Mr. GRiTFm on a Ctuxrcocd Support for Blowpipe Experiments. 161 



removed from the fire. The ignited support is to be rested on a por- 

 celain capsule in the manner represented by fig. d, and a quantity of 

 microcosmic salt, sufficient to form a bead, is placed upon its red hot 

 surface. The salt instantly smelts and sinks into the central cavity, so 

 as to form a bead, fig. F, the heat, the form, and the smoothness of the 

 surface of the support, facilitating this part of the process. The salt is 

 then heated before the blowpipe till it is melted into a transparent 

 colourless bead. The support is again placed on the porcelain capsule, 

 and the metallic substance intended to be incorporated in the bead, is 

 added to it The support continuing to be red hot, and the bead con- 

 sequently continuing soft, the substance so added is immediately 

 absorbed and its loss by dispersion prevented. Whereas, upon com- 

 mon charcoal, the fused salt solidifies soon after it is removed from 

 the flame, and the substance added for examination, not adhering to 

 it, is often blown away by the first blast from the blowpipe jet. The 

 bead is now again fused till the substance added to it is decomposed, 

 and the resulting glass is observed to fuse quietly. It is then ready 

 for examination, but it is sunk in the bottom of the hollow in the sup- 

 port, (see fig. F,) and cannot be seen by transmitted light unless the 

 projecting sides of the support be removed. This is effected as fol- 

 lows: — The support is placed as before upon the procelain capsule, 

 and the operator blows with his mouth, without using the blowpipe, 

 strongly down upon its surface. The pastile then burns away rapidly, 

 and the force of the blast of air disperses the ashes, until the whole 

 rim of the support is consumed, down to the part 

 marked, in fig. F, with dotted lines. The bead 

 then appears situated on the summit of a cone, 

 as shown in fig. G, and can be examined either 

 by reflective or transmitted light. It is also in 

 a position adapted for exposure to the different action of the oxidating 

 and reducing flames, so as to have the character of the included metal 

 fully developed. If, finally, the charcoal is allowed to burn wholly 

 away, the coloured bead can be lifted from the ashes and preserved in 

 a closed glass tube for subsequent examination and comparison. 



2). If the surface of one of the Supports for Reductions is heated 

 before the blowpipe, it bums at fii-st like the simple charcoal support, 

 but in proportion as the charcoal is consumed, the fluxes which were 

 mixed with it, and which are not volatile, concentrate and fuse upon 

 tlio surface of the residue. If, therefore, a reducible metallic com- 

 pound is heated upon such a support, it becomes exposed at once to 

 the reducing action of the high temperature, of the nascent oidde of 

 carbon, and of the carbonate of soda, whilst any earthy matter that 

 it may contain is vitrified by the attendant borax. It is easy there- 

 fore to conceive tliat these supports should possess a powerful reduc- 

 ing action, and so in fact they do. For example, a crystal of sulphate 

 of copper, as large as the surface of a support, can be decomposed upon 



