Lives of the Engineers / The Locomotive. George and Robert Stephenson

by Samuel Smiles

Arrived at the bottom of the shaft with the lamp, the party directed their steps towards one of the foulest galleries in the pit, where the explosive gas was issuing through a blower in the roof of the mine with a loud hissing noise. By erecting some deal boarding round that part of the gallery into which the gas was escaping, the air was made more foul for the purpose of the experiment. After waiting about an hour, Moodie, whose practical experience of fire-damp in pits was greater than that of either Stephenson or Wood, was requested to go into the place which had thus been made foul; and, having done so, he returned, and told them that the smell of the air was such, that if a lighted candle were now introduced, an explosion must inevitably take place. He cautioned Stephenson as to the danger both to themselves and to the pit, if the gas took fire. But Stephenson declared his confidence in the safety of his lamp, and, having lit the wick, he boldly proceeded with it towards the explosive air. The others, more timid and doubtful, hung back when they came within hearing of the blower; and apprehensive of the danger, they retired into a safe place, out of sight of the lamp, which gradually disappeared with its bearer in the recesses of the mine. [95]

Advancing to the place of danger, and entering within the fouled air, his lighted lamp in hand, Stephenson held it finally out, in the full current of the blower, and within a few inches of its mouth. Thus exposed, the flame of the lamp at first increased, then flickered, and then went out; but there was no explosion of the gas. Returning to his companions, who were still at a distance, he told them what had occurred. Having now acquired somewhat more confidence, they advanced with him to a point from which they could observe him repeat his experiment, but still at a safe distance. They saw that

when the lighted lamp was held within the explosive mixture, there was a great flame; the lamp became almost full of fire; and then it smothered out. Again returning to his companions, he relighted the lamp, and repeated the experiment several times with the same result. At length Wood and Moodie ventured to advance close to the fouled part of the pit; and, in making some of the later trials, Mr. Wood himself held up the lighted lamp to the blower.

Before leaving the pit, Stephenson expressed his opinion that by an alteration of the lamp which he then contemplated, he could make it burn better; this was by a change in the slide through which the air was admitted into the lower part, under the flame. After making some experiments on the air collected at the blower, by bladders which were mounted with tubes of various diameters, he satisfied himself that, when the tube was reduced to a certain diameter, the foul air would not pass through; and he fashioned his slide accordingly, reducing the diameter of the tube until he conceived it was quite safe. In about a fortnight the experiments were repeated, in a place purposely made foul as before; on this occasion a larger number of persons ventured to witness them, and they again proved successful. The lamp was not yet, however, so efficient as the inventor desired. It required, he observed, to be kept very steady when burning in the inflammable gas, otherwise it was liable to go out, in consequence, as he imagined, of the contact of the burnt air (as he then called it), or azotic gas, which lodged round the exterior of the flame. If the lamp was moved horizontally, the azote came in contact with the flame and extinguished it. “It struck me,” said he, “that if I put more tubes in, I should discharge the poisonous matter that hung round the flame, by admitting the air to its exterior part.” Although he had then no access to scientific books, nor intercourse with scientific men, nor anything that could assist him in his investigation, besides his own indefatigable spirit of inquiry, he contrived a rude apparatus by which he tested the explosive properties of the gas and

the velocity of current (for this was the direction of his inquiries) necessary to enable the explosive gas to pass through tubes of different diameters. In making these experiments in his humble cottage at the West Moor, Nicholas Wood and George’s son Robert usually acted as his assistants, and sometimes the gentlemen of the neighbourhood interested in coal-mining attended as spectators.

These experiments were not performed without risk, for on one occasion the experimenting party had nearly blown off the roof of the cottage. One of these “blows up” was described by Stephenson himself before the Committee on Accidents in Coal Mines, in 1835: “I made several experiments,” said he, “as to the velocity required in tubes of different diameters, to prevent explosion from fire-damp. We made the mixtures in all proportions of light carburetted hydrogen with atmospheric air in the receiver, and we found by the experiments that when a current of the most explosive mixture that we could make was forced up a tube 4/10 of an inch in diameter, the necessary current was 9 inches in a second to prevent its coming down that tube. These experiments were repeated several times. We had two or three blows up in making the experiments, by the flame getting down into the receiver, though we had a piece of very fine wire-gauze put at the bottom of the pipe, between the receiver and the pipe through which we were forcing the current. In one of these experiments I was watching the flame in the tube, my son was taking the vibrations of the pendulum of the clock, and Mr. Wood was attending to give me the column of water as I called for it, to keep the current up to a certain point. As I saw the flame descending in the tube I called for more water, and Wood unfortunately turned the cock the wrong way, the current ceased, the flame went down the tube, and all our implements were blown to pieces, which at the time we were not very able to replace.”

Stephenson followed up those experiments by others of a similar kind, with the view of ascertaining whether

ordinary flame would pass through tubes of a small diameter and with this object he filed off the barrels of several small keys. Placing these together, he held them perpendicularly over a strong flame, and ascertained that it did not pass upward. This was a further proof to him of the soundness of the course he was pursuing.

In order to correct the defect of his first lamp he resolved to alter it so as to admit the air to the flame by several tubes of reduced diameter, instead of by a single tube. He inferred that a sufficient quantity of air would thus be introduced into the lamp for the purposes of combustion, while the smallness of the apertures would still prevent the explosive gas passing downwards, at the same time that the “burnt air” (the cause, in his opinion, of the lamp going out) would be more effectually dislodged. He accordingly took the lamp to a tinman in Newcastle, and had it altered so that the air was admitted by three small tubes inserted in the bottom of the lamp, the openings of which were placed on the outside of the burner, instead of having (as in the original lamp) the one tube opening directly under the flame.

This second or altered lamp was tried in the Killingworth pit on the 4th November, and was found to burn better than the first, and to be perfectly safe. But as it did not yet come quite up to the inventor’s expectations, he proceeded to contrive a third lamp, in which he proposed to surround the oil vessel with a number of capillary tubes. Then it struck him, that if he cut off the middle of the tubes, or made holes in metal plates, placed at a distance from each other, equal to the length of the tubes, the air would get in better, and the effect in preventing explosion would be the same.