110 Dr Turner's Experiments on the Application of 
employed for the purpose. A jet of coal-gas and oxygen from 
separate vessels was thrown upon spongy platinum, without the 
least luminous appearance whatever ; hut if the metal be first 
strongly heated before the blowpipe, and a jet of coal-gas be 
thrown upon it immediately after all light has disappeared, the 
platinum quickly becomes red, and will continue so for any 
length of time. A vivid light is emitted, but the gas itself is 
not enflamed. This result would, a priori , be expected, [be- 
cause the heat necessary to inflame an explosive mixture of coal 
gas and atmospherical air, is greater than the white heat of solid 
bodies. 
Coal-gas was mixed with rather more than twice its volume 
of oxygen. I heated a piece of spongy platinum to vivid red- 
ness ; put it quickly on a little basin of platinum-foil, floating 
on the mercury, and covered it with a jar full of the explosive 
mixture. Watery vapour condensed on the surface of the mer- 
cury, the platinum became red, and rapid diminution followed : 
the redness, however, speedily disappeared, and the progress of 
the operation was arrested long before either gas was consumed. 
The platinum w r as left two hours after this in contact with the 
residue, but did not cause any marked reduction of its volume. 
The carbonic acid was absorbed by fused potash, and the remain- 
der detonated strongly with the electric spark. This experiment 
was several times repeated with a similar result. It is curious 
that the process was in each case so quickly interrupted, for it 
is obvious that heat enough would be generated for its continu- 
ation. The cause is to be sought in the atmosphere of carbonic 
acid gas, which, as it forms, collects around the platinum, and 
thus prevents an adequate supply of the explosive mixture from 
reaching the metal, till its temperature has fallen below the 
point at which the combination can go on. I heated the balls 
No. 1. and 2. in a similar manner, and covered them with a 
jar full of the explosive mixture of coal-gas and oxygen. Ra- 
pid action ensued, without any visible redness ; the process 
ceased when much of the mixture remained, and after the car- 
bonic acid had been absorbed by potash, a spark of electricity 
exploded the residue. 
A mixture of coal-gas and oxygen was divided into three por- 
tions. Pure spongy platinum was put into one portion, and 
