ESSAY XIX. 



ON THE CONSTITUENT PARTS OF LAPIS PONDEROSUS, 

 OR TUNGSTEN. 1781. 



IT is probable that the constituent parts of this species of fossil 

 have been hitherto unknown to the chemists. Cronstedt 

 enumerates it among the ferruginous stones, under the name 

 of Ferrum calciforme terrd quddam incognitd intime mixtum. 

 That which I employed in rny experiments was of a pearl 

 colour ; it was taken from the iron mines of Bitsberg ; and 

 as I made many experiments upon it, and have discovered 

 its constituent parts, I take the liberty of communicating 

 the following account to the Eoyal Academy : 



SECTION I. 



(a) In the fire tungsten does not undergo any perceptible 

 change, nor does glass of borax produce any sensible effect 

 upon it; (b) but with microcosmic salt it forms, by means 

 of the blowpipe, a glass of a sea-green colour. If the globule 

 be kept in fusion at the extreme point of the flame, the 

 colour gradually disappears ; a very little nitre also very soon 

 destroys the colour ; but it returns whenever the blue part 

 of the flame is driven on the globule ; consequently it is the 

 phlogiston of the flame which is the cause of the colour. 

 (c) One part of tungsten, reduced to a fine powder in a glass 

 mortar, was mixed with four parts of alkali of tartar, and 



placed in the fire in an iron crucible. The mixture, when 



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