gS^ PHILOSOPHICAL TRANSACTIONS. [aNNO 1750. 



Extract of a Letter from William Brownrigg, M.D., F. R. S. to Wm. Watson, 

 F.R.S. Dated Whitehaven, Dec. 5, 1750. p. 584. 



Dr. B. here communicates an account of a semi-metal called platina di Pinto ; 

 which, so far as he knew, had not been taken notice of by any writer on mine- 

 rals. Presuming therefore that the subject was new, he requested the favour to 

 have this account laid before the r. s. The experiments related were several of 

 them made by a friend, whose exactness in performing them, and veracity in 

 relating them, he could rely on : however, for greater certainty, he should him- 

 self repeat them. 



Memoirs of a Semi-metal called Platina di Pinto, found in the Spanish West 



Indies, p. 585. 



Though the history of minerals, and other fossil substances, has been dili- 

 gently cultivated, especially by the moderns ; yet it must be acknowledged, that 

 among the vast variety of bodies which are the objects of that science, there still 

 remains room for new inquiries. 



Gold is usually esteemed the most ponderous of bodies; and yet he had seen, 

 in the possession of the late professor Gravesande, a metalline substance, 

 brought from the East Indies, that was specifically heavier than gold, by at least 

 a 20th part.* Mercury, next to gold, is commonly said to be the heaviest 

 body; yet mercury was greatly exceeded in specific gravity by a semi-metal -|- 

 brought from the West Indies, of which he had presented specimens to the r. s. 

 This semi-metal seems more particularly to deserve attention, as it is endued 

 with some very singular qualities, which plainly demonstrate that certain general 

 theorems, though long established, and universally received by the metallurgist, 

 yet do not hold true in all cases, and ought not to be admitted into their arts, 

 without proper limitations and restrictions. For instance, that gold and silver 

 may be purified from all heterogeneous substances by coppellation, is a proposition 

 that all assayers and refiners have long thought true and undeniable; yet this 

 proposition ought not to be received by those artificers, without an exception to 

 the semi-metal here treated of; since, like those nobler metals, it resists the 

 power of fire, and the destructive force of lead in that operation. 



This semi-metal was first presented to him (Dr. Brownrigg) about Q years pre- 



• This metalline substance, in the possession of Gravesande, though brought from the East In- 

 dies, (indirectly from commercial intercourse by the Spaniards with South America) was probably 

 the very metal here treated of, viz. platina (now called platinum), of which the specific gravity in its 

 purest state is 23.000, while that of gold is only 19.3. 



■\ Wrongly termed a semi-metal, but at that time taken for such, as the means of reducing it to i 

 reguline and malleable state were then unknown. 



