nomena produced
when brought in contact with them.

The number of reagents employed in blowpipe analysis is not great, and
therefore we shall here give a brief description of their preparation
and use. It is indispensably necessary that they should be chemically
pure, as every admixture of a foreign substance would only produce a
false result. Some of them have a strong affinity for water, or are
deliquescent, and consequently absorb it greedily from the air. These
must be kept in glass bottles, with glass stoppers, fitted air-tight
by grinding.

A. REAGENTS OF GENERAL USE.

1. _Carbonate of Soda._--(NaO, CO^{2}) Wash the bicarbonate of soda
(NaO, 2CO^{2}) upon a filter, with cold water, until the filtrate
ceases to give, after neutralization with diluted nitric acid
(NO^{5}), a precipitate with nitrate of baryta, (BaO, NO^{5}), or
nitrate of silver, (AgO, NO^{5}). That left upon the filter we make
red hot in a platinum, silver, or porcelain dish. One atom of carbonic
acid is expelled, and the residue is carbonate of soda.

A solution of soda must not be changed by the addition of sulphide of
ammonium. And when neutralized with hydrochloric acid, and evaporated
to dryness, and again dissolved in water, there must be no residue
left.

Carbonate of soda is an excellent agent in reduction, in consequence
of its easy fusibility, whereby it causes the close contact of the
oxides with the charcoal support, so that the blowpipe flame can reach
every part of the substance under examination.

For the decomposition and determination of insoluble substances,
particularly the silicates, carbonate of soda is indispensable. But
for the latter purpose, we use with advantage a mixture of ten parts
of soda and thirteen parts of dry carbonate of potash, which mixture
fuses more easily than the carbonate of soda alone.

2. _Hydrate of Baryta_ (BaO, HO).--This salt is used sometimes for the
detection of alkalies in silicates. Mix one part of the substance with
about four parts of the hydrate of baryta, and expose it to the
blowpipe flame. The hydrate of baryta combines with the silicic acid,
and forms the super-basic silicate of baryta, while the oxides become
free. The fused mass must be dissolved in hydrochloric acid, which
converts the oxides into chlorides. Evaporate to dryness, and dissolve
the residue in water. The silicic acid remains insoluble.

The hydrate of baryta is prepared by mixing six parts of finely
powder