962 
cation. The two forms coexist at low temperatures (—36° to —15°; 
31° to —18°) for several days (12—10 days) and even at room 
temperature it takes a long time before the process of stabilisation 
has come to an end. 
These measurements were confirmed by GERNrz ') some years later. 
5. Just as electrolytes cause an enormous acceleration of the 
rate of stabilisation of metals, so solvents act in the case of sulphur. 
Very small quantities are sufficient. (1 already mention this here in 
connexion with some phenomena to be described in $ 9). 
Reicner says: If sulphur which has been crystallised from carbon 
disulphide is melted, without previously removing the solvent com- 
pletely by drying, the solid monoelinie sulphur is very quickly 
transformed into the rhombic form. If the sulphur is again melted, 
(during which procedure a part of the disulphide volatilizes) the 
transformation takes place more slowly and on treating the sulphur 
once again in this way, the transformation velocity is still further 
decreased. 
6. Considering now the chemical compounds, inorganic as well 
as organic, it may be pointed out that the number of substances 
known to show polymorphy increases every day. While a century 
ago only one such compound was known, to day we count them 
by hundreds, if not by thousands. There hes before us, therefore, 
ready to be brought under cultivation, a large region in the domain 
of inorganic as well as of organic chemistry. 
With regard to those compounds which are every day in hands 
of the chemist I mention NH,Cl, NH,Br, Hgl,, HeS, PbO, KNO,, 
AgNO,, Pb(NO,),, K,SO,, K,CrO,, CaCO,, KCNS, NH,CNS etc., ete. 
as being known in more than one form. In a good many cases 
these modifications are enantiotropic. 
7. The question arises whether the same phenomena as have 
been observed with the metals also occur here, i.e. whether the 
same strong retardations exist here, which make it possible for the two 
(or several) forms of chemical compounds to coexist within a range 
of temperatures where one or more of the modifications is meta- 
stable. The investigations I have now carried out prove that this is 
really the case. 
8. Thallous picrate is especially suitable for such an investiga- 
1) Ann. de Chim. et de Phys. (6) 7, 233 (1886). 
