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followed. Kunckel observes, that by putting th? goldinto the aqua fortis first;, and then adding the salt by littleand little at a time, less of the menstruum will sufficethan if the salt was previously dissolved in the acid ; theconflict, excited by each addition of the salt, promotingthe dissolution of the gold : this method appeared uponcomparison to have a sensible advantage above the other,whether the sal ammoniac directed by Kunckel, or com-mon salt was used : the common salt is to be preferred ;for sal ammoniac, especially when a strong heat is calledin aid to hasten the solution, is apt to occasion some smallpart of the gold to be dissipated during the effervescence.

A solution in water of common salt, nitre and alum,boiled with leas gold to dryness; or the salts in substance,mixed with the gold leas, and urged with a slight red heatfor some hours in a close vessel; corrode a considerablequantity of the gold into a saline form so as to be dissolvedupon adding water. The mixture of these salts, from itsacting insensibly and without effervescence, has been com-monly called menjlruum fine firepitu : it can be consideredno otherwise than as an impure aqua regia, acting onlyby virtue of the acids of the nitre and marine salt, whichare extricated from their bases by the acid of the alum.

V. General properties ofisolutions of gold.

Solution of gold, whether made in spirit of salt, orin any of the foregoing aquæ regiæ, is of a bright yellowcolour, resembling that of gold itself. It stains the skinof a deep purple colour, which cannot be washed out;and gives a like durable stain, though with some varia-tions in the species of the colour, to sundry animal andvegetable substances, as dressed leather, ivory and bones,feathers, woollen cloth, silk, linen, cotton, wood :

O to