FURNACES. 
Bergens, where coals are used as fuel, the coals are always 
prepared before they are used, by pounding them to a 
powder, and mixing them up with an equal weight of clay, 
and a sufficient quantity of water to form the whole into a 
mass, which is kneaded together and formed into cakes ; 
which cakes are afterwards well dried, and kept in a dry 
place for use. And it has been found, by long experience, 
that the expense attending this preparation is amply repaid 
by the improvement of the fuel. The coals thus mixed 
with clay not only burn longer but give much more heat 
than when they are burnt in their crude state. 
It will doubtless appear extraordinary to those who have 
not considered the subject with some attention, that the 
quantity of heat produced in the combustion of any given 
quantity of coal should be increased by mixing the coals 
with clay, which is certaiuly an incombustible body; but 
the fact is certain. 
In composing fire balls it is probable that a certain pro 
portion of chaff, of straw cut very fine, or even of saw 
dust, might be employed with great advantage. It is wished 
that those who have leisure would turn their thoughts to 
this subject ; for it is conceived that very important im 
provements would result from a thorough investigation of it. 
For the purpose of lighting a fire speedily, kindling 
balls, composed of equal parts of coal, charcoal, and clay, 
the two former reducéd to a fine powder, well mixed, and 
kneaded together with the clay moistened with water, and 
then formed into balls of the size of hen’s eggs, and 
thoroughly dried, might be used with great advantage in 
stead of wood. 
These kindling balls may be made so inflammable as to 
take fire in an instant, and with the smallest spark, by dip 
ping them in a solution of nitre and then drying them 
again; and they would neither be expensive nor liable to 
spoil by long keeping. Perhaps a quantity of pure charcoal, 
reduced to a very fine powder, and mixed with the solution 
of nitre in which they are dipped, would render them still 
more inflammable. 
FURNACES IN GENERAL. 
THE principal, and most critical parts of the apparatus sub 
servient to chemistry, being the furnaces employed for the 
preparation of those substances which come within the 
chemical class, the structure of these is more complex,