The importance of the coal-dust question, and the interest that is now being taken in this subject, have induced the writer to place on record a number of experiments, with particulars of the method used to reduce the danger of coal-dust ; and it is hoped that the information given will be of interest to the members.

In the first place, a large number of experiments were made to ascertain the hygrometric condition of the seams, which are dry and dusty. In Table I. the observations on the leading district of one seam only are given, as the results tabulated are identical with those in all the districts and seams. These results have been plotted as a curve, and are shown in Fig. 1, the conditions, before spraying was resorted to, being also shown. The usual conditions prevailing in mines of this depth are as follows :— The temperature of the air-currents in their passage in-bye gradually approximate to the normal temperature of the mine, whether by a gradual increase, as in winter, or by a decrease, as in summer. The atmospheric conditions, both as regards temperature and moisture, have an important bearing on the conditions prevailing underground.

When air enters a mine at a low temperature, and in a dry state, with its corresponding great capacity for absorbing moisture, the coal-dust on the engine-planes is rendered very dry and sensitive. On the other hand, when the conditions are exactly reversed, the air-currents may actually deposit moisture, and thus make the coal-dust on the roadways damp.

The efforts of the writer have been directed by two considerations, namely, 1) the establishment of wet sections in various parts of the main intakes, with the hope that these may prevent the extension of an initial explosion; and (2) an attempt to bring the air-current into such a fully saturated condition as to prevent the desiccation of the coal-dust. As there is already in operation a system of watering by means of a hose-pipe, fed from water-pipes laid along the engine-planes, it was decided to make these service-pipes available for extended treatment by water.

After several trials of various types of sprayers, it was decided to use the Saint sprayer, and it has given entire satisfaction. The water is thrown off from these sprayers in such a comminuted form as to resemble a "Scotch mist," and thus thoroughly saturates the air. The pressure of water at these sprayers varies from 112 to 179 pounds per square inch, and each discharges from 170 to 260 gallons per day. The water is conveyed down the shaft from the service reservoir by means of pipes; and the above-mentioned pressures are obtained by the depth of the pit, which to the several seams varies from 400 to 500 feet. All this water is, of course, not absorbed by the air current; a large portion is deposited on the floor through the "wet sections," and arrangements must be made to convey it to the water-levels. In fact, the position of the sprayers will be determined to some extent by the facilities for getting rid of the surplus water.

Near the downcast shaft in each seam the first wet section is 300 feet in length, the remaining sections being 150 feet long. In each case either side brick-walls, with steel girders on the top, or brick-arching was erected for the length stated, so that the conditions were less favourable to the accumulation of dust; or advantage was taken of the position of stone drifts. At the intake entrance to each wet section (and repeated at the end of 150 feet in the 300-foot section) there are in operation several sprayers, varying from two to four, according to the sectional area of the airway. These are kept in continuous operation. The sprayers erected in the downcast shaft are shut off during coal-drawing hours, for the comfort of the workers at the shaft-bottom. In these wet sections there is absolutely no dry coal-dust, the whole of the exposed roadway being kept in a dripping condition. Figs. 2, 3, and 4 show the sprayers in one of the pits, and illustrate the method of erection under varying conditions. It is still necessary to continue the old arrangement of having the accumulated dust filled up and removed from the main roads. During coal-drawing hours much dust is brought down the shaft by the air-current from the screens, as well as that which is blown off the tubs in the cages. On the main roads the greatest amount of dust is deposited where the velocity of the air-current is greatest. The effect of these sprayers on the hygrometric condition of the air-currents is shown in Table I.

Before the sprayers were set to work, a length of intake road of about 1,500 feet was watered every night from the service-pipes laid along the engine-plane. During the day this water was absorbed by the air-current, as shown by the increase in the humidity. In fact, so far as the coal-dust was concerned, the effects of the watering ceased soon afterwards, when the incoming air was very dry. From the figures given in Table I., it is calculated that 1,373 gallons of water were absorbed per day on the route, or, say, 1 gallon per minute. The total quantity of water in the form of moisture brought out of the seam per day was 4,580 gallons, and nearly the whole of this water was absorbed by the air-current from the surface of the main intakes. On the same route the air-current passes through five sets of sprayers. In summer all these sprayers would probably not be required, although no alteration has been made.

As an example of the power of the sprayers, one of many such trials is here given. A set of four sprayers, acting on 36,000 cubic feet of air per minute, gave the following results :— Before entering the sprayers: thermometer, dry- and wet-bulb, 48° and 45° respectively; humidity, 79 per cent. ; after leaving the sprayers at a point 300 feet farther inbye : thermometer, dry- and wet-bulb, 46° and 45° respectively; humidity, 93 per cent.

Under the influence of a fully saturated air-current the condition of the coal-dust between the sections has undergone an advantageous change; and whilst the writer does not feel justified in saying that he has solved the coal-dust problem, he has the conviction that the coal-dust has been rendered to some extent less dangerous than under former conditions.

The timber in the main intakes soon shows signs of decay in the fully-saturated air, and in consequence it is being replaced by steel girders with brick pillars. The effect on the roof and sides has caused no inconvenience, and very little extra cost.