x$21.] Dr, Clarke upon the Gas Blowpipe. 421 



which is an infallible sign of the excellence of his gaseous mix- 

 ture for all experiments when the highest temperature is required. 

 The stoutest platinum wire will run before it into rapid jfusion, 

 and is immediately exposed to combustion. Pure magnesia may 

 thus be easily fused, and be made to form a frit, which cuts 

 glass like a diamond. The edges of Iceland spar, that most 

 refractory of all bodies, when exposed in thin laminae, are by' 

 the flame of this mixture invested with a white opaque enamel. 

 Rubies and sapphires become liquid, and flow together into one 

 boiling mass. Grains of iridium melt and burn like platinum. 

 Under these circumstances, if the earth of harytes be now 

 exposed to the powerful heat of the burning gaseous mixture, 

 unless the valve be partially opened, so as to allow a very small 

 body of flame, like the point of a fine needle, to act upon it, it 

 will be converted into a greenish glass, or into a substance exter- 

 nally resembling horn, disclosing no metallic lustre to the action 

 of the file. In my first experiment this year for exhibiting the 

 metallic base of harytes, the attempt entirely failed ; but 1 was 

 thereby guided, for the first time, to the cause of the failure ; 

 for the harytes which failed was taken out of the same bottle as 

 that which afterwards exhibited, in so imminent a degree, the 

 metallic lustre I have already described. The cause was owing 

 to the length of time in which fusion had been going on, and 

 the too powerful heat to which the revived metal had been 

 exposed : it came away altogether in white fumes, settling upon 

 the forceps, and tinging the flame with that olive-green colour 

 which always characterizes the combustion of the metalhc base 

 oibarytes. The same would happen with silver ; the whole of the 

 metal would be dissipated in white fumes, which would settle upon 

 the supporter if the heat be continued 4ong enough, and the 

 flame also is in this experiment tinged of a paler greenish hue. 

 For exhibiting, therefore, the metallic lustre of plutonium, call it 

 a metal, or a protoxide, or by whatsoever other name chemists 

 may hereafter decide, it is necessary that the experiment should 

 be conducted with care. The harytic earth should be, in the 

 first place, rendered as perfectly an anhydrate as possible ; the 

 presence of an atom of water would inevitably cause the experi- 

 ment to fail. Of course it is hardly necessary to add, that 

 water ought by no means to be used as a substitute for oil in the 

 safety cylinder ; for this would again give rise to failure. 

 Having a small cake of the hard anhydrate of harytes, supported 

 by a pair of forceps, allow the flame gradually to act upon it, 

 until it exhibits after fusion the deep jet-black substance I have 

 . before alluded to. Then while it is hot, rub one of the promi- 

 nent points of this black substance upon the sharpest and finest 

 'file, previously made warm before the fire, taking care not to cut 

 ^ it too deep, because that would disclose the harytic earth yet 

 'remaining below the part which has been fused. The metallic 



