430 On Indigo. 
lected without some carbonate of lime in the 
first instance; it) must therefore be submitted 
to water acidulated with muriatic acid, which 
dissolves the lime, and leaves the pure indigo 
to subside. Afterwards it may be collected 
on a filter and dried. The theory of this 
process is now well understood. Pure indigo, 
deprived of a certain portion of oxygen, is 
known to be soluble in lime water; the pro- 
toxide of iron, precipitated by the lime, de- 
prives it of this oxygen, and hence the so- 
lution of the deoxidized indigo. Such how- 
ever is the affinity of indigo in this state for 
oxygen, that it resumes it from atmospheric 
air the moment they are brought into contact. 
Pure indigo thus obtained is called precipt- 
tated indigo: the solution may also be had 
from a blue dyer’s vat, by plunging an empty 
phial into the liquid a few inches below the 
surface. 
The other way of obtaining pure indigo is 
by sublimation. Take 20 or 30 grains of 
pulverized common indigo and place it in an 
iron spoon, which must be gradually heated 
to 500 or 600° Fahrenheit. A purple smoke 
will then exhale copiously, and at the same 
time a fine tissue of small, shining, silky 
needles will start up on the surface of the 
indigo. These may be withdrawn by the 
