otherwise detected, but through a troublesome and tedious process,
involving both prolixity and time; for instance, the detection of
manganese in minerals.

Many substances have to go through Blowpipe manipulations before they
can be submitted to an analysis in the wet way. The apparatus and
reagents employed are compendious and small in number, so that they
can be carried easily while on scientific excursions, a considerable
advantage for mineralogists and metallurgists.

The principal operations with the Blowpipe may be explained briefly as
follows:

(_a._) By _Ignition_ is meant the exposure of a substance to such a
degree of heat, that it glows or emits light, or becomes red-hot. Its
greatest value is in the separation of a volatile substance from one
less volatile, or one which is entirely fixed at the temperature of
the flame. In this case we only take cognizance of the latter or fixed
substance, although in many instances we make use of ignition for the
purpose of changing the conditions of a substance, for example, the
sesquioxide of chromium (Cr^{2}O^{3}) in its insoluble modification;
and as a preliminary examination for the purpose of ascertaining
whether the subject of inquiry be a combination of an organic or
inorganic nature.

The apparatus used for this purpose are crucibles of platinum or
silver, platinum foil, a platinum spoon, platinum wire or tongs,
charcoal, glass tubes, and iron spoons.

(_b._) _Sublimation_ is that process by which we convert a solid
substance into vapor by means of a strong heat. These vapors are
condensed by refrigeration into the solid form. It may be termed a
distillation of a solid substance. Sublimation is of great consequence
in the detection of many substances; for instance, arsenic, antimony,
mercury, etc.

The apparatus used for the purposes of sublimation consist of glass
tubes closed at one end.

(_c._) _Fusion._--Many substances when exposed to a certain degree of
heat lose their solid form, and are converted into a liquid. Those
substances which do not become converted into the liquid state by
heat, are said to be infusible. It is a convenient classification to
arrange substances into those which are fusible with difficulty, and
those which are easily fusible. Very often we resort to fusion for the
purpose of decomposing a substance, or to cause it to enter into
other combinations, by which means it is the more readily detected. If
insoluble substanc