136 F U R N 
tion. When at any time the brightnefs of the tuyere 
fails, and becomes dull white or reddifh white, then a 
change is indicated ; the iron-ftone and linie-flone will 
again appear in the folid unfeparated date, and the change 
of colour in the cinder infallibly betokens an irregularity 
in the movements of the furnace. 
At the introdudlion of the blaft, the interior of the 
furnace at the tuyere is fimply a mixture of ignited malfes 
of cokes and iron-ftone, the latter partly femifufed, but 
the greateft part merely heated to a bright red heat. In 
the defcent through the furnace, in conta6l with ignited 
coke, the particles of metal in the ore may, by parting 
with the oxygen, have received a difpofition to become 
revived. The increafed temperature creates an addi¬ 
tional tendency, by eftablifliing a greater force of affinity 
betwixt the fuel and the iron. But the metal approach¬ 
ing to its proper ftate, meeting the current of blaft, is 
immediately fubjedl to a partial combuftion. The por¬ 
tion thus oxydated conveys to the lava, in proportion to 
its quantity and oxygenation, the colour already menti¬ 
oned. As foon as the continuation of the blaft conveys 
a higher temperature to the fuperior regions of the fur¬ 
nace, the appearance of the folid matter at the tuyere 
ceafes. The fufion and reparation of the metal from the 
ore are effefted in fttuations more remote from the blaft, 
or chief fource of decompofition, in a temperature more 
fuited to the nature and exiftence of the metal. The 
iron, once formed into a fluid, and its fluidity preferved, 
its defcent to the blall is attended with little or no in¬ 
jury to its carbonation. 
The quantity of air difcharged into the furnace, under 
the appellation of blafl, depends upon the number of 
ftrokes of the blowing cylinders which the engine makes 
per minute, and on the area and diameter of the air pump. 
Tills is independent of every confideration of denfity and 
increafe of power in the fteam cylinder; fo long as the 
blow'ing or air cylinder remains the lame, and the engine 
performs the fame difcharges, the meafure of atmof- 
pheric air, which enters the furnace, will remain the fame. 
The rapid improvements, which of late years have been 
made in the blowing machine, have increafed the quan¬ 
tity fiom 1000 to 4000 feet per minute per furnace; and 
the quantity or produce in iron has been thus con.flderably 
increafed. 
In the manufa( 5 lure of iron, it has always been the un- 
cealing pbieft of the iron-maker to improve his blowing 
apparatus ; for uniformly he has found, that in proportion 
as he can raife air, and make it enter the furnace, fo will 
his weekly quantity of metal be increafed. When char¬ 
coal of wood was the matter of fuel made ufe of, the 
affinities betwixt the latter and the ore were eftabliflied 
with more facility. Small furnaces, called bloomeries, were 
fufiiciently large, and deemed of profitable capacity, if 
they produced a bloom or two of iron per day, of 90 to 
laolbs. each. Hand bellows, and what were called fuel 
blafts, were fufiiciently large for the minor operations. 
After the general introduction of the refinery furnaces, 
and the divifion of the manufacture into the making of 
pig iron, and the refining of this into bar or malleable 
iron, the advantages of a powerful blaft were immediately 
perceived. Water wheels, working two pairs or moreof 
leather bellows, were.found to produce powerful effeCts, 
and, in confequence, almoft every fituation that prefented 
a command of materials and a waterfall, became the 
feite of an'iron mill. The Ample mode of blowing fur¬ 
naces by means of a trompe, was at the fame time intro¬ 
duced; but in general it was found, that much greater 
advantage could be derived from the defcent of water 
upon.a wheel, either as to denfity or quantity, than by 
means of the beft conftruCted trompe. 
