313 Intelligence and Miscellaneous Articles. 



EXPERIMENTS WITH POTASSIUM AND SODIUM. 

 Dr. Ducatel, Professor of Chemistry in the University of Mary- 

 land, after referring to Serullas's experiments on the same subject, 

 (See Phil. Mag. and Annals, N.S. vol. vi. p. 149.) repeated them with 

 the following results: 



1. A mucilage made with one drachm of powdered gum arabic, 

 and half an ounce of water, will inflame sodium, most probably for 

 the reasons assigned by Serullas, as stated above. 



2. On wood, sodium most generally inflames in contact with a drop 

 of cold water; the action being at the same time so violent as to 

 cause the globule of metal to roll along the dry surface of the table 

 with considerable rapidity, leaving a white streak of caustic soda 

 over its path. This experiment, however, does not always succeed. 



3. On a -pane of glass, sodium will not inflame, when the glass is 

 clean and smooth ; but any particles of dust adhering to it will cause 

 the firing of the metal, with scintillations. 



4. On a metallic surface the sodium could in no instance be made 

 to inflame. 



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 

 rapid abstraction of caloric, which prevents a sufficient elevation of 

 temperature for manifesting the phaenomenon 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-coloured flame fringed with blue. The potassium, in se- 

 veral repetitions of this experiment, always emitted light ; the sodium 

 did not. 



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

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

 sphere be dry ; but when breathed upon, it immediately acquires, as 

 observed 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 sur- 

 face of the mercury, and at some distance from the large globule. 



