From what hath been already said it is clear, that all these combinations of Silver with acids may be decompounded by absorbent earths and by fixed alkalis; it being a general law with regard to all metallic substances. We shall not therefore repeat this observation when we come to treat of the other metals; unless some particular occasion require it. With regard to Silver I must take notice that, when separated by these means from the acids in which it was dissolved, it requires nothing but simple fusion to restore it to its usual form; because it does not, any more than Gold, lose its Phlogiston by those solutions and precipitations. Silver unites with sulphur in fusion. If this metal be only made red-hot in a crucible, and sulphur be then added, it immediately flows; the sulphur acting as a flux to it. Silver thus united with sulphur forms a mass that may be cut, is half malleable, and hath nearly the colour and consistence of Lead. If this sulphurated Silver be kept a long time in fusion, and in a great degree of heat, the sulphur flies off and leaves the Silver pure. But if the sulphur be evaporated by a violent heat, it carries off with it part of the Silver. Silver unites and mixes perfectly with Gold in fusion. The two metals thus mixed form a compound with properties partaking of both. Metallurgists have hitherto sought in vain for a perfectly good and easy method of separating these two metals by the _dry way_ only: (this term is used to signify all operations performed by fusion): but they are conveniently enough parted by the _moist way_, that is, by acid solvents. This method is founded on the above-mentioned properties of Gold and Silver with respect to acids. It hath been shewn that _aqua regis_ only will dissolve Gold; that Silver, on the contrary, is not soluble by _aqua regis_, and that its proper solvent is the acid of nitre; consequently, when Gold and Silver are mixed together, if the compound mass be put into _aqua fortis_, this acid will take up all the Silver, without dissolving a particle of the Gold, which will therefore remain pure; and by this means the desired separation is effected. This method, which is commonly made use of by Goldsmiths, and in Mints, is called the _Parting Assay_. It is plain, that if _aqua regis_ were employed instead of _aqua fortis_, the separation would be equally effected; and that the only difference between this process and the former would consist in this, that now the Gold would be dissolved, and the Silver remain pure. But the operation by _aqua fortis_ is preferable; because _aqua regis_ does take up a little Silver, whereas _aqua fortis_ hath not the least effect on Gold.