
PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 3038 
immediate neighbourhood,—and of stimulating to the chemical union of the 
material of its own mass with the constituents of that rock ? 
Among the physical agencies which induce a change from the amorphous 
or colloidal to the structural or crystalloidal condition, we find plication and 
heat. Sir JAMES HALL’s experiments have shown that direct heat under pres- 
sure will change limestone into marble or calcite ; and plication, in the very act 
transforming a colloid into a crystalloid, does so at the cost, so to speak, of 
-an elimination of heat from the substance so plicated. Melt lead, pour it 
ty 
out on a flat stone,—in cooling it assumes the structureless, amorphous form, 
with rounded colloidal outline ; if, after cooling, it is bent in the hand, it gives 
out heat, becomes crystalline in structure, gradually loses its plability, and 
assumes the brittleness inseparable from the crystalloidal state. The same 
holds for iron and all metals capable of assuming the colloidal state; bend or 
beat them, they give out heat, becoming crystalline and brittle in the so doing. 
The heat here eliminated is doubtless partially the representative of arrested 
motion ; but it is probably chiefly an outcome of the change from the colloidal 
to the crystalloidal condition ; the agent of the elimination was the plication to 
which the substance was subjected, which plication was at the same time the 
immediate agent of the physical transformation. 
I would venture to predict that it will come to be found that the specific 
heat of substances in their colloidal state is always greater than that of their 
erystalloidal. 
I am not aware that any researches have been made specially to determine 
this point ; or even that the attention of physicists has been directed to it ; but 
the following table, which embodies all that I have been able to find, seems 
clearly to bear out such a view :— 

COLLOID. CRYSTALLOID. 
Water, A ites . : pulls Tee, .. : ’ : : Se 
Lamp Black, : ; 626 Graphite, . : ; ap 201 
Diamond, . : : Wes 
Limestone and Chalk, . : . ‘264 | Calcite and Marble, 4 , ec 20k 
Chalcedony, z ? : a LO5 Quartz, ; : , : 5 PE) 
Titanic acid (artificial), : ae ha | Piva: ee L63 
Peroxide of Iron (artificial), . ‘176 | Hematite, . Peg) e: 7166 
Should it prove to be the case that the amorphous form has a specific heat 
Bivays exceeding that of the crystalline, a step probably will be gained in the 
explanation of metamorphism generally ; it may at least be held that the high 
Specific heat of limestone, and the much lower heat of calcite or granular 
marble, explains the local metamorphism which we are now considering; as 
the plication, crushing and folding of the strata expressed, or extricated as heat 
VOL. XXVIII. PART II. 4K 
