101 
Now, supposing that in a solution of equivalent quantities of the con- 
stituents the dissociation constants of these and the double salt are such 
that approximately equal numbers of molecules of the three kinds exist 
un-ionized, and the solution be concentrated, the double salt will separate 
if its molecular solubility (solubility divided by molecular weight) is less 
than that of either constituent, but not otherwise. Of.course, it is not 
probable that the constants are such as to even approximately produce a 
condition like that imagined in the example just described, but inasmuch 
as normal salts do not differ very widely in their dissociation constants, 
the facts may be nearly enough in harmony with the supposition to make 
a study of these molecular solubilities not without interest in this con- 
nection, though the data availabie are not so numerous as might be 
desired. 
An examination of the solubilities of twelve double salts selected at 
random showed the facts to be in accordance with this theory without a 
single exception. The figures are given in the following table, the 
formulas selected being those of the substances separating out as crystals 
from their solutions. 
Formula. Ss Aan raat ne b+aX 100 
[SL ed ee a 174 12.5 7.2 
PS LONGO! ws Gb as Saw es + sees 665 85 12.8 
KEAT(S Ome ile Orie enacts cine eae 474 9.5 2.0 
(ON LR ASSL 6 ie ae BENS Al ret ca 132 ak 57.6 
EMS) a) gu VS Liha Os renee cys oo esare enc aiese 665 85 12.8 
OND AUS Oven tt Oma ora ce 452 9 2.0 
PIO Tce siasiersiin ue ae Secret eM as a ola 174 12.5 7.2 
Sens OM mISEOe no cer ease ace 717 120 16.7 
CHGS SA: GO ie 500 20 4.0 
RRA Orta rire shes arte tTiogs sis metry 3 132 ii 57.6 
EN SOn) sel Sle OU, aoade os eee Ss 717 120 16.7 
CNG CrysO) ood On re a aeeernn =, 478 over 12 over 2.5 
ES SOA ga ate MR See he ea 174 12.5 7.2 
Ber S On) an Qlis Oe weetiel tenses or 562 over 80 over 14.1 
PET SOs IIHS OL. 2 aac horasc ences 503 20 4.0 
