FUEL 
while they burn. This fort of lai is even greatly fupe- 
rior to the other in fome proper 
a — ftronger fuel, or contains the combuttible 
eater quantity, or ina more condenfed ffate. 
It is, therefore, confumed much more lowly ¢ on all occa~ 
jer 
fore, liable to collect in fuch quaatity as to obftruct the free 
paflage of air through the fire; and further, that when 
the heat is very intenfe thefe afhes are difpofed to melt or vi- 
trify into a tenacious droffy fubftance, which clogs the 
grate, the fides of the furnace and the veffels. This lait 
inconvenience is only troublefome, however, when the heat 
eat the afhes do no 
get dee 
s fuel, ee is preferable, in moft cafes, to the 
charcoal of wo t of its burning = oe 
ng muc b ce efore it is conty 
het pes ee d, by caer peer ies, by wei cht, Foi pit-c oal, 
wo charcoal and wood itfelf, are nearly in prop 
th thefe kinds of charcoal 
hae 
$3 
yp 
=) 
as 
aes 
of aco ar quantity of ¥ water, and fo ‘ ot ther woletile 
aa aa a re evaporated during the cels 
charring, in the form of footy {m {moke or flame. Thefev 
ee pats while they remain in the fuel, make it unfit le 
efs fit) for many purpofes in chemiftry. For befides ob- 
ftrading the vents with footy matter, they require a 
us to evaporate them ; and, therefore, the ae : of the 
nace, in which he an 
e al, until Ge frefh fuel 
is completely inflamed, aa a ote the heat to its former 
ftrength. 
Ba thefe ‘great and fudden variations of the heat 
furnace are quite inconvenient in 
In - greater number of. et operations, therefore, 
it is much more convenient to ufe charred fuel, than the 
ee fuel in its natural ftate 
- There are, at the fame ‘ime, fome kinds of foffil coal, 
of a 
of ae country, that d 
any fenfible a es “of wa or other a Tone e prin- 
ciples. But this may be calle da yan of native charcoal. 
It has the jovi . ordinary coal, but, when thrown 
into : e. fire, not emit {moke or 
es red, ae a fubtile blue flame, en plait like 
arena only it lafts ape el long, or con 
give heat. "for a very lo ong time before it 1s totally bata ed 
But it cannot be made to burn fo as to produce a gentle heat. 
If not in confiderable panei and violently heated, it is 
foon extingujfhed. 
In ufing this kind of fuel, it is proper to be on our guard 
againit the dangerous | nature of the burnt air, which arifes 
from charcoal of all kinds. 
inoke.. The air arifing from it appears to the eye as pure 
as cledr as common air. Hence it is much ufed abroad 
mott chemical proceffes. ° 
Charcoal burns without vifible . 
aL thofe who are fludious of neatnefs, and cleanlinefs im 
ir apa oe nts. But t 
gr 
The firft fenfation isa flight fen 
gerous, 
a little ston to 
the limbs feem to require 
falling. flight giddinefs, ecrapnie by a diftingt feeling 
f a flufh, or glow in the face and on after, the 
uld fi 
ny hae co 
ad re 
a {fnoring as inan apoplexy. If the ae rfon is ae 
in time, and efcapes into the open air, he is commonly feized 
— a ara headeach, which gradually abates. 
en the effect is completed, as wae defcribed, 
death ve ie ai dhaapeige unlefs ja = obtai 
ufually a foam reat 
over the face ae and every indication of an oppreffion 
of the brain, by this accumulation of blood. Them oft fuc- 
cefsful Shaye is to take off a series ‘of blood imme- 
diately, cold a on the head repeatedly. A 
rong ints, fuch as ses applied to the foles of the 
feet, has alfo a very goo 
The fifth aa lak kind of fuel i is wocd, or foffil Saag in 
their crude ftate, which it is proper to diftingui m the 
charcoals of the “fame fubftances, The difference confitts in 
a cannot a managed like the charcoals. If 
little a air i admitted, it gives no flame, but footy vapour, 
and a diminution of heat. And if ich air be admitted to 
make thofe vapours break out into flame, the heat is too vio- 
lent. Thefe flaming fuels, however, have their: particular 
ufes, for which the others are far lefs proper. 
fa&t, that ame, when dash 
b 
lity c of it — 
As th ener tact and action of air are neceffary 
to the acne of ae combuttible body ; fo the air, when 
properly applied, aéts, with far greater advantage cn flame, 
than on the folid and fixed inflammable bodies: for wher 
air is applied to thefe laft, it can only a& on their furface, or 
the particles of them that are outermoit; whereas flame 
i Y proper contri- 
bei yapou ic flui 
ranc - can i piso mixed with it, and m de to act on 
it to burn sn beeatife fon 
with it, but ats only on the ae, and: ‘the qua ntity of 
burning matter in the furface' of a {mall flame is too {mall ta 
produce ae e 
But when flame is ‘produced { in large. quantity, and is pro- 
perly m xed and agitated with air,-its power to heat bodies: 
is Dee tely increafed.: It is therefore peculiarly proper 
for heating large quantities of matter ‘to a: violent degree, 
efpecially if the contact of folid fuel with fuch matter is 
inconvenient. eg fuel is. ufed for this eee in man 
operations performed on large quantities of m -or me-: 
tallic minerals, in a makes of ale; ee in oo baking or. 
3G2 ng 
