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Oxyhydrogen
Nineteenth-century
electrolytic cell
for producing oxyhydrogen.
Oxyhydrogen
is a mixture of
hydrogen
(H
2
) and
oxygen
(O
2
) gases. This gaseous mixture is used for torches to process
refractory
materials and was the first
[1]
gaseous mixture used for
welding
. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an
oxidizing flame
.
[2]
This mixture may also be referred to as
Knallgas
(Scandinavian and German
Knallgas
: "bang-gas"), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".
[3]
Brown's gas
[4]
and
HHO
are
fringe science
terms for a 2:1 mixture of oxyhydrogen obtained under certain special conditions; its proponents claim that it has special properties.
Hydrogen
Hydrogen
is a
chemical element
with
chemical symbol
H
and
atomic number
1. With a
standard atomic weight
of circa 1.008, hydrogen is the lightest element on the
periodic table
. Its
monatomic
form (H) is the
most abundant
chemical substance in the
Universe
, constituting roughly 75% of all
baryonic
mass.
[9]
[note 1]
Non-
remnant
stars
are mainly composed of hydrogen in the
plasma state
. The most common
isotope
of hydrogen, termed
protium
(name rarely used, symbol
1
H), has one
proton
and no
neutrons
.
The universal emergence of atomic hydrogen first occurred during the
recombination epoch
. At
standard temperature and pressure
, hydrogen is a
colorless
,
odorless
,
tasteless
, non-toxic,
nonmetallic
, highly
combustible
diatomic
gas
with the
molecular formula
H
2
. Since hydrogen readily forms
covalent
compounds with most nonmetallic elements, most of the hydrogen on Earth exists in
molecular forms
such as
water
or
organic compounds
. Hydrogen plays a particularly important role in
acid–base reactions
because most acid-base reactions involve the exchange of protons between soluble molecules. In
ionic compounds
, hydrogen can take the form of a negative charge (i.e.,
anion
) when it is known as a
hydride
, or as a positively charged (i.e.,
cation
)
species
denoted by the symbol H
+
. The hydrogen cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds are always more complex. As the only neutral atom for which the
Schrödinger equation
can be solved analytically,
[10]
study of the energetics and bonding of the hydrogen atom has played a key role in the development of
quantum mechanics
.
Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. In 1766–81,
Henry Cavendish
was the first to recognize that hydrogen gas was a discrete substance,
[11]
and that it produces water when burned, the property for which it was later named: in Greek, hydrogen means "water-former".
Industrial production
is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the
electrolysis of water
.
[12]
Most hydrogen is used near the site of its production, the two largest uses being
fossil fuel
processing (e.g.,
hydrocracking
) and
ammonia
production, mostly for the fertilizer market. Hydrogen is a concern in
metallurgy
as it can
embrittle
many metals,
[13]
complicating the design of pipelines and storage tanks.
[14]
Oxygen
Oxygen
is a
chemical element
with symbol
O
and
atomic number
8. It is a member of the
chalcogen
group
on the
periodic table
and is a highly
reactive
nonmetal
and
oxidizing agent
that readily forms
oxides
with most elements as well as other
compounds
.
[3]
By mass, oxygen is the third-
most abundant element
in the universe, after
hydrogen
and
helium
.
[4]
At
standard temperature and pressure
, two atoms of the element
bind
to form
dioxygen
, a colorless and odorless
diatomic
gas
with the formula O
2. This is an important part of the
atmosphere
and diatomic oxygen gas constitutes 20.8% of the
Earth's atmosphere
.
[5]
Additionally, as oxides the element makes up almost half of the
Earth's crust
.
[6]
Dioxygen is used in
cellular respiration
and many major classes of
organic molecules
in
living organisms
contain oxygen, such as
proteins
,
nucleic acids
,
carbohydrates
, and
fats
, as do the major constituent
inorganic compounds
of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Conversely, oxygen is continuously replenished by
photosynthesis
, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form (
allotrope
) of oxygen,
ozone
(O
3), strongly absorbs ultraviolet
UVB
radiation and the high-altitude
ozone layer
helps protect the biosphere from
ultraviolet radiation
. But ozone is a pollutant near the surface where it is a by-product of
smog
. At
low earth orbit
altitudes, sufficient atomic oxygen is present to cause
corrosion of spacecraft
.
[7]
Oxygen was discovered independently by
Carl Wilhelm Scheele
, in
Uppsala
, in 1773 or earlier, and
Joseph Priestley
in
Wiltshire
, in 1774, but Priestley is often given priority because his work was published first. The name
oxygen
was coined in 1777 by
Antoine Lavoisier
,
[8]
whose experiments with oxygen helped to discredit the then-popular
phlogiston theory
of
combustion
and
corrosion
. Its name derives from the
Greek
roots ὀξύς
oxys
, "acid", literally "sharp", referring to the
sour taste
of
acids
and -γενής
-genes
, "producer", literally "begetter", because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition.
Common use of oxygen includes residential
heating
,
internal combustion engines
, production of
steel
,
plastics
and
textiles
,
brazing, welding and cutting
of steels and other
metals
,
rocket propellant
,
oxygen therapy
, and
life support systems
in
aircraft
,
submarines
,
spaceflight
and
diving
.
