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is heated in chlorine gas. It forms a sublimate of beautiful red
crystals, which are resolved by water into tungstic and hydro-
chloric acids. A chlorotungstic acid, or double compound of
terchloride of tungsten and tungstic acid, WO 2 Cl, or WC1 3 -f
2WO 3 , is prepared by heating tungstic oxide in chlorine gas.
It condenses in yellow crystalline scales : when suddenly heated,
it is resolved into tungstic acid, bichloride of tungsten, and
chlorine. Another compound is known, 2 WC1 3 -f WO 3 (Bonnet.)

Eg. 598.5 or 47.96, Mo.

This metal is closely allied to tungsten. Its native sulphuret
was first distinguished from plumbago by Scheele, in 1778 ; and
a few years afterwards, molybdic acid, which he had formed, was
reduced, and molybdenum obtained from it, by another Swedish
chemist, Hjelm. The name molybdenum is derived from the
Greek term for plumbago.

The oxides of molybdenum are easily reduced, when exposed
to a strong heat in a crucible lined with charcoal, but the metal
itself is very refractory. Bucholz, who obtained it in rounded
buttons, found it to be a white metal, of density between 8.615
and 8.636". It is not acted upon by hydrochloric, hydrofluoric,
or diluted sulphuric acid ; but is dissolved by concentrated
sulphuric acid, by nitric acid, and aqua regia. Hydrate of
potash does not dissolve this metal by the humid way. It
combines in three proportions with oxygen, forming molybdous
oxide, MoO, molybdic oxide, MoO 2 , and molybdic acid, MoO 3 .


Molybdous oxide, MoO, 698.5 or 55.96. This oxide is ob-
tained by adding to the concentrated solution of any molybdate,
so much hydrochloric acid as to redissolve the molybdic acid
which is at first thrown down, and placing zinc in the liquid ;
this becomes first blue, then reddish-brown, and finally black,
and contains the chloride of zinc and protochloride of molyb-
denum. To separate the oxide of molybdenum from the oxide
of zinc, ammonia is added to the liquid in quantity no more
than sufficient to precipitate the former, while the latter remains
in solution. The molybdous oxide carries down with it a por-
tion of oxide of zinc, from which it may be freed by washing
with ammonia : it is thus obtained as a hydrate of a black
colour. The hydrate of molybdous oxide dissolves with diffi-
culty in acids, forming solutions which are almost black and
opaque, and which do not yield crystallizable salts. It is not
dissolved by potash, nor by the fixed alkaline carbonates 5 but,
on the contrary, is soluble in carbonate of ammonia, when
freshly precipitated. Molybdous oxide resists, after ignition,
the action of all acids.

Molybdic oxide, MoO 2 ; 798.5 or 63.96. This oxide may be
obtained by igniting molybdate of ammonia in a covered cruci-
ble, but mixed with a little molybdic acid. It is better pro-
cured by igniting rapidly, in a covered crucible, a mixture of
anhydrous molybdate of soda (which may contain an excess of
soda) with sal ammoniac. Water poured upon the fused mass
dissolves common salt, and leaves a brown powder almost
black. But molybdic oxide prepared in this way is insoluble in
acids. The hydrated oxide may be obtained in various ways,
one of which consists in digesting molybdic acid with hydro-
chloric acid and copper, till all the molybdic acid is dissolved.
From the solution, which is of a deep red colour, molybdic oxide is
precipitated in appearance exactly similar to the hydrated per-
oxide of iron, by ammonia, added in sufficient excess to retain
all the oxide of copper in solution. The hydrate has a certain
degree of solubility in pure water, and should, therefore, be
washed with a solution of sal ammoniac, and lastly by alcohol.
This hydrate reddens litmus paper, but possesses no other pro-
perty of an acid. It is not dissolved by the hydrated alkalies,
but is soluble in their carbonates, like several earths and metallic
oxides. It dissolves in acids and forms salts, which are red
when they contain water of crystallization, and black when an-


hydrous. The oxalate of molybdic oxide can be obtained in
crystals by spontaneous evaporation.

Molybdic acid., MoO 3 ; 898.5 or 71.96. The native sulphuret
of molybdenum, in fine powder, is roasted in an open crucible,
with constant stirring, at a heat not exceeding low redness, so
long as sulphurous acid comes off. It leaves a dull yellow
powder, which is impure molybdic acid. This is dissolved in
ammonia, and the molybdate of ammonia purified by evapora-
tion, during which some foreign matters are deposited, and
crystallized. The crystallized salt, exposed to a moderate heat,
sq as to avoid fusion, loses its ammonia, and leaves molybdic
acid in a state of purity. The acid thus prepared is a white and
light porous mass, which may be diffused in water, and divides
into little crystalline scales of a silky lustre. It fuses at a red
heat, and forms on cooling a straw-coloured crystalline mass, of
which the density is 3.49. This acid forms no hydrate. It
requires 570 times its weight of water to dissolve it. Before
being ignited, it is soluble in acids, and forms a class of com-
pounds, in which it appears to play the part of base, but of
which not much is known. When boiled with bitartrate of
potash, molybdic acid dissolves, even after being fused by heat.

