232 ANNUAL OF SCIENTIFIC DISCOVERY. 



its boiling point. Bousingault has attempted to use baryta for the pur- 

 pose of extracting oxygen from the atmospheric mixture in larger pro- 

 portion. The method is simple. The air is conducted over pieces of 

 baryta, at a dark-red heat, until it has become converted into peroxide 

 of barium ; the oxygen is, subsequently, again expelled, by the appli- 

 cation of a more intense heat. The moisture and carbonic acid, usually 

 present in the air, do not materially interfere with the process. The 

 baryta, however, contained so much alumina and silica, that, after re- 

 peated use, it became caked, and hence no longer of any use. Pure 

 baryta was free from this inconvenience. According to Bousingault, 

 on a large scale, on using ten kilogrammes of baryta, which absorb 

 730 litres of oxygen, and should again part with it, 600 litres is the 

 quantity always obtained in practice. Hence, with furnaces in which 

 100 kilogrammes of baryta, distributed in eight to ten tubes, can be 

 heated at once, from 24,000 to 30,000 litres of oxygen may be produced 

 in twenty-four hours. Comptcs Rendus, vol. xxxii. 



NEW METHOD OF DETERMINING THE AMOUNT OF OXYGEN IN THE 



ATMOSPHERE. 



'LIEBIG, in the Annalcs, recommends the employment of an alkaline 

 solution of pyrogallic acid, the rapid absorbent capacity for oxygen of 

 which has been long known, as a means of determining the amount of 

 oxygen in atmospheric air. When a solution of caustic potassa, and 

 then a solution of pyrogallic acid, is conveyed into a tube filled with 

 mercury, the liquids mix without alteration ; but, when a bubble of 

 oxygen or air is passed into the tube, the liquid immediately acquires a 

 blackish-red, or nearly black color, and the oxygen is as rapidly ab- 

 sorbed as carbonic acid is by caustic potassa. The quantity of oxygen 

 which is absorbed, under these circumstances, by one part, by weight, 

 of pyrogallic acid, is enormous. According to experiments, one grm. 

 of pyrogallic acid, in an ammoniacal solution, absorbs 0.38 grm., or 

 260 cub. centim. of oxygen ; this is more than the quantity absorbed 

 by one part in weight of sodium, on its conversion into oxide, which 

 only amounts to 236 cub. centim. In one experiment, which was made 

 with special care, a solution of one grm. of pyrogallic acid in caustic 

 potassa absorbed 189.8 cub. centim. oxygen. Since one grm. hydrate 

 of potassa, (KO, Aq,) in order to pass into neutral carbonate, absorbs, at 

 32, 192 cub. centim. carbonic acid, the absorbent capacity of pyrogal- 

 lic acid for oxygen, it will be seen, is not less than that of potassa for 

 carbonic acid. Gallic acid may be employed instead of the pyrogallic 

 acid, and with the same result ; but its employment has this inconven- 

 ience, that the absorption of the oxygen requires at least one and a 

 half or two hours, instead of as many minutes. Owing to the sparing 

 solubility of gallic acid in water, it must be previously converted into 

 gallate of potassa, a cold saturated solution of which is employed. 



Dr. Stenhouse has described a most excellent method of preparing 

 pyrogallic acid. He obtained, by sublimation from the dry aqueous 

 extract of gall nuts, precisely in the same manner as benzoic acid is 

 prepared from benzoin resin, above ten per cent., in sublimed acid of 

 the weight of the extract. 



