BY CLEAVAGE, ETC. 35 
When phosphuret of calcium is thrown into wa- 
ter, a decomposition takes place, and phosphu- 
retted hydrogen gas is evolved. Hach bubble of 
this gas, as it comes in contact with the atmo- 
sphere, takes fire spontaneously, and throws off a 
ring of white smoke. These pretty rmes of smoke 
are luminous in the dark. 
In the year 1851, M. Petrie discovered that the 
metal potassium is phosphorescent when exposed 
to the air, like phosphorus. (‘Annuaire de Millon 
et Reiset,’ 1851.) He covered the potassium with 
bees’-wax,and then cut itin two. Hach segment re- 
mained luminous for about half an hour, the ight 
bemg about one-tenth the intensity of that pro- 
duced by a piece of phosphorus of the same size. 
M. Linnemann published another note in 1859 
(Journ. fiir prak. Chem., Ixxv.), upon the phos- 
phorence of potassium and sodium, showing that 
both these metals are luminons upon their freshly- 
cut surfaces. The hght emitted by potassium is of 
a reddish tint, that of sodium greenish, according 
to this author. At 60° or 7U° (centigrade), the 
light of sodium is quite as intense, if not more so, 
than that of phosphorus. I have had occasion to 
examine sodium whilst phosphorescent. Its light 
is very feeble at the ordinary temperature of the 
atmosphere, and ceases when the newly-exposed 
surfaces of the metal are covered with a layer of 
oxide (soda). The luminosity lasts for a few mi- 
D2 