When a solution of bichloride of molybdenum is poured into
a solution saturated, or nearly so, of molybdate of ammonia, a
blue precipitate falls, which is a molybdate of molybdic oxide,
MO 2 , 2MO 3 . This compound is likewise readily formed in a
variety of other circumstances.* The salts of molybdic acid are
colourless, when their base is not coloured. When they are
treated with other acids, molybdic acid precipitates, which dis-
solves, however, in an excess of the acid, except in nitric acid.
It forms both neutral and acid salts with the alkalies. Molyb-
date of potash is formed by dissolving molybdic acid in car-
bonate of potash ; it is easily soluble in water and crystallizable.
Molybdate of soda has the same form, and resembles in proper-
ties the ttmgstate of soda. Bimolybdate of soda crystallizes in
large fine crystals, which effloresce in air. Molybdate of magnesia
is soluble in twelve or fifteen times its weight of water, and
may be crystallized. Molybdate of lead occurs finely crystallized

* It will be observed, that the atom of this compound contains three atoms
of metal, so also does the remarkable combination of tungstic oxide and soda,
(page 618) ; both thus containing a sali-molecule of metal, like the compound
oxide of iron, which appears to be a condition of stability.


as a mineral. Chromate of lead is dimorphous, and corresponds
in the least usual of its forms with molybdate of lead : hence
molybdenum is connected with the magnesian metals, and
tungsten also with the same class, from the isomorphism of the
tungstates and molybdates.

Sulphurets of molybdenum. The bisulphuret is the ore from
which the compounds of this metal are derived. It occurs in
many parts of Sweden, and might be procured in quantity if
any useful application of the metal were discovered. It is a
lead-grey mineral, having the metallic lustre, composed of flexible
laminae, soft to the touch, and making a streak upon paper, like
plumbago. Nitric acid oxidates it easily, without dissolving it.
Its density is from 4.138 to 4.569. A tersulphuret of molybde-
num is obtained in the same way as the corresponding com-
pound of tungsten, and affords crystallizable sulphur salts >
which are red. The sulphomolybdate of sulphuret of potassium
combines likewise with nitrate of potash. When a solution of
the former salt is boiled with tersulphuret of molybdenum in
excess, the latter is converted into bisulphuret of molybdenum,
and a quadri sulphuret of molybdenum dissolves in combination
with the sulphuret of potassium. The quadrisulphuret may be
precipitated by hydrochloric acid, and when dried is a cinnamon
brown powder.

Chlorides of molybdenum. A protochloride is formed when
molybdous oxide is dissolved in hydrochloric acid ; the bichlo-
ride when molybdenum is heated in dry chlorine gas, as a dark-
red gas, which condenses in crystals, like those of iodine. It
forms a crystallizable double salt with sal ammoniac. The
chloromolybdic acid, or compound of terchloride of molybdenum
and molybdic acid, MoO 2 Cl or MoCl 3 + 2MoO 3 , is formed with
molybdic acid, when molybdic oxide is exposed to chlorine gas
at a red heat. It sublimes under a red heat, and condenses
in crystalline scales, which are white with a shade of yellow.


Eq. 801.8 or 64.25; Te.

Tellurium is a metal of rare occurrence, and appeared at one
time to be almost confined to certain gold mines in Transyl-


vania ; but it has been found lately, in considerable abundance,
at Schemnitz, in Hungary, combined with bismuth ; and in the
silver mine of Sadovinski in the Altai, united with silver and
with lead. It was first described as a new metal by Klaproth,
who gave it the name tellurium, from tellus, the earth. Tellu-
rium is separated from the foreign bodies with which it is mixed
and combined in its ores, by processes of a very complicated
nature. (Berzelius, Traite, I. 344.)

