Tli.' law of o iiul lining volumes and the l;t\\ i multiple proportions 

 \\eiv discoveied independently of each other the one in 1-Yanee by 

 ( lay-Lr.ssae, the oilier in Kmjand by 1 )altoii. alinosi simultaneously. 

 In tin- ianmiau'e of the atomic hypothesis ii mav lie -aid that atomic 

 quantities of elements occupy eijiial o!' multiple Volumes. 



The tirM la\v of (!ay-Lussae expresses the relation l>et \veen the 

 volumes ' >t the component parts ot a compound ; let u- now consider 

 tin- relation existing between the volumes of the eomponent parts and 

 of the c impounds which proceed trom them. This ma\" sometimes be 

 determined by direct observation. Thus the volume occupied by \vatei 1 , 

 formed by 1 \vo volumes of hydrogen and one \olume of oxvgen, ma}' be 

 determined bv the aid of the apparat us shown in tie;. ~i(\. 'Jne long 

 gla-s tube is closed at the top and open ai the bottom, which is 

 immersed in a cylinder containing mercury. 1 he cio>cd end i> 

 fui'iii-hed \\ ith \\'ires like a eudiometer (p. H> ). The t u'oe is idled with 

 inercurv. and then a certain \olume of detonating u'as is introduced. 

 Thi> ga> is obtained from the decomposition of water, and therefore in 

 every three volumes contains two volumes of hydrogen and one volume 

 of oxygen. The t ube is surrounded by a second and wider glass tube, and 

 the vapour of a substance boiling above \(^> that is. whose boiling point 

 is higher than that of water is passed through the annular space be- 

 tween them. Amvl alcohol, whose boiling point is \-\\l , may betaken 

 for this purpose. The amyi alcohol is boiled in the vessel to the right 

 hand and its vapour passed bet ween the walls of the t \\ o tubes. In the 

 case of amvl alcohol, the otiter glass t ube would be connected with a 

 Condenser to present the escape into the air of the unpleasant-smelling 

 vapour. The detonating gas is thtis heated up to a temperature of 1 .'!' . 

 \\ hi'ii its \olume becomes constant it is measured, the height of the 

 column of mercury in the tube above the le\el of the mercury in the 

 cylinder being noted. Let this volume equal r; it will therefore con- 

 tain ; ' of oxygen and r! r of h\-drogen. The current of \apour is 

 then stopped, t he open end of the tube tilled \\ith merrur\', and then 

 closed, and the gas exploded ; water is formed, which condenses into a 



liquid. 'I IH \oluine oeell pled by the \ a poll I' ot the Water fol'llU'd lias 



no\\ to bi' det ermined. l-'or this purpose the \apoiir of the amvl 

 aleohol is a -a in passed between the 1 llbes, and the \\ hole of t he \\ at er 

 foi'ined is converted iiito \ajiour at the --,(\\\c lempei'al lire as that at 

 \\hii-h t he detonat ing gas \\as measured, and the cylinder of mercury 

 beinu' raised until the column of mercury in the t ube stands at t he same 

 hcj._dii abo\ - e 1 he surface of the luercui'V in the cylinder as it did lie fore 



