T. E. (Thomas Edward) Thorpe.

A dictionary of applied chemistry (Volume 4) online

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manganate material were dusted over with
manganese peroxide instead of with oxide of
copper. In Chapman's process (Eng. Pat.
11504, 1892) 'oxide of manganese (or the like)
in a powdered form is kept suspended in fused
soda (or the like) so that the charge is practically
in the condition of a liquid,' and the alternate
supplies of air and steam were driven into the
liquid at the bottom, thereby keeping the oxide
in a state of suspension. But though these
modifications have been tried on the practical
scale, none of them has proved commercially
economical.

9. Kassner (Eng. Pat. 11899, 1889) found
that when an intimate mixture of lead oxide and
chalk is heated to 600 in contact with the air, a
calcium plumbate Ca 2 Pb0 4 is formed. If this
plumbate is then introduced into a solution of
potassium or sodium carbonate it is decomposed,
an insoluble precipitate of calcium carbonate
and lead peroxide is formed, and caustic potash
or soda remains in solution. This is removed by
decantation, and the precipitate washed. The
precipitate, in which the lead peroxide is, of
course, the active part, may then either be used
directly as an oxidant, or it may be introduced
into a decomposing vessel, dried with super-
heated steam, and heated to about 500, when
oxygen is evolved, the mixture of lead oxide and
calcium carbonate left being then ready for re-
generation. The decomposition of the plumbate
may also be effected by suspending it in water
and treating with carbonic acid. The following
equations indicate the reactions taking place :
2CaC0 3 +PbO+0(air)=Ca 2 Pb0 4 +2C0 2 ;
Ca 2 Pb0 4 +2Na 2 C0 3 +2H 2

=4NaOH+2CaC0 3 +Pb0 2 ;
2CaC0 3 +Pb0 2 =2CaC0 3 +PbO+0.

The inventor lays stress on the cheapness of
the process owing to the caustic soda obtained
being a valuable by-product. The complexity of
the process and the large amount of labour
entailed by it, leave very little chance of its being
practically applicable, except possibly in chemical
works, where it is to be used in conjunction
with the manufacture of caustic alkali, and even
here its economy is very doubtful.



40



OXYGEN.



The decomposition of the plumbate into lime
and lead peroxide may also be effected in situ by
means of a current of moist furnace gases at
80-100, and the oxygen then liberated by rais-
ing the temperature. The great changes of
temperature, however, thus involved, render
the method impracticable, and in addition the
sulphur impurities in the furnace gases rapidly
deteriorate the mixture.

Salamon (Eng. Pat. 6553, 1890) proposes to
decompose the calcium plumbate without re-
moving it from the producer in which it is
formed by allowing the temperature to fall ' to
a certain point,' and then introducing a current
of pure carbon dioxide. The following reaction
then occurs :

Ca 2 Pb0 4 +2C0 2 =2CaC0 3 +PbO-fO.

This necessitates the use of at least four times
the volume of carbon dioxide as of , oxygen
obtained, a condition which at once puts the
process out of the question as a technical and
economical one. It has been suggested that the
quantity of pure carbon dioxide required may be
largely reduced by carrying out the earlier part
of the reaction by means of the carbon dioxide
in furnace gases, and using it pure only at the
last. But the drawbacks so introduced fully
neutralise any advantage.

10. By the alternate formation and decom-
position of barium peroxide. In 1851 Boussin-
gault found that when barium oxide (baryta)
is heated to a dull-red heat in a current of air
it is converted into barium peroxide, and that at
a higher temperature this peroxide is again re-
solved into barium oxide and oxygen. But his
attempts to utilise this reaction as a practical and
economical source of oxygen failed owing to the
fact that after a few oxidations and deoxidations
the baryta lost its power of re-absorbing oxygen.
Many other attempts were made to overcome this
difficulty, but for long without success. In 1879,
however, the MM. Brin freres were more success-
ful, and took out a patent for the process (Eng.
Pat. 1416 of 1880). Further improvements were
made under the auspices of the company formed
to develop and work the patents, and the process
was made practical and economical, and was
worked on a large scale at various places.

