The following strange story is related by Helvetius, physician to the Prince of Orange, in his Vitulus Aureus: Helvetius was a disbeliever of the philosopher’s stone, and the universal medicine, and even turned Sir Kenelm Digby’s sympathetic powder into ridicule. On the 27th of December, 1666, a stranger called upon him, and after conversing for some time about a universal medicine, showed a yellow powder, which he affirmed to be the philosopher’s stone, and at the same time five large plates of gold, which had been made by means of it. Helvetius earnestly entreated that he would give him a little of this powder, or at least that he would make a trial of its power; but the stranger refused, promising however to return in six weeks. He returned accordingly, and after much entreaty he gave to Helvetius a piece of the stone, not larger than the size of a rape-seed. When Helvetius expressed his doubt whether so small a portion would be sufficient to convert four grains of lead into gold, the adept broke off one half of it, and assured him that what remained was more than sufficient for the purpose. Helvetius, during the first conference, had concealed a little of the stone below his nail. This he threw into melted lead, but it was almost all driven off in smoke, leaving only a vitreous earth. When he mentioned this circumstance, the stranger informed him that the powder must be enclosed in wax, before it be thrown into the melted lead, lest it should be injured by the smoke of the lead. The stranger promised to return next day, and show him the method of making the projection; but having failed to make his appearance, Helvetius, in the presence of his wife and son, put six drachms of lead into a crucible, and as soon as it was melted he threw into it the fragment of philosopher’s stone in his possession, previously covered over with wax. The crucible was now covered with its lid, and left for a quarter of an hour in the fire, at the end of which time he found the whole lead converted into gold. The colour was at first a deep green; being poured into a conical vessel, it assumed a blood-red colour; but when cold, it acquired the true tint of gold. Being examined by a goldsmith, he considered it as pure gold. He requested Porelius, who had the charge of the Dutch mint, to try its value. Two drachms of it being subjected to quartation, and solution in aqua fortis, were found to have increased in weight by two scruples. This increase was doubtless owing to the silver, which still remained enveloped in the gold, after the action of the aqua fortis. To endeavour to separate the silver more completely, the gold was again fused with seven times its weight of antimony, and treated in the usual manner; but no alteration took place in the weight.[13] [13] Bergmann, Opusc. iv. 121.