According to the important experiments of Proust,[[374]] it appears, that if lead be associated with tin, it will be incapable of furnishing to acids any saturnine impregnation. The following are the interesting conclusions at which this philosopher has arrived, viz.
“That the tinning, which contains even so large a proportion as an equal part of lead, cannot be dangerous; since it is sufficient that the lead should be combined with tin, in order to prevent it from being dissolved, either in lemon juice, or vinegar, the two acids most to be feared. The tin, being more oxidable than the lead, dissolves exclusively in these acids, and prevents the second from being attacked. The lead cannot appropriate to itself an atom of oxygen, but the tin would carry it off in an instant.”
Sugar of Lead—Saccharum Saturni—Cerussa Acetata—Plumbi Super-acetas.
This salt of lead, to whose presence the numerous accidental maladies above enumerated are to be chiefly attributed, occurs in commerce in the form of irregular masses resembling lumps of sugar, being an aggregation of acicular four-sided prisms terminated by dihedral summits; its taste is sweet and astringent. It is soluble in 25 parts of water, hot, or cold; when common spring water, however, is employed for such a purpose, a white precipitate occurs from the presence of a certain proportion of sulphates and carbonates.
When this salt is exposed to the action of heat, it undergoes aqueous fusion, then dries, and at length is decomposed, leaving a globule of metallic lead, mixed with the yellow protoxide, and an acid product of a fetid smell. This decomposition is similar to that which vegetable substances undergo when heated for some time. The quantity of metallic lead, thus obtained, will be more considerable if the salt has been previously mixed with charcoal, and particularly if it be submitted for a long time to the action of a powerful heat. The strong sulphuric acid of commerce, when poured upon sugar of lead in powder, decomposes it with effervescence, and disengages vapours of acetic acid.
This must be considered as an active preparation, and may, when administered in doses of a few drachms, speedily occasion death. At the same time, like other poisons, it may by judicious administration, become a valuable remedy. See Pharmacologia, art. Plumbi Super-acetas.
In consequence of the sweet taste of this salt, children have been induced to swallow it.
Goulard’s Extract. Liquor Plumbi Sub-acetatis.
This liquor is a saturated solution of the sub-acetate of lead. Spring water, from the salts which it contains, produces with it a very milky and turbid appearance; and even when distilled, in consequence of the carbonic acid diffused through it, it will occasion precipitation. It is principally used as an external application to diminish inflammation, an effect which it probably produces by paralysing the nerves of the part. Cases have occurred where this lotion has been accidentally swallowed, and the usual symptoms of saturnine poisoning have supervened. How far its external application may be capable of occasioning mischief, will form a subject of inquiry under the consideration of the physiological action of the preparations of lead.