The Romance of Modern Chemistry

HIGH TEMPERATURES which now contain a certain proportion of barium dioxide, are connected with a suction pump. The effect of this diminution of pressure is the same as that of a rise of temperature, and from the engineering point of view it is better to alter the pressure than to alter the temperature. The barium dioxide accordingly gives up the extra oxygen which it extracted from the air, and the oxygen so obtained is compressed in steel bottles under a pressure of 120 atmospheres and sent into the market The barium oxide may be used over and over again in the same fashion, and, theoretically at least, a given quantity of this substance should suffice for the winning of unlimited quantities of oxygen from the air, by alternate association and dissociation. The highest temperatures reached in furnaces fed with ordinary fuel—the furnaces employed for technical pur- poses—lie about 3200° Fahrenheit, but it is possible to get a few hundred degrees beyond that with the oxy- hydrogen blowpipe. When we feed a coal-gas flame with a blast of air as in an ordinary blowpipe, we get a very high temperature, but the effect is wonder- fully increased by substituting oxygen for air. The reason of this is not far to seek. Roughly speaking, air consists of one part of oxygen to four parts of nitrogen; the latter gas, although it takes no part in the combustion, yet passes through the flame and has to be warmed up, thereby absorbing a considerable pro- portion of the heat produced by the combustion. In the oxyhydrogen or oxy-coal-gas flame the nitrogen is not there to dilute the active oxygen, so that the temperature reached is very much higher. The increased heating effect secured in this way makes it possible to melt platinum, and the operation is actually 196