Ki-J 



'1 i' 1 /'/'"/"/'//. s / ti.i-i/t/i //.' s It is a ] lerma iH'iii o - a> -tliat is, it can- 

 not In- liquefied by pressure at the ordinary t empcrat ure, and further, 

 i- only li<|Uelird with difficulty (although more easily than hydrogen) at 

 temporal ures below 1 '_'<). because this i~> its absolute boiling point. 

 As its critical pressure ''' is about ')() atmospheres, it can lie easily 

 1 ii] netied HIM ler prosnres ureat pr than -^ ' atmospheres at temperat ures 

 belo\y 1 L!U . 1 Met cT obtained liquid oxygen at 1 I 1 ' . l>v employing a 

 preure above 100 atmospheres. According t () I*ewar, the density <>f 

 \y^cn in a critical stale is ()().") (\\-atcr=l ), Inn it. like all (ilici 1 sub- 

 >taiH't'.s in tliis Mate.-'" varies considerablv in clen>itv \\'itli a clianicc <>t' 

 ] ircs>tn - f and t cnijieraturc, and therefore inanv in \ cst i^'ators \vlio made 

 their observations tiudei 1 hi^li ]>ressiii'c-> ^i\-e a ^i-eatei- density, as much 

 as I'l. ( >.\yu'e]i, like all u'ase^, is transparent, and like the majority of 

 u'a>e>, colourless. It has no smell or taste, which is evident from the 

 tact of it-- lieinu 1 a component of air. The weight of one cubic centi- 

 metre in grains at U and 7(50 mm. pressure is (i-(K)l l^'.is Drains, and a 

 litre weighs Tll'liS u'rams : it is therefore ^li^htly denser than air. 

 Its den.Mtv in respect to air=l'10">(), and in ropect to hydrogen =1(5 

 (more exactly 1 .V'.ir,).-' 1 



'" IT musl lir rcninrl^fd that in all tin- above-cited rea 

 may lie prevented by the adinixtuve of substances ca]i 

 example, charcoal, many carbon (organic] conipoiiiiiU. ^n 



lower oxi.lation product's, ^c-. These substances absorb the oxygen evolved, coinhiiu- 

 with it . a nd a coin] lound containin^r oxygen, but not free oxygen, is formed. Thus, if a 



Lin-e of potassium chlorate and charcoal be heated, no oxyp-n is obtained, but 

 an explo-ion takes place from the rapid formation of ^ r ases rr-nlt in;j from the com- 

 bination of the oxygen of the pota--inm chloi-jite \\ith the charcoal. 



The oxygen ol)tained by any of the abo\ c-descrilied methods is rarely -pure. It 



chloride, which retain- the water. IJesides this, the oxygen nearly always contain-- 



-.a. f carbonic anhy<lride. and very <.f'ten small trace- of chlorine. The oxygen may 



b'- treed troni the^e impni'itie-. by pas, MIL;' it tlii'oii'jh a solution of caustic potash. 



Tin- i- done in \Voiflte's bottle-, a- was described in the la-t chapter. If the potassium 



te be dr\ and pure, it -i\e, almosl pure oxygen. However, if the oxygen be 



' loi- i-e.piration in ca-es of sickness, it should be wa-hed b\ passing it thr.n-h a 



-olntion ol caustic alkali and through water. The be-t wa\ to obtain pure oxygen 



d rertly. i N, take pot a- in in perch lorale i K('lO.,i. which can be well pnrilie.l and then 



pun o \ \ j en on heating. 



' ' i i ice riling the absolute boil in;/ poii it. critical prr-siir*-. and on t he critical state in 

 i . -'I. -ee Chaji II. Note ii'.l and :', \ . 



.In<l-in- IVom -ah.it ha been -,,id in Not- ::i of the ia-t clui|it-r. and also from the 

 re-ult , of direct ob.ervation, if i- evidenl that all nb-t a nee i n a crit ieal -t ale ha\ e a 



i . and I hat thev are \ er\ compn lile. 



A uatercon i-t ot 1 volume o| oxygen and -2. -, . .In me- ol hydrogen, and contain* 



IT, part- b\ weight of oxy-en per '2. part-- b\ Wei'jhl ol hydrogen, it therefore alread\ 

 . ~ from thi . that o\ \-en i Hi time- denser than h\dro'_'en. ( 'on \erselv. the com 



