6 CHEMISTRY. 
Other methods are employed when the heat required is not so intense as 
that we have just supposed. In many cases glass vessels well annealed 
may be used to much advantage. 
2. Apparatus for Converting Solid Bodies into Gaseous. 
For the above-mentioned purpose, much the same apparatus may hs 
employed as is used in vaporizing liquids, namely, alembics, matrasses, and 
retorts. An operation of the kind may, for instance, have for its object the 
separation of bodies from each other. Thus, if it be desired to obtain the 
valuable mercury used in the construction of mirrors from its amalgam, the 
latter must be introduced into an iron retort (pl. 30, figs. 25 and 26). The 
first form differs from the second in having a small tube, a, opening into 
the head of the retort, for the purpose of more conveniently filling it, 
especially in cases where the neck must not be soiled by the material 
introduced. After fillmg the tube is to be closed by an iron stopper or 
other appropriate substance. When the bulb of the retort is introduced 
into a furnace and heated, the mercury passes over through the neck into 
a receiver, cooled by a stream of water, where it is again condensed. The 
tin remains in the retort, and both metals may thus be obtained sepfrately. 
An apparatus of iron, provided with necks of leaden or glass tubes, may 
also be employed. 
Similar retorts, of glass, porcelain, or clay, may be used when the heat 
required for vaporization is not so great. Should it simply be required to 
drive off, without collecting, the more vaporizable of two substances, we 
may frequently make use of the matrass, constructed of iron, porcelain, glass, 
or clay. The bottom of such a vessel, into which the mixture has been 
introduced, is heated, and the vapor allowed to escape through the open 
neck, the heat being so managed as always to be below what would vaporize 
the second substance. ° 
Operations of this kind are frequently iflstituted by the chemist, and often 
find application in the arts. Thus zinc, in this way, may be driven off from 
its combination with many other metals, as it evaporates at a comparatively 
low temperature. Sulphur, also, is expelled in a similar manner, although 
the heat required is much less than in the case of zinc. An operation of this 
kind is called a distillation when the vapor thus produced becomes converted 
into a liquid on cooling, and a sublimation when this vapor assumes a solid 
state, apparently without previously passing through the liquid. Distillation 
takes place much more frequently in the case of liquids than of solids. 
3. Apparatus for Converting Liquid Substances into Gaseous. 
Nature exhibits to us on a large scale the conversion of liquid substances 
into gaseous. The evaporation of water is an instance of this kind. The 
most varied applications are made in Chemistry and the arts of that 
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