Corrosive Sublimate is the most violent and the most active of all corrosive poisons. It is never used in Medicine, but in external applications. It is a powerful escharotic; it destroys proud flesh, and cleans old ulcers: but it must be used by those only who know how to apply it properly, and requires an able hand to manage it. It is not commonly applied by itself, but mixed in the proportion of half a dram to a pound of lime-water. This mixture is yellowish, and bears the name of Aqua Phagadenica.
Water dissolves Corrosive Sublimate, but in a small quantity. If a Fixed Alkali be mixed with this solution, the Mercury precipitates in the form of a red powder. If the precipitate be procured by a Volatile Alkali, it is white; if by Lime-water, it is yellow. This Mercurial Salt dissolves pretty easily in boiling Spirit of Wine.
PROCESS VIII.
Sweet Sublimate.
Take four parts of Corrosive Sublimate; pulverize it in a glass or marble mortar; add by little and little three parts of Mercury revivified from Cinabar; triturate the whole carefully, till the Mercury be perfectly killed, so that no globule thereof can be perceived. The matter will then be grey. Put this powder into an apothecary's phial, or into a matrass, whose neck is not above four or five inches long, leaving two thirds thereof empty. Set the vessel in a sand-bath, and put sand round it to one third of its heighth. Apply a moderate fire at first; and afterwards raise it gradually till you perceive that the mixture sublimes. Keep it up to this degree till nothing more will rise, and then break the vessel. Reject, as useless, a small quantity of earth which you will find at the bottom; separate also what adheres to the neck of the vessel, and carefully collect the matter in the middle, which will be white. Pulverize it; sublime it a second time, in the same manner as before; and in the same manner separate the earthy matter left at the bottom of the vessel, and what you find sublimed into the neck. Pulverize, and sublime a third time, the white matter you last found in the middle. The white matter of this third sublimation is the Sweet Sublimate, called also Aquila Alba.
OBSERVATIONS.
The Acid of Sea-salt in the Corrosive Sublimate is very far from being perfectly saturated with Mercury; and thence comes the corrosive quality of this saline compound. But though Mercury, as appears by this combination, is capable of imbibing a much greater quantity of Acid than is necessary to dissolve it; nay, though it naturally takes up this superabundant quantity of Acid, yet it doth not follow from thence that this redundant Acid may not combine with Mercury to the point of perfect saturation, so as to lose its corrosive acidity.
This is the case in the operation here described. A fresh quantity of running Mercury is mixed with Corrosive Sublimate; and the fresh Mercury, combining with the super-abounding Acid, deprives the Sublimate of its acrimony, and forms a compound which comes much nearer the nature of a Neutral Metallic Salt.
Trituration alone is not sufficient to produce an union between the newly added Mercury and the Acid of the Corrosive Sublimate: because, generally speaking, the Acid of Sea-salt cannot dissolve Mercury without the help of a certain degree of heat, and unless it be reduced into vapours.
Thus, though the newly added Mercury becomes invisible by trituration, and seems actually combined with the Corrosive Sublimate, yet the union is not intimate. There is only an interposition of parts, but no true dissolution of the newly added Mercury by the super-abundant Acid of the Corrosive Sublimate. For this reason the mixture must be sublimed; and by this sublimation only is the true union effected. Nor is one single sublimation sufficient: no less than three are necessary to deprive the Sublimate of the corrosive quality which renders it poisonous. After the third sublimation, the Sublimate being put upon the tongue gives no considerable sensation of acrimony; nor doth it retain any more of its former activity than is requisite to make it a gentle purgative, when administered from six to thirty grains for a dose.