498 
case of these acid forms. This was the more probable, since it is 
clear from their communication that they had formed no adequate 
idea of the nuclei in question. Although they mention the “beim 
Einfüllen der Lösung etwa an den Wandungen entstandenen Keime” ’), 
they neglect to give sufficient attention to the nuclei which can 
occur in the solution, and to those which are notoriously present 
in the air. 
Before describing how the experiments of SroBBr and SCHÖNBURG 
were repeated, it is desirable to discuss the considerations which 
form the basis of the experimental method adopted. 
By ‘nuclei’ are to be understood molecular complexes which 
remain over from the solid state after solution, and which can be 
formed in the liquid as a preliminary to crystallisation. 
According to the solvent used, nuclei and single molecules, or 
nuclei, double molecules and single molecules can oecur in the 
solution. 
If a solution of one of the forms of allocinnamic acid is prepared, 
a complete or an incomplete dissociation into single molecules 
results, according to the temperature and the concentration. The 
higher the temperature and the smaller the concentration, the more 
complete is the dissociation. It is thus possible to prepare two 
kinds of solutions, namely, those which contain only single mole- 
cules, and those which, in addition, contain also nuclei. In solvents 
in which double molecules can occur, a third kind of solution is 
also possible containing single and double molecules, while a 
solution with nuclei may also at the same time contain single and 
double molecules. 
While within the solutions equilibria between the different kinds 
of molecules are established, for which, of course, a longer time 
is required according as the molecules are more strongly held together, 
the concentration of the solution is greater, and the temperature 
lower; equilibria are also established above the solutions between 
the nuclei, the double-molecules and the single molecules. These 
equilibria are dependent on the composition of the solution. 
It is now sufficiently known from experimental investigation, 
that the atmospheric nuclei of the forms of allocinnamic acid are 
very persistent. It follows therefore from this that the equilibrium 
in the air lags behind variations in the solution. As a consequence 
nuclei are often still present in the air when the solution consists 
of single molecules only. 
1) loc. cit. p. 198. 
