8 
Mr. Davy’s Experiments on the 
When potassium and sodium are burnt in oxygene gas 
upon platina, and heated to redness to decompose the per- 
oxide of potassium, the alkalies are of a grayish green colour. 
They are harder than common potash or soda, and, as well as 
I could determine by an imperfect trial, of greater specific 
gravity. They require a strong red heat for their perfect 
fluidity, and evaporate slowly, by a still further increase of 
temperature. When small quantities of water are added to 
them, they heat violently, become white, and are converted 
into hydrats, and then are easily fusible and volatile. 
When potassium or sodium is burnt on glass, freed from 
metallic oxides, and strongly heated, or when potash or soda 
is formed from the metals by the action of a minute quantity of 
water, their colour approaches to white ; but in other sensible 
properties, they resemble the alkalies formed upon metallic sub- 
stances ; and are distinguished in a marked manner by their 
difficult fusibility from the potash and soda prepared by alcohol. 
M. D’Arcet, and more distinctly M. Berthollet, have 
concluded that the loss of weight of common fused potash and 
soda, during their combination with acids, depends upon the 
expulsion of w r ater, which M. Berthollet has rated at 13.9 
per cent, for potash, and M. D’Arcet, at 37 or 28 for potash, 
and 28 or 29 for soda.* 
I have stated in the last Bakerian Lecture, that my own 
results led me to conclude, that fused potash contained about 
16 or 17 parts in the 100 of w'ater, taking the potash formed, 
by adding oxygene to potassium as a standard. 
The experiment from which I drew my conclusions, was 
made on the action of silex and potash fused together, and 
* Annales de Chimie, tom. 68, page igo. 
