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.