102 PHILOSOPHICAL TRANSACTIONS. [aNNO 1750. 



small value, yet they are extremely curious, and worthy to be esteemed, as well 

 for their great antiquity, as for their being the performances of those barbarous 

 people." 



Some of these piedras de Inga Mr. W. laid before the Society, both in their 

 rough and in their polished state. They were brought hither with several other 

 curiosities from America, by Don Pedro Maldonado, and were presented by him 

 to the president, who was pleased to put them into his hands. They are doubt- 

 less of a metalline substance, and have, in his opinion, evident marks of having 

 been fused and cast. They very much resemble, as will be seen by comparing 

 them, the platina before mentioned : and though they are called (piedras) stones 

 by Don Antonio d'UUoa, he likewise gives the same appellation to the platina. 

 He cannot therefore help recommending to some curious metallurgist of the So- 

 ciety to make the experiment, whether, when the piedras de Inga are, by a 

 proper process, divested of their stony and other heterogeneous parts, the metal- 

 line residuum will not resemble, as well in specific gravity, as ip other properties, 

 the purified platina. 



The fourth communication on this subject is from M. da Costa, who states 

 that in Jan. 1742-3, there were brought from Jamaica, in a Man of War, se- 

 veral bars (as thought) of gold, consigned from different merchants of that island, 

 to their different correspondents here, as bars of gold. These bars had the same 

 specific gravity, or rather more than gold, and were exactly like that metal in 

 colour, grain, &c. A piece of one of these counterfeit bars was sent to the 

 mint to be tested, and it was found to be 21 carats 3 grs. worse than standard. 

 yi The 5th communication is an extract of a letter from Wm. Brownrigg, m.d., 

 F.K.s. to Wm. Watson, f.r.s., containing some further experiments on the pla- 

 tina. Dated Whitehaven, Feb. 13, 1750. Wherein he thanks Mr. Watson 

 for his trouble in presenting his specimen of platina to the r.s., together with 

 his memoir relating to it ; and he further thanks him for the addition made to it 

 of the extract from Don d'UUoa's Voyage. 



The gentleman, whose experiments on platina Dr. B. mentioned to the r.s., 

 was Mr. Charles Wood, who permitted him to make what use of them he 

 pleased ; and he did not pretend to have made any new discovery, nor to know 

 so much of that body, as had long been known to the Spaniards. 



The chief thing about which he had any difficulty, was what had been asserted 

 of the platina's resisting the force of lead in coppellation. This experiment he 

 had tried, therefore, by adding to 26 grs. of platina, 1 6 times its weight of pure 

 lead, that he had reduced from litharge. To the lead put into a coppel, and 

 placed in a proper furnace, as soon as it was melted he added the platina, which 

 in a short time was dissolved in the lead. After the lead was all wrought off^ 

 there remained at the bottom of the coppel a pellet of platina, which he found to 



