( 380 ) 



A condensation was seen on the mirror of the dew-point apitaratns 

 (s'ee § 1 and Go mm. X". 92 p. 233) at a pressure of 157.4 em. mercury 

 and disappeared at 134.6 cm. As mean we may take 156.0 cm., 

 and the accuracy may he put at 1 "'o. 



§ 8. Determination of the end condensation, pressure. In the first 

 place tiie condensation pressure (vapour tension) of jture methyl 

 chloride was determined with the aid of the sipall [jiezometer (§ 5 

 Comm. N". 92). At — 2^5"^ we found 72.9 cpi. Avhen the piezo- 

 meter was tilled to the capillary tube, 72.8 cm. when the liquid 

 had nearly all evaporated. In both cases the li(pii(l in the piezometer 

 was stirred. TJje agreement of these values speaks for the purity of 

 the methyl chloride. At — 37°. 4 the vapour tension was found to 

 be 42.7 cm. 



In order to determine the end condensation pressure of tiie mix- 

 ture with .V = 0.5042 of methyl chloride the temperature of the 

 piezometer had to be loAvered down to — 38°. 5 ; at higher tem- 

 peratures condensation took place at other places in the apparatus. 

 (Cf. § 5 of the Comm. N". 92 "On the determination of the condi- 

 tions of coexistence etc." It may further be observed, tiiat no 

 arrangement was applied to heat the press tube and the capillary 

 tube above the ordinary temperature). For the determination of the 

 conditions of coexistence (according to § 5 Just mentioned), are 

 wanted : in the first place the observed end pressure /> „ , for which 



6.13 alms. Avas found. Then the volume I^j, of the vapour with the 

 composition -'',,.. The vapour occupied 0.488 cc. under 6.13 atms. 



at — 38°. 5. Finally the volume I", which vapour and liquid phase 

 together would occupy in normal circumstances; by blowing off in 

 the volumenometer we found 347.7 cc. at 20° C. and 760 mm. (reduced 

 according to the law of Boyle, Gay-Lussac). The composition x 



was determined with van ukk Waals' hyperbolic formula, which 

 yields x =3 0.0375. From these data follows (see I.e. § 5) 

 .V, ,, = 0.5084, p, ,, = 6.13, t = — 38°.5. 



Ipl ' ^ Ixl 



The circumstances were not favouitible for an accurate determi- 

 nation of the correction. It appears, however, to be so slight, that 

 we may safely assume the composition to be accurate dowii to 1 7o- 



§ 9. Comparison of the conditions of coexistence ivith theory. For 

 this purpose it is required in the first place to know the vapour tension 

 of methyl chloride and carbon dioxide at — 25° C. and — 38°.5 C. 

 We have calculated the coetïicients for metiiyl chloride in tiie formula 



of T>v?m and Uanklne ln.p=:A — .,, — CluT with Hartman's value 