In a state of purity, tellurium is silver-white and very bril-
liant. It is very crystallizable, assuming a rhombohedral form,
in which it is isomorphous with arsenic and antimony. It is
brittle, and an indifferent conductor of heat and electricity for a
metal. Its density is from 6.2324 to 6.2578, according to
Berzelius. Tellurium is about as fusible as antimony; at a
higher temperature it may be distilled. It burns in air, at a
high temperature, with a lively blue flame, green at the borders,
and diffuses a dense white smoke, which generally has the odour
of decaying horse-radish, from the presence of a little selenium.
Tellurium belongs to the sulphur class of elements. Like sele-
nium and sulphur, it dissolves to a small extent in concentrated
sulphuric acid, and communicates to it a fine purple red colour.
In this solution, the metal is not oxidated, for it is precipitated
again, in the metallic state, by water. This metal has also
considerable analogy with antimony, and may probably connect
together the sulphur and phosphorus families. Tellurium com-
bines in two proportions with oxygen, forming tellurous acid,
TeO 2 , and telluric acid, TeO 3 .

Tellurous acid, TeO 2 ; 1001.8 or 80.?5. This acid differs
remarkably in properties according as it is anhydrous or hydrated,
forming two isomeric modifications of the same acid, of which
the anhydrous acid has been named alphatellurous acid, and the
hydrated betatellurous, by Berzelius, to whom we are indebted
for nearly all our accurate knowledge of the acids of tellurium.
But a sufficient distinction will be made between these bodies
by retaining one of these terms, alphatellurous, as applied
to the anhydrous acid, and confining the term tellurous acid to
the hydrated acid. The proper tellurous acid then is obtained
by precipitating the bichloride of tellurium by cold water ; or
by fusing anhydrous tellurous acid with an equal weight of car-
bonate of potash, so long as carbonic acid is disengaged, dis-
solving the tellurite of potash in water, and adding nitric acid

s s


to it, till the liquor distinctly reddens litmus paper. A white
and bulky precipitate is produced, which is washed with ice-cold
water, and afterwards dried without artificial heat. Tellurium
likewise dissolves with violence in pure nitric acid of density
1.25, and if after the first five minutes, the clear liquid be poured
into water, tellurous acid is precipitated in white flocks. But if
not immediately precipitated, the nitric acid solution undergoes
a change.

The hydrated acid obtained by these processes forms a light,
white, earthy mass, of a bitter and metallic taste. It instantly
reddens litmus paper, and while still humid, dissolves to a sen-
sible extent in water. It is very soluble in acids, and these
solutions are not subject to change, except that in nitric acid.
Ammonia and the alkaline carbonates also dissolve it easily, the
latter becoming bicarbonates. It is this tellurous acid which
plays the part of acid in the tellurites, and also that of base in
some compounds which the tellurous, like vanadic, tungstic,
and molybdic acids, forms with the stronger acids. The tellu-
rites of potash and soda, which are neutral in composition, are
very soluble, and have a strong alkaline reaction ; their solu-
tions are decomposed by the carbonic acid of the air.

Alphatellurous acid. When the solution of tellurous acid in
water is heated to 104, it deposits alphatellurous acid in grains,
and loses its acid reaction. The same change occurs when it is
attempted to dry the hydrated tellurous acid by heat. It parts
with combined water, and becomes granular. The solution of
tellurous acid in nitric acid changes spontaneously -in a few
hours, and in a quarter of an hour when heat is applied to it,
and allows the alphatellurous acid to precipitate* When the
deposition of the acid is slow, it forms a crystalline mass of fine
grains, among which octohedral crystals may be perceived by
the microscope. The acid is then anhydrous. Alphatellurous
acid does not redden litmus, or not till after a time. It is but
very slightly soluble in water; the solution has no acid reaction.
No salts of alphatellurous have been formed in the humid
way, although from its analogy to a corresponding telluric acid,
it is probable that such salts may exist. At a low red heat, it
fuses into a clear transparent liquid of a deep yellow colour,
which on cooling becomes a white and highly crystalline mass,
easily detached from a crucible. Tellurous acid is volatile,
although less so than the metal itself.


Bitellurite of potash, KO, Te 2 O 4 , is obtained by fusing two
atoms of tellurous acid with one atom of carbonate of potash.
It appears to be capable of existing in a hot solution, and of
crystallizing in certain circumstances ; but it is decomposed by
cold water, which resolves it into the neutral salt, which dis-
solves, and a quadritellurite of potash, KO, Te 4 O 8 + 4HO. The
latter salt cannot be redissolved again in water, without decom-
position. In losing its water when heated, it swells up like borax.

