204 
Iron . 
the boshes ; but as this is more than four feet above the 
tuyere hole, the blast must be delivered with great veloci- 
ty, and in a direction somewhat slanting upwards, in order 
that it may be reflected by the opposite wall of the cruci- 
ble, and arrive at its proper place without undergoing any 
material decomposition* When the blast enters too rapid- 
ly, and in too concentrated a state, it renders the line of its 
passage before it is reflected so cool, that the descending 
slag which comes within its influence is suddenly solidi- 
fied, and blown into a tube reaching perhaps half way 
across the crucible through which the blast continues to 
rush, and in consequence of this protection, is conveyed 
with greater precision, and in a less decomposed state into i 
the upper part of the furnace. If after this, the compres- 
sion of the air is somewhat diminished, the tube still re- 
mains firm, often for days together, and the furnace works ! 
in the best manner. But on the other hand, when too i 
loose and soft a blast is admitted, and more especially if I 
it be charged with moisture, it is unable to reach the top of I j 
the crucible without being decQmposed, and the reflection 
which it undergoes from the wall of the crucible, weakens 
and disperses it to such degree, that the combustion which 
ought to take place within the boshes, now occupies the 
whole upper part of the crucible : in consequence of this, 
the tube of scoriae is presently burnt away, the iron almost 
as fast as it is melted is ignited and oxydized, the tuyere 
hole glows like the sun, with an intensely vivid white 
light ; the scoriae from being yellowish white, streaked with 
blue, becomes green, brown, and finally black, nearly the 
whole of the iron in the state of oxyd being taken up by ) 
it ; the blocks of refractory gritstone with which the lower 
part of the furnace is lined are worn into great holes, and 
in the space of a few hours prodigious damage is sustain- 
ed,. 
