Page:The American Cyclopædia (1879) Volume XII.djvu/784

 7TO OXYGEN permanganates, or chromates of the alkalies or alkaline earths, in a current of superheated steam. The operation is conducted as follows : Binoxide of manganese is stirred to a paste with a solution of caustic soda. This paste, subjected to the action of hot air deprived of carbonic acid, is converted into manganate of soda. If now the manganate is subjected to the action of a stream of superheated steam, the salt is decomposed, the soda becoming a hydrate, and the manganic acid being reduced to a lower degree of oxidation, while a portion of its oxygen is liberated. Cylindrical iron retorts are used, through which hot air and superheated steam are alternately passed, each operation producing alternate oxidation and deoxidation of the mass, so that it may be continuous. It is said that a charge of 10 Ibs. of the mass will yield 80 gallons of oxygen gas, even after it has undergone 80 operations. Apparatus of the kind is used in New York for street illumination. Properties. Oxygen is colorless, tasteless, and inodorous, and the least refractive of all the gases. Compared with atmospheric air, it is as 0'83 to 1. No degree of cold or pressure yet applied has re- sulted in its liquefaction. Its specific grav- ity is 1-1056, 16 times heavier than hydrogen. Its specific heat compared with that of an equal volume of air, according to De la Roche and Berard, is 0-9765. According to Tyndall, it has less power to absorb and to radiate heat than other gases. Faraday showed that it is the most magnetic of all gases ; compared with air its magnetic power is as 5 to 1 ; with nitro- gen, about 40 to 1. In this respect its position among gases is like that of iron among metals, and like this metal its magnetism is destroyed by heat, but on account of its gaseous condi- tion returns on cooling, while iron remains de- magnetized from its molecules having received a set. Faraday suggested that the diurnal va- riation of the magnetic needle may be caused by the increase and decrease of the magnetic force in the atmospheric oxygen from the va- riation of solar heat. Water dissolves oxygen sparingly, 100 volumes of water at 60 F. dis- solving 3 volumes of the gas, and at 32 about 4 volumes. The- air which is held in solution by terrestrial waters contains a much larger proportion of oxygen than atmospheric air, and this condition adapts it to the respiration of aquatic animals. Oxygen is what is usually termed an active supporter of combustion ; most bodies which are called combustibles, as hydrogen and carbohydrogen gases, coal, wood, and the various oils, burn with vividness in it when raised to a red heat. But it is strictly more correct to say that all the elements which unite in combustion are supporters of combus- tion. A jet of oxygen may be burned in an atmosphere of hydrogen, as well as a jet of hydrogen in an atmosphere of oxygen. Char- coal bark, heated to redness and introduced into a vessel of oxygen, is consumed with bril- liant scintillations, unaccompanied with flame, in consequence of the instantaneous conver- sion of the carbon into carbonic acid, without the intermediate production of carbonic ox- ide, which in ordinary charcoal combustion is produced and causes a faint blue flame. (See FLAME, and COMBUSTION.) Phosphorus, when ignited in a small cup attached to a bent wire, and lowered into a vessel of oxygen (cautious- ly, to avoid burning the hand), burns with exceeding brilliancy. If the piece is large enough not to be consumed before it boils, the vapor, becoming somewhat diffused, will give the bell glass the appearance of an incandes- cent body. The product of the combustion is phosphoric acid (P 2 6 ), the highest oxide of phosphorus. The products of the union of oxygen with the other elements, particularly the binary compounds, are called oxides, as the oxides of the metals, like lime or oxide of cal- cium, potash or oxide of potassium, and lith- arge or oxide of lead; and the oxides of the non-metallic elements, as the oxides of nitro- gen, like nitric oxide and nitric acid. (See NITROGEN.) The various oxides will be found under the heads of the elements of which they are formed. (See also OXIDES.) Although, as has been remarked, oxygen is not necessary, as Lavoisier supposed, to the production of an acid, yet there is no non-metallic body which is so widely associated with the production of acid properties in compounds. In the va- rious proportions in which a metal combines with oxygen, those compounds containing the smallest proportions are not acid, but act the part of bases, while the more highly oxidized compounds are acid. This is illustrated in the various oxides of manganese and iron. (See MANGANESE.) In the different proportions in which it combines with nitrogen similar re- sults are seen. (See NITROGEN.) One of the important applications of oxygen gas is its employment as one of the elements in the oxyhydrogen blowpipe, which, with the ex- ception of the galvanic battery, yields the highest known degree of artificial heat. The ordinary mouth blowpipe test, by which a small button of metal may be oxidized or de- oxidized, according as it is placed in the outer or the inner flame, or placed upon charcoal, or mingled with an oxidizing flux, depends upon the agency of oxygen (see BLOWPIPE) ; and the process of cupellation depends upon the same principle. In these operations nitrate of potash (K 2 N0 3 ) is often used with advantage for this purpose. The wide range of affinity possessed by oxygen is evidenced by the important part it plays in the processes of chemical analysis and synthesis, and in the changes which take place during decay and fermentation, as well as in the phenomena of life in plants and ani- mals. (See EEEMAOAUSIS, and FERMENTATION.) Eremacausis is a process of slow oxidation. Oxygen is one of the most important support- ers of animal life, and was therefore called by the older chemists vital air. In fermenta- tion oxygen plays an active part in the de-