Phenomena of some Substances and Mixtures. 179 



precautions have been taken to avoid retardation and 

 impurities*. The phenomenon, if confirmed, would have 

 been worth completely investigating. The results which I 

 have obtained contradict Dewar's experiment. 



Preparation of Carbonic Acid. 



11. Both carbonic acid and acetylene were prepared before 

 I was in a position to apply the method of purification de- 

 scribed for ethane by condensation and distillation. I had 

 therefore to resort to chemical methods of purifying the gases. 

 Carbonic acid was made from sodium bicarbonate and sulphuric 

 acid. The acid was contained in a boiling-flask provided 

 with a dropping-funnel with the sodium bicarbonate solution. 

 All solutions used were previously boiled and cooled in a 

 current of carbonic acid. The gas passed through sulphuric 

 acid and phosphorus pentoxide. Before the solution was 

 admitted the whole apparatus had been exhausted with a 

 mercury air-pump. 



12. The purity of the carbonic acid was first tested in the 

 compression-apparatus and appeared to be quite satisfactory. 



Table IV. 

 Carbonic Acid. 



14-95 

 205 

 25-85 

 31-1 



Pb- 



50-02 

 57-16 

 6492 



P. 



73-26 



5024 

 65-06 



Aniagat. 



50 

 57 

 64-5 



Amagat's values for the critical point are 31 0- 35, 72*9 atm. 

 The agreement is very close, the deviations of my values 

 being probably due to a slight admixture of permanent gas. 

 This would, in fact, make the vapour-pressures and critical 

 pressure higher and the critical temperature lower. Similar 

 deviations will be noticed by comparing some of Andrews's 

 values with Amagat's, the former having been reduced to 

 atmospheres. 



t- Andrews. Amagat. 



13-09 48-05-49-50 47-6 



21-46 58-94-61-35 58-2 



* Prof. Dewar, on learning that I had repeated this experiment of his 

 (forming part of an essentially qualitative investigation carried out in 

 1880), told me that his acetylene contained C 2 H 3 Br. This accounts for 

 the high critical temperature and low vapour-pressures observed by 

 him. 



