When _Aqua fortis_ dissolves Silver and not Gold, and _Aqua regia_ dissolves Gold and not Silver, may it not be said that _Aqua fortis_ is subtil enough to penetrate Gold as well as Silver, but wants the attractive Force to give it Entrance; and that _Aqua regia_ is subtil enough to penetrate Silver as well as Gold, but wants the attractive Force to give it Entrance? For _Aqua regia_ is nothing else than _Aqua fortis_ mix'd with some Spirit of Salt, or with Sal-armoniac; and even common Salt dissolved in _Aqua fortis_, enables the _Menstruum_ to dissolve Gold, though the Salt be a gross Body. When therefore Spirit of Salt precipitates Silver out of _Aqua fortis_, is it not done by attracting and mixing with the _Aqua fortis_, and not attracting, or perhaps repelling Silver? And when Water precipitates Antimony out of the Sublimate of Antimony and Sal-armoniac, or out of Butter of Antimony, is it not done by its dissolving, mixing with, and weakening the Sal-armoniac or Spirit of Salt, and its not attracting, or perhaps repelling the Antimony? And is it not for want of an attractive virtue between the Parts of Water and Oil, of Quick-silver and Antimony, of Lead and Iron, that these Substances do not mix; and by a weak Attraction, that Quick-silver and Copper mix difficultly; and from a strong one, that Quick-silver and Tin, Antimony and Iron, Water and Salts, mix readily? And in general, is it not from the same Principle that Heat congregates homogeneal Bodies, and separates heterogeneal ones?