N. B. But this is not to be understood of sandy stones, waxing red in some part, in the fire, containing no gold, but of flints out of which by a mutual percussion fire is brought forth, which the more pure they are the purer gold do they yield. There are also flints out of which fire is forced by percussion being red in the fire, which contain no gold but Iron; which you may know by that clear redness before the burning, which being burnt is changed into an obscure redness, not shining and crude: but the flints containing Gold, being burnt do acquire a fair golden yellowness, or reddish colour, as if they were covered with gold, and that through the whole substance if they be broken in pieces. And these give a pure gold, but those other yield a red extraction like blood, yielding not gold, but the purest and malleable iron, good in Chymick uses, (but chiefly for silver to be cemented and exalted) for gold is seldome to be found in them; the which is well to be observed lest thou draw out iron in stead of gold, and so lose thy labour. Also the best stones containing gold, are those which are white and shining, here and there throughout having in the whole substance green spots and lines, red, yellow, skie-coloured and brown. There are also black flints out of which fire is forced by percussion, having gold and iron, which may be separated with profit, yielding sometimes plenty of ironish Gold, which may in like manner, be separated of which afterward. They are very good flints also which being burnt retain a whiteness, with veins green, skie-coloured, and such like, neither are they disesteemed which burnt, have black spots, and not veins. But the stones (_Quartzen_ and _Hornstein_) although they in burning are not altered, yet if there be seen before gold volatile and spiritual, they by separation of themselves yield gold. Gross and subtle sand having light and yellow gold, yields in the burning a skie-coloured smoak, and is exalted in colour, _viz._ brownish: but that hath nothing which is not altered. Subtle earth, yellow or red, passing through sand or a mountain like a vein contains also gold, which is for the most part volatile, and not mature, flying away in reduction, having ingress into silver and other metals, and therefore for this reason conservable. For thy better knowledge thou mayst prove the stones, with white fusile glass, which thing is treated of in the fourth part of the Philosophical Furnaces, that thou mayst not have cause to impute the fault of thy errour to me; therefore I would have thee understand, _viz._ that all stones contain not gold, neither in all is it separable by the spirit of salt: they are therefore to be known before they be applyed to the work. _Now follows the preparation of flints, and the extraction of the gold contained in them, by the spirit of salt._ First the flints being made red hot in the fire, they must be quencht in cold water, after taken out and cooled, and finely powdered.