CHEMISTRY. 9) 
out by a horizontal channel into the vertical chimney, D, which may be 
walled in the chimney of the building. By applying very high chimneys, a 
much greater draught can be obtained than with the preceding construction. 
The crucible furnace (pl. 30, fig. 21) is still another arrangement, 
especially applicable when valuable metals, as gold and silver, are to be 
melted. The larger upper figure represents a small closed space, whose 
walls are formed of an infusible clay, and made in two pieces, the upper ot 
which can be lifted off like a cover. The metal (or metals) to be melted 
is introduced into a crucible of plumbago, or into a Hessian crucible, and 
this placed on a block of infusible earth in the bottom of the furnace: 
burning coals are now to be placed round the crucible, and after replacing 
the top, the remaining space is filled with fresh coal. In the bottom of the 
furnace are six or eight channels, so arranged that the air forced by a pair 
of bellows into the space E, and thence through the channels, may be 
directed principally against the lower part of the crucible. The cover has 
a lateral aperture through which examinations may be made or fresh coal 
supplied. The crucible is removed after complete fusion of the metal has 
taken place. fg. 23 represents a pair of tongs for handling the heated 
crucible. The lower figure, marked fig. 21, is a smaller crucible furnace 
for melting minute quantities of matter; its application follows readily from 
what has just been said. 
In melting operations which are exclusively scientific, and not technical 
in their object, as, for instance, in ascertaining whether a substance can be 
melted by some of the fluxes at our command, we may in many cases make 
use of the blowpipe (pl. 31, figs. 62, 63). This consists of a brass tube 
inserted into one end of an expansion, a, into whose side is attached a 
smaller tube, b, with its extremity tapering to a very fine aperture. Air is 
blown from the mouth into the tube, and the extremity held above the wick 
of an alcohol lamp, so that the flame is driven into a horizontal pointed 
cone by the fine current of air: a very intense heat will thus be produced, 
and gspecially just before the point of the blowpipe. The substance to be 
tested is placed in small portiops, in a hollow excavated in a piece of 
charcoal or clay, or held in platinum forceps, and the flame directed upon 
it. The object of the central chamber of the blowpipe, as just described, 
is to condense the moisture of the breath (the air too is condensed to a 
certain amount) ; there are sometimes several jet pieces, of different calibres, 
for slipping on b. Quite frequently the blowpipe consists merely of a 
tapering tube of brass, bent at right angles near the extremity. 
The ozy-ethereal lamp (pl. 31, figs. 1 and 2) is capable of furnishing a 
heat equal in intensity to almost any with which we are acquainted. A is 
a glass lamp filled with ether; B a tube by which the air is brought into 
connexion with the inside of the lamp: C a fine metal tube, leading from 
a gasometer of oxygen, into the middle of the wick of the lamp. The lamp 
rests on a foot, D, through which the tube C passes. The wick of the lamp 
is covered by the ground-glass cap a, to prevent the evaporation of the 
ether when the apparatus is not inuse. The heat of the lamp is capable of 
melting flint sufficiently to permit its being drawn out into a thread. 
435 
