^8 * Sir H. Davy on a new Substance 
substance enters into union in a quantity much more than twice 
as great as that of chlorine, and, considered as an element, it 
offers a number much higher than those of the simple inflam- 
mable bodies, and higher even than those of most of the 
metals. 
The most correct mode of ascertaining the number repre- 
senting the proportion (supposing it to be definite, as is the 
case with all other bodies that have been accurately examined) 
in which it combines, will probably be by ascertaining the 
specific gravity of its gaseous compound with hydrogen. This 
gas, as I have stated, affords only half its volume of hydro- 
gen, and it appeared to me to neutralize an equal volume of 
ammonia, so that supposing it to consist of two proportions 
of hydrogen, and only one of the substance, that is, to be 
analogous to muriatic acid gas in its nature, it must be one of 
the heaviest elastic fluids existing. 
Taking the number representing the proportion in which 
the new substance combines as 165, and supposing that it 
occupies the same volume in this gas that chlorine occupies in 
muriatic acid gas, 100 cubical inches of the gas will weigh at 
mean temperature and pressure 95.27 grains, i, e, supposing 
hydrogen in the same quantity to weigh 2.27 grains. 
l am not at present in possession of an apparatus for weigh- 
ing the gas with accuracy. A particular device will be required 
for this purpose, as the gas cannot be preserved over mer- 
cury. It may be collected during the action of phosphorus on 
the moistened substance in a vessel exhausted of air; or it 
may be made by heating the compound of the substance and 
potassium in muriatic acid gas in a glass vessel : in this case, 
there is, I find, a double decomposition, the chlorine quits the 
