 
NAT. ORDER. LEGUMINOS^E. 
color, and in due time is decanted ; the coloring- principle dissolved by 
the water, absorbs oxygen from the air, and assumes a blue color, be- 
coming- at the same time insoluble ; a gradual precipitation takes place, 
favored by the addition of lime-water, or an alkaline solution : and 
finally, the precipitated matter, having- been washed upon linen filters 
is dried, shaped usually into conical masses, and sent into market. It 
is of an intensely blue color, but assumes a coppery or bronze blue 
when rubbed by a smooth hard body, as the nail. It is insoluble in 
water or alcohol, but is readily dissolved by sulphuric acid, which, 
without destroying- its blue color, so far alters its nature as to render 
it freely soluble in water, and thus afford a convenient method of ap- 
plying- it to the purposes of dying-. The solution in sulphuric acid is 
kept in the shops under the name of sulphate of indig-o. 
Medical Properties and Uses. This plant has recently been in- 
troduced to the notice of the medical profession as a remedial ag-ent. 
Though without odor and taste, it is said, in most individuals, to pro- 
duce color to the stools, to render the urine of a dark-violet or dark- 
green color, without increasing- its quantity, and sometimes to stimu- 
late the secretory functions of the uterus. The character of its general 
influence upon the system has not been well ascertained. 
The complaints in which it has been employed, with supposed 
advantage, are epilepsy, infantile convulsions, chorea, hysteria, and 
amenorrhcea. It has been considered useful internally as an antisep- 
tic, in mortification, and all putrid complaints ; but must be used, how- 
ever, with great caution (internally), especially if in its recent or fresh 
state. 
Externally, the Indigofera may be applied in poultice, wash, 
fomentation, or ointment, to ulcers and swellings of every description, 
but particularly to those which are in a mortifying or inflamed state, 
as it is a great antiseptic or preventive of mortification. 
