490 EXPERIMENTS ON LlGHT-SPECTRA. 



l.mm thick, is bent with the pliers at one end into a small ring, 1 or 

 2mm w i(j e} an( j the other end is fused into a bit of glass tubing. A 

 piece of tube about the thickness of a pencil is drawn out into a 

 point at one end, the point broken off, and the straight end of the 

 wire pushed into the aperture so that about 5 mm are inside the tube. 

 The wire and the end of the glass are then heated strongly over a 

 spirit or gas flame until the glass melts round the wire, and the 

 latter is fixed in it. Fig. 278 shows the wire with the glass handle. 



FIG. 278 ( real size}. 



The substance to be introduced into the flame is moistened with 

 water or dissolved in it, the ring dipped into it and then cautiously 

 brought near the flame from the side, so that the water may eva- 

 porate and the substance become dry. The ring is then held a little 

 higher than the flame until the dry mass is fused and thus firmly 

 adheres to the wire. Not until this is accomplished should the 

 substance be introduced into the flame ; the part of the flame to be 

 employed is the lower one, a few millimetres beyond the point of 

 the blowpipe. If the moist substance is brought too soon into the 

 flame, the greater portion is scattered about by the vapour of water 

 formed ; hence gradual heating is necessary. The glass tube with 

 the wire may also, for greater convenience, be placed between the 

 cork lining in the clamp of the retort-stand, without great pressure, 

 so that it may be taken in and out without the necessity of turning 

 the screw. The clamp should of course have the requisite height 

 for keeping the ring of the wire, when the tube is clamped, in the 

 most suitable part of the flame. 



Many salts which are volatile when exposed to the 

 heat of the hydrogen flame are capable of giving a dis- 

 tinct colour to the flame, which in each case is due to 

 the vapour formed by the substance at this high tem- 

 perature. Common salt is very easily volatilised, even 

 to some extent at the lower temperature of the spirit- 

 flame ; a few small grains of salt sprinkled upon the 

 wick of a spirit-flame or introduced on a platinum wire 

 colour the flame distinctly yellow. For our present 

 purpose a spirit-flame is however not available, as it is 





