Transactions of The Royal Society of Canada 



SECTION III 

 Series III SEPTEMBER 1914 Vol. VIII 



The Vapour Pressures of the Halogen Hydrides and of Hydrogen 

 Sulphide. 



By O. Maass and D. McIntosh, F.R.S.C. 



(Read May 27, 1914). 



In a paper on the halogen hydrides (Phil. Trans. Roy. Soc., A, 

 205 p. 99, 1905), Steele and Mcintosh have given their determinations 

 of the vapour pressures of these liquids between their freezing and 

 boiling-points. Since the halogen hydrides and hydrogen sulphide 

 act, even when carefully dried, on the mercury of a manometer an 

 apparatus was devised to prevent their contact with mercury by means 

 of an inert gas. The method was, apparently, a satisfactory one, 

 and the results obtained were probably nearer the correct values than 

 those of previous experimenters. 



In our study of these liquefied gases we have noticed that they 

 show the phenomenon of supercooling to a remarkable degree, so that 

 the values found may differ markedly from the true vapour pressures 

 unless the liquid is kept at a constant temperature for a long time. 



We have, therefore, redetermined these vapour pressures using 

 the beautiful method devised by Johnson (Zeit. physik. Chem. 61,457, 

 1908), in which a spiral is used as manometer so that the corrosive 

 gas comes only in contact with glass. We have also improved our 

 constant temperature bath so that we believe our results are correct 

 to 0-2°C. 



Apparatus and Methods. 



In making mercury manometers it is customary to fill the 

 inverted tube with mercury and to remove any gas or water vapour 

 by heating the apparatus and reducing the pressure over the mercury. 

 As this usually results in a scum forming on the surface of the mercury, 

 we have filled our manometers in the following way: A distilling 

 flask containing pure mercury was attached to either the short or 

 long arm of the manometer, both of which were connected to a Toepler 

 pump. The pressure was reduced to • 0005 mm., and after the whole 

 apparatus was heated by a Bunsen burner the mercury was distilled 

 Sec. Ill, 1914—5 



