176 ny REPORT—1845. 
of twenty-four feet in the furnace. Now as one of us has elsewhere shown that 
carburetted hydrogen can neither be formed by the direct combination of 
carbon with hydrogen, nor by the decomposition of water at the expense 
of the coals, it must be viewed as a product of distillation, a fact of consider- 
able importance in the theory of the process of smelting in this country, and 
which leads to the following conclusion,—That the region of the furnace in 
which the coking of the coal is effected extends to a depth of twenty-four 
feet from the mouth. 
When we consider that the coals are thrown into the furnace in large 
masses, sometimes 20 Ib. in weight, it will scarcely excite surprise that the 
space required by the coal, before being converted entirely into coke, is above 
one-half of the whole depth of the furnace. 
The tabulated composition of the gases further shows that the quantity of ni- 
trogen in the gaseous mixture, taken at a depth of fourteen feet, is at a minimum, 
while the olefiant gas, carburetted hydrogen and hydrogen is at a maximum. 
As the latter gases are formed from coal only under the influence of an ele- 
vated temperature, we draw from this circumstance the conclusion, that the 
process of distillation of the coal reaches its maximum at a depth of fourteen 
feet. We remarked, in describing the experiments in detail, that the gases 
were free from the vapours of tar to a depth of fourteen feet, but that they 
became richly laden with them on attaining a depth of seventeen feet. The 
absence of these vapours from the upper part of the furnace proves that they 
suffer decomposition as they pass through the upper layers of red-hot coal. 
The water ascending through these layers must also suffer decomposition, 
and this fact explains the irregularity in the proportions between the car- 
bonic acid and carbonic oxide. 
When we compare with each other the different quantities of carbonic 
oxide and carbonic acid at various depths of the furnace, we see a complete 
absence of any mutual dependence, contrary to what was observed to be the 
case in the smaller German furnaces fed with charcoal. In order to under- 
stand this phenomenon, it is necessary to consider attentively the conditions 
under which the materials are exposed. 
We have already seen that the coal has to travel twenty-four feet, from 
the mouth to the doshes of the furnace, before it is deprived of its volatile 
carbonaceous products, hygroscopic water, and water formed by the distilla- 
tion. Now even if we admit that the temperature in this part of the furnace 
is never so much lowered by the uninterrupted gasification of the coal as to 
prevent the reduction of the iron ore, by which carbonic oxide is converted 
into carbonic acid, still the ore would always be exposed not only to the de- 
oxidizing influence of the furnace-gases, but also to the oxidizing powers of 
the steam evolved from the coal, which has escaped being coked. The pro- 
jection of the coal into the furnace in large pieces has therefore the effect of 
subjecting the ore to a simultaneous reduction and oxidation, on account of 
which the relation between the carbonic acid, carbonic oxide and hydrogen 
is made to depend upon local circumstances in the upper part of the furnace. 
Now when we further consider that the carbonic oxide and carbonic acid 
escaping from the mouth of the furnace, and from the part superior to the 
boshes, are almost in equal proportion, we are compelled to look for the 
cause of reduction of the ore in a region of the furnace still deeper. How- 
ever, all doubt as to this fact disappears when we refer to the proportion be- ~_ 
tween the nitrogen and oxygen of the gases collected. If the reduction of 
the ore and evolution of carbonic acid from the limestone had been com- 
pletely effected above the point of the furnace to which we reached, the gases 
formed below would have contained their nitrogen and oxygen in the same 
