All metallic precipitates obtained in this manner are found to be a combination of the metal with Arsenic; whence it necessarily follows that the new Neutral Salt is by this means decompounded, its arsenical part uniting with the metallic substance, and its alkaline basis with the acid in which that substance was dissolved. The affinities of these several bodies must be considered as operating on this occasion in the following manner: The acids which tend to decompound the Neutral Salt of Arsenic, by virtue of their affinity with its alkaline basis, are not able to accomplish it, because this affinity is powerfully counteracted by that which the Arsenic has with the same alkaline basis, and which is equal or even superior to theirs. But if these acids happen to be united with a substance which naturally has a very great affinity with the arsenical part of the Neutral Salt, then, the two parts of which this Salt consists being drawn different ways by two several affinities tending to separate them from each other, the Salt will undergo a decomposition, which could not have been effected without the help of this second affinity. Now, as metallic substances have a great affinity with Arsenic, it is not surprising that the Neutral Salt of Arsenic, which cannot be decompounded by a pure acid, should nevertheless yield to an acid combined with a metal. The decomposition of this Salt, therefore, and the precipitation which of course it produces in metallic solutions, are brought about by the means of a double affinity; namely, that of the acid with the alkaline basis of the Neutral Salt, and that of the metal with the arsenical part of that salt. Arsenic has not the same effect on sea-salt as on nitre, and cannot expel its acid: a very singular phenomenon, for which it is hard to assign a reason; for the nitrous acid is known to have a greater affinity than the marine acid with alkalis, and even with the basis of sea-salt itself. Yet Arsenic may be combined with the basis of sea-salt, and a Neutral Salt thereby obtained, like that which results from the decomposition of nitre by Arsenic: but for that purpose a quadrangular nitre must be first prepared, and Arsenic applied thereto as to common nitre. The Salt produced by uniting Arsenic with the basis of sea-salt very much resembles the Neutral Salt of Arsenic above treated of as well in the figure of its crystals as in its several properties. Arsenic presents another singular phenomenon, both with the alkali of nitre and with that of sea-salt; which is, that if it be combined with these salts in a fluid state, it forms with them a saline compound, quite different from the Neutral Salts of Arsenic which result from the decomposition of nitrous salts.