CHEMISTRY. 
266 
TungJUc Acid ,—With the blow-pipe, in a fpoon ofpla- 
tina, this acid affumes a dark green colour; upon coals, 
it turns almoft entirely black. It diffolves in borax, with¬ 
out changing the colour or tranfparency of the globule, 
even if in a pretty large quantity ; but a very confider- 
able quantity will at length turn the borax black, or 
dark blue. 
The ammoniacal phofphat of foda diffolves this matter 
completely, forming a dark blue globule. By long cal¬ 
cination with exposure to the air, the yellow colour be¬ 
comes darker, and fometimes changes to green ; expofed 
to heat for feveral hours in a covered crucible, it affumes 
a blackilh grey colour. Thus calcined, it has no tafte, 
is not foluble in water, and very little fo in acids. Tri¬ 
turated with water, the acid remains long fufpended, 
forming a kind of yellowilh milk, which does not impart 
a red to the blue vegetable colours. It changes colour 
neither by expofure to the fun, nor to moilfure. The 
nitric acid has no adtion upon this acid. 
From thele experiments Vauquelin concludes, that the 
fubftance formed by the combination of tungften with 
oxygen, does not poflefs the properties generally attri¬ 
buted to acids ; fince it is infallible in water, does not 
change the blue vegetable colours, and has no apparent 
favour. If Scheele, adds the fame chemift, regarded it as 
an acid, it was becaufe he never obtained it but in a tri¬ 
ple combination, which then poffelfes the acidifiable pro¬ 
perties, becaufe it always retains a portion of that acid, 
which was ufed in precipitating the tungftic acid from 
its alkaline lolutions. Vauquelin therefore advifes to 
exclude this fubftance from metallic acids, and to regard 
it as an oxyd of tungften ; fuch as are the oxyds of zink, 
tin, antimony, and arfenic, which, like this fubftance, 
unite with earths, alkalis, and fome other metallic oxyds, 
with which they form a kind of neutral f'alts. To re¬ 
duce the oxyd of tungften to the metallic ftate, put one 
hundred parts of it into a ftrong crucible with a little 
oil, and expofe the mixture for two hours to the violent 
heat of a forge furnace. When it is cold, there is found 
in the crucible a matter of a blackifh grey colour, con¬ 
fiding of a vaft number of globules. Morveau has lately 
difcovered, that the tungftic oxyd renders vegetable co¬ 
lours fo fixed, as not to be adted on even by the oxyge¬ 
nated muriatic acid. 
Tungstat of Magnesia. —Mix oxyd of magnefia 
with carbonat of magnefia and water; boil the mixture 
for fome time, and the ftrained liquor, with the help of 
an acid, precipitates a white powder. By evaporation a 
foluble fait is obtained, of a fimilar tafte to other lalts of 
this pature; it is unchangeable by air, and cryftallizes 
in little bright fpangles. Whether this oxyd will com¬ 
bine with barytes or alumine, is not known. 
Tungstat ofPotash. —Caufticpotafh diflolvesoxyd 
of tungften even when cold; but, if the liquor be boil¬ 
ed, and a certain quantity of the oxyd remains undid- 
folved, the liquor contains always an excefs of potafh: 
by evaporation a fait is obtained, in form of a wdiite 
powder, without any regular cryftallization. This fait 
has a metallic Cauftic tafte, is foluble in water, and ftrongly 
attradfs the moilfure of the air; its aqueous folution is 
decoinpofed by all the acids, which throw down a white 
precipitate, which is a triple fait, differing in its nature 
according to the acid ufed. 
Tungstat of Soda. —This oxyd is to be treated in 
the fame manner, with a falution of cauftic foda, or even 
carbonat of foda. By evaporating the liquor, a fait is 
obtained cryftallized in long hexahedrais. This fait has 
an acrid metallic tafte; it is foluble in four times its 
weight of cold water ; boiiing water diffolves one-half of 
its weight. It reftores the colour of turnfole reddened 
by an acid ; the fulphuric, nitric, muriatic, acetous, and 
oxalic, acids, decompofe it, forming a white triple fait; 
it is precipitated alfo by lime-water; but phofphoric acid 
occasions no precipitation 5 muriat of lime and barytes. 
and the acid fulphat of alumine, occafion a white pre¬ 
cipitate. 
