8o Si r H. Davy’s experiments and observations 
The chemical changes in general produced by slow com- 
bustion appear worthy of investigation. A wire of platinum 
introduced under the usual circumstances into a mixture of 
prussic gas, ( cyanogen ) and oxygene in excess became ignited 
to whiteness, and the yellow vapours of nitrous acid were 
observed in the mixture. And in a mixture of olefiant gas 
non-explosive from the excess of inflammable gas, much 
carbonic oxide was formed. 
I have tried to produce these phenomena with various 
metals; but I have succeded only with platinum and palla- 
dium; with copper, silver, iron, gold, and zinc, the effect is 
not produced. Platinum and palladium have low conducting 
powers, and small capacities for heat compared with other 
metals, and these seem to be the principal causes of their pro- 
ducing, continuing; and rendering sensible these slow com- 
bustions. 
I have tried some earthy substances which are bad con- 
ductors of heat ; but their capacities and power of radiating 
heat appear to interfere. A thin film of carbonaceous matter 
entirely destroys the igniting power of platinum, and a slight 
coating of sulphuret deprives palladium of this property, 
which must principally depend upon their increasing the 
power of the metals to radiate heat. 
Thin laminag of the metals, if their form admits of a free 
circulation of air, answer as" well as fine wires ; and a large 
surface of platinum may be made red hot in the vapour of 
ether, or in a combustible mixture of coal gas and air. 
I need not dwell upon the connection of these facts res- 
pecting slow combustion, with the other facts I have described 
in the history of flame. Many theoretical views will arise 
from this connection, and hints for new researches, which I 
