TUN 
It occurs in primitive mountains, and be- 
longs to the oldest metalliferous formations. 
It is usually accompanied with tinstone, 
wolfram, quartz, mica, steatite, fluor-spar, 
&c. The Cornish tungsten is accompanied 
with iron-stone and hematite. It is found 
in Cornwall, Sweden, Saxony, and Ger- 
many. It is distinguished from tinstone by 
its octahedral crystals, the intensity of its 
lustre, its hardness, and its greater specific 
gravity. When Bergman analyzed this mi- 
neral he conjectured that the basis of the 
acid might be a metallic substance. This 
metallic substance has been ordy found in 
the state of acid in combination with lime, 
iron, manganese and lead. When it is com- 
bined with lime, it is the tungsten of the 
Swedes, and in combination with iron, it is 
called wolfram. To obtain this metal from 
the acid, it is mixed vrith charcoal in a cru- 
cible, and exposed to a very strong heat. 
By this process the metal was obtained in 
the form of a small button at the bottom 
of the crucible in the first experiments 
which were n)ade upon it by the German 
chemists. This crumbled to pieces be- 
tween the fingers ; and when it was exa- 
mined with a magnifying glass, it was found 
to consist of a number of metallic glo- 
bules, none of which were larger than a pin 
head. The colour of this metal is a steel 
grey. The specific gravity is 17.6, or, ac- 
cording to others, 17.22. It is one of the 
hardest of the metals. It is also one of 
the most infusible, requiring a temperature 
of 170" Wedgwood. 
It crystallizes on cooling. When it is 
heated in the open air, it is readily convert- 
ed into a yellow oxide, which afterwards, 
by a stronger heat, becomes of a black co- 
lour, and then by combining with a greater 
proportion of oxygen, it assumes the cha- 
racter of an acid, namely the tungstic acid, 
whose properties and combinations with 
alkalies and earths, vrill be presently de- 
scribed. 
Tungsten combines with phosphorous, 
forming a phosphuret, the properties of 
which are unknown. It also combines with 
sulphur, forming a sulphuret of a bluish 
black colour, and which may be crystal- 
lized. There is no action between this me- 
tal and sulphuric, nitric, or muriatic acids. 
It is only acted on by nitro-muriatic acid 
at a boiling temperature, and nitrons gas is 
disengaged. Nothing therefore is known 
of the combinations of tungsten with the 
other acids. This metal combines with 
TUN ■ 
the other metals, and forms alloys with 
them. 
TUNGSTIC acid. In the year 1781, 
Scheele and Bergman, in investigating the 
nature of tungsten by the Swedes, dis- 
covered that it is composed of lime com- 
bined with a peculiar acid. Their dis- 
covery was afterwards confirmed by several 
chemists, who detected the same acid in 
the mineral called wolfram. This acid al- 
ways exists in combination with lime and 
iron. It may be obtained by reducing the 
former to a fine powder, and treating it 
with nitric or muriatic acids, which unite 
with the lime, and then by alkalies ; which 
dissolve the acid. The alkaline solution is 
to be precipitated by the nitric or muriatic 
acid; the precipitate is to be carefidly 
washed and dried, which is the tungstic 
acid in the solid state. The tungstic acid 
thus prepared, is in the form of a white 
powder, which has an acid and metallic 
taste, changes the colour of vegetable blues 
into red ; and has a specific gravity, accord- 
ing to Bergman, equal to 3.6. Heated 
before the blow-pipe, the tungstic acid be- 
comes first yellow, then brown, and at last 
black; it aflbrds no smoke, and gives no 
sign of fusion. When it is calcined for 
some time in a crucible, it is deprived of 
the property of dissolving in w'ater. Ex- 
posed to the air it suffers no change. It 
is soluble in twenty parts of boiling wa- 
ter, but it is partially separated on cool- 
ing. 
This solution has an acid taste, and red- 
dens the tincture of turnsole. Heated with 
charcoal, it is reduced, but with difficulty, 
to the metallic state. With sulphur and 
phosphorus it becomes of a grey colour, but 
without reduction. The acids do not dis- 
solve the tungstic acid in the form of white 
powder, but they change completely its 
properties. The sulphuric acid changes it 
to a blue, and the nitric and muriatic acids 
convert it into a fine yellow colour. In 
this state it has lost its taste and solubility, 
has become specifically heavier, and has ac- 
quired the property of forming salts with 
the same bases distinctly different from 
those formed with what was called the 
white acid. The compounds which it forms 
with the alkalies, earths, and metallic 
oxides, are a species of neutral salts; but 
the chemical combination is not fully com- 
pleted to hide the alkaline properties of the 
former. In forming these compounds, it is 
the only property in which it agrees with 
Gg 2 
