UNRECOGNISED QUALITIES IN CHARCOAL.

Daily Telegraph (Napier), Issue 3231, 7 November 1881, Page 4

UNRECOGNISED QUALITIES IN CHARCOAL.

(Sclentific American.)

Among the numerous and varied properties possessed by charcoal there is one—one, too, of the most wonderful—which does not seem to be adequately recognised, probably from its being imperfectly known except to physicists. It is that of being able to. condense and store away in its pores many times its own bulk of gaseous bodies, which it retains, thus compressed in an otherwise unaltered condition, and from which they can be withdrawn, as required, as from a reservoir. The eminent scientist, M. Saussure, undertook the task of a systematic examination of this subject, with a result that will prove surprising to the general reader. Operating with "blocks of fine boxwood charcoal, freshly burnt, he found that by simply placing such blocks in contact with certain gasses they absorbed them in the following proportions :— Ammonia 90 volumes Hydrochloric acid gas ... 85 „ Sulphurous gas 65 , Sulphureted hydrogen ... 55 „' Nitrous oxide (laughing gas) 40 „ Carbonic acid ... ... ~, 35 Carbonite oxide ... ... 942 Oxygen ... 9 25 ", Nitrogen 6 50 „ Carbureted hydrogen 5 „ Hydrogen ... ... ... 175 „ It is this enormous ahsorbtive power that renders of so much value a comparatively slight sprinkling of charcoal over dead animal matter as preventitive of the escape of the odours arising from decomposition.! A dead dog having been placed in a box in the warm laboratory of an eminent chemist, and covered with charcoal to tho depth of between two and three inches, could not be discovered to have emitted any smell during several months, after which time an examination showed that nothing of the animal remained but the bones and a pmall portion of the skin. To the large ea;-

cess of oxygen over the nitrogen in the atmosphere, which according to the above table, was absorbed by the charcoal, and which thus rendered harmless the noxious vapours given off by the carcass as they wive being absorbed, is doubtless owing to the fact above stated and the further fact of the charcoal never becoming saturated. A reader of the Scientific American -who has been trying certain experiments on the value of charcoal as a convenient means of storing oxygen, reports favorably to the results. In a box or case containing one cublic feet of charcoal, may be stored, without mechanical compression, a little over nine cubic feet of oxygen, representing a mechanical pressure of a hundred and twenty-six pounds on the square inch. From the store thus preserved the oxygen can be drawn by a small hand pump. From the fact of the charcoal absorbing oxygen in so much greater proportion than nitrogen, we have here means of utilising its discriminative powers of selection in obtaining unlimited supplies of oxygen from the atmosphere, which contains nitrogen five times in excess of its oxygen, or twenty per cent.; whereas by the separating or selective powers of the charcoal the mixed gases capable of being absti-acted from it contain over sixty per cent, oxygen. It only suffices to withdraw this now highly oxygenised air into another vessel of charcoal, by the further exposure to which the proportion of oxygen will he increased to still greater extent. This indicates a most feasible means by which atmospheric air can be decomposed in such a way as to provide a cheap supply of oxygen. One cannot- readily recognise tbe fact, which is nevertheless true, that tho condensing V;_wer of charcoal as applied to ammonia is equal to what would be obtained by subjecting this gas to a pressure of nearly 1260 pounds on the square inch.