The ufe of water wheels and leather bellows continued 
genera! throughout the iron bufinefs, until the principles 
and mechanifm of the fteam.engine were eftabliflied upon 
unerring grounds. This wonderful invention was loon 
applied with tjie happieft effeCt in many fituations rich 
with mineral treafures, but to which nature had denied 
ACE. 
the advantage of wafer fiifficient to turn machinery', ' Cy¬ 
linders, compofed of wood, firmly jointed and hoopecl, 
were firft introduced as a fubftitute for leather bellows: 
thefe were foon after replaced by bored cylinders of caft 
iron ; and with this great difeovery and application of the 
art of calling, the blowing machine alfumed a general and 
well-proportioned form. Tliis took place about forty 
years ago, and continued wdth a few temporary deviations: 
until the introdudlion of Bolton and Watt’s highly im¬ 
proved engine, with the tuattr-blafi. The following is a 
defeription of the air-pump blowing cylinder, mentioned 
above: The diameter of the cylinder for one furnace va¬ 
ries from twenty-five to thirty-fix inches, and for two fur¬ 
naces from thirty-fix to fifty inches. Upon the oppofite 
of the main or working beam, fometimes at equal, and 
fometimes at unequal, diftances from the.centre, is placed 
the air-pump or blowing cylinder. This, in common, is 
equal to four or five times the area of the former; and, 
with the fmall working power of the fteam cylinder, I'el- 
dom condenfe the air beyond ig to ij lbs. per fquare 
inch. The air-pump is commonly conftructed open be¬ 
low, as fltewn at E, in the above-mentioned engraving. 
This plan was fometimes deviated from, and the cylinder 
inverted. T!ie blowing pifton is loaded with weights, 
and the air exprelTed by its defcent. In this mode of. 
working, the atl of the fteam pifton, defeending in va¬ 
cuum, raifes the air-pump pifton loaded with weights. 
Upon tlie return of the ftioke, or while the fteam pifton 
iifcends in the cylinder, tills pifton loaded with weights 
finks the whole length of the ftioke, and by means of this 
loading, proportioned to the powers of the engine, forces 
the air either into the regulator or the furnace. Above, 
or parallel to the air-pump is placed the regulating cy¬ 
linder, as fhewn in the plate. This has a valve of com¬ 
munication, which opens every ftroke the engine makes, 
and admits the whole difeharge gf the air. The pifton of 
the cylinder, frequently called the fly pifton, is loaded 
with weights, and kept conrr:intly vibrating; fo that when 
any deficiency of prelfure ariles from the remitting adtion 
of the air-pump pifton, the blaft is-comparatively equa¬ 
lized by the prell'ure of the fly pifton upon the included 
air. The fize of this cylinder is generally in the propor¬ 
tion of nine to fix of the air-pump. 
The chief objedlions to this mode of blowing, are found¬ 
ed upon the great inequality of the blaft, and a very con- . 
fiderable walte of air that takes place at theyi/or/, or fafety 
valve, to prevent the fly pifton being-blown entirely out 
of the cylinder. The liiort is an opening made in the top 
of the air-pump cylinde;-, on which refts a heavy iron 
valve, faced with leather ftufted with wool ; this is, by 
means of an upright iron rod, attached to a lever, which 
runs 'acrofs the top of the regulating cylinder. As foon as 
the fly pifton riles to a certain height, a blockof wood, or 
other contrivance, lifts one end of the lever, and along 
with it the valve, to a certain height, and permits a quan¬ 
tity of the denfeft air to e.fcape, fufficient to infure the 
fafety of the pifton. Notwithlhmding thefe precautions, 
however, many accidents and (lops are found to enfue. 
In confequence of this, fome iron mafters contrived to, 
take the fpare or wafte air from the fnort, to receive it in 
an inverted cheft above water, and blow to its extent 
fmithy and finery fires. Endeavours of this kind, to eco- 
nomife the air, raifed and condenfed at a great expence, 
were fuincient proofs that a method was ftill wanting to 
complete the blowing machine, to render its motions 
fteady and uniform, and to equalife the denfity of the 
blaft throughout the whole ftroke. This was at length 
accompliftied by inverting large chefts, or cylinders, in 
cifterns of wood, ftone, or iron. The fpace betwixt tlie 
inner and outer cifterns was conftructed of fufficient capa¬ 
city tooppofe the expanfive force of the blaft of a colunm 
of water of equal or fuperior relillance. Hence this in¬ 
vention is called Xhe water-blaji, 
A blowing machine, with the water-blaft, capable of 
fupporting two blaft furnaces, ought to have the inverted 
cheft of the regulator equal to three or four hundred 
fquare 
