es are fused with others more fusible (reagents) for
the purpose of causing a combination which is soluble in water and
acids, the operation is termed _unclosing_. These substances are
particularly the silicates and the sulphates of the alkaline earths.
The usual reagents resorted to for this purpose are carbonate of soda
(NaO, CO^{2}), carbonate of potash (KO, CO^{2}), or still better, a
mixture of the two in equal parts. In some cases we use the hydrate of
barytes (BaO, HO) and the bisulphate of potash (KO, 2SO^{3}). The
platinum spoon is generally used for this manipulation.

Substances are exposed to fusion for the purpose of getting a new
combination which has such distinctive characteristics that we can
class it under a certain group; or for the purpose of ascertaining at
once what the substance may be. The reagents used for this purpose are
borax (NaO, 2BrO^{3}) and the microcosmic salt (NaO, NH^{4}O, PO^{5},
HO). Charcoal and the platinum wire are used as supports for this kind
of operation.

(_d._) _Oxidation._--The chemical combination of any substance with
oxygen is termed _oxidation_, and the products are termed _oxides_. As
these oxides have qualities differing from those which are
non-oxidized, it therefore frequently becomes necessary to convert
substances into oxides; or, if they are such, of a lower degree, to
convert them into a higher degree of oxidation. These different states
of oxidation frequently present characteristic marks of identity
sufficient to enable us to draw conclusions in relation to the
substance under examination. For instance, the oxidation of manganese,
of arsenic, etc. The conditions necessary for oxidation, are high
temperature and the free admission of air to the substance.

If the oxidation is effected through the addition of a substance
containing oxygen (for instance, the nitrate or chlorate of potash)
and the heating is accompanied by a lively deflagration and crackling
noise, it is termed _detonation_. By this process we frequently
effect the oxidation of a substance, and thus we prove the presence or
the absence of a certain class of substances. For instance, if we
detonate (as it is termed by the German chemists) the sulphide of
antimony, or the sulphide of arsenic with nitrate of potash, we get
the nitrate of antimony, or the nitrate of arsenic. The salts of
nitric or chloric acid are determined by fusing them with the cyanide
of potassium, because the salts of thes