so Mr. Davy's Lecture on the Decomposition and Composition 
At a red heat, even the purest glass is altered by the basis 
of potash : the oxygene in the alkali of the glass seems to be 
divided between the two bases, the basis of potash and the 
alkaline basis in the glass, and oxides, in the first degree of 
oxygenation, are the result. When the basis of potash is 
heated in tubes made of plate glass filled with the vapour of 
naphtha, it first acts upon the small quantity of the oxides of 
cobalt and manganese in the interior surface of the glass, and 
a portion of alkali is formed. As the heat approaches to red- 
ness, it begins to rise in vapour, and condenses in the colder 
parts of the tube ; but at the point where the heat is strongest, 
a part of the vapour seems to penetrate the glass, rendering 
it of a deep red brown colour; and by repeatedly distilling 
and heating the substance in a close tube of this kind, it finally 
loses its metallic form, and a thick brown crust, which slowly 
decomposes water, and which combines with oxygene when 
exposed to air forming alkali, lines the interior of the tube, 
and in many parts is found penetrating through its substance.* 
In my first experiments on the distillation of the basis of 
potash, I had great difficulty in accounting for these pheno- 
mena ; but the knowledge of the substance it forms in its first 
degree of union with oxygene, afforded a satisfactory expla- 
nation. 
* This is the obvious explanation in the present state of our knowledge ; but it 
is more than probable that the silex of the glass likewise suffers some change, and 
probably decomposition. This subject I hope to be able to resume on another occa- 
$3 on. 
