1884.] Influence of Change of Condition on Vapour-Pressure. 4^)9 



II. " Influence of Change of Condition from the Liquid to the 

 Solid State on Vapour-Pressure." By William Ramsay, 

 Ph.D., Professor, and Sydney Young, D.Sc., Lecturer and 

 Demonstrator of Chemistry in University College, Bristol. 

 Communicated by Professor James Thomson, LL.D., F.R.S. 

 Received April 15, 1884. 



(Abstract.) 



The object of this paper is to furnish experimental proof of the 

 theory advanced by Professor James Thomson. (" Brit. Assoc. Reports," 

 1871 and 1872, and " Proc. Roy. Soc," vol. 22, p. 27), that the 

 pressure exerted by the vapour of a solid substance at a given tem- 

 perature is less than that of the vapour of the substance in the liquid 

 form at the same temperature. 



This relation was specially sought for by Regnault, and, as shown 

 by Professor Thomson, he unwittingly furnished a proof for it in the 

 formulas devised by him to express the vapour-pressures of ice and of 

 water. Regnault himself, however, from the results of numerous 

 experiments, came to an opposite conclusion, and this conclusion is as 

 yet generally accepted. 



A graphic representation of the results obtained by us on heating 

 camphor in a barometer-tube to temperatures ranging from about 

 150° C. to 200° C. shows (I) considerable irregularity about the 

 melting-point, and (2) that a prolongation of the portion of the curve 

 representing relation of pressure to temperature above the melting- 

 point would intersect the portion below the melting-point. 



With benzene, also, the vapour-pressures of which were determined 

 by the method described by us in a paper shortly to appear in the 

 "Transactions" of the Society, the solid-gas curve is evidently not 

 continuous with the liquid-gas curve. 



Employing the same apparatus, acetic acid was successfully cooled 

 to temperatures far below its freezing-point without solidification, 

 and numerous extremely concordant observations of the vapour- 

 pressures both of the liquid and of the solid acid were obtained. 

 These observations represented graphically, form two widely diver- 

 gent curves which intersect in the neighbourhood of the melting- 

 point of the solid acid, 16°"4. 



The barometric method was next employed; but the results, like 

 those obtained by Regnault, were capricious. That this capricious- 

 ness was not attributable to the presence of air was proved by special 

 experiments, and it remains unaccounted for. 



Several very careful determinations of the vapour-pressures of ice 

 and of water below the freezing-point were made. A comparative 



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