3 i4 EXPERIMENTAL INVESTIGATIONS. 



but the probability is that a slight quantity also exists in it. 

 Whether the oxygen proceeds from portions of air still 

 remaining in solution in the liquid from which the air is 

 exhausted, or whether it is a part of the water actually decom- 

 posed, but of which the oxygen is not absorbed by the zinc, 

 is a question to resolve which farther experiments are neces- 

 sary. 



Hydrogen and carbonic acid mixed in equal volumes were 

 readily acted on by the ignited wire ; they contracted to 0*48 

 of the original volume ; the residue was carbonic oxide ; one 

 equivalent of oxygen had therefore united with the hydrogen ; 

 and the slight additional contraction was probably due to 

 the farther combination of hydrogen with oxygen as above 

 stated. 



Carbonic oxide exhibited a remarkable effect, and one 

 which, coupled with the last experiment, -gave rise to con- 

 siderations which mainly led to the results to be detailed in 

 the body of this paper. Carbonic oxide, very pure and care- 

 fully freed from carbonic acid, was exposed to the ignited 

 wire over distilled water ; the gas increased in volume in one 

 experiment to one-third of its original volume, in the greater 

 number of instances to one-fifth : this increase depended upon 

 the intensity of ignition, which it was very difficult to main- 

 tain at its maximum on account of the frequent fusions of 

 the platinum wires. 



Here again I hacj a long research and many erroneous 

 guesses, which I need not detail. The effect did not take 

 place with perfectly dry gas over mercury, and I thence was 

 led to attribute it to some combination with aqueous vapour ; 

 the increase turned out to be occasioned by the formation of 

 carbonic acid. By agitation with caustic potash or lime-water 

 the gas was reduced to exactly its original bulk, but it was 

 now found to be mixed with a volume of hydrogen equal to 

 the volume of carbonic acid by which it had been increased ; 

 it was thus perfectly clear that half a volume or one equivalent 

 of oxygen derived from the vapour of the water, had combined 

 with one volume or equivalent of carbonic oxide, and formed 

 one volume or equivalent of carbonic acid, leaving in place of 

 the carbonic oxide with which it had combined the one 



