Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/103

104 the gas was driven from the mercury holder through one washing bottle containing strong aqueous potash and through two towers packed with lumps of caustic potash. The cyanogen mixtures were passed direct from the mercury holder into the explosion tube, the gases having been dried in preparation.

The explosion tube was, in most of the experiments, it leaden pipe, 100 metres long and 9 mm. in diameter. With some of the more violent explosives—e.g., cyanogen and acetylene, a leaden tube of 6.5 mm. was used; and in the chlorine experiments straight wrought-iron pipes lined with glass were employed.

The leaden tube was, in most cases, coiled on a drum, 2 feet in diameter, which was immersed in an iron vessel containing water. By heating the water and pumping dry air through the tube, the apparatus could be quickly dried after an explosion in which water was formed. For determinations of the rate of explosion of gases at 100° C. this arrangement was also suitable. Two inconveniences arose from this disposition of the pipe: (1) the difficulty of determining its exact length, and (2) the uncertainty whether the explosion-wave was propagated along the axis of the coiled pipe, or whether it followed a shorter path nearer to the inside wall.

It was found impossible to coil a small leaden pipe without lengthening it appreciably; the outside of the tube was therefore measured after each coil was wound on the drum, and the length of the axis of the pipe calculated. After a series of experiments the coils were then unwound, by rolling the drum along a corridor, and the length was measured directly. The length so obtained did not vary more than an inch, or at most two, from that calculated on winding.

To determine whether the flame was propagated centrally, or whether it took a shorter cut, measurements of the rate of explosion of samples of oxygen and hydrogen from the same mixture were made alternately, in a leaden pipe 9 mm. in diameter (1) coiled on the drum, and (2) lying straight on the floor. The experiments were thrice repeated, and no appreciable difference in the rate could be detected; from which it may be concluded that in a pipe of this bore the wave-front travels quickest along the axis. Possibly in the experiments with tubes of a larger diameter the curvature may have slightly affected the results.

In the experiments made under reduced pressure, the tube was filled from the holder in the ordinary way. The steel stopcock near the second bridge was closed, and the gas was then sucked from the tube by a powerful pump, maintaining a vacuum of about 26 inches of mercury. A gauge showed when the desired reduction of pressure was reached. The other stopcock was then closed, and the spark immediately passed. In the experiments made under increased pressure, the gases were driven into the tube from a strong reservoir, either by water or by mercury, according to the nature of the gaseous mixture. In all cases the gases were fired by an electric spark near one end