200 On Tungsten. {Sepr. 
to redness, and was of a light lemon-yellow colour, were digested 
for some time with a warm selution of concentrated caustic am- 
monia. In about an hour the mixture was raised to the boiling 
temperature ; but 1 did not by this means obtain a complete solu- 
tion. ‘The muxture was allowed to remain at rest for some time ; 
and by this means the liquid was separated from the undissolved 
yellowish-grey oxide, and carefully evaporated in a porcelain bason. 
By this means I] obtained 47 gr. of a pea-coloured, foliated, brilliant 
mnass, easily separated from the porcelain vessel, and possessing 2 
hot bitter taste. It was tungstate of ammonia. 
‘This result was quite contrary to my expectation, and to the 
assertion of other chemists, according to whom pure tungstic oxide 
is very easily soluble in ammonia. This required a further exami- 
nation of the residuum which was insoluble in ammonia. 
Exper. 3.—This residuum was treated with 8 oz. of caustic am~ 
monia, in the same manner as above related; after which the liquid 
part was separated from the solid powder, which still had a very 
grey appearance. By evaporation the solution deposited only 27 gr. 
of asalt having the same colour as in the preceding experiment, of 
a pulverulent appearance, and having a sharp bitter taste. 
Exper. 4.—As | conjectured that the tungstic oxide was some~ 
what deoxidized by the ammonia, and thereby rendered grey, I 
tried, by exposing it to a red heat, to bring this oxide back to its 
original state, and to obtain a greater proportion of it dissolved in 
ammonia. I found that by this treatment the grey oxide again 
assumed a yellow colour, and amounted now to only 230 gr. With 
this powder the following experiment was made. 
Exper. 5.—100 gr. of the same oxide were mixed with 4 oz. of 
caustic ammonia, and the mixture was digested for 12 hours in a 
very moderate heat, being often agitated during the digestion. The 
liquid part was then allowed to separate from the undissolved por- 
tion, and decanted off. This solution by evaporation yielded 55 gr. 
of a white powder, which had a hot and bitter taste, and possessed 
the properties of tungstate of ammonia. The yellowish-grey colour 
of the undissolved residuum showed that even in this case, notwith- 
standing the very moderate heat of the ammonia, a commencement 
of deoxsidation had taken place. 
Exper. 6.—The solid residue of the preceding experiment was 
treated in the same way once more with 4 oz. of caustic ammonia, 
and the liquid portion separated from the undissolved powder, which 
had a light grey colour. This solution, when evaporated, gave 11 
gr. of a pea-yellow powder, which was tungstate of ammonia, and 
possessed the same taste as that obtained in the preceding experi- 
ments. I could not in this case determine the quantity of matter 
that had remained undissolved, because a portion of it had been 
lost. ‘ 
The result of these experiments shows us that our tungstic oxide, 
after being exposed to a red heat, is with difficulty soluble in caustic 
