438 Mr. W. Sutherland on the 
NaCl as the introduction of a doublet in the position shown 
b 4 s oO 5 
thus Nab lech’ the two inner doublets reacting parailel to 
the Hib line, while neutralizing one another’s chemical 
cohering power, and so allowing the molecule to split into 
tNabt ‘and bly, which are the two ions. The central 
problem of ionization is to discover whence the extra doublet 
is derived. We may of course write the formula for NaCl 
in the form £Nab¥hZClb, and so equip the molecule with 
three doublets, which during ionization are resolved into 
two separate doublets, each ‘of which has associated with it 
one of the electrons into which the third doublet has been 
broken. 
To follow out this line of thought and give a logical 
representation of the monatomic molecule of metallic Na, we 
should write its symbol thus ZNabfh, indicating that there 
are two doublets ‘present, one having an electric: moment 
which is negligible in comparison with that of the other. 
Similarly, the symbol for Cl, will become ZClhZhFhZClb. 
It will rot be necessary to use such long formule continually, 
if we remember that 2) may stand for any number of 
associated doublets, the preferable number being the smallest 
that will enable all the known facts to be logically set forth. 
With this notation we can now discuss the separate parts 
of the energy changes whose total forms the heat of the 
chemical reaction given in (24). The formation of 2ZNahZClh 
from Cl, and 2Na involves the work of splitting Clb Clb 
into 2ZClh, which may be denoted by ($8), where 8 means 
any electronegative element, that of bringing ZNab and 
£Clb into the position tNabtCh, involving work depending 
on the distance between J and b in the inner doublet ; this 
work may be denoted by 2( RS), and then in accordance with 
Helmholtz’s idea of the specific attraction between matter 
and electricity there is the work of bringing the J of Cl 
quite close up to Na and that of bringing the b of Na quite 
close up to Cl. Now, in the more powerfully electropositive 
metals the changes of volume of their atoms on combination 
with Cl, Br, and I are approximately the same ; and this facet 
sug ggests that the work of bringing Z of Cl quite close up to 
Na is approximately independent of the electronegative 
reagent, and may be written (R) with R as general symbol 
for a metal. The corresponding quantity for Cl may be 
merged in (8). The work (R) is sometimes accompanied 
with. quite a remarkable change in the volume of the metal 
atom. For the gramme atom of Li the change on passing 
from the metallic to the combined state is 11°-9-2 ; for Na it 
