From this work, it will be easily understood why the author does not give himself out as the inventor of the gold-purple[317], which he is commonly supposed to be, at which Lewis is much astonished. It is seen also by it that Leibnitz calls him improperly a physician at Hamburg, having probably confounded the father and son together[318]. Upon the whole, it is not proved that any of the Cassius’s was the inventor of the above precipitate, else it would certainly not have been omitted[319] in this treatise; and mention of gold-purple is to be found in the works of several old chemists[320]. Something of this kind has, doubtless, been meant by the old chemists, when they talk of red lions, the purple soul of gold, and the golden mantle; but what they wished to conceal under these metaphors, I am not able to conjecture. In the year 1606, when Libavius published his Alchemy, the art of making ruby-glass must have been unknown. He indeed quotes an old receipt for making rubies; and conjectures, that because the real stones of the same name are found in the neighbourhood of gold mines, they may have acquired their colour from that metal; and that by means of art, glass might be coloured by a solution of gold[321]. The later chemists, however, and particularly Achard, found no traces of gold, but of iron, in that precious stone[322]. Neri, who lived almost at the same time as Libavius[323], was better acquainted with the gold-purple, though his receipt is very defective. According to his directions, the gold solution must be evaporated, and the residue suffered to remain over the fire until it becomes of a purple colour. One may readily believe that this colour will be produced; but glass will scarcely be coloured equally through by this powder, and perhaps some of the gold particles will show themselves in it. Kunkel affirms, and not without reason, that something more is necessary to make rubies by means of gold; but he has not thought proper to tell us what it is[324]. Glauber, who wrote his Philosophical Furnace[325] about the middle of the seventeenth century, appears to have made several experiments with the gold-purple. He dissolved the metal in aqua regia; precipitated it by liquor of flint, and melted into glass the precipitate, which contained in it abundance of vitreous earth[326].