' ELECTRICITT, MAGNETISM, AND GRAVITATION. 85 



in a few seconds, was from 67° to 75**, or 80". Some 

 augmentation of heat occurred also to a piece of uncon- 

 densed potassium whea exposed to the atmosphere ; but 

 much less rapidly than the former. TJie rapidity of combi- 

 nation with oxygen increases in ratio with the increased 

 specific gravity of the metal after compression, as will be 

 seen throughout these experiments. 



SPONTANEOUS COMBUSTION. 



When considerable compression had been employed, the 

 metal was found to absorb oxygen so rapidly as to take fire in 

 a few seconds, and consume with considerable energy until 

 the whole had disappeared. This is not the case at all with 

 the uncompressed metal. During this compressed condition, 

 the metal is seen to enter into fusion upon various parts of 

 its surface. When escaping from an orifice under com- 

 pression, if the orifice is of large dimensions, it escapes with 

 triflingly increased heat, unchanged, and of a leaden hue, 

 like fine leaden wire or piping. 



With a smaller orifice, it is projected unseen, and is 

 discovered shortly afterwards, at some distance in the apart- 

 ment, by the spontaneous combustion which takes place 

 sooner or later according to the degree of compression 

 employed. With an orifice of a most minute diameter, 

 heat and flame are seen instantly projected, the potassium 

 exploding with considerable illumination and violence. 



Exp. 8.— An empty bladder was now attached to the 

 percussion orifice by means of a short brass tube. I first 

 tested the apparatus, and on striking the piston with a 

 hammer, a considerable explosion ensued twice, attended 

 with the projection of flame and a report as before. When 

 the bladder was screwed to the orifice, and the piston again 

 struck, a flame was seen within the empty bladder, and 

 projecting about two inches, but there was no explosion, 

 and only the sound of the hammer itself. 



