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ON THE GASES EVOLVED FROM IRON FURNACES. 169 
out the influence exerted on the average composition of the gases by the 
materials introduced into the furnace, the ultimate products of all of which 
changes appear at the mouth of the furnace. We now proceed to the most 
important part of our inquiry by endeavouring to elucidate the nature and 
mutual relation of all the processes in the reduction of iron. To obtain a 
knowledge of them, it was necessary to become acquainted with the changes 
suffered by the ascending column of air from the blast to the mouth of the 
furnace. We have collected the gases from various depths of the furnace in 
the manner employed by one of us in his inquiries into the theory of German 
furnaces in which charcoal is used as fuel. This method has been more 
Jately used by Ebelmen, with several changes which we have been compelled 
to reject, because in them he introduced a source of error which vitiated his 
results. 
The apparatus for collecting the gases in our experiments consisted of 
a system of tubes twenty-six feet in length, made of soft malleable iron. 
The tube was one inch in diameter, and consisted of pieces of five feet in 
length, screwed together so as to be air-tight. ‘The depth of the tube in the 
furnace was known by white marks placed at the distance of one foot, and 
we found that about three of these sunk in an hour during the first part of 
the experiment, although more slowly afterwards. ‘The top part of the tube 
was furnished with a lead pipe, through which the gases were conducted to 
a place fit for experiment. The system of tubes was balanced by a chain 
passing over a block fixed to a stout wooden upright, and fastened by chains 
round the furnace. The strong heat of the flame issuing from the top of the 
furnace rendered it necessary to wet the support from time to time, and this 
was effected by a fire-engine placed at some distance on the platform. The 
gases themselves were collected in glass tubes four inches Jong and 3 inch 
wide, these tubes being drawn out at both ends and connected with each other, 
and also with the lead tube, by caoutchouc joints. ‘The pressure of the gas, 
which amounted often to several inches of water, was too powerful to allow 
the glass tubes to be hermetically sealed while they remained in connection 
with the lead pipe. We therefore found it necessary to heat the tubes so as 
to expand the air to a certain extent, then to tie the caoutchouc joints, and 
. hot to seal the tubes hermetically until they had cooled down sufficiently to 
prevent any small explosion during the melting of the glass. A vertical sec- 
tion of the furnace upon which our experiments were made is represented in 
fig. 6 ; it is of the usual size of furnaces in this country, and is supplied with 
air heated to 626° Fahr., 330° C. This air passes into the furnace under a 
pressure of mercury of 6°75 inches, out of a nozzle of 2°75 inches in diameter. 
The iron ore melted in this furnace is an aluminous sphareosiderit, which 
is previously roasted so as to free it from moisture and carbonic acid, and 
by this means is converted into an argillaceous peroxide of iron. The fur- 
nace is supplied with eighty charges in the course of twenty-four hours; 
each of these charges, as we have already mentioned, consisting of 420 lbs. 
of calcined ironstone, 390 lbs. of coal, and 170 lbs. of limestone, the product 
of which is 140 lbs. of pig-iron. The limestone is broken up into pieces 
about the size of the fist before being introduced into the furnace, but the 
coal and ironstone are projected in lumps which not unfrequently weigh above 
twenty pounds. Iron ore and limestone are thrown into the furnace without 
any previous mixture. We have collected the gases in all the regions below 
and above the zone of fusion, for in the latter the collection was impossible, 
owing to the high temperature, which softened the tubes, or melted them 
completely. Although the gases under the zone of fusion are actually at a 
higher temperature than they are at that point of the furnace, we succeeded 
