53 
Sir H. Davy’s researches on flame. 
elusions, and proves that hydrogene stands at the head of the 
scale, and gaseous oxide of carbon at the bottom. It might 
at first view be imagined that, according to this scale, the 
flame of carbonic oxide ought to be extinguished by rare- 
faction, at the same degree as that of carburetted hydrogene ; 
but it must be remembered, as I have mentioned in another 
place, that carbonic oxide is a much more combustible gas. 
Carbonic oxide inflames in the atmosphere when brought into 
contact with an iron wire heated to dull redness, whereas 
carburetted hydrogene is not inflammable by a similar wire, 
unless it is heated to whiteness so as to burn with sparks. 
II. On the effects of rarefaction by heat on combustion and 
explosion.. 
The results detailed in the preceding section are indirectly 
opposed to the opinion of M. de Grotthus, that rarefaction by- 
heaPdestroys the combustibility of gaseous mixtures. Before 
I made any direct experiments on this subject, I endeavoured 
to ascertain the degree of expansion which can be commu- 
nicated to elastic fluids by the strongest heat' that can be 
applied to glass vessels. For this purpose I introduced into a 
graduated curved glass tube some fusible metal. I heated 
the fusible metal and the portion of the tube containing the 
air included by it, under boiling water for some time. I then 
placed the apparatus in a charcoal fire, and very gradually 
raised the temperature till the fusible metal appeared luminous 
when viewed in the shade. At this time the air had expand- 
ed so as to occupy 2.25 parts in the tube, it being 1 at the 
temperature of boiling water. Another experiment was made 
in a thicker glass tube, and the heat was raised until the tube 
