77 
after carefully drying, these were subjected without previous 
annealing to the heat of an intensely heated air furnace, 
and when thoroughly heated to the temperature of the 
furnace, suddenly withdrawn and exposed to a current of 
cold air. The following table shews the result obtained in 
each case : — 
ABCDEFGHIKL 
Degree of power of ) 
resistance to change V 536o-±3546o4 
of temperature. ) 
On comparing the results of these experiments, it appears 
obvious that those clays in which, according to the analysis 
given, the minimum amount of oxides of iron, and the 
alkaline earths is present in their composition, are the best 
adapted to resist fusion, or crack on being exposed to any 
sudden change of temperature ; desiderata most essential 
for the purposes they have to be applied to. It is now 
universally admitted by chemists that clays are definite 
chemical compounds of silica, alumina, and water, the 
composition of such consisting of one equivalent of alumina 
combined with two of silicic acid, and two of water, and 
thus the various other bodies with which they are found 
associated are mere mechanical mixtures, to be regarded 
only as impurities ; the presence of these substances 
materially impairing the qualities of the clays in which 
they are present. 
ON SOME OF THE DIFFERENCES IN THE DEPOSITION OF COAL. 
BY SAMUEL BAINES, ESQ., OF LIGHTCLIFFE. 
Coal is of such paramount importance to this, or even any 
district, that it would be a work of supererogation to dilate 
upon the fact. It would not be too much to say that we owe 
more to coal for the prosperity of our country than to that 
boasted Anglo-Saxon variety of the proud Caucasian family 
of man, to which we belong. 
