M. Berthelot has reminded us[107] that the transmission of receipts for such processes from early times to our own has been naturally and inevitably secured by the unbroken continuity of practice in the arts which gave them birth, and that they thus passed safely from generation to generation, and even spread from the tribes that originated them to other and distant peoples. He cites in support of this observation a papyrus of the third century, preserved at Leyden, which, he says, contains what are substantially the same directions as those of the chief mediæval authorities in such matters: the _Mappae Clavicula_ and the _Compositiones ad Tingenda_.[108] These receipts are not unnaturally entitled ‘How to make Gold,’ and it is curious to find in them the veritable starting-point of the dreams which made so many a furnace smoke, and so many a crucible glow during the course of centuries, in the vain hope of effecting an actual transmutation of substance. Thus it was that in the first ages, long before authentic record, in the dimness of early Egyptian history, or of that still more ancient Pelasgic civilisation from which the pyramid-builders learned so much, the germs of this science may already be perceived. Only one source of genuine gold seems then to have been known: the mines of Ophir. This circumstance, by making the supplies of precious metal small and uncertain, mightily encouraged the art which taught men to counterfeit its appearance in a colourable way. How this was done may be judged of by the receipts themselves. The _Mappae Clavicula_, for instance, has the following: ‘To make gold. Silver, one pound; copper, half-a-pound; gold, a pound; melt, etc.’ Here indeed a considerable proportion of the precious metal itself was required, but there are other receipts which dispense with any such admixture. It is said, for example, that one hundred parts of copper and seventeen of zinc joined in a state of fusion with divers small proportions of magnesia, sal ammoniac, quicklime, and tartar, yield an alloy which is fine in grain and malleable, which may be polished and used in damascening just as if it were the pure gold that it has all the appearance of being. Such then were the receipts which formed the hereditary riches of the mighty clan of the _Smiths_. It is easy to see how the famous ‘powder of projection,’ so much sought in later times, was, in fact, but the transfiguration of one of these formulae.