VOL. XLVIII.] PHILOSOPHICAL TRANSACTIONS, 495 



A[ypellations qfPlatina. Platina di Pinto, Juan Blanca. By fVilliam Lewis * 



M.B., F.R.S. p. 638. 



PAPER I. 



Expcr. ] . — The substance brought into England under the name of platina 

 appears a mixture of dissimilar particles. The most conspicuous, and by far the 

 largest part of the mixture, are white shining grains, of seemingly smooth sur- 

 faces, irregular figures, generally planes with the edges rounded oiF. On exa- 

 mining these with a microscope, the surface appeared in some parts irregular, 

 tlie prominencies smooth, bright, and shining ; the cavities dark-coloured and 

 roughish. A few of them were attracted, though weakly, by a magnetic bar. 

 These grains are the true platina. The heterogeneous matters intermixed among 

 them, in the several parcels, were, 



1. A blackish dust, separable by a fine sieve. This was further divided, by 

 a magnetic bar, into 1 different substances : the part attracted was of a fine 

 sparkling black colour, much resembling the black sand from Virginia : the part 

 not attracted was of a dark brownish hue, with several bright molecuL-e, which 

 appeared to be fragments of the grains of platina. 2. Among the larger grains, 

 separated by a coarse sieve, were sundry irregular dark-coloured particles, some 

 blackish, others with a cast of brownish red, in appearance resembling frag- 

 ments of emery or loadstone. Several were attracted weakly by the magnet. 



3. There j\'ere a few rough yellow particles, resembling gold, which on further 

 examination they were found to be, though probably not entirely free from pla- 

 tina. 4. A few globules of quicksilver, containing gold, with some particles of 

 platina intermixed and pretty strongly adhering. 3. Some fine transparent par- 

 ticles, probably spar. 6. A very few irregular particles, of a jet black colour. 

 These broke easily, and looked like the finer kinds of pit-coal. Laid on a red- 

 hot iron, they emitted a yellowish smoke, and smelt like burning coal. -|- 



• Tills memoir, with its continuations in the 50th vol. of the Phil. Trans, is one of the most va- 

 luable chemical papers which had hitherto been presented to the u. s. Some years afterwards, these 

 papers were reprinted by Dr. Lewis, accompanied with an account of all that was then known re- 

 specting platina, in his Commercium Philosophico-Technicum, a work containing much useful infor- 

 mation, and, at the same time, suggesting various improvements in the arts connected with chemistry. 



Beside these. Dr. L. published a Course of Practical Chemistry j a translation, with notes, ot" 

 Neumann's Chemistry ; a New Dispensatory ; and an Experimental History of the Materia Medica. 

 The last 2 works are of the highest merit in their kind, exhibiting (to use the words of an able critic 

 on this subject) correct descriptions of drugs, with useful experiments in their treatment by different 

 menstruums, while the author is very chaste in ascribing virtues, and in repeating from former 

 writers. And from his own experience, as well as that of the most skilful London practitioners, he 

 gives a sounder judgment of the real virtues of medicinal substances than had been given before. 



When Dr. Lewis died, or what was his age, at the time of his decease, or any other particulars 

 concerning his life, we have not been able to learn. 



\ From the experiments of later chemists, it appears that the ores of platina contain several distinct 



