:
i
458 Preparations and Compositions. Part III.
the bottom of the crucible is moderately red, throw into ita small piece of zinc, about the weight of a drachm. Thezinc soon inflames, and is, at the same time, converted intowhite flakes, which are to be from time to time removedfrom the surface of the metal with an iron spatula, that thecombustion may be more complete ; and at last, when thezinc ceases to flame, the oxide of zinc is to be taken out ofthe crucible. Having then put in another piece of zinc,the operation is to be repeated, and may be repeated asoften as is necessary. Lastly, the oxide of zinc is to beprepared in the same way as the carbonate of lime.
Dub.
Take of
Zinc, broken into pieces, any quantity.
Throw it at different times into a sufficiently deep crucible,heated red hot, and placed with its mouth inclined towardsthe mouth of the furnace. After each time that any zincis thrown in, cover the crucible with another inverted overit, but loosely, so tbat the air may have access to the zinc.Preserve the white and very light sublimed powder for use.
Lond.Inject successively small pieces of zinc into a large, deep cru-cible, heated to whiteness. It must be inclined to oneside, and covered with another crucible, so that the zincmay be exposed to the action of the air, and may be stir-red with an iron spatula. Immediately take out the oxide,which arises from time to time, and pass its white andlighter part through a sieve. Pour water upon this, andreduce it to an impalpable powder, as directed for the pre-paration of chalk.
This is an instance of simple oxidizement. At a red heat,zinc attracts the oxygen of the atmosphere so strongly, that itis quickly covered with a crust of white oxide, which preventsthe air from acting on the metal below ; and therefore we aredesired to operate only on small pieces at a time, and to placethe crucible, so that we may easily take out the oxide formed,and introduce fresh pieces of zinc. As soon as the crust ofoxide is broken, or removed, the zinc inflames, and burnswith a brilliant white, or greenish blue flame, being at thesame time converted into very light flocculi. To save these asmuch as possible, we are directed to use a very deep and largecrucible, and to cover it with an inverted crucible. But aswe must not cover it, so as to prevent the access of the gift it