The permanence of the baryta is mainly
dependent on its physical condition, the use
of reduced pressure during deoxidation, and
consequent avoidance of excessively high tem-
peratures, and the careful purification of
the air used. It was found possible to dispense
with change of temperature in the reaction,
change of pressure being alone trusted to for
determining the respective phases of oxidation
and deoxidation. Neither the oxidation nor
the deoxidation is as complete as when two
temperatures are used, and the yield per opera-
tion is much less. But the duration of the
operation was reduced from about 4 hours to
8-15 mins., and the total daily yield therefore
largely increased. At the same time the opera-
tion was much simplified, the wear and tear of
furnace, retorts, &c., very greatly reduced, and
the fuel required lessened. Labour was also
economised, the multiplied reversals of cocks, &c.,
necessitated by the single-temperature method of
working being effected automatically by revers-
ing gear designed by K. S. Murray. The labour



required was therefore little more than that
needed for stoking the furnace, and oiling and
supervising the pumps, &c. The oxygen
obtained had a purity of about 93-96 p.c.

For a producer capable of delivering 10,000
cubic feet of oxygen per 24 hours the consump-
tion of coke in the furnace is about 12-15 cwt.
per day, and for plant of that or smaller size the
pump power required is about 1 I.H.P. per 1000
feet of oxygen produced per day, the ratio de-
creasing for larger plants.

It is necessary that the barium oxide should
be as hard and as porous as possible, and this
is best obtained by preparing it by igniting the
nitrate. The nitrate fuses and decomposition
soon commences with evolution of a mixture
of oxygen and oxides of nitrogen. This action
continues for about 2-3 hours, during which
time the contents of the crucible remain in
ebullition. A porous mass is then left, which
is heated for another hour to complete, as
far as possible, the decomposition. In this
way a very hard but also very porous baryta is
obtained.

This process was thoroughly practical and
economical, and large numbers of plants were
erected all over the world and worked success-
fully for many years. It was described in
detail with illustrations of plant in the first
edition of this dictionary (see also K. S. Murray,
Proc. I. Mech. E. 1890, 131 ; Thome, J. Soc.
Chem. Ind. 1890, 246). Some plants are still
working, but in the last few years the process
has been largely superseded by the still cheaper
liquid air process, which also produces oxygen
of greater purity (v. infra).

Cost of production. It is very difficult to
obtain data of the cost of production of
oxygen under the earlier methods described,
but the following figures probably approxi-
mate to the cost per 1000 cubic feet : from
chlorate 8L-1QL, from pyrolusite 4Z.-6J. ; from
sulphuric acid 21. 10s.-3l. (probably higher when
only the oxygen and not the sulphur dioxide
is utilised) ; by the Tessi6 du Motay process
3Z.-4Z. ; by the Brin process 7*.-12*. No
authentic data of the cost of producing oxy-
gen by dialysis or by solution in water are
obtainable, but it would probably be at least as
high as that by the Tessie du Motay process.
In the Kassner process the cost depends largely
on the amount realised by the sale of the caustic
alkali, but would certainly be prohibitive for
technical purposes. For cost by the liquid air
and electrolysis processes, v. infra.

Properties. The International Committee en
Atomic Weights has now adopted 0=16 as the
standard of comparison for all atomic weights,
and under this scale H=l-008 (1-0076 Morley).
Oxygen is a colourless, tasteless, and inodorous
gas, of sp.gr. 1-1056 (air=l) : at and 760 mm.
pressure a litre of the gas weighs 1-429 grms.
(1-42893 at and 760 mm., and 0-29071 grms.
at 1067'4 and 760 mm., Jacquerod and Perrot,
Compt. rend. 1905, 140, 1542), and at 30 ins.
pressure and 15-5 100 cubic ins. weigh 34-206
grs. 1 grm. of oxygen measures 0-6997 litres
and 1 Ib. 11-84 ft. Oxygen also occurs in an
active allotropic form called ozone, which
is treated of in a separate article (v. OZONE).

