332 



Artjon and its 



increase, although the product does not reach the theoretical value 

 at 100 atmospheres pressure ; with krypton the change with rise of 

 pressure is a still more marked decrease, and with xenon the decrease 

 is very sudden. At the higher temperature the results are more 

 difficult to interpret; while nitrogen maintains its nearly constant 

 value for P.V., helium decreases rapidly, then increases, and the same 

 peculiarity is to be remarked with the other gases, although they do 

 not give the product of P.V. coinciding with that calculable by 

 assuming that the increase of P.V. is proportional to the rise of 

 absolute temperature. 



These last experiments must be taken as merely preliminary ; but 

 they show that further research in this direction would be productive 

 of interesting results. 



The spectra of these gases have been accurately measured by Mr. 

 E. C. C. Baly, with a Rowland's grating ; the results of his measure- 

 ments will shortly be published. It may be remarked, however, that 

 the colour of a neon-tube is extremely brilliant and of an orange-pink 

 hue ; it resembles nothing so much as a flame ; and it is characterised 

 by a multitude of intense orange and yellow lines ; that of krypton is 

 pale violet ; and that of xenon is sky-blue. The paper contains plates 

 showing the most brilliant lines of the visible spectrum. 



That the gases form a series in the periodic table, between that of 

 fluorine and that of sodium is proved by three lines of argument : 



(1) The ratio between their specific heats at constant pressure and 



constant volume is 1-66. 



(2) If the densities be regarded as identical with the atomic weights, 



as in the case with diatomic gases such as hydrogen, oxygen, 

 and nitrogen, there is no place for these elements in the periodic 

 table. The group of elements which includes them is : 



(For arguments in favour of placing hydrogen at the head of the 

 fluorine group of elements, see Orme Masson, ' Chem. News,' vol. 73, 

 1896, p. 283.) 



