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Rh then interacts with water to form hydrogen peroxide (see also W. Manchot, Ann., 1901, 314, p. 177; 1902, 325, p. 95).

Oxygen is a member of the sixth group in the periodic classification, and consequently possesses a maximum valency of six. In most cases it behaves as a divalent clement, but it may also be quadrivalent. A. v. Baeyer and V. Villiger (Ber., 1901, 34, pp. 2679, 3612) showed that many organic compounds (ethers, alcohols, aldehyde's, ketones, &c.) behave towards acids, particularly the more complex acids, very much like bases and yield crystallized salts in which quadrivalent oxygen must be assumed as the basic element. These salts are considered to be derived from the hypothetical base OHs-OH, oxoniurn. hydroxide (compare sulphonium salts). Further see J. Schmidt, " Über die basischen Eigenschaften des Sauerstoffs " (Berlin, 1904). Baeyer and Villiger assume for the configuration of

the salts of carbonyl compounds the arrangement > C: O <^-y, whilst

J. W. Bruhl and P. W. Walden point out from the physico-chemical standpoint that in water and hydrogen peroxide the oxygen atom is probably quadrivalent.

The atomic weight of oxygen is now generally taken as 16, and as such is used as the standard by which the atomic weights of the other elements are determined, owing to the fact that most elements combine with oxygen more readily than with hydrogen (see ).

Oxygen is widely used in medical practice as well as in surgery. Inhalations of the gas are of service in pneumonia, bronchitis, heart disease, asthma, angina and other conditions accompanied by cyanosis and dyspnoea. They often avert death from asphyxia, or render the end less distressing. Oxygen is also administered in chloroform poisoning, and in threatened death from the inhalation of coal gas or nitrous oxides. It is of value in cyanide and opium poisoning and in the resuscitation of the apparently drowned. The mode of administration is by an inhaler attached to an inhalation bag, which serves to break the force with which the oxygen issues from the cylinders in which it is sold in a compressed form. It can be administered pure or mixed with air as required. If given in too great quantity a temporary condition of apnoea (cessation of breathing) is produced, the blood being fully charged with the gas. Oxygen may be applied locally as a disinfectant to foul and diseased surfaces by the use of the peroxide of hydrogen, which readily parts with its oxygen; a solution of hydrogen peroxide therefore forms a valuable spray in diphtheria, tonsillitis, laryngeal tuberculosis and ozaena. It can also be used with advantage in inoperable uterine cancer, favus and lupus, and as an injection in gonorrhoea and suppurative conditions of the ear. It relieves the pain of wasp and bee stings. Internally hydrogen peroxide is used in various diseased conditions of the gastro-intestinal tract, such as dyspepsia, diarrhoea and enteric fever. The B.P. preparation Liquor Hydrogen Peroxidi dose 5 to 2 drs. is synonymous with the Aqua Hydrogen Dioxidi of the U.S.P. and the ten-volume solution termed eau oxygence in France. It is customary to use oxygen in combination with chloroform, or nitrous oxide in order to produce insensibility to pain (see ).

OXYHYDROGEN FLAME, the flame attending the combustion of hydrogen and oxygen, and characterized by a very high temperature. Hydrogen gas readily burns in oxygen or air with the formation of water. The quantity of heat evolved, according to Julius Thomsen, is 34,116 calories for each gram of hydrogen burned. This heat-disturbance is quite independent of the mode in which the process is conducted; but the temperature of the flame is dependent on the circumstances under which the process takes place. It obviously attains its maximum in the case of the firing of pure " oxyhydrogen " gas (a mixture of hydrogen with exactly half its volume of oxygen, the quantity it combines with in becoming water, German Knall-gas). It becomes less when the " oxyhydrogen " is mixed with excess of one or the other of the two reacting gases, or an inert gas such as nitrogen, because in any such case the same amount of heat spreads over a larger quantity of matter. Many forms of oxyhydrogen lamps have been invented, but the explosive nature of the gaseous mixture rendered them all more or less dangerous. It acquired considerable application in platinum works, this metal being only fusible in the oxyhydrogen flame and the electric furnace; and also for the production of limelight, as in optical (magic) lanterns. But these applications are being superseded by the electric furnace, and electric light.

