into the receiver, is aqua regis.—Aqua fortis, or spirit of nitre, is a nitrous acid separated from its basis, nitre, by the vitriolic acid. Aqua regis only will dissolve gold. Silver is not soluble by aqua regis; its proper solvent is the acid of nitre or aqua fortis. — But if you want to separate a mass of gold and silver, either will do. You may dissolve the gold by aqua regia, and let the silver remain pure: or, dissolve the silver by aqua fortis, and let the gold remain pure. Only note in this case of a mixed lump of gold and silver, the operation by aqua fortis is preferable, for this reason; that aqua regis in dissolving the gold, takes up likewise a little silver; but aqua fortis hath not the least effect on gold:—And note further, that if there be equal parts of gold and silver in the mixture, they cannot be

parted by aqua fortis. It has not then the least effect on the silver, which is very strange. To make aqua fortis act duly on silver mixed with gold, the silver must be at least in a triple proportion to that of the gold. The reason of the singular effect is, that when the gold exceeds, or the parts of both are equal in quantity, then, as both are intimate, united in the mass, the parts or minims of the gold coat over the parts of the silver, and defend them from the action of the aqua fortis. In this case, aqua regia must be used to dissolve the gold, and leave the silver pure: or, as aqua regia takes up a little of the silver, when it dissolves the gold, melt the metalline mass, and add as much silver, as will make it a triple proportion to the gold. Then you may by aqua fortis take up all your silver in the dissolution, and leave all the gold pure.
But as to the third criterion of gold, its being the most fixed of all bodies, this is evident from the violence of fire having no effect on it. An ounce of it exposed for the space of two months, in the eye of a glass furnace, does not lose half a grain. It may from thence be said to be incorruptible.
As to gold's resisting antimony, and not turning into scoriae by its force, it is most certain from hence, that if you take a mass consisting of gold, silver, copper, the other metals, with stones, &c. and fuse it with antimony, the

bodies