OXG 
a quantity equal to its own weight. This 
acid is decomposed by the sulphuric acid 
with heat, and charcoal is deposited : at 
the boiling temperature it is decomposed 
by the nitric acid, and converted into wa- 
ter and carbonic acid : its component 
parts are 
Oxygen 77 
Carbon 13 
Hydrogen •■■■10 
too 
It combines with alkalies, earths, and 
metallic oxides, and the salts thus formed 
are denominated oxalates. The great at- 
traction which this acid has for lime renders 
it of great utility in detecting that sub- 
stance in every soluble combination. 
OXALATE.S, in chemistry, salts formed 
of the oxalic acid and certain bases, are 
distinguished by the following properties : 
when exposed to a red heat, the acid is de- 
composed and driven off, and the base only 
remains. Lime water precipitates a white 
powder from their solutions, provided no 
excess of acid be present : the earthy oxal- 
ates are in general nearly insoluble in water, 
but they may be rendered soluble by an 
excess of the more powerful acids. See 
Oxalic acid. 
OXALIS, in botany, wood-sorrel, a ge- 
nus of the Decandria Eentagynia class and 
order. Natural order of Gruinales. Ge- 
rania, Jussieu. Essential character ; calyx 
five-parted ; petals five, often connected at 
the base ; capsule five-celled, five-cornered, 
opening at the corners ; seeds arilled. 
There aie ninety-six species, of which the 
O. acetosella, common wood-sorrel, has a 
perennial, branched, knobbed, creeping 
root, having fine fibrils on every side, 
partly red and partly white, with an ovate, 
acute, rigid scale, like a tooth at the knobs ; 
scapes one or two, jointed at the base, the 
length of the leaves ; calycine leaflets, ob- 
long, acute, sometimes bifid, ciliate, purple 
at the tip, upright. Linnseus remarks, that 
the leaflets in wet weather are erected, but 
hang down in dry weather. It has been 
observed, that this elegant little plant has 
the leaves of trefoil, the taste of sorrel, and 
the flower of geranium; from which last 
genus this is distinct, in the number of 
styles, the form of the capsule and manner 
of its opening, its straight corcle, or heart, 
without any perisperm or albumen : it is 
common all over Europe. 
OXGANG, or Oxgate, is generally 
OXI 
taken, in our old law-books, for fifteen 
acres, or as much ground as a single ox can 
plough in a year. 
OXIDE, in chemistry. Metallic sub- 
stances are not only of vast importance in 
the arts of civilized life, on account of the 
properties which belong to them in the me- 
tallic state ; but many of them are not less 
valuable in those changes which they under- 
go by new combinations, and the new pro- 
perties they acquire, in consequence of 
these changes. One of the first and most 
ordinary changes to which metallic sub- 
stances are subject, is their combination 
with oxygen. This is called, in chemical 
language, oxydation. If a metal, as, for 
instance, a piece of iron, is exposed to 
the air, when it is moist, it soon undergoes 
a remarkable change. It loses its metallic 
lustre, and the surface is covered, with a 
brownish powder, well known by the name 
of rust. This change is owing to the com- 
bination of oxygen with the metal, and the 
rust of the metal in this state is known in 
chemistry by tlie name of oxide. The pro- 
cess by which this compound of oxygen and 
a metallic substance is formed, is called 
oxydation, and the product is denominated 
an oxide. The process of oxydation is ef- 
fected more rapidly when metals are ex- 
posed to the action of heat ; and, indeed, 
many metals require a very high tem- 
perature to produce the combination, while 
it cannot be accomplished in others by the 
greatest degree of heat that can be pro- 
duced. This process was formerly called 
calcination, or calcining the metal ; and the 
product, now denominated an oxide, was 
distinguished by the name of calx or calces, 
from its being reduced to the state of pow- 
der, in the same way as limestone, by burn- 
ing. Metals differ very much from each 
other in I’ne circumstances in which this 
oxydation takes place, as in the tempera- 
ture which is necessary, the facility of the 
combination, the proportions of oxygen 
which combine, and the force of affinity 
between the constituent parts of the oxide. 
Some metals are oxydated in the lowest 
temperature, as, for instance, iron and man- 
ganese; w'hile others require the greatest 
degree of heat that can be appUed. Such 
are silver, gold, and platiua. 
The facility with which oxydation take.s 
place in some metals is so great, such as in 
iron, tin, lead, copper, and manganese, that 
they must be completely defended from 
the action of oxygen ; but in gold and p!a- 
tina, no perceptible change is observed. 
