A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...

162 THE METALLURGY OF ANTIMONY.
pipes, the condensed steam of which may be carried outside, without
being mixed with the liquors. In this manner we avoid the useless
dilution of the liquors producing the vermilion of antimony.
" When the pressure of the boilers has reached two or three atmospheres,
the tanks are filled with the solution of hyposulphite of lime
up to seven-eighths of their height. We then pour the solution of
chloride and antimony into the first tank, 2 or 3 litres at a time.
There is formed a white precipitate which is rapidly dissolved at the
beginning; but when solution becomes slow, even when the liquor
is stirred, the addition of chloride of antimony is discontinued,
because there should always be a certain excess of hyposulphite of lime.
" The liquor of the tank should be perfectly clear and limpid; if
there is any white precipitate, it should be dissolved by adding small
quantities of hyposulphite.
" Steam is then let in, and the temperature of the liquors is gradually
raised to 50° or 60° or even 70° C. while stirring goes on. The reaction
soon becomes manifest; the liquid is successively coloured a strawyellow,
then a pure lemon-yellow, orange-yellow, orange, reddishorange,
and lastly a very deep and bright orange-red. The steam is
then stopped, and the acquired heat of the liquid, aided by a slow
stirring, is sufficient to complete the reaction* and impart to the
colour its maximum of intensity. Should the heating be continued,
the red-orange colour would pass successively to a pure red, then to
a more or less crimson red, which in its turn would grow darker
and darker, and become brown, blackish brown, and, lastly, nearly
black.
"We see that by graduating the temperature it is possible to
obtain all the intermediate hues between orange and brown-black.
The tank is covered, and the coloured precipitate is allowed to
deposit.
" The clear and limpid liquor, which smells strongly of sulphurous
acid, is decanted through holes bored in the tank at different heights,
and is conducted by means of leaden pipes or wooden troughs into a
large quantity of sulphide and oxysulphide of calcium. The sulphurous
liquor regenerates a certain proportion of hyposulphite of lime.
" As the solution of chloride of antimony always contains a large
proportion of chloride of iron, it becomes easy to watch the working
of this latter operation. All the iron remains in solution in the
mother-liquors of the sulphide of antimony; but as soon as these are
brought in contact with sulphide of calcium the insoluble sulphide
of iron is formed. As long as the black precipitate remains, the.
mother-liquors, charged with sulphurous acid, have not been added