02 Experiments with Potassium and Sodium. 



5. On charcoal, which is not mentioned by Serullas, sodium never 

 fails to inflame, with brilliant scintillations. This is the mode which 

 I adopt with most confidence, for firing sodium in contact with cold 

 water. It confirms the truth of the reason given by Serullas, why- 

 sodium will not inflame under the same circumstances as potassium ; 

 namely, the superior temperature which the latter acquires, during its 

 combination with the oxygen of the water : hence the necessity of 

 placing the former on a bad conductor, in order to avoid the too ra- 

 pid abstraction of caloric, which prevents a sufficient elevation of 

 temperature for manifesting the phenomenon of combustion. 



6. It is commonly stated, that in the decomposition of water by 

 sodium, pure hydrogen is evolved. This is a mistake. A portion 

 of the metal, as in the case of potassium, combines with the hydro- 

 gen, as may be shown by the following experiment. — Take a globule 

 of sodium, wrap it up in a small piece of paper, and introduce it un- 

 der a small receiver provided with a stop-cock and jet, filled with 

 water and standing over the pneumatic trough. The decomposition 

 of the water will be effected as usual, and sodiuretted hydrogen 

 will be collected, which (on opening the jet attached to the receiver) 

 being inflamed, burns with a characteristic bright yellow flame. Po- 

 tassiuretted hydrogen, obtained under the same circumstances, burns 

 with a rose-colored flame fringed with blue. The potassium in sev- 

 eral repetitions of this experiment always emitted light j the sodium 

 did not. 



7. A globule o^ potassium placed on a bath of mercury gradually 

 amalgamates with the latter, without any rotary motion, if the atmos- 

 phere be dry ; but when breathed upon, it immediately acquires, as ob- 

 served by Serullas, a very rapid revolving motion, which continues for a 

 long time. The surface of the mercury becomes tarnished, apparently 

 by the accumulation of minute particles of the amalgam formed, which, 

 at intervals are seen to emerge from beneath the surface of the mercu- 

 ry, and at some distance from the large globule. The surface of the li- 

 quid metal, within a circle of half an inch to an inch in diameter, re- 

 tains its brilliancy. The minute particles of amalgam, which 'I sup- 

 pose to be the cause of the tarnish, seem to be repelled by the large 

 globule of potassium, and, occasionally, as new accessions are made 

 to them, they become singularly agitated, exhibiting somewhat of the 

 appearance observed when a drop of vinegar, or of an acid, comes 

 in contact with a drop of water. 



