LABORATORY. 
firate, being constructed as m any other 
furnace. It will be easily understood by 
considering the section represented in fig. 3. 
The base, represented by the dotted line 
ABC, and the top, KLM, are oval plates 
of iron, the longer diameter, A C, being to 
the shorter as three to two nearly. The 
base and top are equal, so that the sides, 
K A, M C, are upright, the whole body 
forming an oval cylinder. D E F, is half of 
tte hole in the bottom, which is occupied 
by the grate fixed on the top of the ash-pit. 
G H I is half of the mouth of the furnace, 
which receives a stilt, or a sand-pot, for dis- 
tillation, with a retort. This is a little 
nearer to the fiont, K, of the top, than the 
grate-hole is to the front. A, of the bottom, 
so that the luting is thicker below than 
above. Near the back, M, of the furnace 
is a smaller hole, P, for the vent. The 
luting at Q and R is so formed that the 
cavity of the furnace does not greatly differ 
from a cylinder, except in so far as the 
vent, P O, does not communicate with it 
abruptly, but is gradually curved down- 
wards, as represented in the figure, making 
the middle of the cavity more roomy back- 
wards, by which means it contains a greater 
quantity of fuel. S is the section of the 
luting, which forms a sort of an arch, or 
bridge, contracting the entry of the vent. 
An iron pipe is set on at P to increase the 
draught of the chimney. The fuel is put 
into the furnace by the aperture P, and the 
sloping form of the cavity causes it to dis- 
tribute itself pretty uniformly. 
When the furnace is used for smelting, 
the crucible is set on a pedestal standing 
on the grate, and the fuel is placed round it 
with great ease, the mouth of the furnace 
being open. This is then shut up by a 
stopper made on purpose, or by a flat fire- 
tile simply laid on it. 
When we would distil with a naked fire, 
the retort has its bulb resting on a ring 
which hangs on the mouth of the furnace by 
three hooks, and the neck of the retort lies 
over the front of the furnace. The space 
round the retort, at the mouth of the fur- 
nace is closed, as much as is necessary, by 
two or three pieces of tile, shaped so as 
nearly to fit the bulb of the retort when 
they are laid on the mouth of the furnace. 
A quantity of light ashes are now to be laid 
on these tiles, and heaped up so as to cover 
the bulb and part of the neck of the retort, 
lir. Black found that this produced a very 
gradual diminution of the heat, as it recedes 
from the fuel, and is less liable to crack the 
• * 
retort, by inequality of heat, than any other 
contrivance. Scarcely any process occurs 
which this furnace does not answer with 
great ease. 
In using the furnaces most convenient 
for experimental chemistry, (namely, those 
made of pWte iron) it is necessary that the 
iron be defended from the heat by lining or 
lute, as we call it, on the inside ; and 
such lutes are necessary in other occasions 
in chemistry ; as when we have occasion to 
close the joining of the vessels with one an- 
other, or to give a coating to retorts, or even 
to crucibles, which is sometimes done. The 
materials employed for these purposes have 
their general denomination from clay, of 
which some of the most useful are partly 
composed, though there are some that do 
not contain any of it. They may be divided 
into such as contain animat or vegetable 
matter, of the glutinous or adhesive kind, 
and such as are composed only of earthy 
substances. The first are used for closing 
the joining of vessels, when the heat we 
mean to apply is not to be strong, nor the 
vapours to be produced corrosive. The 
second serve for the lining of furnaces, or 
for closing the joinings of vessels, in opera- 
tions in which the vapours are very corro- 
sive, or in which a strong heat must be em- 
ployed, which would scorch, or burn and 
destroy, any animal or vegetable glutinous 
matter. 
The joinings of vessels with one another, 
which we have the most fi equent occasion 
to close up by means of Jutes, are those of 
retorts with receivers. And we may re- 
mark, in the first place, with regard to 
these, that there are not many operations in 
which it is necessary to make the joining 
perfectly close, except when the receiver is 
provided with an air-pipe. On the contrary, 
it is dangerous on account of the air which 
must be allowed to escape in some manner. 
Therefore we are not anxious to contrive 
the most close and compact. They are 
sufficient and better if they be moderately 
so, and in some cases, when we think the 
lute too close we even obviate it by a pin- 
hole. The animal and vegetable lutes, em- 
ployed in this way, are g)ue and chalk mix- 
ed in thin paste, and spread on slips of 
paper; or gum arabic and chalk, used in 
the same manner; or flour and water; or 
a bladder ; or linseed meal ; or fat lute. 
M. Lavoisier recommends, for joinings 
wHich we desire to be air tight, but which 
are not to be exposed to heat, the follow- 
ing; to sixteen ounces of bees-wax add 