Oxygen normally acts as a divalent element,
but in many compounds, especially in many



OXYGEN.



41



organic compounds having somewhat basic
char;' ct eristics, acts as a tetrad. When
examined through very thiek and highly com-

d lavers, Caseous oxygen lias a slight
blue tinge of colour. It is sparingly soluble in
water. As with all gases, the quantity of
oxygen dissolved by water depends on the

n of the oxygen in the atmosphere in
contact with the water. Thus pure water
shaken up in contact with pure oxygen will
absorb nearly five times as much oxygen as it
would when shaken up, at the same temperature
and under the same pressure, with air which
only contains 20-9 p.c. by volume of oxygen.
The following table gives the coefficients of
solubility (i.e. the volume of oxygen absorbed
by one volume of water when shaken up with
pure oxygen under 760 mm. pressure) at different
temperatures as determined by different ob-
servers :



Is

I?


| Coefficient of solubility


Bunsen Ditt-
(1855) mar


Eoscoe
and
Lunt


Winkler
(1861)


Bohr&
Bock
(1891)


Fox
(1905)


oc.

10
20
30
40


0-0411 !
0-0325 0-0383
0-0284 0-0312


0-0377
Q'0308


0-0489
0-0380
0-0310
0-0262


0-0496
0-0390
0-0317
0-0268
0-0233
0'0207


0-0492
0-0384
0-0314
Q'0267
0-0233
0-0209



These numbers multiplied by 1000 give at
once the number of c.c. oxygen absorbed by a
litre of water from pure oxygen.

The older numbers of Bunsen appear, from
the results of more recent observers with more
delicate apparatus, to be rather too low.
\\ inkier gives the following formula for calcula-
ting the coefficient of solubility () of oxygen in
water at any temperature (*).

0=0-04890-0-0013413*+0-0000283* 2

-0-00000029534* 3 .

Fox (Trans. Far. Soc. 1909, [v.] 68-81) gives
the formula :
0=0-04924-0-0013440*+0-000028752* 2

-0-0000003024* 3 .

The coefficient of solubility of oxygen in
alcohol at is 0-2337; at 20 it is 0-2201
(Timofejeff), so that oxygen is much more soluble
in alcohol than in water.

Nearly all natural waters contain oxygen in
solution and can only be freed therefrom by
prolonged boiling in vacuo. This dissolved
oxygen, though small in amount, is the source
from which fish obtain the oxygen necessary to
sustain life.

The solubility of oxygen in sea water at
6 is about 78 p.c. of its solubility in pure water
(Clowes and Biggs).

Oxygen, though long regarded as a permanent
gas, was liquefied in 1877 by Pictet at a pressure
320 atmospheres, and a temperature of 140.
Cailletet had a few days previously observed
the formation of a mist due to liquefaction when
oxygen at -29 under a pressure of 300 atmo-
spheres was allowed to expand suddenly.
Iszewski in 1883 showed that the critical
temperature of oxygen (i.e. the temperature
i bove which no amount of pressure will liquefy
113, the pressure needed to liquefy it



at that temperature being 50 atmospheres,
and this was confirmed by Wroblewski and by
Deuar in 1885.

