4 CHEMISTRY. 
1. Apparatus for Melting Solid Bodies. 
Contrivances for melting solid bodies have the most extensive application 
in the arts. All workers in metal need them for producing the various 
forms or mixtures required. The daily operations of life involve them to a 
very great extent. Confining our attention to what is required for the more 
infusibie substances, among which the metals are most conspicuous, we have, 
as most generally used, the wind furnace ( pl. 30, figs. 3 and 7), and the 
crucible furnace (figs. 21 and 22). Thus, when a mixture of copper and 
zinc is required in making brass, pieces of both metals are introduced into a 
Hessian crucible (figs. 80-34), constructed of an exceedingly infusible clay. 
Charcoal powder is introduced into the crucible to prevent the loss of zine, 
which arises from its ready combination with oxygen. The philosophy of 
the action of the carbon consists in its taking hold of the oxygen of the 
air entering the crucible, and being converted by it into carbonic acid. 
The zinc is thus protected from the influence of the oxygen, which would 
have been exhibited by the conversion of the metal into an oxyde’ by 
combustion ; combustion or burning, in technical phrase, simply indicating 
a combination of oxygen with any inflammable base. The crucible is now 
set on the grate of the portable wind furnace (fig. 3), placed a few inches 
above the door a, and surrounded by red hot coals. The space above is 
then to be filled with fresh coal, and the door b, leading to the space below 
the grate, opened; the door a must be kept closed, its object being to allow 
an examination of the interior of the furnace with respect to the temperature, 
amount of fuel, &c. The funnel or cap, represented more fully in jig. 3% is 
finally to be laid on the upper opening of the furnace As soon as the fuel 
has commenced to burn, a powerful draught of air draws through the 
furnace, owing to the heated air within being specifically lighter than that 
outside, and ascending continually through the cap, its place being supplied 
by fresh air entering at b. A great quantity of atmospheric air, consisting 
of seventy-nine parts of nitrogen and twenty-one of oxygen in the hundred, 
by volume, is thus introduced among the burning coals. The oxygen com- 
bining with the carbon with great avidity, produces an increase of heat, 
and the carbonic acid being immediately carried up and out through the 
funnel, permits a fresh accession of oxygen. The amount of heat generated 
will be in direct proportion to the amount of oxygen which has access to the 
carbon of the fuel, and to the rapidity with which the carbonic acid is 
removed. 
When many operations of this kind are required it is customary, besides 
or instead of the portable furnace, to use one that is fixed, but similar in 
principle and action. A furnace of this character is shown in pl. 30, fig. 6; 
fig. 7 represents it in section. A is the space for the fuel, C the grate on 
which stands the crucible, supported by a block of crucible earth, as in 
fig. 21; Bis the bottom of the ash-hole. The opening of A is closed by a 
well-fitting iron cover, which may be coated on the under side with clay. 
The draught in this furnace passes in at the ash-pit, through the fuel, and 
A34 
