PROCESS II.
To sublime Zinc into Flowers.
Take a very deep, large crucible: place it in a furnace, so that it may stand inclining in an angle of forty-five degrees nearly. Throw some Zinc into it, and kindle a fire in the furnace somewhat stronger than would be necessary to keep Lead in fusion. The Zinc will melt. Stir it with an iron wire, and there will appear on its surface a very bright white flame: two inches above this flame a thick smoke will be formed, and with this smoke exceeding white Flowers will rise, and remain some time adhering to the sides of the crucible, in the form of a very fine light down. When the flame slackens, stir your melted matter again with the iron wire: you will see the flame renewed, and the flowers begin again to appear in greater abundance. Go on thus till you observe that the matter will not flame, nor any more Flowers rise.
OBSERVATIONS.
Zinc takes fire very easily as soon as it is affected by a certain degree of heat; which proves, that in the composition of this semi-metal there is very much phlogiston, united but slightly with its metallic earth. The Flowers into which Zinc resolves, during its combustion, are of a perfectly singular nature, and differ greatly from all the other productions obtainable out of metallic substances.
They may be considered as the very calx of Zinc, or its metallic earth robbed of its phlogiston, and sublimed during the combustion of this semi-metal, being probably carried up by the phlogiston in flying off. For these Flowers, when once sublimed, are afterwards exceedingly fixed: they sustain the greatest violence of fire without rising, and are converted by it into a sort of glass.
None of the methods hitherto employed, for restoring to the Flowers of Zinc their metalline form, have ever succeeded. When treated like other metalline calces in a crucible, with every kind of inflammable matter, and different sorts of reducing fluxes, they never can be re-metallized: they only melt with the flux, and produce a kind of Glass.
Mr. Marggraff indeed, as mentioned before, obtained Zinc from these Flowers, by treating them as he did Calamine in a retort with charcoal-dust: but as the Flowers often carry up with them little particles of undecomposed Zinc, there still remains some doubt concerning the reduction of these Flowers, even by this method.
If the crucible, into which you put the Zinc to be converted into Flowers, instead of being left open, as directed, be covered with another crucible inverted, the two vessels luted together, placed in a melting furnace, and a strong fire immediately kindled and kept up for about half an hour; you will find, when the vessels are cold, that all the Zinc hath left the lower crucible, and is sublimed into the upper one, in its metalline form, without suffering any decomposition. This experiment proves, that Zinc, to be converted into Flowers, must necessarily be set on fire and burnt. As it cannot burn in close vessels, any more than other combustible bodies, and as it is volatile, it sublimes without suffering any decomposition. Regulus of Antimony and Bismuth may be sublimed in the same manner; but not so easily as Zinc, which is still more volatile than those other semi-metals.
It is necessary to stir the Zinc in fusion from time to time with an iron wire, when you intend to convert it into Flowers: for there forms on its surface a grey crust that obstructs its deflagration, and beneath which it is gradually converted into a clotted calx. In order, therefore, to promote the rising of the flowers, care must be taken to break this crust, as oft as it begins to form. On this there immediately appears a very bright white flame: two inches above the flame is seen a thick smoke, and with this smoke very white Flowers rise, that continue some time adhering to the inside of the crucible, in the form of a fine down.