SIR G. S. MACKENZIE on the Formation of Chalcedony. 101 



formed, not from a solution, but from matter fluid per se,a 

 fluid that has become solid as it advanced, in the same manner as 

 water during frost ; or, in other words, which has become solid 

 by the deprivation of heat, and not by the evaporation of a fluid. 

 Arriving at this conclusion we must examine the effects of heat 

 on other substances, in order to obtain an analogy which may 

 reconcile all the forms in which we find the very interesting sub- 

 stance I have been considering. 



I have already pointed out the fact, that wax, when poured 

 into a candle-mould, arranges itself around the wick in the same 

 manner as Chalcedony appears to do around the matter which 

 we find in the centre of the concentric pendulous form. But 

 what we have now to observe of wax is, that when it arrives at a 

 certain temperature, it passes suddenly from a state of solidity, 

 (I should say cohesion perhaps) to that of extreme fluidity ; and 

 its transition from fluidity to the solid state is equally rapid. 

 To this substance, therefore, we may compare some forms of 

 Chalcedony, in respect to their previous condition and forma- 

 tion. 



Glass passes very slowly from the fluid to the solid state ; 

 and to this we may compare other forms of Chalcedony in the 

 same manner. But the same thing cannot be similar in its pro- 

 perties to two dissimilar things ; and we must, therefore, imagine, 

 that some adventitious circumstances in the composition of Chal- 

 cedony, have had the power of altering its properties ; and that 

 these circumstances are too minute for us to discover. That 

 very minute additions to earthy compounds greatly alter their 

 figure and properties, we know by the facts brought to light by 

 the labours of analysts ; and we may hope that Chalcedony may 

 yet attract their notice more than it has hitherto done. 



No chemist, so far as I know, has observed water in Chalce- 

 dony, except KLAPROTH, who found in the green variety (He- 

 liotrope) 2.5 per cent, of water. BERGMANN obtained 16 per 



