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

by Pierre Joseph Macquer

It is necessary in this operation, and more so than in any other, to warm the vessels gradually, and to proceed exceeding slowly; otherwise the artist runs the risque of seeing his vessels burst to pieces with violence, and with great danger to his person: for Arsenic acts on Nitre with incredible vivacity; insomuch that, if a mixture of Nitre and Arsenic be heated to a certain degree, the Nitre is decomposed almost as rapidly, and with as great an explosion, as when it is made to fulminate with an inflammable matter. In short, the appearances are such, that one would be almost induced to think the Nitre really takes fire on this occasion: though it be only decomposed just as it is by the Vitriolic Acid.

The solution of the caput mortuum of this distillation contains, at the same time, several sorts of Salts: to wit, 1. the Neutral Salt of Arsenic, formed by the union of the Arsenic with the basis of the Nitre; this shoots into the prismatic crystals above-mentioned: 2. some Nitre that hath not been decomposed; this forms the needles and part of the vegetations: 3. a small portion of Arsenic, that is known to be soluble in water; this forms the thin dark pellicle that covers the surface of the liquor when it begins to evaporate.

For the properties of this new Neutral Salt of Arsenic you may consult what we have said thereupon in our Elements of the Theory, and in the Memoirs of the Academy of Sciences.

PROCESS V.

To alkalizate Nitre by Arsenic.

Melt in a crucible the Nitre you intend to alkalizate. When it is melted, and moderately red, project upon it two or three pinches of pulverized Arsenic. A considerable effervescence and ebullition will immediately be produced in the crucible, attended with a noise like that which Nitre makes, when it detonates with an inflammable matter. At the same time a thick smoke will rise, which at first will smell like garlic, the odour peculiar to Arsenic; it will also smell afterwards like Spirit of Nitre. When the effervescence in the crucible is over, throw again upon the Nitre as much pulverized Arsenic as you did the first time; and all the same phenomena will be repeated. Continue thus throwing in Arsenic in small parcels, till it produce no more effervescence; taking care to stir the matter at every projection with an iron wire, the better to mix the whole together. Then increase your fire, and melt what remains. Keep it thus in fusion for a quarter of an hour, and then take the crucible out of the fire. It will contain a Nitre alkalizated by Arsenic.

OBSERVATIONS.

This operation, as well as the preceding one, is a decomposition of Nitre by Arsenic; yet the result is very different: for, instead of a Salt capable of crystallizing, and discovering no tokens either of Acid or Alkali, we obtain, on this occasion, only a Salt that runs into a liquor by the moisture of the air, doth not crystallize, and hath all the properties of an Alkali.

These differences arise only from the different manner in which the decomposition of the Nitre, and the union of the Arsenic with the basis of that Salt, is brought about. When the Nitrous Acid is distilled by the interposition of Arsenic, with a view to obtain the Arsenical Salt, the operation must be performed in close vessels; no greater degree of heat must be applied to the mixture than is necessary for enabling the Arsenic to act; and that heat must be administered very slowly and by insensible degrees. But, when the business is to alkalizate Nitre by the means of Arsenic, the operation is performed in a crucible, in a naked fire, with a strong degree of heat, and that suddenly applied. The violence of the heat, the suddenness with which it is applied, the vivacity wherewith the Arsenic unites with the basis of the Nitre; and, still more than all these, the free access of the air, occasion the greatest part of the Arsenic, which at first combines with the basis of the Nitre after having expelled its Acid, to be presently carried off and dissipated in vapours; and consequently the basis of the Nitre, not being sufficiently saturated, discovers its Alkaline properties.

I say, the concurrence of the air contributes, still more than all the rest, to separate the Arsenic from the Alkaline basis of the Nitre; experience having taught me that the Neutral Salt of Arsenic is not to be alkalizated by the most violent force of heat, as long as it continues in close vessels, and the external air hath no communication with it; but that some of the Arsenic contained in that Salt is dissipated, by exposing it to a strong heat in open vessels.