■q 6 Mr. Davy's Lecture on the Decomposition and Composition 
equal in size* was placed: the tube was small at one end, curved, 
#nd brought to a fine point, but suffered to remain open ; and 
the other end was fitted to a tube communicating with a 
gazometer, from which the oxygene gas was introduced, for 
neither water nor mercury could be used for filling the appa- 
ratus. The oxygene gas was carried through the tube till it 
was found that the whole of the common air was expelled. 
The degree of its purity was ascertained by suffering a small 
quantity to pass into the mercurial apparatus. The lower orifice 
was then hermetically sealed by a spirit lamp, and the upper 
part drawn out and finally closed, when the aperture was so 
small, as to render the temperature employed incapable of 
materially influencing the volume of the gas ; and when the 
whole arrangement was made, the combination was effected by 
applying heat to the glass in contact with the metallic tray. 
In performing these experiments many difficulties occurred. 
When the flame of the lamp was immediately brought to play 
upon the glass, the combustion was very vivid, so as sometimes 
to break the tube ; and the alkali generated partly rose in 
white fumes, which were deposited upon the glass. 
When the temperature was slowly raised, the bases of the 
alkalies acted upon the metallic tray and formed alloys, and 
in this state it was very difficult to combine them with their 
full proportion of oxygene ; and glass alone could not be 
employed on account of its decomposition by the alkaline 
bases ; and porcelain is so bad a conductor of heat, that it was 
* When the globules were very small, the comparison with mercury, which may be 
quickly made by means of a micrometer, was generally employed as the means of 
ascertaining the weight : for in this case the globule could be immediately introduced 
into the tube, and the weight of mercury ascertained at leisure. 
