216 ESSAY XIX. 



SUPPLEMENT TO THE FOREGOING ESSAY. BY T. BERGMAN. 



Several years ago I began an investigation of the 

 constituent parts of tungsten. Its great specific gravity 

 induced me to seek for ponderous earth in it; but 

 the process by which this earth is usually extracted 

 gave, instead of it, common calcareous earth ; and when 

 the first alkaline solution, made in the moist way, was 

 poured off, and an acid added to the solution, it gave 

 on saturation a white precipitate of an acid nature. I 

 need not relate the experiments, as I obtained the same 

 results as Mr. Scheele. Some small differences, however, 

 in my experiments with the blowpipe, deserve to be 

 mentioned. 



Tungsten, by itself, decrepitates with the blowpipe, 

 but does not melt. 



In a small gold or silver spoon it unites with mineral 

 alkali with some effervescence, and the bit of tungsten 

 falls into powder. 



With microcosmic salt it effervesces a little at first, 

 and then leaves a residuum of difficult solubility ; but the 

 glass globule assumes a bright sky-blue colour, without 

 the least sign of that redness when it is held between 

 the eye and the light which is produced when cobalt is 

 used. If more tungsten be added, the globule becomes 

 brownish, but remains still transparent ; with a further 

 addition, it becomes black and opaque. 



Borax dissolves it without motion, and almost without 

 colour ; but when the globule is overloaded with tungsten, 

 it at length becomes brown or white, and opaque in 

 cooling. 



