bstance upon the wax or tallow, will cause it to melt and run down
the side of the candle; while again, candles do not give heat enough.
The lamp is much the most desirable. The subjoined figure, from
Berzelius, is perhaps the best form of lamp. It is made of japanned
tin-plate, about four inches in length, and has the form and
arrangement represented in Fig. 5. K is the lamp, fastened on the
stand, S, by a screw, C, and is movable upwards or downwards, as
represented in the figure. The posterior end of the lamp may be about
one inch square, and at its anterior end, E, about three-quarters of
an inch square. The under side of this box may be round, as seen in
the figure. The oil is poured into the orifice, A, which has a cap
screwed over it. C' is a wickholder for a flat lamp-wick. _a_ is a
socket containing the wick, which, when not in use, is secured from
dirt by the cap. The figures B and _a'_ give the forms of the cap and
socket. The best combustible for this lamp is the refined rape-seed
oil, or pure sweet oil. When this lamp is in use, there must be no
loose threads, or no charcoal on the wick, or these will produce a
smoky flame. The wick, likewise, should not be pulled up too high, as
the same smoky flame would be produced.

[Illustration: Fig. 5]

THE SPIRIT-LAMP.--This is a short, strong glass lamp, with a cap, B,
Fig. 6, fitted to it by grinding, to prevent the evaporation of the
alcohol. The neck _a_ contains a tube C, made of silver, or of tin
plate, and which contains the wick. Brass would not answer so well
for this tube, as the spirits would oxidize it, and thus impart color
to the flame. The wickholder must cover the edge of the neck, but not
fit tight within the tube, otherwise, by its expansion, it will break
the glass. It is not necessary that alcohol, very highly rectified,
should be burnt in this lamp, although if too much diluted with water,
enough heat will not be given out. Alcohol of specific gravity 0.84 to
0.86 is the best.

[Illustration: Fig. 6]

This lamp is generally resorted to by blowpipe analysts, for the
purpose of experiments in glass apparatus, as the oily combustibles
will coat the glass with soot. Some substances, when exposed to the
dark part of the flame, become reduced and, _in statu nascendi_,
evaporated; but by passing through the external part of the flame,
they become oxidized again, and impart a color to the flame. The
spirit flame is the most efficient one for the