PHARMACY. 
The heavy tui f of marshes is preferable to 
the light, superficial turf. Coal is the fiiel 
most commonly used in this country : its 
heat is considerable, and sufficiently per- 
manent, but it produces mucb flame and 
smoke. Charcoal, especially of the dense 
woods, is a very convenient and excellent 
fuel : it burns without flame or smoke, and 
gives a strong, uniform, and permanent 
heat, which may be easily regulated, espe- 
cially when it is not in too large pieces, and 
is a little damp ; but it is costly, and burns 
quickly. Coke, or charred coal, possesses 
similar properties to charcoal ; it is less ea- 
sily kindled, but is capable of producing 
a higher temperature, and burns more 
slowly. 
When an open grate is, used for chemical 
purposes, it should be provided with cranes, 
to support the vessels operated in, that they 
may not be overturned by the burning 
away of the fuel. 
Furmci'S. In all these, the principal ob- 
jects are, to produce a sufficient degree of 
heat, with little consumption of fuel, and to 
be able to regulate the degree of heat. An 
unnecessary expenditure of fuel is prevent- 
ed by forming the sides of the furnace of 
very imperfect conductors of caloric, and 
by constructing it so, that the subject ope- 
rated on may be exposed to the full action 
of the fire. The degree of heat is regu- 
lated by the quantity of air which comes in 
contact with the burning fuel. The quan- 
tity of air is in the compound ratio of the 
size of the aperture through which it enters, 
and its velocity. The velocity is increased 
by mechanical means, as by bellows, or by 
increasing the height and width of the chim- 
ney. The size and form of furnaces, and 
the materials of which they are construct- 
ed, are various, according to the purposes 
for which they are intended. 
The essential parts of a furnace are, a 
body for the fuel to burn in ; a grate for it 
to burn upon ; an ash pit to admit air, and 
receive the ashes ; a chimney for carrying 
ofl’ the smoke and vapours. 
The ash-pit should be perfectly close, 
and furnished witli a door and register- 
plate, to regulate the quantity of air ad- 
mitted. The bars of the grate should be 
triangular, and placed with an angle pointed 
downwards, and not above half an inch 
distant. The grate should be fixed on the 
outside of the body. The body may be 
cylindrical or elliptical, and it must have 
apertures for introducing the fuel and the 
subjects of the operation, and for convey- 
ing away the smoke and vapours. When 
the combustion is supported by the current 
of air naturally excited by the burning of 
the fuel, it is called a wind-furnace ; when 
it is accelerated by increasing the velocity 
of the current by bellows, it forms a blast- 
furnace j and when the body of the furnace 
is covered with a dome, which terminates 
in the chimney, it constitutes a reverbera- 
tory furnace. 
Furnaces are either fixed, and built of 
fire brick, or portable, and fabricated of 
plate-iron. When of iron, they must be 
lined with some badly conducting and re- 
fractory substance, both to prevent the 
dissipation of heat, and to defend the iron 
against the action of the fire. A mixture 
of scales of iron and powdered tiles work- 
ed up with blood, hair, and clay, is much 
recommended ; and Professor Hagen says, 
that it is less apt to split and crack when 
exposed at once to a violent heat, than 
when dried gradually, according to the 
common directions. , Dr. Black employed 
two different coatings. Next to the iron 
he applied a composition of three parts by 
weight of charcoal, and one of fine clay. 
These are first n)ixed in, the state of fine pow- 
der, and then worked up with as much water 
as will permit the mass to be formed into 
balls, which are applied to the sides of the fur- 
nace, and beat very firm and compact, with 
the face of a broad hammer, to the thick- 
ness of about one inch and a half in general, 
but so as to give an elliptical form to the 
cavity. Over this, another lute, composed 
of six or seven parts of sand, and one of 
clay, is to be applied in the same manner, 
to the thickness of about half an inch. 
These lutes must be allowed to become 
perfectly dry before the furnace is heated, 
which should at first be done gradually. 
They may also be, lined with fire bricks of 
a proper form, accurately fitted and well 
cemented together before the top plate is 
screwed on. 
The general fault of furnaces is that they 
admit too much air, which prevents us from 
regulating the temperature. It either be- 
comes too violent and unmanageable, or 
when more cold air is admitted tlian what 
is necessary for supporting the combustion, 
it carries off heat, and prevents us from 
raising the temperature as high as we other- 
wise would. The superior merit of Dr, 
Black’s furnace consists in the facility 
with which the admission of air is regulated > 
