98 Mr Graham on Phosphuretted Hydrogen. 



stroys the spontaneous inflammability, but requires a period of 

 not less than twenty or thirty hours. 



Olefiant gas has a negative influence of quite a different cha- 

 racter, which has already been alluded to, and which is in action 

 the moment the gases are mixed, but which does not appear un- 

 less the proportion of olefiant gas be very considerable. It is 

 probable that ether-vapour and the gaseous hydrocarburets like- 

 wise have an influence of the same kind. An astonishingly mi- 

 nute quantity of an essential oil suffices to destroy the inflamma- 

 bility of the gas over mercury, if allowed an hour or two to act. 

 Hence it is very difficult to preserve gas in the inflammable con- 

 dition, in the mercurial trough, if any portion of the mercury has 

 been soiled by an essential oil. 



7. The action of potassium on the peculiar principle is equally 

 remarkable. A most minute quantity of this metal, or of its 

 amalgam, destroys the self-accendibility of the gas in a few mi- 

 nutes, without occasioning any sensible reduction of volume that 

 could be measured. 



The fact is, potassium, or its amalgam, is without effect upon 

 phosphuretted hydrogen itself, at the temperature of the air, 

 neither absorbing nor decomposing the gas ; but upon the pecu- 

 liar principle the action of this metal is rapid and certain. One 

 grain of potassium, amalgamated with fifty pounds of mercury, 

 rendered that large quantity of mercury quite unfit for retaining 

 gas over it, in the self-accendible condition, for more than a few 

 minutes. In such experiments the interference of naphtha 

 vapour was perfectly excluded. Zinc and tin, either by them- 

 selves or in the state of amalgam, have no sensible effect upon 

 self-accendible gas, at least in a period of five or six hours. Pro- 

 toxide of mercury speedily withdraws the peculiar principle, but 

 afterwards also reacts slowly upon the gas itself. On the other 

 hand, the peroxide of the same metal is nowise injurious to 

 the self-accendible gas. Arsenious acid in powder acts in the 

 same manner as protoxide of mercury. The solution of proto- 