Liquid oxygen is a pale steel-blue transparent
and very mobile liquid showing a clear meniscus
(Dewar; Olszewski) boiling at 182-5 at 760
mm. pressure. When the pressure is reduced
or removed, evaporation takes place so rapidly
that a part of the oxygen is often frozen.
Solidification takes place under 9 mm. pressure
at -211-5 (W.), under 172 mm. at -219
(Dewar, Boy. Soc. Proc. 1911, 85, 589). This
latter temperature is therefore the lowest
obtainable by the evaporation of liquid oxygen.
Travers, Sinter and Jacquerod (Proc. Roy. Soc.
1902, 70, 484) found the b.p. of oxygen to be
182-8 at 760 rnm., 185 at 600 mm., 188-5
at 400, and 193-8 at 200 mm. Dewar ob-
tained solid oxygen as a hard, pale-blue mass
by cooling liquid oxygen in a spray of liquid
hydrogen. Its m.p. is 219 under a pressure
of 1-12 mm. The density of liquid oxygen
is 1-1181 at -182-5, 1-1700 at -195-5,
1-2386 at 210-5, and that of solid oxygen
1-4256 at 252-5 (Dewar) corresponding to the
general formula (for liquid and solid) d=
1-5154-0-00442T (where T=absolute tempera-
ture). 781-8 volumes of oxygen at and 760
mm. are contained in 1 volume of liquid oxygen
at 182-5. The latent heat of vaporisation of
liquid oxygen varies with the temperature
(Alt), at 760 mm. pressure (i.e. 182-5) it is
50-97 cals., at -205 it is 55-5 cals. The
specific heat between 200 and 183 is
0-3470-014. The vapour density at 182 is
normal. The refractive index of liquid oxygen
is 1-2236. Liquid oxygen absorbs nitrogen
readily, absorbing at 190-5 380 times its
volume, or 42 p.c. of its weight of gaseous
nitrogen, the b.p. being thereby reduced to
188-8. This was probably the cause of the
discrepancies in the boiling-points given by the
earlier observers. Liquid oxygen is a very per-
fect insulator, and is also comparatively inert
in its chemical properties. Phosphorus, potas-
sium, sodium, &c., may be immersed in it with-
out any action taking place (Dewar).

When liquid oxygen is subjected to the
action of strong light, and particularly of
the ultra-violet rays, some of it is converted
into ozone (Dewar). It is diathermanous, a
non-conductor of electricity, but is strongly
magnetic, its magnetic moment being 1 when
iron is taken as 1000. The magnetic suscepti-
bility of liquid oxygen at the freezing-point is
1-3 times as great as that of the solid. Its
susceptibility is diminished or temporarily sus-
pended by elevation of temperature. Oxygen
is the least refractive of all gases; it gives a
characteristic though not very strong absorption
spectrum, but to obtain this it is necessary to
view the source of light through great thicknesses
of liquid or through the highly compressed
gas. The spectrum first appears in the form of
a number of fine lines, but as the pressure is
increased or a layer of liquid oxygen is employed,
it shows a number of broader and shaded dark
bands, with almost complete absorption in the
violet and ultra-violet. Six absorption bands
have been observed, two in the red corresponding
to the A and B Fraunhofer lines. The absorption
spectrum of liquid oxygen is practically identical



42



OXYGEN.



with that of gaseous oxygen. Oxygen shows a
luminous spectrum in a Geissler tube containing
a bright band in the red, two in the green, and
one in the blue, but the spectrum varies under
varying conditions.

The chemical activity of air depends upon
the oxygen it contains, air being simply, in its
chemical relations, oxygen diluted with nitrogen.
Free oxygen, whether diluted with nitrogen or
not, manifests considerable chemical activity,
even at ordinary temperatures, this activity in-
creasing with rise of temperature. There are
only few elements viz. fluorine, chlorine,
bromine, iodine, silver, gold, platinum, neon,
argon, and helium which do not unite directly
with oxygen. Most of the non-metallic elements
unite with oxygen to form anhydrous acids.
Of the exceptions, hydrogen forms a neutral
oxide (water), whilst no oxides of fluorine, argon,
neon, or helium have yet been obtained.