 '''OYAMA. IWAO''', Prince (1842–), Japanese field-marshal, was born in Satsuma. He was a nephew of Saigo, with whom his elder brother sided in the Satsuma insurrection of 1877, but he nevertheless remained loyal to the imperial cause and commanded a brigade against the insurgents. When war broke out between China and Japan in 1894, he was appointed commander in-chief of the second Japanese army corps, which, landing on the Liaotung Peninsula, carried Port Arthur by storm, and, subsequently crossing to Shantung, captured the fortress of Wei-hai-wei. For these services he received the title of marquess, •and, three years later, he became field-marshal. When (1904) his country became embroiled in war with Russia, he was appointed commander-in-chief of the Japanese armies in Manchuria, and in the sequel of Japan's victory the mikado bestowed on him (1907) the rank of prince. He received the British Order of Merit in 1906.

 OYER AND TERMINER, the Anglo-French name, meaning " to hear and determine," for one of the commissions by which a judge of assize sits (see ). By the commission of oyer and terminer the commissioners (in practice the judges of assize, though other persons are named with them in the commission) are commanded to make diligent inquiry into all treasons, felonies and misdemeanours whatever committed in the counties specified in the commission, and to hear and determine the same according to law. The inquiry is by means of the grand jury; after the grand jury has found the bills submitted to it, the commissioners proceed " to hear and determine " by means of the petty jury. The words oyer and terminer are also used to denote the court which has jurisdiction to try offences within the limits to which the commission of oyer and terminer extends.

By the Treason Act 1708 the crown has power to issue commissions of oyer and terminer in Scotland for the trial of treason and misprision of treason. Three of the lords of justiciary must be in any such commission. An indictment for either of the offences mentioned may be removed by certiorari from the court of oyer and terminer into the court of justiciary.

In the United States oyer and terminer is the name given to courts of criminal jurisdiction in some states, e.g. New York, New Jersey, Pennsylvania, and Georgia.

 OYSTER. The use of this name in the vernacular is equivalent to that of Ostrea (Lat. from Gr. ὄστρεον}, oyster, so called from its shell, ὄστεον}, bone, shell) in zoological nomenclature; there are no genera so similar to Ostrea as to be confounded with it in ordinary language. Ostrea is a genus of Lamellibranch Molluscs. The degeneration produced by sedentary habits in all lamellibranchs has in the oyster reached its most advanced stage. The valves of the shell are closed by a single large adductor muscle, the anterior adductor being absent. The muscular projection of the ventral surface called the foot, whose various modifications characterize the different classes of Mollusca, is almost entirely aborted. The two valves of the shell are unequal in size, and of different shape; the left valve is larger, thicker and more convex, and on it the animal rests in its natural state. This valve, in the young oyster, is attached to some object on the sea-bottom; in the adult it is sometimes attached, sometimes free. The right valve is flat, and smaller and thinner than the left. In a corresponding manner the right side of the animal's body is somewhat less developed than the left, and to this extent there is a departure from the bilateral symmetry characteristic of Lamellibranchs.

The organization of the oyster, as compared with that of a typical lamellibranch such as Anodon (see ), is brought about by the reduction of the anterior part of the body accompanying the loss of the anterior adductor, and the enlargement of the posterior region. The pedal gangha and auditory organs have disappeared with the foot, at all events have never been detected; the cerebral ganglia are very minute, while the parieto-splanchnic are well developed, and constitute the principal part of the nervous system.

According to Spengel, the pair of gangha near the mouth, variously called labial or cerebral, represent the cerebral pair and pleural pair of a gastropod combined, and the parietosplanchnic pair correspond to the visceral ganglia, the commissure which connects them with the cerebro-pleural representing the visceral commissure. Each of the visceral ganglia is connected or combined with an olfactory ganglion underlying an area of specialized epithelium, which constitutes the olfactory organ, the osphradium. The heart and pericardia chamber in the oyster lie along the anterior face of the adductor muscle,