182 ANNUAL OP SCIENTIFIC DISCOVERY. 



the cold attained by the carbonic acid and ether bath. Atmospheric 

 air was compressed by pressure alone to 1-3 7 1st of its original vol- 

 ume, and by the united action of pressure and a cold of 106 Fah. to 

 1-6 75th; in which state its density was little inferior to that of water. 

 Oxygen gas was reduced by pressure to l-324th of its volume, and by 

 pressure and cold to 1 -554th ; hydrogen, by the united action of cold 

 and pressure, to l-500th; carbonic oxide by pressure to 1-2 78th, by 

 pressure and cold to 1-2 78th ; nitric oxide, by pressure to l-310th, by 

 pressure and a cold of 160 Fah. to l-G80th. None of the gases 

 exhibited any appearance of liquefaction even in these high states of 

 condensation. The amount of contraction was nearly proportional to 

 the force employed, till the gases were reduced to from about l-300th 

 to 1 -350th of their volume ; but, beyond that point, they underwent 

 little further diminution of volume from increase of pressure. Hy- 

 drogen and carbonic oxide appear to resist the action of pressure 

 better than oxygen or nitric oxide. 



PREPARATION OF OXYGEN ON A LARGE SCALE. 



H. St. Clair Deville and Debray, the well-known French chemists, 

 in studying the economical production of oxygen upon the large 

 scale, have arrived at results which promise to be of great practical 

 importance. The authors find that sulphate of zinc, when heated 

 alone in an earthen or porcelain vessel, yields a light and white oxide, 

 which may be utilized in painting ; sulphurous acid, which is easily 

 absorbed by water ; and, finally, pure oxygen. The temperature re- 

 quired is not milch higher than that which is necessary for the decom- 

 position of peroxide of manganese. 



Another and very elegant process consists in the decomposition of 

 sulphuric acid by heat. A fine stream of the acid is allowed to flow 

 into a retort of about five litres capacity, filled with thin platinum 

 foil and heated to redness. The acid is completely decomposed into 

 oxygen, water, and sulphurous acid, which last is absorbed by an 

 appropriate washing apparatus. The sulphurous acid may again be 

 converted into sulphuric acid, in the usual manner. 



In addition, they also state that chlorid of lime (bleaching powders), 

 when heated to low redness, gives off, per pound, from twenty to 

 twenty-five litres of oxygen. This gas is mixed with a little chlorine, 

 from which it may be freed by washing with an alkaline solution, or, 

 better, the formation of this impurity may be prevented by adding 

 enough slaked lime to the chlorid employed that this shall be strongly 

 alkaline ; if this precaution be attended to, the operation may be 

 conducted in iron vessels. It is of importance only to avoid heating the 

 mass to the fusion point of the chlorid of calcium. The calcination 

 may be made in glass vessels. The production of oxygen from this 

 source is very regular, and unattended with danger. The process is 

 moreover economical, as compared with those commonly employed by 

 chemists; in the experiments of the authors the cubic meter (35.316 

 cubic feet) of oxygen, when prepared from black oxide of manganese, 

 costs about four francs, from chlorid of lime five francs, while from 

 chlorate of potash it could not be obtained for Jess than ten francs ; 

 but the process is nevertheless far more expensive than their sulphuric 