Phosphorus combines with oxygen at ordi-
nary temperatures, as do also moist iron, moist
lead, moist saw-dust, and many metallic com-
pounds such as cuprous chloride, manganous
hydroxide, ferrous hydroxide, &c. This oxidation
at ordinary temperatures is called autoxidation,
and substances undergoing autoxidation often
induce the oxidation of other substances present
which otherwise would not oxidise spontaneously.
The alkali metals, especially rubidium, are
especially active in this wa}^. In many cases
ozone is simultaneously produced. Light, and
particularly sunlight, greatly assists oxidation
by gaseous oxygen. Potassium and sodium are
at once attacked by dry oxygen at ordinary
temperatures, becoming coated with their
respective oxides. The majority of metals
remain bright under similar conditions, but
many become oxidised when moisture is present.
In some of the metals oxidised by exposure
to air the first coating of oxide formed acts
as a protective covering and prevents further
oxidation, as is the case with lead. In others,
however, the oxide first formed gradually be-
comes converted into a higher oxide and may
then give up part of its oxygen to the metal in
contact with it, and the oxidation is thus propa-
gated through the mass of the metal. The rust-
ing of iron is not a simple case of oxidation (v.
RUST). Some metals which in their ordinary
condition are comparatively inert towards oxygen
combine with it readily at ordinary temperatures
when they are in a finely divided state, offering
a very large surface for chemical action. Thus
lead or antimony when obtained by the ignition
of their tartrates, and iron, nickel, cobalt,
and copper, when reduced from their precipitated
oxides in a current of hydrogen at a low tempera-
ture, all ignite spontaneously in contact with
air or oxygen, and when in this finely divided
state are therefore often termed pyrophori.
Silver, gold, and platinum are not acted on
directly by oxygen at any temperature. Some
metals in a molten state absorb considerable
quantities of oxygen which is given out again
wholly or in part when the metal solidifies.
10 grms. of molten silver at 1020 absorb about
20 c.c. oxygen (v. Donnan and Shaw, J. Soc.
Chem. Ind. 19 JO, 987).

Molten platinum and palladium also absorb

oxygen. Heated at 450 silver gradually absorbs

occludes) about 5 times its volume of oxygen,



gold 35-45, platinum 65-75, and palladium
about 500 (7 p.c. by weight). Platinum
black absorbs about 100 times its volume of
oxygen and palladium sponge 1000, of which
the whole is not given up again below a
red heat. Wood charcoal absorbs oxygen at
ordinary temperatures about 18 times its
volume (Goldstein) but this absorptive power
increases enormously at very low temperatures.
At 185 1 c.c. absorbs 230 c.c. of oxygen
with the evolution of 34 cals., and this action
may be employed to produce an oxygen vacuum,
the pressure being reduced to that of a
Geissler tube (Dewar).

The activity of oxygen is increased greatly by
increase of temperature, and with most sub-
stances (except under the conditions already
mentioned) an initial heating is necessary to
start free oxidation, the heat evolved during
oxidation being then sufficient to maintain it.
Thus iron heated to bright redness in an atmo-
sphere or stream of oxygen takes fire and burns
brightly. A mixture of oxygen and hydrogen
may be kept at ordinary temperatures for any
length of time without change, but if the tem-
perature of any part of the mixture be raised to
bright redness either by the electric spark, by
the presentation of a flame or by other means
ignition at once takes place with explosive force
throughout the whole mass. Under certain cir-
cumstances, however, this combination may be
effected at ordinary temperatures. Thus, if a
piece of clean platinum foil be hung in the mix-
ture, combination takes place gradually at ordi-
nary temperatures. This appears to be due to
the power possessed by palladium, platinum,
and some other substances of condensing gases
and especially hydrogen on their surfaces, the
activity of the gases so condensed being thereby
greatly increased. If platinum or palladium
black or sponge is used instead of foil, the action
is so much increased that the heat evolved in
the combination soon raises the temperature of
the metal to the ignition-point of the gaseous
mixture, and ordinary combustion ensues. This
effect has been taken advantage of in the
Dobereiner lamp (named after the investigator
who first noticed this property of platinum)
wherein a piece of spongy platinum is sus-
pended over a jet connected with an automatic
hydrogen-generating vessel. When the tap is
turned on, the jet of hydrogen becoming mixed
with air and at the same time impinging on
the spongy platinum, oxidation takes place
rapidly, the platinum soon becomes red hot
and ignites the jet of hydrogen. Similar effects
are produced with oxygen (or air) and gaseous
hydrocarbons.

