Young — Vapour-Pressures, ^~c., of Thirty Pure Substances. 399 

 The volume of liquid, if all the vapour were condensed, would be 



n = n' + -j^ = I'l' + ^ ■ • • W 



so that there are four independent values of the orthobario volume of liquid. 



The orthobario volume of a gram of liquid = Vi = —• 



The pressure-apparatus cannot be employed for liquids, such as stannic 

 chloride, which attack mercury ; and for these quite a different method, which 

 will be termed the "sealed-tube method," was employed.' 



A piece of barometer-tubiug, of very even bore (about 1-5 mm.) and 

 about 60 em. long, is closed at the blow-pipe at d (fig. 6) about 20 cm. from 

 one end, the closed part being carefully rounded. The portion of the tube 

 de serves as a handle, and the end e may conveniently be closed. 



The tube from d to c is then graduated in millimetres, and calibrated in 

 tiie usual way by weighing with mercury. 



e d e 



The end c is then sealed to the apparatus shown in fig. 7 (p. 400) ; and the 

 whole apparatus is thoroughly dried by repeated exhaustion and admission 

 of air dried over phosphoric anhydride. The freshly distilled liquid is then 

 admitted into tlie apparatus at g, either by means of a fine funnel, or, if 

 the liquid is hygroscopic, by means of a siphon arrangement, such as that 

 described by Thorpe,^ until the wide protuberance / is about one-third filled. 

 A piece of thick-walled india-rubber tubing, provided with a sorew-clip, is 

 then passed over g ; and the apparatus is connected with a pump and exhausted. 

 The clip is then closed, the apparatus removed from the pump, and the liquid 

 in the tube cd made to boil vigorously for some time, so as to completely 

 remove air dissolved in liquid or adhering to the walls of the tube. (The 

 narrow tube h, drawn out and bent at the end, prevents the projection of 

 the liquid against the india-rubber.) Lastly, the liquid is allowed to fill the 

 tube completely, and is then boiled from above downwards until only the 

 required amount remains in the tube, when the apparatus is tilted, so that 

 the greater part of the liquid above h flows into/. The tube, while bubbles 

 of vapour are still escaping slowly at h, is at once sealed at c. 



1 Tvans. Chera. Soc, lix., pp. 37, 126 and 929, 1891 ; Proc. Phys. Soc, xiii., p. 617, 1895. 

 ^ Trans. Chem. Soc, sxxvii., p. 22, 1880. 



3i 2 



