656 Scientific Proceedings, Royal Dublin Society. 
vival of some property or properties of the respective elements in 
the compounds into which they enter.’ 
Mixtures of the monoclinic and anorthic felspars furnish 
striking examples of the crystallizing together, in what must be 
regarded as isomorphous mixtures, of substances belonging to dif- 
ferent crystal systems; and the extremely close resemblances 
which compounds may display and yet be of different systems is 
yet more strikingly exemplified by the arsenious and antimonious 
oxides, which, until a few years ago, were regarded as furnishing 
an exceptionally good example of an isodimorphous group with 
erystal form and cleavage practically identical. The latter com- 
pounds have been shown by des Cloizeaux to belong to different 
crystal systems.’ 
To compare with our conclusion that assemblages which are 
not isomorphous, but which are nevertheless capable of quasi 
homogeneous intercalation, may exist, we have the fact that in 
recent years a number of substances have become known which 
are not chemically analogous, and do not possess isomorphous 
forms, but which yet form homogeneous solid solutions.* 
The following are some other less-conspicuous properties of 
isormorphous homogeneous assemblages to which observed phe- 
nomena furnish resemblances. 
We may have two assemblages whose composition is such, that 
when exposed to similar conditions of a certain kind they are 
isomorphous, but which under another set of conditions attain 
equilbrium in different symmetries, one or both of the assemblages 
being therefore dimorphous. And since we hayé already concluded — 
that an assemblage, if sufficiently near a critical point, may have its 
symmetry determined by the symmetry of a small solidified por- 
tion of similar composition which comes in contact with it,* we see 
that in a rough mixture of the two assemblages the order in which 
the two kinds commence to solidify may suffice to determine whether 
they shall be isomorphous and crystallize together or not. 
1 Journ. Chem. Soc., 1893, p. 887; or Zeitschr. f. Kryst., 21, p. 491, &c.; also 
Journ. Chem. Soc., 1894, p. 628; or Zeitschr. f. Kryst., 24. p. 1. 
* Bull. Min., vol. x., p. 303, 1887. 
3 Pope’s translation of Fock’s ‘‘ Chemische Krystallographie,”’ p. 141. 
4 See pp. 576 and 581. 
