Experiments with Potassium and Sodium. 91 



metals on water appear to be due to the superior temperature ac- 

 quired by the potassium, while that obtained by the sodium is not 

 sufficient for the purpose : for, if a solution of gum-arabic be used, 



not too dense nor too thin, then the sodium fires : because the fraa:- 



o 



ments, being retained at one point, become sufiiciently heated ; they 

 ignite ; burn with a yellow flame, and then move over the surface 

 of the fluid like potassium. Again, according to Serullas, if sodium 

 be fixed upon a bad conductor of caloric, as wood, then water will 

 fire it ; but if it be placed upon glass, or porcelain, then the effect 

 will not be produced ; the abstraction of caloric in these cases, as 

 well as in that when a surface of pure water is used, being too rapid 

 to allow the necessary elevation of temperature. 



In the fourth American Edition of Dr. Turner's Elements of Che- 

 mistry, edited by Dr. Franklin Bacbe, of Philadelphia, it is stated, 

 daat when sodium is thrown into water, it swims upon its surface, oc- 

 casions violent effervescence and a hissing noise, and is rapidly oxida- 

 ted, but no light is visible. The action is stronger, it is added, with 

 hot water, and a few scintillations appear ; but still there is no flame. 

 Upon which Dr. Bache remarks, that the sodium which he has had 

 occasion to use, uniformly inflames on boiling water ; and he invites 

 the attention of chemical lecturers to the latter experiment. I have 

 frequently repeated Dr. Bache's experiment, and always with success. 

 But it has occurred to me, that the phenomenon would be made much 

 more satisfactory to a class, by adopting some mode of firing the 

 sodium on cold water. With a view to this, Serullas's experiments 

 were repeated with the following results. 



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

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

 the reasons assigned by Serullas, as stated above. 



2- Oawood, 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. 



'6. On di 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. 



