208 On Tungsten. _ [Supr. 
which possessed the following properties. Its external appearance 
was similar to that of gum-arabic ; but it was more easily reduced to 
powder, and had a peculiar bitter, biting, and sharp metallic taste. 
This easily soluble tungstate of ammonia, being exposed for an hour 
to a gentle red heat in a glass with a narrow mouth, left 40 gr. of a 
light blue oxide, which at the commencement was yellow. These 
AO gr. were put into a crucible, and exposed for an hour to a strong 
white heat in a blast furnace without any mixture of charcoal 
powder. It was converted into an oxide of a deep blue colour. 
Being mixed with charcoal powder, and treated as in experiment 16, 
a regulus was obtained in small grains, possessing the properties 
already described. 
The salt remaining undissolved by the ammonia exhibited the 
properties of the quadruple compound, only it was somewhat more 
difficultly soluble, and probably contained a greater proportion of 
oxygen. It consisted of small clear crystals, and weighed 85 gr. 
Exper. 20.—20 gr. of the quadruple compound were put into a 
glass vessel, and exposed to a heat raised by degrees till the glass 
melted. The resulting substance possessed the properties described 
in experiments 17 and 18, excepting that it was less blue, and more 
inclined to grey. 
These last experiments show us not only that the preparation of 
pure tungstate of ammonia, by employing yellow oxide obtained 
from the triple compound of oxide of tungsten, potash, and mu- 
riatic acid, is very unprofitable; but that in this case a hitherto 
unknown quadruple compound of potash, oxide of tungsten, am- 
monia, and mariatic acid, is formed : and, lastly, they establish the 
conjecture hazarded in experiments 17 and 18, respecting the reality 
of the unfitness for reduction of the tungstate of ammonia altered 
as described in these experiments. This unfitness is the consequence 
of a mixture of the tungstate of ammonia with the so often men- 
tioned triple compound, which has been dissolved by means of the 
ammonia, and converted into the quadruple compound. 
Results established by the Experiments related in this Memoir. 
1. The statement of other chemists, and particularly of Richter, 
respecting the great difficulty, or even impossibility, of obtaining a 
pure yellow oxide of tungsten by treating Scheele’s tungstie acid 
with nitric acid, is established. 
2. The employment of an oxide of tungsten obtained by the 
method described above is improper on two accounts. If we employ 
it after it has been exposed to a red heat, we obtain by means of it 
an apparently pure tungstate of ammonia; but for the extraction of 
the oxide of tungsten which it contains, an excessive quantity of 
ammonia is necessary; as by the red heat the oxide of tungsten is 
united with the undecomposed triple compound mixed with it, and 
forms a very cohesive compound, and therefore very difficultly acted 
on by ammonia. If we employ the oxide without exposing it to a 
red heat, we form, when we dissolve it in ammonia, a great quantity 
