A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...
A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...
A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...
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THE ANTIMONY PREPARATIONS AND THEIR USES. 163<br />
in excess; but when they are in excess the black precipitate disappears,<br />
owing to its being changed into the soluble hyposulphite of<br />
iron. The contents of the reservoir are then well stirred, and, if<br />
necessary, sulphide of calcium is added, until the black precipitate<br />
of sulphide of iron reappears and remains permanent. At the same<br />
time a certain proportion of hyposulphite of iron should remain in<br />
solution. This condition is easily fulfilled when we operate upon a<br />
sufficiently large amount of materials. After the precipitate has<br />
settled the liquor is decanted, and is a neutral solution of hyposulphite<br />
of lime, with a certain proportion of hyposulphite of iron<br />
and of chloride of calcium.<br />
"We should carefully avoid, in this regeneration of the hyposulphite<br />
of lime, leaving in an excess of sulphide of calcium, which<br />
will impair the coloration of the vermilion by causing the formation<br />
of the ordinary orange-yellow sulphide of antimony. Therefore, if<br />
the solution of hyposulphite of lime be yellow and alkaline, a liquor<br />
charged with sulphurous acid should be added, until complete<br />
neutralisation of the alkaline reaction.<br />
"This solution of hyposulphite of lime, like the first, is employed<br />
in the preparation of a new quantity of vermilion of antimony. The<br />
mother-liquors, charged with sulphurous acid, are again neutralised<br />
in the large reservoir by a new proportion of sulphide and oxysulphide<br />
of calcium, and so on, until the liquors become so much<br />
loaded with chloride of calcium that it becomes necessary to throw<br />
them away, or to reserve them for some other purpose. But this<br />
takes* place only after twenty or thirty operations.<br />
"It is even possible to save the sulphurous acid in these exhausted<br />
mother-liquors, by saturating them with a milk of lime. This produces<br />
a precipitate of oxide of iron and of sulphite of lime, and leaves<br />
chloride of calcium only in the mother-liquors. The precipitate,<br />
mixed with sulphide of calcium, is transformed by sulphurous<br />
acid into the hyposulphites of lime and iron. And if the proportion<br />
of iron be too great, it may be precipitated by a slight<br />
excess of milk of lime.<br />
" The precipitate of vermilion of antimony left on the bottom of<br />
the first tank is received into a conical cloth filter, and the drained<br />
liquors are added to those of the reservoir. The tank is then rinsed<br />
with tepid water, which is made to pass through the filter.<br />
" The washing of the vermilion should be done very carefully, and<br />
it is often necessary to empty the contents of the filter into a large<br />
volume of pure water and to wash the filtrate several times by<br />
decantation. The red sulphide is afterwards filtered again and dried