of Change of Condition on Vapour-pressure. 63 



dence at the melting-point) no longer existed. As in the case 

 of water and ice, solid and liquid acetic acid, solid and liquid 

 bromine, and solid and liquid iodine, which have formed the 

 subject of our experiments (Phil. Trans. 1884, p. 461, and 

 Trans. Ohem. Soc. 1886, p. 453), solid and liquid benzene 

 exert the same vapour-pressure at the melting-point. 



For recalculating Fischer's results, his pressures at — 7°, 

 —-2°, and +3° were taken. At — 7°, the vapour-pressure of 

 the solid determined by him was 15*273 millim.; at —2°, 

 21-679 millim.; and at +3°, 30*324 milium The constants 

 are a=4*81664; log b = 0*5602315 ; log «= 1*99628446; b is 

 negative ; and t = temperature centigrade + 7. For the 

 vapour-pressures of liquid benzene, Fischer's results agree well 

 with his formula. As data are in existence whereby the 

 vapour-pressures of solid benzene can be calculated for a short 

 interval of temperature below the melting-point, provided 

 those of the liquid are accurately known, it was deemed ad- 

 visable to check Fischer's results with liquid benzene by the 

 dynamical method already described by us (Trans. Chem. Soc. 

 1885, p. 42). 



This was accordingly done. A large quantity of commer- 

 cial benzene was distilled, and the first half, boiling within 

 five degrees, was frozen twice, the liquid portion being poured 

 off each time. The solid portion was then shaken repeatedly 

 with sulphuric acid until the acid was no longer coloured, 

 thiophene being thus removed. The remainder was shaken 

 with water and dried, and then fractionated until a product of 

 constant boiling-point was obtained. The actual boiling-point, 

 at a pressure of 753*4 millim., was 79°*9. 



The following determinations with the liquid were made. 

 At the lower temperature, thermometers graduated in -fa divi- 

 sions were employedo The zero-points of these thermometers, 

 and the apparent lowering of temperature consequent on 

 reduction of pressure, were determined, and corresponding 

 corrections introduced. For higher temperatures (above 50°), 

 a thermometer previously used for determination of vapour- 

 pressures, and of which the corrections had been thoroughly 

 investigated, was used. The three -^q thermometers we shall 

 name A, B, and C ; the one used at higher temperatures, D. 



