ON CYANOGEN AND ITS COMPOUNDS. 235 
The time required for reducing the alkali, and converting 
it into cyanide, is in direct ratio to the intensity of the heat; 
with a good white heat, two or three hours are sufficient 
to convert almost the whole of the alkali into cyanide.' — 
Whether the retorts are fed by machinery or otherwise, care 
must be taken to keep them constantly full, according to the 
working of the extractor, which, as before mentioned, de- 
livers the cyanized charcoal into the dip-pipe, where it drops 
into the saline solution below ; but previous to this it may 
be cooled in the iron retort, by surroundiug a part of that 
vessel with a cold water-chamber. 
The liquor in the under-back should always contain a 
slight excess of iron or ferrosalts, or the alkaline cyanides 
will be decomposed into formiates of potash and soda and 
carbonate of ammonia. It is easy to ascertain when suffi- 
cient iron is present : by taking out a small quantity of the 
clear liquor, and dropping into it a little weak solution of 
protosulphate, or any other protosalt of iron, a white precipi- 
tate will fall without any tinge of red; but when, on the 
contrary, the liquor gives a brown red precipitate, or a mix- 
ture of red and white, it wants iron. When it is certain 
that the liquor contains a slight excess of iron, the charcoal 
is taken out and thrown into vats or cisterns, and washed, 
either with cold or warm water, until the salt is completely 
extracted; the weak liquors are passed successively through 
new charcoal, by which they are easily brought to 20° 
Beaume's hydrometer. At this strength the liquors may be 
thrown into evaporating pans, and be boiled until the sul- 
phate of potash falls down ; this is separated as usual, and 
drained. The remainder of the liquor is then drawn off into 
other vessels to crystallize ; or, instead of drawing it off, the 
evaporation may be carried still further, until the prussiate also 
falls down and separates in a similar manner. The potash 
mother-liquors serve for fresh operations. The first rough crys- 
tals are washed and crystallized a second time, as usual. — 
Sealed Dec. 13, 1843.— Chem. Gaz. 
