Rupert's inventions were many, and were connected chiefly with the improvement of weapons and materials of war. He made an improved lock for fire-arms; increased the power of gunpowder ten times; invented a kind of revolver; a method of making hail-shot; a means of melting black-lead like a metal; a substance composed of copper and zinc, and called "Prince's metal" to this day; and a screw which facilitated the taking of observations with a quadrant at sea. In 1671 he took out a patent "for converting edge-tools forged in soft iron, after forged; and for converting iron wire, and softening all cast or melted iron, so that { 338} it can be wrought and filed like forged iron."[16] He also had a patent for tincturing copper upon iron,[17] and he built a house at Windsor for the carrying on of his works. Besides his scientific works and studies, he had on hand innumerable projects, adventurous and commercial. He was deeply interested in African trade, and was a patentee of the Royal African Company, formed for its promotion. In 1668 he had conceived a scheme for discovering the north-west passage. The idea had been suggested to him by a Canadian, and he forthwith demanded of the King a small ship, the "Eagle," which he despatched on the quest.[18] As a result of this, he became first President of the Hudson Bay Company, to which the King granted in 1670 the sole right to trade in those seas.[19] In the same year he was appointed to the Council of trade and plantations. During the Dutch wars he fitted out four privateers, the "Eagle," the "Hawk," the "Sparrow Hawk," and the "Panther."[20] In 1668 he petitioned, in conjunction with Henry Howard, for the sole right to coin farthings, for which he had invented a new model.[21] This petition was regarded with great favour by the nation at large, for "every pitiful shopkeeper" coined at his own pleasure, and the abuses of the system were many. The farthings of Prince Rupert were "much talked of and desired;"[22] and, in consequence of his petition, he was empowered, with Craven and others, to examine into the abuses of the Mint.[23] Later he started a project, in partnership with Shaftesbury, for working supposed silver-mines in Somersetshire.[24]