^ 30Y - 



degree to that metal ; and it may be remarked as a ge^ 

 neral rule, that the gases more easily liquified by pres- 

 sure and cold are absorbed in the greatest proportion. 



Thus, if ammoniacal gas box-woo 1 charcoal absorbs 

 90 times its own volume ; of hydro chloric and gas 85 ; 

 of sulphurous acid gas 65 ; of sulphuretted hydrogen 

 55 ; of nitrous oxide gas 40 ; of carbonic acid gas 35 ; 

 of carbonic oxide 9. 42 ; of oxygen 9 25 ; of nitrogen 

 7.5; and of hydrogen 1.75. — Combination does not ap- 

 pear to be produced between oxygen and hydrogen 

 when absorbed by porous charcoal ; but sulphuretted 

 hydrogen is completely decomposed, with formation of 

 water and deposition of sulphur. Nitric oxide gas is 

 absorbed in large quantity and undergoes partial de- 

 compontion. All these gases with the exception of 

 oxygen, cease after a time to undergo further absorp- 

 tion ; but in the case of oxygen absorption continually 

 goes on although in decreasing quantity, within the 

 formation of carbonic acid, which is retained in the 

 pores of the charcoal. This curious reaction of char- 

 coal with oxygen will be adverted to hereafter. 



Other porous organic substances, such as wood, silk 

 and woollen stnflfs, absorb several times their bulk of 

 gases, but always less than wood charcoal, and larger 

 relative quantities of some than of other gases. Oxy- 

 genic substances, however, are not the only ones that 

 absorb and condense gases within their pores. Meers- 

 chaum, some schists, and even dry earth absorb gases in 

 the same manner as charcoal, but to a less extent, and 

 likewise effect chemical combinations and decomposi- 

 tions of the more easily altered organic compounds. 

 The earth acts to a considerable extent in this way as 

 a deodoriser and also as a disii»fectant. 



W^■ have seen that charcoal by m<»ans of the oxygen 

 condensed Avithin its pores, is capable of completely de- 

 composing sulphuretted hydrogen, and of partially de- 

 composiuij nitric oxide ga^^, two stable compounds, com- 

 pared with those I have described as constituting tho 

 chief part of the fa'tid emanations from night soil,- and 

 the matters condensed with the aqueous vapour from 

 the atmosphere of foul localities, which undergo spon- 

 taneous decomposition or change when left for a few 



