A temperature of over 200° C. can be easily obtained with an ordinary Argand flame and maintained fairly constant. When a thermometer was placed inside as well as one outside the drying tube, it was found that the temperatures only differed by a few degrees when a water pump was drawing air through the system at the rate of about 8 liters per hour. If this bath is protected from draught, any temperature can be maintained within a few degrees easily.—Journal of the Society of Chemical Industry.
FIREDAMP TESTING STATION AT MARCHIENNE-AU-PONT.[1]
In a previous paper[2] a description was given of the experimental gallery at the St. William pit of the Kaiser-Ferdinands-Nordbahn Colliery at Mahrisch-Ostrau (Moravia). In the present article a similar experimental station, designed for the same purpose, but presenting certain considerable advantages on the score of economy by reason of the moderate expense of its installation, will be described.
Some few years ago the Société des Explosifs Favier obtained permission from the proprietors of the Marchienne-au-Pont, near Charleroi, Belgium, to construct there an experimental station for testing the explosives manufactured by the company. Though of but modest proportions, this station is well designed, and many valuable researches and tests have been made on the explosives used in the fiery pits of Belgium, thanks to which investigations one is able to readily determine in a practical manner the degree of security offered by any explosive intended for use in pits containing coal-dust in suspension or firedamp.
In order to avoid the expense of constructing a large gallery above ground, recourse was had to the cylindrical shell of a disused boiler of large dimensions—some 5 m. in length by 1½ m. internal diameter—one end of which was taken out, and the shell made to do duty for a testing gallery. With this object it was mounted on two settings of brickwork (Fig. 2), and the further end backed by a brick wall of very substantial construction, being 1½ m. thick and 2 m. in height, and forming the base of a high bank of earth. The boiler, as may be seen in Figs. 1 and 2, was let into the ground a little, in order that in case of an explosion there might be less chance of the debris being projected to a distance. On one side the boiler was pierced by six rectangular openings 20 cm. in height fitted with thick glass panes in caoutchouc frames, to prevent their becoming fractured by the aerial vibrations resulting from explosions. These windows enable the operators to observe the phenomena occurring within the chamber at the moment the explosion is produced. At the top of the boiler, two circular apertures, each 50 cm. diameter, were made for the purpose of acting as safety valves. By means of two rabbets, one fixed at the open end of the gallery and the other in the center, the testing chamber could be made either large or small by means of paper disks pasted on to the first or second rabbet. The capacity of the large chamber was double that of the smaller one, and the cubical area of each was known beforehand.
In the backing wall was fitted a large mortar of cast steel, which in carrying out the tests served to replace the borehole used in actual mining operations. A pipe for conveying the gas and another for steam were laid on the floor of the chamber, the latter for heating purposes, in order to ascertain whether, in certain cases, an increase in temperature exerts any sensible influence on the inflammability of the explosive mixture. The temperature of the chamber is read off from a thermometer placed at the top of the boiler, its position being indicated by T in Fig. 2.
In view of the possibility of the boiler, notwithstanding its strength, bursting, in the event of a violent explosion of the gas, it became necessary to make special arrangements for allowing the operators to observe everything occurring in the testing chamber without being themselves exposed to the consequences of any accident that might ensue. A special shelter was, therefore, erected for occupation by the operators at the moment of the explosion. This shelter, at about a dozen yards away from the boiler, consisted of a chamber protected on the side next the gallery by a stout bank of earth, in which a longitudinal aperture was provided (by means of a lining of boards) at about the height of the face, through which the operators could observe the progress of the tests, without danger. It may be stated, however, that hitherto no accident has occurred, the boiler effectually resisting the force of the explosions. The chamber of shelter likewise contained the gasometer for regulating the supply of gas to the testing apparatus, and the electrical machine for firing the cartridges under test.
There being no continuous current of firedamp at disposal, use was made of illuminating gas in preparing the explosive mixtures for the tests. The borehole is charged with the explosive to be fired, and the temperature is regulated by means of the steam pipe. The entrance of the chamber and the two safety apertures in the roof having been closed by disks of paper fastened by paste, the gas is turned on until the desired percentage, has been introduced; the mixture of the air and gas takes merely a short time to effect by diffusion, the difference in density causing the gas to rise on issuing from the jet, which is on the floor of the chamber. The detonating cap is then ignited by the passage of the electric current and the shot fired. The operator, placed in his shelter, can observe, by means of the small lateral windows, whether any flame is produced, and indeed, a little experience will enable him to determine by the sound alone, whether an explosion has ignited the mixture or not.