Young — Vapour-Pressures, Sfc, of Thirty Pure Substances. 405 



cork glass tubes pass. One of these, C, is bent at right angles, and reaches 

 only a few millimetres below the cork ; it is connected with an exhaust and 

 compression-pump and two gauges, by means of which the pressure on 



the mercury in A can be regu- 

 lated and read. The other tube, 

 D, reaches nearly to the bottom 

 of ^ ; it is bent twice at right 

 angles above the cork, and is pro- 

 vided with a stopcock or an india- 

 rubber tube and screw-clip. The 

 vapour-density tube is lieated by 

 the vapour of a pure liquid boiling 

 in the bulb E under reduced pres- 

 sures, regulated and measured by 

 the pump and gauge with which 

 the upper end of the jacketing- 

 tube is connected, fluctuations 

 of pressure are avoided by inter- 

 posing a glass globe of about 10 

 litres caj)acity between the jacket- 

 ing-tube and the gauge. 



The vapour-density tube is 

 supported only by the india- 

 rubber tube through wliich it 

 passes. The jacketing-tube is 

 kept in a vertical position by the 

 large retort-stand and clamp 

 shown in the figure. The cyl- 

 inder A is placed on a stand 

 provided with three screwed feet, 

 and by means of these screws 

 the vapour-density tube is easily 

 centred. 



In order to avoid the presence 

 of air in the vapour-density tube, 

 ^'°- ^- it was supported in a sloping 



position, after being thoroughly cleaned and dried, with the closed end 

 resting on a piece of asbestos cardboard on the laboratory bench. It 

 was then thoroughly exhausted, and was heated to remove the film of 

 air adhering to the glass. Filtered mercury was then run into the liot 



SCIENT. PKOC. R.D.S., VOL. XII., NO. XXXI. " S 



ToPump 

 caidGcui^re 





