470 Capt. W. A. Ross on Pyrology, or Fire Analysis. [June 2(3, 



emitting a smell of burnt fat when heated in a matrass) produced, when 

 dissolved to a supersaturated extent in borax, a fine cerulean-blue bead of 

 extreme hardness*. Both this mineral and gunpowder (the latter alone, the 



former combined with sulphur) were found, when ground with water in 

 agate mortars, to give them a deep violet tint, best seen by transmitted 

 light, which is quite ineradicable even by the strongest acids f. 



86. If sulphur and clear drinking water be heated as at a c, fig. 7, a white 

 sublimate is deposited on the polished leg of the forceps, similar in appear- 

 ance to that afforded by fusing chloride of sodium. It was thus extracted, 

 though in extremely minute quantity, from even distilled water. To observe 



* Can the blue colour of the sapphire be due to this fact ? 

 f Nitrate of silver gives the agate a purplish-black tint. 



