( 639°) 
in the second case. The necessary condition for the appearance of 
the phenomenon will, therefore, easily be satisfied. 
The above phenomenon is one of retrograde solidification if 
we consider the liquid crystalline condition as a solid. 
Fortunately another instance has been found recently with mixed 
erystals which are solid in the ordinary meaning of the. word. 
With the aid of my theory, Heycock and NevitLe when inter- 
preting the results of their studies on the solidification pheno- 
mena of alloys of copper and tin, have come to the conclusion 
that a mixture containing 27 atom ®% of tin which solidifies 
between 720°—633° to homogenous mixed crystals, breaks up when 
the lower temperature is passed into the solid compound Cuz Sn 
(25 at. 0/, of Sn) and a liquid containing 42 at 0/, of Sn. Calcu- 
lation shows that a maximum of 6.5 °/, by weight may again become 
liquid below 633°. Whether this quantity of liquid metal would 
be visible between the crystals is perhaps doubtful. As the inter- 
pretation in question was only brought to light after the experiments 
were finished, it could only be proved by a microscopical examination 
of the completely solidified mass, that at 633° a partial liquefaction 
of the previously solid mixed crystals had taken place. 
The theory of phases has here again explained the exact connection 
and there is no doubt that the liquefaction of binary mixtures by 
cooling is not an extremely rare plienomenon. 
Geology. — “STARING and the coal-question of Southern Limburg.” 
By Prof. J. L. C. SCHROEDER VAN DER KOLK. 
(Communicated in the meeting of March 29, 1902). 
Lately the coal-fields of Southern Limburg have repeatedly been 
discussed, also in the report of the Royal mining commission, 
instituted April 17th 1899. 
The name of STARING is however invariably omitted, and the 
result of his researches simply laid aside. Therefore I wish to point 
out, in this paper, the extent of all that was known to STARING, 
already full forty years ago. I wish to do so, not only from a 
feeling of justice towards STARING, for much that now seems new 
to us, was already known to him, but also because to my opinion, 
his knowledge may be of use to us, even now. 
The principal object of this paper is, clearly to bring out STARING’s 
standard of knowledge, at the time, so I shall almost exlusively 
make use of his statements. I borrow those statements from: Plate 
