38 Mr. T. Wedgwood's Experiments and Observations 
8. Clear, blackish gun-hint (2). 
g. Tawney semitransparent flint (3). 
10. Unglazed white biscuit earthen ware (4). 
11. Fine white porcelain (2). 
12. Clear, blackish gun-flint, made opake by heat (3). 
13. Flint glass (o). 
14. Plate glass ; green bottle glass (o). 
13. Fine hard loaf sugar (o). 
16. Moorstone, from Cornwall (l). 
Corune, semitransparent, from the East Indies (1). 
17. Iceland spar (o). 
18. White enamel (2) ; tobacco pipe (3). 
White Mica (o). 
ig. Unglazed biscuit earthen ware, blackened by exposing it, 
buried in charcoal in a close crucible, to a white heat (4.) 
20, * Black vitreous mass, made by melting together 5 of fluor, 
1 of lime, and some charcoal powder (4). 
21. Fluor; aerated and vitriolated barytes; white and black 
Derbyshire marble ; calcareous spar ; crystals of borax ; 
deep blue glass; mother of pearl. 
Rock crystal, quartz, flint glass, and many other hard 
bodies, during attrition, emit now and then reddish sparks of 
a vivid light, which retain their brightness in a passage of one, 
two, and even three inches, through the air. 
A piece of opake agate, applied to the circumference of a 
wheel of fine grit, revolving at a moderate rate, becomes 
* Some of this mixture taken out of the crucible before it was perfectly fused, 
gave out, when rubbed, a strong smell like phosphorus of urine; and on throwing 
some of it pulverized on a plate of iron, heated just below redness, it was very lumi- 
nous, and presented every appearance of burning phosphorus. 
