the Carinthian Molybdate oj Lead. 335 
and the effects were nearly the same whether this substance 
was a metal or an alkali. 
The portion of molybdic acid which I detected in the nitric 
acid employed to purify the ore, and Mr. Klaproth's experi- 
ments made with the same acid, prove the first, and the expe- 
riment mentioned in § VIII. is a proof of the latter. 
The phenomena which appeared in the last experiment 
throw some light on the effects produced by nitric acid on 
molybdaena ; for when the sulphuric and muriatic solutions of 
the molybdic acid were saturated with pot-ash or soda, they 
gradually changed to yellowish green, and so on to blue, in 
proportion as the alkali was added ; but when nitric acid was 
added to the alkaline solution, the change of colour was ex- 
actly the reverse of the former, for the changes were then blue, 
green, and yellow, in proportion to the quantity of nitric acid. 
The cause of these effects I conceive to be the different de- 
grees of oxygenation of the molybdsena ; for when the first 
portion of nitric acid was added, it rather combined with the 
alkali than with the molybdic acid, and the latter was there- 
fore in some degree separated with a diminution of the ori- 
ginal quantity of oxygen, and consequently appeared as the 
blue oxyde in solution. After this, the second portion of ni- 
tric acid began to oxygenate the blue oxyde, and therefore 
changed the colour of the solution to green ; but the third ad- 
dition of nitric acid acted immediately on the oxyde, turned 
the solution yellow, and when assisted by heat, caused a quan- 
tity of the yellow molybdic acid to be precipitated. The 
alkali, however, appears to have impeded the complete sepa- 
ration of the molybdic acid, and retained a part of it together 
with the nitric acid, so as to form a yellow triple salt. 
MDCCXCVI. X X 
