EXPEKIMENTAL KNOWLEDGE OF THE PROPERTIES OF MATTER. 121 



with this substance, which sometimes he attributed to the pi'csence of water 

 and sometimes to the presence of acetone ; and the least trace of im- 

 purity, as he has pointed out, affects the results seriously, especially 

 those obtained by the statical method ; for over the thermometer vacuum 

 any accidental presence of a trace of air does not get eliminated as in the 

 dynamical method by boiling for a short time. By their method Ramsay 

 and Young got a series of values of pressures for solid acetic acid 

 from — 5"68° to 16'41° volatilising point, and for liqtiid acetic acid from 

 2'72° to 117"15° boiling-point. The results so obtained agree closely with 

 those given by the usual process when a perfectly pure acetic acid was 

 used, and disagreed with vapour- pressures previously given byRegnault,' 

 Laudolt,^ Bineau,^ and Wiillner.'' 



Vapour-pressures from Solids and Liquids — W. Fischer. 



W. Fischer,-^ independently of Ramsay and Young, and by a quite 

 different method, investigated the lines of solid vapour-pi'essure and of 

 liquid vapour- pressure for water and benzene for a range of temperature 

 throughout which, in each case, the body could exist either as solid or as 

 liquid ; he arrived at results substantially similar to those of Ramsay and 

 Young. He showed that the curve of pressures for each substance (for 

 temperatures below the melting-point) was lower for solid than for liquid. 



In the case of ice and water he gives four sets of experiments, in each 

 of which experiments there are given the thermometer reading below 0°, 

 the barometer reading and the reading of an ice- pressure mercury tube 

 and of a water- pressure mercury tube, the three tubes being near together 

 so that they can all be read with the cathetometer, as well as the thermome- 

 ters giving the temperature of the ice and water in each experiment. A 

 fifth set of experiments was made for vapour-pressure of water at tem- 

 peratures above 0°. From these he deduced two equations of the form 

 p=-a + 'bt + cir, which represented very accurately his observations, one 

 for p the vapour-pressure of water, and the other for p the vapour- 

 pressure of ice. 



These results were got in the winter of 1882-3, and they did not well 

 agree with theory, and especially gave a difference for ice and water at 0°, 

 differing too seriously from that deduced fi'om Clausius' formula. 



In the winter 1884-5 he resumed the investigation, and succeeded in 

 improving the method employed so as to make his results more accurate. 

 In the equation ^=rt + ii + cf- he obtained the values of a, h, c, his results 

 for the different pairs of values of p and t giving him from the equation 

 between j; and t a large number of equations in a, b, and c. This was 

 done for water-vapour and for ice- vapour ; the equation for pressure of 

 water-vapour at temperatures between 1"35° and — 10'15° was 



2j=4-628-f-0-32535/-f 0-008705^2 

 and for ice- vapour pressure 



' p=4-641 -h 0-37190/ + 0-011041/2 



the difference of - " for ice and water at 0° is "04655 ; Kirchhoff calcu- 

 dt 



' Mem. 1862, xxvi. p. 51. 



- Liebig's Annalen, Suppt. 6, 157. 



3 A/males de C/iimie et de Phygiqiie (3), xviii. 226. 



■* PoggendorflE's Annalen, ciii. p. 529. 



* Wiedemann's Annalen der Physik ■und Cheviic, 1886, No. 7, p. 400. 



