232 
ON CYANOGEN AND ITS COMPOUNDS. 
milk of lime, so as to deprive them of sulphurous and nitrous 
vapour. The nitrogen so obtained is employed in the same 
manner as if obtained directly from atmospheric air. 2. The 
nature of the carbonaceous material which is employed in 
the process is not of much consequence ; satisfactory results 
have been obtained with wood-charcoal, coke, pit-coal, peat, 
spent-bark, wood, and other similar substances; but as re- 
gards economy, produce and convenience, wood-charcoal 
in pieces of the size of a hazel-nut is preferable to any other. 
3. With respect to the potash and soda, the carbonates are 
preferred : but any other salt capable of being resolved ulti- 
mately into carbonate, oxide or metal, may be employed. 
Although the choice of the materials is not of much conse- 
quence, it is not so with regard to the mode in which they 
are employed ; thus the more or less intimate mixture of the 
charcoal with the alkali, and the proportions of the two, 
have a great influence. If the alkaline salt is easily fusible 
it may be previously fritted with the charcoal, or the two 
substances may be carefully mixed. It is, however, in gen- 
eral preferable to soak or steep the charcoal in a concentra- 
ted alkaline solution, and to dry the mixture before using 
it ; but whatever be the way of mixing the matters, it is of 
the greatest importance that they should be perfectly dry 
before they are placed in the retorts. The proportions of 
alkali and charcoal may be varied to a certain extent, but 
there are limits which should not be passed ; an excess of 
alkali renders the chemical decompositions incomplete, and 
a too small proportion is not economical ; but according to 
the difference in the density of the charcoal, it may vary 
from 25 to 100 parts of alkaline salt to 100 parts of charcoal. 
With hard wood charcoal, the proportions which have been 
found to answer best are from 30 to 50 parts carbonate of 
potash to 100 parts of charcoal, according to the intensity 
of heat in the retort. As regards the quantity of nitrogen 
gas, it must be used in excess to hasten the operations ; still 
a too rapid current of gas must be avoided, because it would 
carry off with it a part of the cyanides already formed, and 
