IND 
bustibles have any effect upon indigo, ex- 
cept it is in a state of solution ; and the 
same remark applies to the metallic bodies. 
The fixed alkaline solutions have no action 
on indigo, except it is newly precipitated 
from a state of solution. In that case they 
dissolve it with facility. The solution has at 
first a green colour, which gradually disap- 
pears, and the natural colour of the indigo 
cannot be again restored. Hence we see 
that the alkalies, when concentrated, de- 
compose indigo. Pure liquid ammonia 
acts in the same way. Even carbonate of 
ammonia dissolves precipitated indigo, and 
destroys its colour ; but the fixed alkaline 
carbonates have no such effect. Lime- 
water has scarcely any effect upon indigo 
in its usual state ; but it readily dissolves 
precipitated indigo. The solution is at first 
green, but becomes gradually yellow. When 
the solution is exposed to the air, a slight 
green colour returns, as happens to the so- 
lution of indigo in ammonia ; but it soon 
disappears. 
The action of the acids upon indigo has 
been examined with most attention, it cer- 
tainly exhibits the most important pheno- 
mena. When diluted, sulphuric acid is di- 
gested over indigo, it produces no effect, 
except that of dissolving the impurities ; 
hut concentrated sulphuric acid dissolves it 
readily. One part of indigo, when mixed 
with eight parts of sulphuric acid, evolves 
heat, and is dissolved in about twenty-four 
hours. According to Haussman, some sul- 
phurous acid and hydrogen gas are evolved 
during the solution. If so, we are to as- 
cribe them to the mucilage and resin which 
are doubtless destroyed by the action of the 
concentrated acid. 
The solution of indigo is well known in 
this country by the name of liquid blue, or 
sulphate of indigo. While concentrated it 
is opaque and black ; but when diluted it 
assumes a fine deep blue colour ; and its in- 
tensity is such, that a single drop of the 
concentrated sulphate is sufficient to give a 
blue colour to many pounds of water. Berg- 
man ascertained the effect of different re- 
agents on this solution with great precision. 
Dropt into sulphurous acid, the colour was 
at first blue, then green, and very speedily 
destroyed. In vinegar it becomes green, 
and in a few weeks the colour disappears. 
In weak potash it becomes green, and then 
colourless. In weak carbonate of potash, 
there are the same changes, but more 
slowly. In ammonia and its carbonate, the 
colour becomes green, and then disappears. 
IND 
In a solution of sugar, it became green, and 
at last yellowish. In sulphate of iron, the co- 
lour became green, and in three weeks 
disappeared. In thesulphurets the colour was 
destroyed in a few hours. Realgar, white 
oxide of arsenic, and orpiment, produced 
no change. Black oxide of manganese de- 
stroyed the colour completely. From these 
and many other experiments it was in- 
ferred, that all those substances which have 
a very strong affinity for oxygen give a 
green colour to indigo, and at last destroy 
it. Hence it is imagined, that indigo be- 
comes green by giving out oxygen. Of 
course it owes its blue colour to that prin- 
ciple. 
INDIGOFERA, Indigo or Indicum, in 
botany, a genus of the Diadelphia Decan- 
dria class and order. Natural order of 
Papilionaceae, or Leguminosaa. Essential 
character: calyx spreading; keel of the 
corolla, with an awl shaped spreading spur 
on each side; legume linear, "there are 
thirty-five species. The indigo’s are shrubs, 
under shrubs, or herbs ; the leaves are in 
some few cases simple, in more ternate , in 
most unequally pinnate; the leaflets in 
some jointed and awned at the base, as in 
phaseolus ; stipules distinct from the peti- 
ole ; peduncles axillary, one or two-flow- 
ered, in spikes or racemes. The herb in 
most of the species yields a blue dye, which 
is not peculiar to this genus, many plants, of 
this natural class abounding with the blue 
colouring matter. 
INDIVIDUAL, in logic, a particular 
being of any species, or that which cannot 
be divided into two or more beings equal or 
alike. 
The usual division in logic is made into 
genera, those genera into species, and those 
species into individuals. 
INDIVISIBLE, among metaphysicians. 
A thing is said to be indivisible absolute, 
absolutely indivisible, that is a simple be- 
ing, and consists of no parts into which it 
may be divided. Thus God is indivisible in 
all respects, as is also the human mind, not 
having extension or other properties of 
body. 
Indivisibles, in geometry, the elements 
or principles into which any body or figure 
may be ultimately resolved ; which elements 
are supposed infinitely small : thus a line 
may be said to consist of points, a surface 
of parallel lines, and a solid of parallel and 
similar surfaces ; and then, because each of 
these elements is supposed indivisible, if in 
any figure a line be drawn through the ele- 
