For an easy and striking lecture experiment, I employ a tube open at both ends and bent like a W. The two open arms are short and the platinum wires are fixed at the highest bend. The tube is filled with hot mercury--one of the ends being closed by a caoutchouc stopper for the purpose--and a dry mixture of 5 volumes of air and 2 volumes of carbonic oxide is introduced into the bent tube over the mercury. A little phosphoric oxide is passed up one arm. After a few minutes the gases may be submitted to the spark without exploding. A little water may then be introduced through a pipette into the other arm; and if the spark is passed directly the gases ignite in the wet and not in the dry arm of the tube. The admixture of the inert nitrogen renders a larger quantity of aqueous vapor necessary for the explosion than when only carbonic oxide and oxygen in proper proportion are present.

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