acid are eliminated. If the acid be in too minute a
quantity to be thus distinguished, a portion of the substance may be
intimately mixed with some bisulphate of potash, and treated as above.
The sulphuric acid of the bisulphate combines with the base, and
liberates the nitric acid, while the tube contains the nitrous acid
gas.

The nitrate of potassa, when heated in a glass tube, fuses to a clear
glass, but gives off no water. When fused on platinum wire, it
communicates to the external flame the characteristic violet color.
When fused and ignited on charcoal, its surface becomes frothy,
indicating the nitric acid.

(3.) _Carbon_ (C).--Carbon is found in nature in the pure crystallized
state as the diamond. It occurs likewise in several allotropic states
as graphite, plumbago, charcoal, anthracite, etc. It exists in large
quantities combined with oxygen as carbonic acid.

The diamond, although combustible, requires too high a heat for its
combustion to enable us to burn it with the blowpipe. When excluded
from the air, it may be heated to whiteness without undergoing fusion,
but with the free access of air it burns at a temperature of 703 deg. C,
and is converted into carbonic acid. If mixed with nitre, the potassa
retains the carbonic acid, and the carbon may be thus easily
estimated. If a mineral containing carbonic acid is heated, the gas
escapes with effervescence, or a strong mineral acid as the
hydrochloric will expel the acid with the characteristic
effervescence.

(4.) _Phosphorus, Phosphoric Acid _(PO^{6}).--This acid occurs in a
variety of minerals, associated with yttria, copper, uranium, iron,
lead, manganese, etc. Phosphoric acid may be detected in minerals by
pursuing the following process: dip a small piece of the mineral in
sulphuric acid, and place it in the platinum tongs: this is heated at
the point of the blue flame, when the outer flame will become colored
of a greenish-blue hue. This color will not be mistaken for those of
boracic acid, copper, or baryta. Some of the phosphoric minerals, when
heated in the inner flame, will color the outer flame green.

If alumina be present with the phosphoric acid, the following wet
method should be adopted for the detection of the latter: the
substance should be powdered in the agate mortar with a mixture of six
parts of soda, and one and a half parts of silica. The entire mass
should now be placed on charcoal, and melted in the flame of
oxidation.