136 SCIENCE PROGRESS 
salts must be isomorphous. The series of combinations thus 
formed, named mixed crystals, are of the nature of solid 
solutions; their physical properties are continuous functions of 
the composition; their chemical properties are those of the 
two constituent simple salts, ze. the analytical reactions are 
those of the ions of the two simple salts. Thus KClO, and 
KMnO, are isomorphous and form mixed crystals of all shades 
of depth of colour, from almost colourless through pink to deep 
purple, according to the relative amounts of colourless KClO* 
TABLE of 
CLASSIFICATION OF CoMBINATIONS mMA.xzM’A FORMED FROM 
Two SimpLE Satts MA anp M’A 
I. MIXED CRYSTALS | II. DOUBLE SALTS | III. SALTS OF COMPLEX 
| ACIDS 
(1) Composition 
Series 
from = var to {7% =0 m and m = simple whole numbers. 
nm=0O m = 100 
(2) The physical properties of the solid mMA.2M’'A are: 
additively those of the con- in no definite way related to those of 
Stituent salts, continuous the constituent simple salts. 
functions of the chemical 
composition in terms of the 
simple salts. 
(3) The chemical properties of solutions of mMA.nM'A are: 
those of the ions of the simple salts, z.e. those | not those of the ions of the 
of M, M’, and A. simple salts MA and M’A, 
but of ions M and M’A, 4». 
and deep purple KMnQ, present in the crystals. The same 
additive relation holds for other physical properties, such as 
specific volume, refractive index, etc. Moreover, a solution of 
the mixed crystals will give the reaction for the potassium 
cation and the perchlorate and permanganate anion. Retgers,} 
through his investigations of the relation between the physical 
properties and the composition of whole series of such salts, 
has supplied us with definite principles whereby to recognise 
mixed crystals, the chief interest attaching to this class of complex 
salts being in connection with the study of isomorphism. 
1 “Zur Kenntnis des Isomorphismus,” I.-XII., Zs. Ahysik. Chem. 4-20, 
1889-1896. 
