328 Dr. Wollaston on the Discovery of Palladium. 
precipitated from a neutral solution by prussiate of mercury, 
the precipitate thus formed has the property of detonating 
when heated. The noise is similar to that occasioned by firing 
an equal quantity of gunpowder, and accordingly the explo- 
sion is attended with no marks of violence unless occasioned 
by close confinement. The heat requisite for this purpose is 
barely sufficient to melt bismuth, consequently is about 500° of 
Fahrenheit. The light produced is proportionally feeble, and 
can only be seen in the absence of all other light. 
In endeavouring to dissolve a piece of palladium in strong 
colourless nitric acid for the purpose of forming the detonating 
prussiate, I found that, although the acid shortly acquired a red 
colour surrounding the metal, the action of the acid was ex- 
tremely slow, and I was surprised to observe a fact that appears 
to me wholly singular : the metal was taken up without any 
extrication of nitrous gas ; and this seemed to be the cause of 
the slow solution of this metal, as there was not that circula- 
tion of the fluid, which takes place in the solution of other 
metals until the acid is nearly saturated. 
As the want of production of gas appeared to retard the solu- 
tion of palladium, I tried the effect of impregnating a quantity 
of the same acid previously with nitrous gas, and observed its 
action to be very considerably augmented, although the expe- 
riment was necessarily tried in the cold, because the gas would 
have been expelled by the application of heat. 
Beside those properties which are peculiar to palladium there 
are others, not less remarkable, which it possesses in common 
with platina. I have on a former occasion mentioned that these 
metals resemble each other in destroying the colour of a large 
quantity of gold. Their resemblance, however, in other 
