More distinct are the bisons, forming the sub-genus Bison, represented by the European and the American species (see Bison), the forehead of the skull being much shorter and wider, and the horns not arising from a crest on the extreme vertex, while the number of ribs is different (14 pairs in bisons, only 13 in oxen), and the hair on the head and neck is long and shaggy. Very close to this group, if indeed really separable, is the Tibetan yak (q.v.), forming by itself the sub-genus Pöephagus.
The most widely different from the true oxen are, however, the buffaloes (see Buffalo), which have consequently the most claim to generic distinction. From all other Bovinae they differ by the triangular section of their horns. They are divisible into two groups, an African and an Asiatic, both of which are generally included in the sub-genus, or genus, Bubalus, although the latter are sometimes separated as Buffelus. The smallest member of the group is the anoa (q.v.) of Celebes.
As regards the origin of the ox-tribe we are still in the dark. The structure of their molar teeth affiliates them to the antelopes of the Oryx and Hippotragus groups; but the early bovines lack horns in the female, whereas both sexes of these antelopes are horned.
Remains of the wild ox or aurochs are abundant in the superficial deposits of Europe, Western Asia, and Northern Africa; those from the brick-earths of the Thames valley indicating animals of immense proportions. Side by side with these are found remains of a huge bison, generally regarded as specifically distinct from the living European animal and termed Bos (Bison) priscus. In the Pleistocene of India occurs a large ox (Bos namadicus), possibly showing some affinity with the Bibos group, and in the same formation are found remains of a buffalo, allied to, but distinct from the living Indian species. Large oxen also occur in the Lower Pliocene of India, although not closely allied to the living kinds; while in the same formation are found remains of bison (or [?] yak) and buffaloes, some of the latter being nearly akin to the anoa, although much larger. Perhaps, however, the most interesting are the remains of certain oxen from the Lower Pliocene of Europe and India, which have been described under the sub-generic (or generic) title of Leptobos, and are characterized by the absence of horns in the females. In other respects they appear to come nearest to the bantin. Remains of extinct bisons, some of gigantic size, occur in the superficial formations of North America as far south as Texas.
See R. Lydekker, Wild Oxen, Sheep and Goats (London, 1898). (R. L.*)
OXALIC ACID, H2C2O4⋅2H2O, one of the oldest known organic
acids. Scheele prepared it by oxidizing sugar with nitric acid,
and showed it to be identical with the acetosellic acid obtained
from wood-sorrel. It is found in the form of its acid potassium
salt in many plants, especially in wood-sorrel (Oxalis acetosella)
and in varieties of Rumex; as ammonium salt in guano; as
calcium salt in rhubarb root, in various lichens and in plant
cells; as sodium salt in species of Salicornia and as free acid
in varieties of Boletus. It is also present in urine and in urinary
calculi. It is formed in the oxidation of many organic compounds
(e.g. sugar, starch and cellulose) by nitric acid, and also by the
fusion of many oxygen-holding compounds with caustic alkalis,
this latter method being employed for the manufacture of oxalic
acid. In this process cellulose (in the form of sawdust) is made
into a stiff paste with a mixture of strong caustic potash and soda
solution and heated in flat iron pans to 200–250° C. The somewhat
dark-coloured mass is lixiviated with a small amount of
warm water in order to remove excess of alkali, the residual
alkaline oxalates converted into insoluble calcium oxalate by
boiling with milk of lime, the lime salt separated, and decomposed
by means of sulphuric acid. It is found that the sawdust
obtained from soft woods is the best material for use in this
process. It may be obtained synthetically by heating sodium
in a current of carbon dioxide to 360° C.; by the oxidation of
ethylene glycol; by heating sodium formate to 400° C. (V. Merz
and W. Weith, Ber., 1882, 15, p. 1513), and by the spontaneous
hydrolysis of an aqueous solution of cyanogen gas.
The hydrated acid crystallizes in prisms which effloresce in air, and are readily soluble in water. It loses its water of crystallization at 100° C, and begins to sublime at about 150–160° C., whilst on heating to a still higher temperature it partially decomposes into carbon dioxide and formic acid, or into carbon dioxide, carbon monoxide and water; the latter decomposition being also brought about by heating oxalic acid with concentrated sulphuric acid. The anhydrous acid melts at 189·5° C. (E. Bamberger, Ber., 1888, 21, p. 1901) and is frequently used as a condensing agent. Phosphorus pentachloride decomposes it into carbon monoxide and dioxide, the reaction being the one generally applied for the purpose of preparing phosphorus oxychloride. When heated with glycerin to 100° C. it yields formic acid and carbon dioxide; above this temperature, allyl alcohol is formed. Nascent hydrogen reduces it to glycollic acid. Potassium permanganate in acid solution oxidizes it to carbon dioxide and water; the manganese sulphate formed has a catalytic accelerating effect on the decomposition.
