194 



Dr. W. Ramsay. 



[Dec. 16 r 



II. " On the Critical Point." By W. Ramsay, Ph.D., Professor 

 of Chemistry in University College, Bristol. Communicated 

 by E. J. Mills, D.Sc, F.R.S., Young Professor of Technical 

 Chemistry in Anderson's College, Glasgow. Received 

 November 8, 1880. 



The experiments to be described were undertaken with a view to 

 determine the difference in behaviour of two pure compounds, and a 

 mixture of the two, at high temperatures, and under great pressures. 



The two liquids selected were benzene, C 6 H 6 , and ether, C 4 H 1() ; 

 for both are remarkably stable bodies, and both can be obtained easily, 

 and in a perfectly pure condition. They are also without action on 

 each other. 



The benzene was produced by the distillation of calcium benzoate 

 with lime ; it was dried by cohobation with sodium for four days, and 

 then distilled. It boiled at 81°'4 at a pressure of 750 millims. The 

 ether was also cohobated with sodium for four days, and boiled at 

 34°-4. 



The pressure- apparatus resembled that used by Dr. Andrews in his 

 experiments on the critical state of carbonic acid, somewhat modified 

 to suit the altered conditions. The gauge for measuring pressure was 

 a carefully calibrated thermometer tube with round bore. ~No correc- 

 tion of capacity was necessary to allow for a conical space at the end, 

 as is usual with air manometers, for the sealing of the tube was 

 accomplished by drawing up a plug of fusible metal, and allowing it 

 to solidify. 



As the gauge lay horizontally, no correction was necessary for 

 varying height of mercury. It was carefully filled with dry air, after 

 its capacity had been ascertained by filling it with mercury, and sub- 

 sequently weighing the mercury. The probable error of the volume 

 of one division is 0'23 per cent., and the probable error of the total 

 capacity 0'084 per cent. The measurements of pressure may therefore 

 be regarded as a close approximation to absolute correctness, and as- 

 perfectly correct relatively to each other. 



The temperature was corrected for the mercury outside of the heat- 

 ing apparatus, and after the experiments were over, was compared 

 with a good unused new thermometer. The readings did not differ 

 by more than 0*5 degree. 



The liquid to be examined was contained in a piece of very narrow 

 barometer-tubing, graduated in millimetres, and was introduced at a 

 temperature close to its boiling point, after a portion had been boiled 

 off, so as to ensure absence of air. While entering the experimental 

 tube the liquid never came in contact with air, and from the results 

 of experiments it appears that none was present. 



Observations of the condition of the liquid experimented on, and 



