PERFUME VAPORISER. 237 



spiral obtained by carefully slipping the pencil out of the coil, 

 using the uncoiled end as a handle. The wire will be heated red 

 hot, and glow brightly. Now turn off the gas so as to extinguish 

 the flame, and immediately turn it on again ; a mixture of coal 

 gas and air will pass upwards from the lamp, and coming in contact 

 with the hot platinum wire will be absorbed by the metal, at any 

 rate on its surface. The effect of this is that the coal gas and air 

 can act on each other chemically in the pores of the platinum, 

 just as they do when the lamp burns with a blue flame ; and, in 

 consequence, heat is produced which ke,eps the platinum wire red 

 hot for as long a time as the gas and air come in contact with it. 

 Sometimes so much heat is produced that the wire becomes almost 

 white hot, and lights the burner just as a match would do. By 

 turning off the gas and turning it on again when the wire has so 

 far cooled down that it is not visibly red hot, you can generally 

 succeed in first making the wire glow gently, then more brightly, 

 and finally intensely, so that after a quarter of a minute or so the 

 gas becomes re-lighted. Whether this occurs or not depends 

 upon the exact diameter of the wire, the place where the 

 spiral is held in the issuing gas and air current, whether this 

 current gets blown on one side by the breath or a draught of air, 

 and such like circumstances. 



Expt. 284. Perfume Vaporiser. A kind of perfume vaporiser 

 is sometimes sold acting on the above principles, consisting of a 

 spirit lamp containing scented spirit; a little pin of platinum, 

 shaped something like a clove, is stuck into the wick, the head 

 being made of a sort of miniature cage of fine wire, containing a 

 little plug of "spongy platinum," i.e., platinum prepared by 

 chemical processes in a loose porous condition (Expt. 199). The 

 spirit lamp is lit for a few moments, whereby the pin, and especi- 

 ally its head, becomes heated ; the flame is now blown out, when 

 the spongy platinum will continue to glow and diffuse perfume 

 throughout the room. This arises because the spirit passing up 

 the wick becomes evaporated by the heat of the head, a little of 

 the vapour being absorbed by the platinum along with air, giving 

 rise to what is equivalent to burning the vapour without flame, 

 like the gas in the previous experiment, the heat thereby produced 

 keeping the platinum red hot, and consequently maintaining the 

 action as long as any spirit remains in the lamp. To extinguish 

 the vaporiser and stop its action, all that is requisite is to put on 

 the cap of the spirit lamp ; this prevents any air having access to 

 the platinum, and consequently stops the action just as an 

 extinguisher puts out an ordinary candle. 



Expt. 285. Dobereiner's Lamp. By using platinum in an 



