( 659 ) 
based on the equilibrium of phases will take the course indicated by 
theory. But the reverse is by no means the case and the question 
as to the existence of “isomorphy”” can only be satisfactorily solved 
by a erystallonomie investigation. 
The problem has a particular interest in so far as it relates to the 
determination of the limits in which morphotropously-related kinds 
of molecules may exhibit such a miscibility. For the word “isomorphy”’ 
relates to a number of special cases in a series of much more general 
phenomena of crystallonomy, namely, to those which show the rela- 
tion between the chemical constitution of the substances which have 
substitution-relations, with their innate erystalline form, which pheno- 
mena are expressed by the name of morphotropy. If the chemical 
relation of such substitution derivatives is confined within certain 
limits such morphotropous substances may become “isomorphotro- 
pous’ and will then be able to combine with each other in a 
limited or may be unlimited proportion. And if the relation of such 
substances has become so intense that a nearly identical property 
must be attributed to their crystal-structures on account of a// their 
physical properties, such isomorphotropous substances actually become 
“isomorphous” and mixing is then always possible. 
From the above it follows that the idea of “isomorphy’’ admits 
of a certain gradation; only the crystallonomer can determine in 
eacli case the degree of “isomorphy” by measuring the size indi- 
cated by the parameters of the molecular structure in the cases to 
be compared and particularly by studying the analogy in the cohesion- 
phenomena of the crystal-phase. As the differences in the values of 
the said molecular structure-parameters become smaller and a more 
complete similarity in the directions of cleavage and nature of surface 
of the similar limiting planes is found, a more complete isomorphy 
exists and the probability of a complete miscibility in the crystallised 
condition is at the same time enhanced. 
It cannot be doubted that in the cases investigated by Brunt there 
may be instances of such rea/ isomorphy and the following research 
may even prove this fact. But it must also not be lost sight of that 
many cases of miscible substances supposed to be instances of ““iso- 
morphy” are only cases of isomorphotropy or even only of morpho- 
tropy within relatively large limits. 
All this renders it highly desirable to undertake an exhaustive 
investigation of organic substances as to their miscibility in the solid 
condition, coupled with that of their crystalline form so as to elucidate 
the matter. The following research is a first communication on this 
subject. 
