-o lining. u'ive up the oxygen absorbed that is, lv making use of re- 

 versible react io] i v. 'llms. ft>i' instance, the oxv^'en < f t he at niosphere 

 may In- made to oxidise sulphurous anhydride, S( )., (bypassing directly 

 over ignited spongy platinum), and to form sulphuric 1 anhydride, or 

 sulphur trioxide. S( ) ;j : and this su list a net 1 (which is a solid and volatile, 

 and therefore, easily separated from the nitrogen and sulphurous 

 anhydride), ly heating again, gives oxvgen and sulphurous anhydride. 

 Caustic >oda or lime extracts (absorbs) the sulphurous anhydride from 

 this mixture, whil>t the oxygen is not absorbed, and thu> it is isolated 

 from the air. < hi a lar^e scale in works, as we >hall afterwards see, 

 sulphurous anhydride is transformed into hydrate of .-ulphuric tri oxide, 

 or sulphuric acid. H._,S(),: if this is made to fall in drops on reddiot 

 flagstones, water, sulphurous anhydride, and oxygen are obtained. 

 The oxygen i^ ra-ilv isolated from this mixture bv parsing the gases 

 over lime. The extraction of oxvgen from oxide of mercury 

 (Priestley, Lavoisier;, which is obtained from meivurv and the oxvgen 

 ot the atmosphere, is also a reversible reaction bv which oxygen mav be 

 obtained from the atmosphere. So also, bv passing diy air through a 

 red-hot tube containing barium oxide, it is made- to combine with tin 

 oxygen of the air. \}y this reaction the so-called barium peroxide. 

 Ia< ) is formed from the barium oxide I>a() and -at a higher tempe- 

 rature the former evolves the absorbed oxygen, and leaves the bari 

 oxide originally taken. 7 



[f the process of dialv-i- 1"' repealed on the ;iir \vlucl 

 i i ndia- ruhl icr. then a mixture coiitainin.;' i'.,"> p.c. l>y volnnn 

 uiy lie thouudit that the cause ol this phen. nneiimi i- the ah 

 .11 -,, Chap. 1 1 of : _:ases l,y india-ruhher and the ,.\ ,,liH imi of the -a- 

 iim : and. indeed, india rnld'cr does ali-orli ptsex, especially carlimiii 

 metal-, especially mi an increase of temperature. al>-<>H> ^ases, as \va- 

 ipter. (iraham called the ahove method of the decompositi. i 



; Ti e preparation ot oxygen li\ tin- method, uhidi is due to !'.nn-.en. i- conducted ii 

 .1 porcelain tnl.e. whicli i- placed in a stove heated liv charcoal, -o that it- emU project 



pn dried ; ed in the tnl.e. one end of \\ Inch i> cmuiecteil \\ ith a pair ci 



:. d< . Mr keeping up a current of air tliroii-h it. The air is previmish 



pa ed t h)-oii. _d i .1 -olnt ion i ,f can-.! ic pota-h. to renio\-e all t race- it carl ionic anhydride 



a .1 ' er> caret, ill;, rii-ie,] t . H' 1 1 1C hy d 1M t e 1 5a I I ,< ) , doe> not - i S e t he p, ToX ide I. At; 



:, -on tin , de ot liai-iuni ah-orlis o.xy_ r en from the air. so that the j. r a! 



im-t i-nl i'el\ of nil i-o-en. Wln-n I he a li~orpt ion cea--es, t he ail 



i - Thekn inn i,\i.|e i-, ciiiix erled into pei'ovide under tlie~e circumstances 



' i- all o I'll all. .lit one part of o\\ -en l.\ Wei-lit. When tin 



,1, ..,,,,,: '. ., . , ., , .... elided, a em-k with a ja-cmidiictiii'_' tiihe istixiM 



