Improvements in the Roberts- Austen Recording Pyrometer. 50 



ratio x calculated from the formulae, the quotient will give 

 the degree of aggregation of the molecules of acetic acid in the 

 solution. In this way Linebarger found molecular weights 

 which steadily increased with the concentration of the acid, 

 and by extrapolation found 210 for the molecular weight of 

 the pure liquid at 35°. My results for alcohol do not, how- 

 ever, at all confirm the accuracy of the method. On drawing 

 smooth curves of partial pressure from the observations 

 given in the tables above, and treating them in the way just 

 indicated, we get 



Molecules of 

 Alcohol. 



Aggregation ( 

 Molec 



Benzene. 



>f the Alcohol 

 ules in 



Toluene. 



10 



60 



20 



30 



5-7 



26 



50 



o-3 



42 



70 



50 



57 



90 



49 



60 



It will be seen that the two series disagree altogether, and 

 that neither leads to any reasonable value for the aggregation 

 of pure alcohol. I can only conclude that the partial pressure 

 of the hydrocarbon vapour is not necessarily linear in mixtures, 

 and that therefore the rule proposed by Linebarger for deter- 

 mining the molecular weight of liquids is not correct. 



Further theoretical conclusions would not, I think, be 

 justified at the present time on account of the small amount 

 of material accumulated by experiment. 



Davy-Faraday Laboratory of the Royal Institution, 

 London, December 1897. 



IV. On some Improvements in the Roberts-Austen Recording 

 Pyrometer, with Notes on Thermo-JEilectric Pyrometry. By 

 Alfred Stansfield, B.Sc, A.R.S.M., Royal College of 

 Science, London *. 



HHHE method of recording pyrometry which involves the 

 _L use of the thermo-j unction has, as is well known, been 

 devised by Prof. Roberts- Austen. He suggested that the 

 author should undertake the investigations described in the 



* Communicated by the Physical Society: read March 25, 1898. 



