Fiff. 4. 



Vapour-Densities of some Carhon Compounds* 503 



The actual densities of the various vapours were deteriuined 

 at three temperatures, namely, the temperatures of chloro- 

 benzene boilino- under a pressure of 292*75 mms., 4H8"5 mms., 

 and 719"0 mms. of mercury. In order to ascertain these 

 temperatures the pressure exerted by a constant volume of 

 oxygen was measured, first at the temperature of melting 

 ice ; second at 99*82°, the temperature of water boiling under 

 a pressure of 755*1 mms.; third, at the temperature of 

 chlorobenzene boiling under a pressure of 292*75 mms. ; 

 and lastly M'ith chlorobenzene under a pressure of 

 719*0 mms. 



For this purpose the portion of the apparatus A and D 

 (Hg. 1) was replaced by that shown in fig. 4, w^here a^ is 



a smaller tube, the volume of 

 which was about 92 c.cs. ; this 

 tube was dried very carefully, 

 filled with warm dry mercury, 

 and the mercury was displaced 

 with perfectly dry oxygen which 

 had been prepared by the de- 

 composition of potassium per- 

 manganate. The tube a' was 

 then connected with the mano- 

 meter^ after the thermometer ^ 

 had been inserted. It was next 

 jacketed successively with chloro- 

 benzene, with water, and with ice. 

 For each measurement a num- 

 ber of readings were made, which 

 are given later on. It is neces- 

 sary first to explain the various 

 corrections that have to be applied 

 to the actual readings. 



These will best be understood 

 by aid of the Greek letters on 



fig. 1, 



Section a, the manometer 

 column, is surrounded with run- 

 ning water, the temperature of 

 which is observed ; a correction 

 must here be applied to reduce the height of the mercury 

 column to its height at 0°. This correction is given in 

 the table under a. 



Section /3, forming the connecting tube between manometer 

 and volume-tube, is not jacketed ; but its vertical height is 

 small, and an error of even a few degrees in its temperature 



