52 



DENSITIES OF OXYGEN AND HYDROGEN 



its coiiiiectiuiis li;i\ iiig bet- ii exbaustt'i,! and the vacuum liaving been measured, the 

 pumj) was shut off by means of a stopcock, and oxygen was then admitted till the 

 desired pressure was obtained, when a seccjiid stopcock near '/ was closed. The 

 pressure of the oxygen was then mejisured. The globe was left in the ice for this 

 purpose for from one to fnur hours. Tlic stopcock near '/ was not ie(juiic(l to l)e 



l"li;. 22. — Killint; a glulic «iih nxygcii , u.'.c i>( ict. 



I 



tight against any material dirt'ereuce of pressure on the two opposite sides ul its 

 key ; its oidv office was to shut off from the globe, during the measurement of 

 pressure, the part of the apparatus who.se temperature was .somewhat variable. 

 The use of a fusible metal I'lug at a convenient part of the tube prevented leak- 

 age during the exhaustion of the jflobe and connecting tubes. 



8;"). — o\v(;kn r.v iiiikk mi/iuoh. soriicKs ok o.\v<.kn. 



In seven of the experiments of this .series, oxygen w.is olitjiined from potassium 

 (ddorate : the process was in all respects exactly like that in the picvious sei'ies. In 

 the other expeiiments, oxygen was pro<luceil by the electrolysis of pure dilute sul- 

 phuric acid. The gas issuing from the voltametei- passed through a strong solution 

 of pota-ssium hydroxide, where the time of contact was over fifty seconds ; then over 

 heated copper oxide, and tiiroiigh drying tubes filled with calcium chloride, pow- 

 dered potassium hydroxide, and phosphorus pentoxide, each of which was one 

 inetve long and two and a half centimetres in diameter, All were connected by 