Various substances which expose large sur-
faces to air (or oxygen) become gradually heated
through slow oxidation or combustion, and, if
the heat cannot get away, ignition eventually
occurs. Thus oily or greasy woollen and cotton
rags and refuse are capable of absorbing oxygen
fairly rapidly, and if present in any quantity the
heat produced may accumulate and cause spon-
taneous combustion, and this action is a not in-
frequent cause of fires in factories. A similar
generation of heat and eventual ' spontaneous
combustion ' often arises from the storing of
moist hay in hayricks, and from the storage of
damp coal in ships or heaps. The allegation



OXYGEN.



43



that the ignition of coal is duo to the oxidation
of pyrites has been disproved by the work of
.1 !ie liters and Lewes, who have .shown thai the
is generated by the absorption of oxygen
and its action on the bituminous constituents
of the coal.

Dixon, Baker, Traube, and others have
shouii that even at high temperatures the
presence of a trace of moisture is necessary for
free oxidation (combustion), and that in abso-
lutely dry oxygen, sulphur and phosphorus can
be distilled, and carbon made red-hot without
combustion taking place. A jet of burning dry
carbon monoxide is even extinguished when
introduced into pure and absolutely dry oxygen.
The presence of the minutest trace of moisture
is, however, sufficient to restore to oxygen its
activity.

In ordinarily dry oxygen all substances which
burn in air burn with much greater brilliancy,
and many substances which do not burn in air
burn vividly in oxygen. Thus iron, zinc, &c., if
the ignition is started by a portion being raised
to a white heat in an atmosphere of oxygen, con-
tinue to burn with great brilliancy and with the
olution of a very high temperature. The
tual amount of heat given out during the com-
ite oxidation of any substance is the same
iet her the combustion is slow or rapid, and is
ried on in air or in oxygen. But it is quite
ifferent in regard to the temperature developed,
iis depending on the concentration of the heat,
id HO being higher the more rapid the combus-
tion and the less extraneous matter is present
to absorb the heat. Thus, when phosphorus is
burned in oxygen, the temperature produced is
very high, and the combustion takes place with
dazzling brilliancy. The temperature of a
hydrogen or a coal-gas flame burning in oxygen
is very much higher than that of a similar flame
burning in air. The temperature of a flame of
hydrogen burning in oxygen is 2800 ; of carbon
monoxide 2600 ; and of acetylene 3000. These
facts have been utilised in the construction of the
oxy-hydrogen and oxy-acetylene blow-pipes for
obtaining very high temperatures (v. infra). If
coal-gas is substituted for the hydrogen, a very
hot flame is still obtained, but the tempera-
ture is not as great as when hydrogen is
employed. 16 grms. of oxygen combining
with hydrogen to form water evolve 68,400
cals.

Oxygen is the only gas capable of supporting
respiration, and forms the life-maintaining con-
stituent of air. In the pure state it may be in-
haled for a time with impunity, and acts as a
mild tonic or exhilarant. But its long-continued
respiration is harmful, feverishness and weak-
ne<s being produced ; and it becomes poisonous
if breathed under pressure. Dr. Richardson
kept a rabbit in an atmosphere of pure oxygen
at a temperature of 23-9 for 3 weeks. It
ate voraciously all the time, but became so
emaciated from inability to assimilate new
material fast enough to supply waste that it
was found necessary to discontinue the experi-
ment. At 7-2 the rabbit became speedily
narcotised, and would have died had it not been
removed. Richardson found that cold-blooded
animals were very little affected by being intro-
duced into an atmosphere of oxygen, whilst most
warm-blooded animals (dogs, cats, guinea-pigs,



&c., but not the rabbit) speedily showed strong
febrile ; symptoms (Asclepiad 1887-89). Some
observers have noticed very derided narcotic



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