234 
ON CYANOGEN AND ITS COMPOUNDS. 
terial capable of supporting a white heat ; it is slightly coni- 
cal, tapering downward, and open at top and bottom; the 
best form in the transverse section is elliptic. This is placed 
vertically in a furnace, heated intensely, and as regularly as 
possible ; its lower end rests upon the flange of a second 
retort, or refrigerator of cast iron, and of a similar shape, 
having at the bottom an extractor, mounted on suitable 
bearings, which is worked periodically by an attendant, to 
convey the cyanized charcoal into an extinguisher or dip- 
pipe, the mouth of the latter being plunged into a saline so- 
lution, which acts as a hydraulic valve. From the side of 
the dip-pipe, at a short distance below the extractor, is the 
waste gas-pipe, which conducts the gases and vapours into 
the hydraulic main ; the end of this pipe is turned down- 
ward, and plunged into water or a solution of a salt of iron. 
By another pipe the incondensable gases are drawn off from 
the main by a pump, or other convenient aspirating machine. 
In the other form of the apparatus there are ten retorts 
working with one air-pump and one hydraulic main/ besides 
contrivances for drying alkalized charcoal, and a method of 
working the feeding and extracting apparatus by machinery. 
The pans or under-backs, which receive the cyanized char- 
coal as it drops from the extractor, are kept constantly 
charged with a protosalt of iron, or with hydrated protoxide 
of iron dirTused t in the liquor, for the purpose of converting the 
simple cyanides into ferrocyanides the moment they fall into 
the liquor. If thought desirable, a fire may be lighted be- 
neath these pans to warm the liquor. The management of 
the furnace-fire requires much attention, to prevent varia- 
tions of temperature, and coke is preferred to bituminous 
coal. 
The working of the apparatus will be easily understood. 
The retort is kept constantly full of alkalized charcoal, and 
the air-pump set to draw a steady current of air through 
the materials in the retort. The gas drawn through maybe 
either burned air, common atmospheric air, or hot air, as 
supplied to ordinary blast furnaces. 
