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 frag- 
ments, being retained at one point, become sufficiently heated ; they 
ignite ; burn-with a yellow flame, and then move over the a a 
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 Bache, of Philadelphia, it is stated, 
that when sodium is thrown into water, it swims upon its surface, oc- 
casions violent éffervescence 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 aiieiaiel gum arabic, 
and half an ounce of water, will inflame sodium, most probably for 
the reasons assigned by Serullas, as stated above. wh 
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. 
%. On a pane of glass, sodium will not inflame, when the glass is 
clean and smooth ; but any particles of dust athens: to it will cause 
the firing of the neiih with scintillations. . 
4. On a metallic surface the sodium could in no instance be made 
to inflame. 
