26 Report of Dr. Turner's Lecture 



Hence the quantity of silica carried off in solution was 

 enormous. 



The lecturer then went on to explain how it happened that 

 silica, existing in solution, was deposited so as to constitute 

 minerals. One obvious principle, he stated, was the molecular 

 attraction which exists between similar particles of matter, as 

 was proved by facts without number. Its existence was at- 

 tested by the globular form assumed by water, oil, mercury, 

 and other liquids; — by the separation from one another of 

 salts in crystallizing out of mixed solutions; — by the formation 

 of crystals during the slow deposition of vapour, as when cam- 

 phor was subliming slowly in a glass bottle, the particles at- 

 taching themselves to one another rather than spreading uni- 

 formly over the surface on which they collect; — and by the 

 tendency of like molecules to get together and cohere while 

 intermixed with a mass of dissimilar matter rendered liquid 

 by heat, as when particles of titanium, diffused in a furnace 

 through a mass of iron, seek out each other and form regular 

 crystals, or when minerals crystallize out of melted lava or 

 basalt. So from solutions of silex, whether strong or dilute, 

 the particles are disposed to adhere together whenever they 

 cease to remain in solution. 



Another principle applicable to this question, was the fol- 

 lowing: Whenever substances, insoluble in their ordinary state, 

 were dissolved by the force of favourable circumstances, such 

 solutions were very prone to decomposition. They formed 

 instances of peculiarly unstable equilibrium. The slightest 

 disturbing causes, — as agitation, change of temperature, or the 

 affinity, though slight, of some other body for the solvent, — would 

 in such cases put an end to the solution. Illustrative examples 

 of this principle were afforded by solutions of tin, titanium, 

 and peroxide of iron in a neutral state. He might probably 

 quote albuminous solutions as an instance from the animal 

 kingdom. Water cooled carefully below its usual point of con- 

 gelation, and saturated solutions of Glauber's salt, were liquids 

 in which a similar instability of equilibrium was conspicuous. 

 The lecturer, in illustration, here showed two solutions of Glau- 

 ber's salt: — he explained that the mere pressure of the atmo- 

 sphere on removing the cork, or the slightest agitation, often 

 caused such solutions to become solid; and that when these 

 failed, the introduction of a solid body, especially a crystal of 

 Glauber's salt, or of any substance having even a feeble affinity 

 for the salt or its solvent, — such as a globule of air or carbonic 

 acid gas, — generally determined immediate crystallization. The 

 solutions on the lecture-table retained their form after removal 