Oxalic acid is very poisonous, and by reason of its great similarity in appearance to Epsom salts, it has been very frequently mistaken for this substance with, in many cases, fatal results. The antidotes for oxalic acid poisoning are milk of lime, chalk, whiting, or even wall-plaster, followed by evacuation brought about by an enema or castor oil. Only the salts of the alkali metals are soluble in water. Beside the ordinary acid and neutral salts, a series of salts called quadroxalates is known, these being salts containing one molecule of acid salt, in combination with one molecule of acid, one of the most common being “salt of sorrel,” KHC2O4⋅H2C2O4⋅2H2O. The oxalates are readily decomposed on heating, leaving a residue of carbonate, or oxide of the metal. The silver salt decomposes with explosive violence, leaving a residue of the metal.
Potassium ferrous oxalate, FeK2(C2O4)22⋅H2O, is a strong reducing agent and is used as a photographic developer. Potassium ferric oxalate, FeK3(C2O4)3, is used in the preparation of platinotypes, owing to the fact that its solution is rapidly decomposed by sunlight, 2FeK3(C2O4)3 = 2FeK3(C2O4)2+K2C2O4+2CO2. Ethyl oxalate, (CO⋅OC2H5)2, prepared by boiling anhydrous oxalic acid with absolute alcohol, is a colourless liquid which boils at 186° C. Methyl oxalate (CO⋅OCH3)2, which is prepared in a similar manner, is a solid melting at 54° C. It is used in the preparation of pure methyl alcohol. On treatment with zinc and alkyl iodides or with zinc alkyls they are converted into esters of hydroxy-dialkyl acetic acids. An impure oxalyl chloride, a liquid boiling at 70° C, has been obtained by the action of phosphorus pentachloride on ethyl oxalate. Oxamic acid, HO2C⋅CONH2, is obtained on heating acid ammonium oxalate; by boiling oxamide with ammonia; and among the products produced when amino-acids are oxidized with potassium permanganate (J. T. Halsey, Zeit. f. physiol. Chem., 1898, 25, p. 325). It is a crystalline powder difficultly soluble in water and melting at 210° C. (with decomposition). Its ethyl ester, known as oxamaethane, crystallizes in rhombic plates which melt at 114–115° C. Phosphorus pentachloride converts it into cyan-carbonic ester, the ethyl oxamine chloride first formed being unstable: ROOC⋅CONH2→ROOC⋅C(Cl2)⋅NH2→CN⋅COOR. Oximide, (CO)2NH, produced by the action of a mixture of phosphorus pentachloride and oxychloride on oxamic acid (H. Ost and A. Mente, Ber., 1886, 19, p. 3229), crystallizes in prisms, and when boiled with water is rapidly hydrolysed to oxamide and oxalic acid. Oxamide, (C0NH2)2, is best prepared by the action of ammonia on the esters of oxalic acid. It is also obtained by the action of hydrogen peroxide on hydrocyanic acid, or of manganese dioxide and sulphuric acid on potassium cyanide. It is a white crystalline powder which is almost insoluble in cold water. It melts at 417–419° C. (with decomposition) when heated in a sealed tube (A. Michael, Ber., 1895, 28, p. 1632). When heated with phosphorus pentoxide it yields cyanogen. It is readily hydrolysed by hot solutions of the caustic alkalis. Substituted oxamides are produced by the action of primary amines on ethyl oxalate. Semioxamazide, H2N⋅CO⋅CO⋅NH⋅NH2, is prepared by the action of hydrazine hydrate on oxamaethane (W. Kerp and K. Unger, Ber. 1897, 30, p. 586). It crystallizes in plates which melt at 220–221° C. (with decomposition). It is only slightly soluble in water, but is readily soluble in acids and alkalis. It reduces silver salts rapidly. It condenses with aldehydes and ketones to produce semioxamazones.
OXALIS, in botany, a large genus of small herbaceous plants, comprising, with a few small allied genera, the natural order Oxalidaceae. The name is derived from Gr. ὄξυς, acid, the plants being acid from presence of acid calcium oxalate. It contains about 220 species, chiefly South African and tropical and South American. It is represented in Britain by the wood-sorrel, a small stemless plant with radical trefoil-like leaves growing from a creeping scaly rootstock, and the flowers borne singly on an axillary stalk; the flowers are regular with five sepals, five obovate, white, purple-veined, free petals, ten stamens and a central five-lobed, five-celled ovary with five