Telluric acid, TeO 3 ; 1101.8 or 88.25. This acid is obtained
in combination with potash, on fusing tellurous acid with nitre.
It may then be transferred to barytes, and the insoluble tellu-
rate of barytes decomposed by sulphuric acid. The solution of
telluric acid gives bulky hexagonal prismatic crystals. Its
taste is not acid, but metallic, resembling that of nitrate of
silver. Indeed, it appears to be a feeble acid, reddening litmus
paper, although with difficulty, when the solution is diluted.
The crystallized acid contains 3 HO, of which it loses 2HO by
efflorescence, a little above 212. It thereafter appears insoluble
in cold water, but may be redissolved completely by long diges-
tion, particularly with ebullition, and is not permanently altered.
Telluric affects the same multiples in its salts as tellurous acid.
The neutral tellurate of potash is KO,TeO 3 + 5HO, bitellarate
of potash, KO, Te 2 O 6 +4HO, quadritellurate of potash,
KO,Te 4 O 12 + 4HO. All these salts may be obtained directly,
in the humid way, by dissolving the proper proportions of
hydrated acid and carbonate of potash together, in hot water.
A portion of the combined water, in the last two salts, is un-
questionably basic, but how much of it is so has not been deter-
mined. They cannot be made anhydrous by heat without being
essentially altered in properties.

Alphatelluric acid. The crystals of hydrated telluric acid
lose all their water at a heat under redness, and become a mass
of a fine orange yellow colour, without changing their form.
This yellow matter, which is distinguished as alphatelluric acid
by Berzelius, is remarkable for its indifference to chemical
reagents, being completely insoluble in cold or boiling water, in
hot hydrochloric and nitric acids, and in potash ley. At a high
temperature it is decomposed, losing oxygen, and leaving tellu-
rous acid white and pulverulent. The salts of telluric acid are
also converted into tellurites, at a red heat, by the loss of

s s 2


The neutral tellurate of potash undergoes no change in con-
stitution under the influence of heat, resembling in that respect
those tribasic phosphates, of which the whole three atoms of
base are fixed. The bitellurate of potash loses its water and
becomes yellow at a temperature under redness, and is changed
into a quadritellurate, which is insoluble alike in water and
dilute acids. Water dissolves out neutral tellurate from the
yellow mass. The insoluble salt is named the alphaquadritellurate
of potash, by Berzelius. The elements of this compound are
united by a powerful affinity. It is formed when hydrated
telluric acid is mixed intimately with another potash salt, such
as nitre or chloride of potassium, and the mixture calcined at a
temperature which should be much inferior to a red heat ; also
when tellurous acid is ignited with chlorate of potash, and in other
circumstances. Hydrate of potash dissolves the alphaquadri-
tellurate by fusion, and nitric acid by a long continued ebulli-
tion ; but in both cases the acid is found as ordinary telluric
acid in solution.

Telluretted hydrogen, TeH, is a gaseous compound of tellurium
and hydrogen, analogous in constitution and properties to sul-
phuretted hydrogen. It is obtained by fusing tellurium with
zinc or with tin, and acting on the mixture by hydrochloric

Definite sulphurets of tellurium have been obtained, corres-
ponding with tellurous and telluric acids. They are sulphur

Two chlorides of tellurium have been formed, a protochloride,
Te Cl, to which there is no corresponding oxide, and a bichlo-
ride, Te C1 2 , No higher chloride, corresponding with telluric
acid, has been obtained.






Eg. 940.1 or 75.34 (470.04 or 37.67, Berzelius and Turner), As.

This metal is found native, but more generally in combination
with other metals, particularly cobalt and nickel, and is largely
condensed, during the roasting of their ores, in the state of
arsenious acid. The metal may be easily obtained, in a state of
purity, by subliming a portion of native arsenic in a glass tube
or retort, by the heat of a lamp, or by reducing a mixture of
one part of arsenious acid and three parts of black flux, in the
same apparatus. The metal forms a crust, in condensing, of a
steel-grey colour and bright metallic lustre. It has been ob-
served to crystallize by sublimation in rhombohedral crystals,
and is isomorphous with tellurium and antimony. It is a brittle
metal, and very easily pulverised. The density of arsenic is
from 5.7 to 5.96. It rises in vapour at 356 (180 Cent.) with-
out first undergoing fusion. Arsenic vapour is colourless ; its
density is 10,370; and, like phosphorus and oxygen, its com-
bining measure is one volume. It has as strong an effect upon
the organ of smell as selenium : its odour resembles that of
garlic. Arsenic combines in three proportions with oxygen,
forming a grey suboxide by spontaneous oxidation in air, of
which the composition is undetermined, with arsenious and
arsenic acids, As O 3 and As O 5 .

