A course of chemistry containing an easie method of preparing those chymical medicins which are used in physick : with curious remarks and useful discourses upon each preparation, for the benefit of such who desire to be instructed in the knowledge of this art / by Nicholas Lemery, M.D.

Calcination of Lead.

Melt Lead in an earthen Pan unglazed, and stir it over the Fire with a Spatule 'till it is reduced to a powder. If you increase the Fire, and still Cal∣cine the Matter for an hour or two, it will be more open and fit to be penetrated by acids.

If you put this Powder to Calcine in a Rever∣beratory Fire for three or four hours, it will be of a red colour, and is that which is called Minium.

Lead is also prepared into Cerusse or White-Lead by the means of Vinegar, whose vapour it is made to imbibe; for it turns into a White Rust, that is gather'd up, and little Cakes made of it.

Two parts of Lead may be melted in a Pot or Crucible, and one part of Sulphur added to it; when the Sulphur is burnt out, you'l find the mat∣ter turned into a black powder, which is called Plumbum ustum.

All these Preparations of Lead are of a drying nature; they may be mixed with unguents and plaisters, they unite with oils or fat substances in the boiling, and they do give them a solid con∣sistence, and the greatest part of our plaisters do derive their hardness from it.

I spoke of the way of reducing Lead into Li∣tharge, when I treated of the Purification of Silver by the Coppel, and it is thither I desire my Reader to return.

Remarks.

There happens an observation in the Calcina∣tion of Lead, as well as several other things, which very well deserves some reflection. 'Tis that although the Sulphureous or Volatile parts of Lead do fly away in the Calcination, which loss should indeed make it weigh the less, nevertheless after a long Calcining 'tis found, that instead of losing it increases in weight.

Some trying to explicate this Phaenomenon do say, that as long as the violence of the flame does open and divide the parts of the Calx of Lead, the acid of the Wood or other matter that burns, does insinuate into tha pores of this Calx, where 'tis stopt or fixt by the Alkali; but this reason will not hold, when 'tis considered that this Aug∣mentation comes to pass as well when Lead is Cal∣cin'd with Coals as Wood, for Coals contain only a fixt Salt that rises not at all.

'Tis better therefore to refer this effect to the disposition of the pores of Lead in such a manner, that part of the fire insinuating into them does there remain imbodied, and can't get forth again, whence the weight comes to be encreased.

If you would revive this Calx of Lead by way of Fusion, its parts do squeez and express the ig∣neous particles that were inclosed, and the Lead

does thereby weigh less than it did when reduced into a Calx, for by this means the Sulphureous parts are separated and lost.