158 REPORT—1845. 
quantity of coal to the products of combustion of the coke formed from that 
coal. 
As no further experiments are required to determine the products of com- 
bustion, the question as to the constitution of gases evolved from coal fur- 
naces is reduced to the examination of the liquid and gaseous products re- 
sulting from the distillation of any given kind of coal. These products will 
be very different, according as they come in contact with the red-hot coal, 
or escape without passing over it. In the last case we obtain the immediate 
products resulting from the decomposition of coal, while in the first we have 
the products arising from their action upon it. The conditions essential to 
the production of the first case are more or less combined in furnaces in which 
the materials are put in in a finely-divided state, and go slowly down from the 
top to the bottom of the furnace. Under these circumstanees the coal be- 
comes heated pretty equably throughout its entire mass by the larger heating 
surface which it offers to the ascending column of gas; and the tar conden- 
sing in the upper parts of the furnace is carried away by this stream of air, 
before the coals saturated with it reach that point in the furnace where the 
temperature is sufficient for the further decomposition of the products, of di- 
stillation. The gases generated from the furnace, under such conditions, must 
contain a smaller quantity of combustible matter. It is therefore of import- 
ance to determine the average composition of the gases formed from the 
products of distillation unmixed with the substances-arising from their ac- 
tion upon the red-hot coal. The composition of a gaseous mixture of this 
kind is also interesting, because it points out the limits to which the quan- 
tity of combustible constituents in furnace gases may be reduced. In order 
to obtain gases of this kind, the most convenient way is to fill a combustion- 
tube with the coal to be examingd, which is placed in a horizontal layer 
and heated from the closed end of the tube to the open end, so that the gases 
are not obliged to traverse over red-hot coal in their escape from the tube. 
The apparatus used by us in the determination of the liquid and gaseous 
products of distillation is drawn in fig. 4. @a@ is a common combustion fur- 
nace, in which is placed the tube coating the coal. The tube is made of 
difficultly fusible green glass, about 3 inch wide, and surrounded by a 
thin sheet of copper containing between it and the glass a layer of powdered 
charcoal, so that the weight may not alter during the heating. The end of 
the tube is drawn out before the flame of the blowpipe, and connected by 
means of a weighed strong caoutchouc tube with the receiver 6, which is 
destined to receive the tar and ammoniacal water : ¢ is a bent tube filled with 
chloride of calcium for the double purpose of retaining the water and am- 
monia which passes over with the gases: d is a Liebig’s tube filled with a 
solution of oxide of lead in caustic potash, behind which is placed another 
tube filled with chloride of calcium for the reception of the aqueous vapour 
carried off from the potash. This arrangement enables us to determine the 
amount of sulphuretted hydrogen and carbonic acid, each of which is de- 
termined by boiling the black precipitate in a platinum vessel with caustic 
potash, and then weighing the precipitate thus freed from carbonate of lead. 
The receiver filled with perchloride of antimony (f) serves for the deter- 
mination of olefiant gas and the volatile hydrocarbons accompanying it. On 
-aecount of the great volatility of this compound of chlorine, it is necessary 
to connect it with a potash apparatus (g), which itself is connected with an 
absorbing tube containing sulphuric acid. As the chloride of antimony is 
apt to become hot during the condensation, and thus cause an escape of a 
volatile chlorinated hydrocarbon, we prefer to use an alcholic instead of an 
aqueous solution of potash. If this be neglected, subchloride of mercury is 
