1815.) _ On Tungsten. 208 
addition of a little ammonia, this portion is dissolved:’ This solu-. 
tion being poured upon a filter, 12 gr. of a white matter were ob- 
tained, similar in its nature to the substance described in the last 
experiment. The ammoniacal solution, being evaporated, yielded 
83 gr. of dry tungstate of ammonia. 
Exper. 13.—A portion of the yellow oxide of tungsten which 
had not been heated to redness was kept for half an hour in a mo- 
derate red heat, by which its colour was changed into light yellow. 
60 gr. of this oxide being agitated with 1 oz. of caustic ammonia 
exhibited the same phenomena as the oxide did in the Ist, 2d, 3d, 
4th, 5th, 6th, and 7th, experiments; that is to say, it dissolved 
with difficulty, and when heated became grey. 
From these last experiments, compared with the preceding onesy, 
we may consider the following propositions as established :— . 
1. That the difficult solubility in ammonia of the oxide, after it 
has been heated to redness, is owing to a portion of the triple com- 
pound of oxide, potash, and muriatic acid, which still remains un- 
decomposed, entering into an intimate combination with the pure 
oxide, the parts of which cohere so strongly together, that the am= 
monia makes its way through them with difficulty in order to dis- 
solve the pure oxide. 
2. That when the triple compound of yellow oxide, potash, and 
muriatic acid, is treated with nitric acid, only an imperfect separa- 
tion of the potash and muriatic acid is produced; so that a pure 
yellow oxide of tungsten cannot be obtained by this method. ‘This 
will appear hereafter in a still more striking point of view, from 
other experiments which I shall state. Among others, I treated the 
triple compound six times successively with eight times its weight 
of nitric acid, and yet I was not able to obtain any pure oxide. A 
result by which the experiments of other chemists, particularly of 
Richter, are confirmed. 
Perhaps the formula given by the last-mentioned chemist for 
obtaining pure oxide of tungsten from wolfram, might be employed 
with advantage, when once it has been established by further expe- 
riments that we obtain by it an oxide really free from lime. This I 
expect to be able to prove hereafter. 
Richter’s process is contained in the sixth volume of the Chemical 
Dictionary of Bourguet continued by Richter, p. 188, and is as 
follows :—One part of wolfram in fine powder is melted with three 
or four parts of nitre, till the mass flows quietly. ‘The potash con- 
taining tungstic oxide thus obtained, which may likewise be obtained. 
by my method, by fusing one part of wolfram and two parts car- 
bonate of potash, is dissolved in 12 or 15 times its weight of water, 
and freed by filtration from the oxides of iron and manganese. The 
colourless solution is now mixed with a very weak solution of mu- 
riate of lime, which is added as long as any precipitate falls. The 
tungstate of lime thus obtained is carefully washed, and treated 
while still moist with nitric or muriatic acid. By this means the 
oxide of tungsten is at once freed from lime, and obtained in a state 
