Elements of the Theory and Practice of Chymistry, 5th ed.

by Pierre Joseph Macquer

In treating of Copper we promised to shew, under the article of Lead, how to separate it from Iron. The process is founded on that property of Lead which renders it incapable of mixing and uniting with Iron, though it readily dissolves all other metalline substances. Therefore, if you have a mass compounded of Copper and Iron, it must be fused with a certain quantity of Lead, and then the Copper, having a greater affinity with Lead than with Iron, will desert the latter and join the former, which being incapable of any union with Iron, as was said, will wholly exclude it from the new compound. The next point is to separate the Lead from the Copper; which is done by exposing the mass compounded of these two metals to a degree of fire strong enough to deprive the Lead of its metalline form, but too weak to have the same effect on the Copper: and this may be done; since, of all the imperfect metals, Lead is, next to Tin, the easiest to be calcined, and Copper on the contrary resists the greatest force of fire longest, without losing its metalline form. Now what we gain by this exchange, viz. by separating Copper from Iron and uniting it with Lead, consists in this, that as Lead is calcined with less fire than Iron, the Copper is less exposed to be destroyed: for it must be observed that, however moderate the fire be, it is hardly possible to prevent a certain quantity thereof from being calcined in the operation.

Lead melted with a third part of Tin forms a compound, which being exposed to a fire capable of making it thoroughly red-hot, swells, puffs up, seems in some sort to take fire, and is presently calcined. These two metals mixed together are much sooner calcined than either of them separately.

Both Lead and Tin are in some measure affected by water, and by a moist air; but they are both much less subject than Iron or Copper to be corroded by these solvents, and of course are much less liable to rust.

The vitriolic acid acts upon and dissolves Lead, much in the same manner as it doth Silver.

The nitrous acid dissolves this metal with much ease, and in great quantities; and from this solution a small portion of Mercury may be obtained. On this subject see our Elements of the Practice of Chymistry.

When this solution of Lead is diluted with a good deal of water, the Lead precipitates in the form of a white powder; which happens because the acid is rendered too weak to keep the Lead dissolved.

If this solution of Lead be evaporated to a certain degree, it shoots into crystals formed like regular pyramids with square bases. These crystals are of a yellowish colour, and a saccharine taste: they do not easily dissolve in water. This nitrous metalline salt has the singular property of detonating in a crucible, without any additament, or the contact of any other inflammable substance. This property it derives from the great quantity of phlogiston contained in, and but loosely connected with, the Lead which is one of its principles.

If spirit of salt, or even sea-salt in substance, be added to a solution of Lead in the nitrous acid, a white precipitate immediately falls; which is no other than the Lead united with the marine acid. This precipitate is extremely like the precipitate of Silver made in the same manner, and that being called Luna cornea hath occasioned this to be named Plumbum corneum. Like the luna cornea it is very fusible, and being melted hardens like it into a kind of horny substance: it is volatile, and may be reduced by means of inflammable matters combined with alkalis. But it differs from the luna cornea in this chiefly, that it dissolves easily in water; whereas the luna cornea, on the contrary, dissolves therein with great difficulty, and in a very small quantity.

As this precipitation of Lead from its solution in spirit of nitre is procured by the marine acid, Lead is thereby proved to have a greater affinity with the latter acid than with the former. Yet, if you attempt to dissolve Lead directly by the acid of sea-salt, the solution is not so easily effected as by the spirit of nitre, and it is always imperfect; for it wants one of the conditions essential to every solution in a liquor, namely transparency.