649 



risen to 13 for TeCl, — where two valencies have been liberated. 

 For entirely free metallic Te Ka will rise still further, namely to 

 about 30. 



What consequences this behaviour of molecules and atoms with 

 regard to the attraction exercised by theui can have for the properties 

 of many substances (volatility, surface tension, etc.), has been set 

 forth at length by me elsewhere. ^) 



4. The heat of dissociation of di-atomic gases. 



After these introductory remarks we may now proceed to the 

 real subject of this Paper, viz. the calculation of the heats of 

 dissociation Q from the values of the increased valency attractions 

 y-^A, which were mentioned above, and which are recorded in 

 table II (the values printed in bold type under the elements), for 

 so far as they are now known. 



Let us take hydrogen as an example. For the internal energy of 

 the not dissociated gas H, we may write: 



Eh, = {E,-Q,) —- -\-cH„T (a) 



V 



in which E^ represents the so-called constant of Energy of the 

 unbound H-atouis, hence E^ — Q^ that of the hound H, -atoms in H,. 

 Hence Q^ is the absorbed (internal) heat of dissociation (in units of 

 energy e.g.) in the dissociation H^ — > 2H, at 7'=:0 — i.e. the 

 chemical energy (at T=rO), wiiich is liberated in the formation of 

 1 Gr. mol. H, from the separate H-atoms). 



For the dissociated H -|- H we have evidently : 



2Eh^E, + 2,chT (6) 



V 



While, namely, for H, the quantity a represented the ordinary 

 rest attraction (per Gr. mol.) between the molecules, A now represents 

 the increased attraction of valency between the separate, now free 

 atoms per Gr. atom, hence 4^ per Gr. mol. = 2 Gr. atoms. 



In the ideal gasstate, where v is very great, we shall simply have: 

 Eh, = (E, - Q,) f CH,T ; 2Eh=E, + 2cff7\ 

 and as these two quantities of energy will just differ the total 

 (internal) heat of dissociation Q, we have then : 



Q = 2Eh~Eh, = Q,-^(2ch-ch.)T (c) 



the well-known expression for Q in the function of T, when ch 

 represents the liuiiting value of the specific heat at constant (large) 



1) Gf. Chemisch Weekblad, Sept. 14, 1918, N". 37 (p. 1124-1137). 



