140 On the Affinities of different Earths for Carlon. 



Wedgwood. I found the silex fused into a rich pearlish 

 green glass containing an immense number of air-bubbles. 

 A minute speck of colour was noticed in one part, which 

 resembled coal. The experiment was therefore repeated a 

 second and third time ; and the fused silex obtained in a 

 state of great purity as to colour, though still containing a 

 number of minute cells. 



XIV. Fifty grains of pure silex and a quarter of a grain 

 of lamp black were mixed. The carbon gave a delicate 

 shade of blue to the silex. The mixture was fused into a 

 singular glass composed of concentric laminae or convexes 

 of thin glass. The colour was indefinite and mixed, of a 

 straw, watery, smoky tinge, and much clouded. It was, 

 however, very transparent, and so buoyant as to float in air. 



XV. 50 grains of pure silex, 



-i grain of lamp black, were fused into a porous 

 glass possessing a watery transparency, but of a light lead- 

 blueish colour. 



XVI. 50 grains of pure silex, 



1 grain of lamp black, formed a glass consider- 

 ably darker in point of colour than the former : the cells 

 were much of the same size, but the thickness of the la- 

 minae much increased, and the transparency proportionally 

 diminished. In these three experiments the carbon had 

 completely disappeared, nor had the interior of any of the 

 crucibles exhibited the usual style of glazing. 



XVII. 50 grains of pure silex, 



2 ditto lamp black. 

 These were intimately mixed together, and exposed to a 

 similar heat with the former. The result was a jet black 

 glass much honey-combed, and apparently approaching 

 a state beyond simple vitrification. The whole carbon had 

 disappeared, and the interior of the crucible remained un- 

 glazed. 



XVIII. 50 grains of pure silex, 



3 ditto lamp black, were fused into an 

 irregular mass of a very dark colour possessing large honey- 

 combs. The transparency of the glass no longer existed, 

 but a minute porosity admitted light with a singular effect. 

 The carbon had disappeared, and the crucible had received 

 a slight degree of colour from the carbon. 



XIX. 50 grains of pure silex, 



5 ditto lamp black. 

 This mixture assumed an earthy appearance of a very black 

 colour, in a few places shining, but in general dull. The 

 honey-combed appearance was less in this than in ihe-for- 



mer, 



