IN GASES: HYDROGEN, CARBONIC OXIDE, AND OXYGEN. 
635 
Mention has been made of the slowness with which the flame travels down the 
explosion tube when a mixture of carbonic oxide and oxygen in a state of comparative 
dryness is ignited. To obtain some idea of the rate of propagation of explosion under 
these conditions, some of the mixture of carbonic oxide and oxygen was brought into 
the well-dried eudiometer of the gas apparatus. A loud-beating seconds’ pendulum 
was set going close by, and a spark sent from the coil as a second struck. By 
watching at the level of the mercury below and listening to the beats of the pen¬ 
dulum, the passage of the flame could be roughly timed. Beginning at 260 millims., 
the pressure was raised 20 millims. between each passage of the spark. The gases 
withstood 480 millims. pressure without igniting; at 500 millims. pressure they 
ignited. The flame was timed to pass down the 360 millims. between the wires and 
the surface of the mercury in 2^ seconds. The eudiometer was re-charged, a drop of 
water passed over and the gases fired under 500 millims. pressure. The passage of 
the flame appeared instantaneous. 
An attempt was made to measure the effect of different quantities of steam on the 
rate of propagation of the explosion. This was done by comparing the pressures 
produced in the tube when equal masses of carbonic oxide and oxygen were succes¬ 
sively exploded, at the same temperature and pressure with different amounts of 
aqueous vapour. Since the total quantity of heat evolved in each explosion was the 
same, and the cooling surface was the same in each experiment, a quicker explosion 
would bring the column of gases to a higher average temperature than a slower 
explosion, and would therefore cause a sharper push on the mercury column. If a 
sufficiently sensitive gauge were attached to the eudiometer, its readings would give 
comparative indications of the rate of explosion of the carbonic oxide and oxygen. 
Near the bottom of the eudiometer in which the gases were exploded, a self-registering 
pressure gauge was attached by a strong glass tube. The gauge (of 1 millim. bore) 
contained air in the closed limb over mercury. An index, similar to those used in 
Six’s thermometer, was carried up and left at the highest position reached by the 
mercury. Near the bend of the gauge two bulbs were blown in the tube as reservoirs, 
enabling the mercury to be lowered in the eudiometer without permitting the air to 
escape from the closed limb of the gauge. This gauge was found to be not very sen¬ 
sitive, but the difference between its readings (1) with the slow combustion of the 
nearly dry gases, and (2) with the rapid explosion of the gases saturated with steam, 
was well marked. 
In two experiments a trace only of aqueous vapour was present. The eudiometer 
was dried at 80° C., by drawing through it for half an hour air which had passed 
through two long sulphuric-acid drying tubes and a small tube containing phosphoric 
oxide. It was found that by this method of drying just sufficient aqueous vapour 
remained in the tube to enable the combustion to take place slowly when sparks from 
a Buhmkorff’s coil were passed through the gases. In the first experiment several 
sparks were passed before the gases took fire. In both experiments the disc of flame 
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