ESSAY XII. 



EXPERIMENTS UPON MOLYBD^ENA. 1778. 



1 DO not intend to treat here of the common niolybdsena 

 which is to be met with in the shops, for that is very 

 different from the sort concerning which I am now com- 

 municating my experiments to the Royal Society. Mine is 

 that kind which Cronstedt in his mineralogy calls molybdcena,, 

 membranacea, nitens, and with which Mr. Quist and several 

 others made their experiments. The specimens, which I had 

 an opportunity to examine, were taken from different places, 

 but were all found to be of the same nature, and to consist of 

 the same constituent parts. 



SECTION I. 



I first wished to know what effects molybdsena would 

 produce in the moist way. It was necessary for this 

 purpose to have it very finely pow r dered. This being 

 impossible to effect without some addition, on account of its 

 flexible lamellae, I triturated it in a glass mortar, with some 

 pieces of vitriolated vegetable alkali, and thus I at last 

 reduced it to a fine powder ; upon which, after it was sifted, 

 I poured hot water, stirring the mass well together. After 

 the molybdsena had sunk to the bottom, I poured off the 

 solution, and repeated the same process several times, till 

 all the vitriolated tartar was entirely washed off; I then 

 dried the powder that remained. 



