17. I am not sure what substance Geber understood by the word _marchasite_. It was a substance which must have been abundant, and in common use, for he refers to it frequently, and uses it in many of his processes; but he nowhere informs us what it is. I suspect it may have been sulphuret of antimony, which was certainly in common use in Asia long before the time of Geber. But he also makes mention of antimony by name, or at least the Latin translator has made use of the word _antimonium_. When speaking of the reduction of metals after heating them with sulphur, he says, “The reduction of tin is converted into clear antimony; but of lead, into a dark-coloured antimony, as we have found by proper experience.”[138] It is not easy to conjecture what meaning the word antimony is intended to convey in this passage. In another passage he says, “Antimony is calcined, dissolved, clarified, congealed, and ground to powder, so it is prepared.”[139] [138] Sum of Perfection, book ii. part iii. chap. 10. [139] Invention of Verity, chap. 4. 18. Geber’s description of the metals is tolerably accurate, considering the time when he wrote. As an example I shall subjoin his account of gold. “Gold is a metallic body, yellow, ponderous, mute, fulged, equally digested in the bowels of the earth, and very long washed with mineral water; under the hammer extensible, fusible, and sustaining the trial of the cupel and cementation.”[140] He gives an example of copper being changed into gold. “In copper-mines,” he says, “we see a certain water which flows out, and carries with it thin scales of copper, which (by a continual and long-continued course) it washes and cleanses. But after such water ceases to flow, we find these thin scales with the dry sand, in three years time to be digested with the heat of the sun; and among these scales the purest gold is found: therefore we judge those scales were cleansed by the benefit of the water, but were equally digested by heat of the sun, in the dryness of the sand, and so brought to equality.”[141] Here we have an example of plausible reasoning from defective premises. The gold grains doubtless existed in the sand before, while the scales of copper in the course of three years would be oxidized and converted into powder, and disappear, or at least lose all their metallic lustre. [140] Sum of Perfection, book i. part iii. chap. 8. [141] Ibid., book i. part iii. chap. 8.