150 Mr. J. Davy on a gaseous Compound 
the mercury will take place, and in less than a minute the 
colour of the chlorine will be destroyed, and in about ten 
minutes the condensation will have ceased, and the combina- 
tion of the two gasses will be complete. 
It is requisite that the gasses should be dried for forming 
this compound ; if this precaution is neglected, the new gas 
will be far from pure ; it will contain a considerable admixture 
of the carbonic and muriatic acid gasses, which are produced 
in consequence of the decomposition of hygrometrical water. 
Indeed there is considerable difficulty in procuring the new 
gas tolerably pure ; a good air pump is required, and perfectly 
tight stop-cocks, and dry gasses, and dry vessels. 
I have endeavoured to procure the gas, by passing a mix- 
ture of carbonic oxide and chlorine through an earthen-ware 
tube heated to redness ; but without success. 
The specific gravity of the gas may be inferred from the 
specific gravities of its constituent parts jointly with the 
condensation that takes place at their union. According' to 
Cruickshank, 100 cubic inches of carbonic oxide weigh 2 9,6 
grains, and according to Sir Humphry Davy, 100 of chlorine 
are equal to 76,37 grains : hence as equal volumes of these 
gasses combine, and become so condensed as to occupy only 
half the space they before filled, it follows that 100 cubic 
inches of the new compound gas are equal to 105,97 grains. 
Thus this gas exceeds most others as much in its density as it 
does in its saturating power. 
To ascertain whether chlorine has a stronger affinity for 
hydrogene than for carbonic oxide, I exposed a mixture of the 
three gasses in equal volumes to light. Both the new com- 
pound and muriatic acid gas were formed, and the affinities 
