( 578 ) 



becomes clear, small luihhles or drops are seen to move from l)elow 

 aiui from al)o^'e towards a certain ])oint in the tube. At last a 

 meniscus appears there. This i-emains at that ])lace. The temperature 

 at Avhich these phenomena were observed was adopted as the plaitjjoint- 

 temperature of the mixture considered, the volume and the pressure 

 as plaiti)oiiit volume and pressure. 



If the tem])erature is a lilllc hi,uiier, the meniscus appears lower 

 in the tul.»e. The exact jxiijU where it appears cannot be observed 

 with certainty : drops are seen to move from above to below, and 

 bubbles from below to above more and more regularly towards one 

 place; at this place the meniscus will appear, but this place is rising 

 already before the meuisc-us has ])ro|»erly formed itself. AVhen it is 

 formed, it generally still rises. If the temperature is still higher the 

 meniscus is distinctly seen to rise from the bottom of the lube. At 

 the lowei' end a (piantily of liquid is gathered by the drops which 

 fall from the top to the meniscus. The same holds, nuUatis mutandis, 

 for temperatures below the plait|)oint temperature. 



Of the data about the ])oint of contact only the tenijierature could 

 accnrately be (to within (V.OJ) derived from the experiment. To 

 determine the |>ressnre sonu' points at the begiujiing and at the 

 eiul of the condensation to uilliin ()°.l of the point of contact 

 were ()l)served ; they \\ ere draw n and the ])oint ^^ here the tangent 

 is at right angles with the axis c»f temperature was found. This 

 ga\e the pressure of the point of contact ^^ ith sufticient accuracy. 

 Then the point of contact volume ^^as deduced from the isothermal. 



The nu)lecular proportion of oxygen Avill be represented by ,r, 

 ]^thx i'^ 'li*' theoretical normal voliuue, for the meaning of Ax,^ 

 comp. this C'omm. 11 p. 552. 



§ 2. Fifsf nu'rt/nr of airhoi) dioA'tdc and <>ii/;/''ii. 



.21 = 0.1047. 

 Before the measurements : 1"^/;^' = (>9.743 cc. 

 After „ „ (i9.725 „ 



mean : 69.734 ,, 



