Se, See 
and the Operations of the Blaft-Furnace. 129 
top has acquired a confiderable degree of heat, it is then 
judged time to introduce the blaft; the preparations neceflary 
for which are the following :— 
The dam-ftone is Jaid in its place firmly imbedded in fire- 
gay; the dam-plate is again “imbedded on this with the fame 
cement, and is fubject to the fame inclination. On the top 
of this plate is a flight depreffion, of a curved form, towards 
that fide fartheft diftant from the blaft, for the purpofe of 
concentrating the feoria, and allowing it to flow off in a con- 
nected ftream, as it tends to furmount the level of the dam. 
From this notch to the level of the floor a declivity of brick- 
work is.erected, down which the fcoria of the furnace flows 
in large quantities. The opening betwixt the dam and fide- 
walls of the furnace, called the fauld, is then built up with 
fand, the loofe bricks are removed, and the furnace bottom 
is covered with powdered lime or charcoal-duft. The ig- 
nited cokes are now allowed to fall down, and are brought 
forward with iron bars nearly to a level with the dam. The 
{pace between the furface of the cokes and the bottom of the 
tymp-plate is next rammed hard with {trong binding fand 3 
and thefé cokes, which are expofed on the outfide, are co- 
vered with coke-duft.  Thefe precautions being taken, the ° 
tuyere-hole is then opened and lined with a foft mixture of 
fire-clay and Joam: the blaft is commonly introduced into 
the furnace at firft with a finall difcharging-pipe, which is 
afterwards increafed as occafion may require. In two hours 
after blowing, a confiderable quantity of Java‘will be accu- 
mulated; iron bars are then introduced, and perforations 
made in the compreffed matter at the bottom of the furnaces: 
the lava is admitted to all parts of the hearth, and {oon tho- 
roughly heats and glazes the furfaces of the fire-ftone. Shortly 
after this it rifes to a level with the notch in the dam-plate, 
and by its own accumulation, together with the forcible ac- 
tion of the blaft, it fows over. Its colour is at firft black ; ‘its 
fraéture denfe, and very ponderous; the form it affumes in 
funning off is flat and branched, fometimes in long ftreams, 
and at other times lefs extenfive. If the preparation has been 
; well conduéted, the colour of the cinder will foon change to 
White; and-the metal, which in the {tate of an oxyde formerly 
i coloured 
