January 16, 1911. THE COLLIERY GUARDIAN. 135 (30 gallons) respectively, being mounted a short distance from the roof in such a manner as to expose their longer sides to the force of the explosion. They were supported on two longitudinal beams, the ends of which nearest the explosion chamber were mounted on an iron rod held by a sheet-iron screen bent round at the lower Fig. 6.—Water-trough for Barrier. edge in the shape of a hook. The pressure wave pre- ceding the flame deflects the screen and deprives the rod of its support, so that the beams and troughs tip over. The whole arrangement is on the mouse-trap principle, and is illustrated in fig. 6. The. troughs are Results. The figs. 7-13 illustrate the results of the experiments with doors. Experiment No. 697 (fig. 7).—The coal dust used was that from Dombrau, and contained :—Moisture 2'4 per cent., ash 14'1 per cent., volatile matter 27’4 per cent. Residue on 1,160-mesh sieve, 3’6 per cent. ; on 3,480- mesh sieve, 13*6 per cent. The door marked A was of 3 in. slabs, faced both sides with in. sheet iron, door B being of 2 in. slabs, with bi. sheet iron on one side- The explosives in both chambers were fired in the open gallery. A powerful explosion resulted, but no flame appeared between the doors, though it penetrated for a length of 6 m. in the blind end. The doors were uninjured, but the dust racks were shattered and hurled to a distance of 140 m. Both doors in the gallery were closed, and the indicator was set up at 55 m. Experiment No. 701 (fig. 8).—Dust from Liebe Gottes pit, Zbeschau (analysis and fineness not stated). Doors same as in fig. 7. Explosives fired in open gallery. Both doors in gallery closed, that in the by-pass being left open. Indicator set up at 90 m. In door A the lower outside crosspiece was broken. Experiment No. 704 (fig. 9). Dust from Julius shaft, containing :—Ash 15T per cent., moisture 0‘9 per cent., dynamite was fired in the open gallery, the black powder in mortars. Explosion very powerful. One of the posts of door A was driven in, and door B was torn from its hinges and broken through in the upper part on both sides, the flame passing through the damaged door. Experiment No. 740 (fig. 13).—Dust from Julius shaft. Door A of three 1 in. boards ; B of two 1J in. boards; C of 2 in. board ; and D of three 1 in. boards. AH doors closed. Dynamite fired in the open gallery, black powder in mortars. The doors checked the explosion completely. Figs. 14-16 illustrate the results of the experiments with concentrated water barriers. Experiment No. 747 (fig. 14).—Dust from Julius shaft. Three long wooden troughs holding 36 litres (8 gallons) of water each, arranged on each side of the gallery at 96 m. The dynamite was exploded in the open gallery, the black powder in mortars. The explosion left the troughs uninjured, only the two lower ones on one side being overturned and emptied, the others remaining full of water. Experiment No. 750 (fig. 15).—Dombrau dust con- taining : Ash 16*5 per cent., moisture 1’2 per cent., volatile matter 25'2 per cent. Residue on coarse sieve, 1’2 per EXPERIMENT 637 FIG 7 J ooorA: 'door B ! ; I COALDUST "zone. l'eo rn 54 kg COAL DUST ’ ___________________________________J Z LENGTH OF- FLAME (30 tri EXPERIMENT 701 FIG 8 spz—1----- -------- j DOOR A 'door B 1 [ I COALOUST ZONE ISO m. 5-4 kg COALDUST I L--------------------------------J LENGTH OF FLAME 14-Om. EXPERIMENT 704- FlG 3 Experiment soog. blackpowder ------------r BARPlEP } COALDUST -ZONE___2oQ m 68 kg coaldust EX PE RIME N T (Soo g. Black P'orx iq 3oo g. dynamiters DOOR A • OOO R B ; INDICATOR^,' 'DOOR D ! door C _______<5oo g.Black pdr ■COALOUST zone’ 5SrrJSC>O9Ovr