Dr. Andrew Fyfe on the Detection of Arsenic. 487 



where <^ is the symbol of a third function, which is the same for 

 all fluids. 



This equation is evidently the mathematical expression of the 

 law of tension mentioned above ; for to apply the function which 

 in the case of any one fluid determines the tension from the tem- 

 perature, to any other fluid, it is only necessary to multiply the 

 temperature by a different constant, which constant is easily 

 found when the tension for a single temperature is known. 



It is thus shown, that, in so far as the validity of equation 

 (V«.) is granted, the two laws expressed by the equations (I) and 

 (II) are so connected with each other that when one of them is 

 true, the other must necessarily be true also. 



But in case both laws are only approximations to the truth, 

 as to me appears most probable, the equation (Va.), which by 

 introducing T instead of t becomes 



enables us at least to conclude as to the manner and degree in 

 which two vapours diverge from each other with regard to their 

 latent heat, likewise as to their divergence from the tension 

 series, and the reverse. Thus, for instance, in comparing water 

 with other fluids, it is observed that the tension of the vapour of 

 the former increases more quickly with the temperature than the 

 tension of other vapours. There is a complete coincidence be- 

 tween this fact and that observed by Andrews*, that the vapour 

 of water possesses a greater latent heat than an equal volume of 

 the vapour of any other fluid which Andrews examined, alcohol 

 excepted. From this we perceive that it is by no means advan- 

 tageous for the application of the above two laws to choose, as 

 is generally done, water as the fluid of comparison ; but that, on 

 the contrary, the comparison of water with fluids of lower boiling- 

 points is peculiarly calculated to support the law of Dalton. 



LXXIII. On the Detection of Arsenic. By Andrew Fyfe, M.D., 

 F.R.S.E,, Professor of Chemistry, University and King's Cot- 

 lege J Aberdeen-]. 



IT is well known that some metals unite with chlorine, not 

 only synthetically, but also by decomposition of their com- 

 pounds, and form volatile chlorides. Arsenic is one of the 

 metals that comes under this class, and hence it can be volatilized 

 as a chloride, and, under certain conditions, can be separated^ 



* Quarterly Journal of the Chem Soc. of London, No. 1 . p. 27. ; 

 t Communicated by the Author, 



