30 per cent. of barium cyanide, corresponding to a
conversion into cyanide of 40 per cent. of the barium present.

We found, however, that the cyanide when exposed to the atmosphere at
a temperature above 300 deg. C. is readily destroyed under reformation of
carbonate of barium, so that it is absolutely necessary to cool it
down to this temperature before exposing it to the atmosphere, a fact
of great importance that had hitherto been overlooked.

The operation for producing ammonia and regenerating the carbonate of
barium by acting upon the cyanide with steam offers no difficulty
whatever, and if the temperature is not allowed to exceed 500 deg. C., the
results are quantitative. The regenerated carbonate of barium acts
actually better than the ground witherite used in the first instance,
and if care is taken that no impurities are introduced by the pitch
which is used to remake the briquettes and to replace the small amount
of carbon consumed at each operation, I see no reason why it should
not continue to act for a very long time.

The cyanide is not acted on by carbonic oxide, but carbonic acid
destroys it at high temperatures, so that it is not possible to
produce it by heating the briquettes directly in a flame free from
oxygen, but containing carbonic acid. The process has, therefore, to
be carried out in closed vessels, and I designed for this purpose the
following apparatus:

Clay retorts of moderate dimensions and thin walls are placed
vertically in a furnace, passing through the hearth as well as through
the arch of the furnace. These are joined at the bottom to cast iron
retorts of the same shape as the earthenware retort. Through a cast
iron mouthpiece on the top of the retort the material was introduced,
while in the cast iron retort below the material was cooled to the
necessary temperature by radiation and by the cold nitrogen gas
introduced into the bottom of it. The lower end of the cast iron
retort was furnished with an arrangement for taking out from time to
time small quantities of the material, while fresh material was in the
same proportion fed in at the top. As a source of nitrogen I used the
gases escaping from the carbonating towers of the ammonia-soda
process. The formation of cyanide of barium from barium carbonate,
carbon, and nitrogen absorbs a very large amount of heat--no less than
97,000 calories per equivalent of the cyanide formed--which heat has
to be transmitted through the walls