Arsenious acid, AsO 3 ; 1240.1 or 99.34. This compound is
also known as white oxide of arsenic, and is an abundant mer-
cantile product. It is in vitreous masses, as obtained by
sublimation, which immediately after sublimation are transparent
and colourless, or have a delicate shade of yellow, but gradually
become white and opaque, (page 153.) The density of the
vitreous acid is 3.7385, of the opaque acid, 3.699. Arsenious
acid sublimes at 380, without softening or fusing, forming a
vapour which is colourless and without odour. The density of


this vapour is about 13,000 (Mitscherlich) ; one volume of
arsenious acid vapour, or the combining measure, contains
accordingly, one volume of arsenic vapour and three volumes
of oxygen gas. When slowly sublimed in a glass tube, it is
always obtained in distinct transparent crystals of adamantine
lustre, which are regular octohedrons. But arsenious acid is
dimorphous, and occurs sometimes, in the roasting of arsenical
ores, in thin, flexible prisms, of a pearly lustre, of which the
form does not belong to the regular system, (Wohler.) Arse-
nious acid dissolves very slowly in water, and the prismatic
crystals in particular require to be heated with it for a long
time. A concentrated solution prepared in this way may after-
wards be cooled without arsenious acid immediately crystallizing
from it. One hundred parts of boiling water dissolve 9.68 parts
of the vitreous acid, and 11.47 parts of the opaque acid ; and
when the solutions cool to 60, 1.78 parts remain in the first,
and 2.9 parts in the latter ; the first reddens litmus paper, the
second makes it blue, although feebly, if already red. When
the vitreous acid in powder, is covered with ammonia, it heats
a little ; no combination of the acid with ammonia takes place^
for the latter may be completely removed by water, but the
washed powder is found to have passed into the condition of
the opaque acid. For these curious facts we are indebted to
M. Guibourt. The taste of powdered arsenious acid is scarcely
perceptible, but it is slightly sweet, and leaves a feeling of
acridity in the mouth.

Arsenious acid dissolves in the solutions of many acids, par-
ticularly hydrochloric acid, to a greater extent than in water,
but without combining with these acids. It is dissolved, how-
ever, by the bitartrate of potash, with the formation of a crys-
tallizable salt, analogous to the potash-tartrate of antimony.
Arsenious acid is dissolved by potash, soda, and ammonia ; but
the salts which it forms with these bases do not crystallize. It
is also dissolved by alkaline carbonates, but is sometimes depo-
sited from these solutions in a free state ; so that it is doubtful
whether arsenious acid displaces carbonic acid in the humid way.
The arsenites of the earths and metallic oxides are insoluble in
water, but soluble in acids ; these precipitated arsenites usually
carry down an excess of arsenious acid, and are not easily ob-
tained in a definite state.

Arsenic acid, AsO 5 , 144,0.1 or 115.34. This acid is obtained


by heating powdered arsenious acid in a bason, with an equal
quantity of water, and adding to the mixture at the boiling point
nitric acid in small quantities, so long as ruddy fumes escape.
An addition of hydrochloric acid to the water is generally made,
to increase the solubility of the arsenious acid, but it is not ab-
solutely necessary. The solution of arsenic acid is then eva-
porated to dryness, to expel the remaining nitric and hydro-
chloric acids, but the dry mass is not heated above the melt-
ing point of lead, otherwise oxygen gas is emitted and arsenious
acid reproduced. Arsenic acid, thus obtained, is milk-white,
and contains no water. Exposed to air, it slowly deliquesces,
and runs into a liquid. But notwithstanding this, when
strongly dried, it does not dissolve completely in water at
once, and a portion of it appears to be insoluble ; but the
whole is dissolved by continued digestion. Arsenic acid, in
absorbing moisture from the air, sometimes forms hydrated
crystals, which are highly deliquescent ; but this acid is easily
made anhydrous, and does not retain basic water with force,
like phosphoric acid. Its solution has a sour taste, and red-
dens vegetable blues. Arsenic acid, indeed, is a strong acid,
and expels, with the aid of heat, all the volatile acids from
their combinations. Arsenic acid undergoes fusion at a red
heat, and is completely dissipated in arsenious acid and oxy-
gen at a higher temperature.

When an equivalent of arsenic acid is ignited with an excess
of carbonate of soda, three equivalents of carbonic acid are
expelled, and a tribasic arseniate of soda formed, which crystal-
lizes when dissolved in water, with 24 equivalents of water,
forming the salt 3NaO, AsO 5 + 24HO, isomorphous with the
subphosphate of soda. The same salt is obtained by treating
arsenic acid in solution, with an excess of caustic soda. When
carbonate of soda is added to a hot solution of arsenic acid, so

Online LibraryThomas GrahamElements of chemistry: including the applications of the science in the arts → online text (page 60 of 103)