Tungstat of Ammoniac. —Ammoniac quickly dif¬ 
folves oxyd of tungften, even when cold; and it pro¬ 
duces a fait which cryftallizes fometimes in little fpan¬ 
gles, like the boracic acid, fometimes in fmall needles, 
which incline to the form of three-fided prifms. This, 
like other falts of the kind, has a metallic tafte ; it is fo¬ 
luble in water, draws no humidity from air, and is com¬ 
pletely decompofed by heat. The ammoniac, as it is 
difengaged, leaves the oxyd of tungften free, and of yel¬ 
low colour : one hundred parts of this fait contain feven- 
ty-eight parts of oxyd of tungften. 
Of MOLYBDENA. 
Certain fubftances have long been confounded under 
the names of black-lead ore, mineral lead, plumbago, or 
molybdena, which the more exadt analyfis of Scheele has 
proved to be of a different nature. Molybdena can now- 
no longer be confounded with that of ore, of which 
drawing-pencils are made, called black-lead; the differ¬ 
ences are fo obvious, that no doubts can remain. Mo¬ 
lybdena is compofed of hexagonal fcales, of greater or 
lefs lize, very ftightly adhering to each other: it is foft 
and fat to the touch, foils the fingers, and leaves traces 
upon paper, which are bluifti, or of a filvery grey cqlour; 
the traces from plumbago are darker and rougher. When 
it is reduced to powder, which is'difiicult to be perform-> 
ed, on account of the elafticity of its fcales, it has a bluifti 
colour; it yields eafiiy to the knife, is not brittle, and 
has not the granulated texture of black-lead, now called 
carbure of iron. In order to pulverize the ore of mo¬ 
lybdena, it is .neceflary, after the procefs of Scheele, to 
throw a fmall quantity of fulphat of potafli into the 
mortar along with it; the powder mult afterwards be 
waffled with hot water, which carries off the fait, and the 
mineral remains pure. By calcination it gives a ful¬ 
phuric fmell, and the refidue is a whitifli earth. The ni¬ 
tric and arfenical acids are the only kinds which attack 
it; it diffolves with effervelcence in foda, with the help 
of the blow-pipe; it makes a detonation with nitrat of 
potafh, and the refiduum is reddifh ; expofed to the blow¬ 
pipe in a metallic fpcon, it emits white fumes. 
Molybdena is found in Iceland, Sweden, Saxony, Spain, 
and France : in Iceland -it is in thin plates, in red feld- 
fpar mingled with quartz. William Bowles fpeaks of 
molybdena found near the hamlet of Beal de Monafte- 
rio; it is in ltone-quarries, fometimes mixed with gra¬ 
nite. Molybdena, according to Mr. Hatchett, in his va¬ 
luable analyfis of the Carinthian molybdat ot lead, (Phil. 
Tranf. for 1796,) feems to exift in four different degrees 
of oxygenation. The firft is that of the black oxyd, the 
fecond the blue oxyd, the third the green oxyd, which 
feems to be an intermediate degree between the blue oxyd 
and the fourth and laft ftate, that of the yellow acid, 
Molybdena cannot be reduced in dole veffels, and is 
very hard to work upon. Muriatic acid has no adlion 
on this mineral; but nitric acid attacks it very violently ; 
emits a great quantity of red vapours, and the molyh- 
dena is diredlly converted into a white powder. Thirty- 
parts of nitric acid will be required to one of molybdena: 
diftil at five fucceflive operations, that is, uiing fix parts 
of the acid at a time. When all the acid is ufed, and no 
more vapours are perceived, take out the white powder 
remaining in the i-etort; wafti it with a little diftilled 
water, to leparate the laft portions of fulphuric acid which 
might adhere ; but it will be proper, previous to wafliing 
it, to warm it in a retort. The oxygen of the nitric acid 
attacks the molybdena and the lulphur, converting the 
one into a metallic oxyd, the other into fulphuric acid. 
Thefe are the means to be ufed for obtaining the tnoljb- 
dic acid. 
The acid of molybdena obtained by calcination, or the 
action of the nitric acid, cannot be reduced, if treated 
with 
