C.—2

48

In the report of the U.S. Bureau of Mines, 1.916, it is stated that investigations have shown that in one case it was found that, a mixture of 77 per cent, of pulverized Pittsburgh coal and 23 per cent, of water (not including the water of composition in the coal) gave a very strong propagation in the experimental mine. In the Sixth Report, of the (British) Explosives in Mines Committee, 1914, page 6, it is stated that "From, the American experiments which were made with artificially prepared dust from a bituminous coal containing about, 35 per cent, of volatile matter and about 5 per cent, of ash, it was concluded that the total moisture-content of the dust must approach 30 per cent, to ensure that it should be incapable of propagating flame. We have repeated these experiments, using not only coaldust containing merely its natural ash, but mixtures of coal and in combustible dust, and have determined quantities of water that it was necessary to mix intimately (by atomizer) with the dust in order to render them incapable of ignition by a stemmed charge of 24 oz. of blasting-powder. Our results are in accordance with those obtained in America." Explosives. —There has been little or no shortage of Imperial-permitted explosives during the year. On the Grey Coalfield there have been numerous complaints that cartridges other than those in which the detonator is inserted have failed to detonate, in. one instance a, consignment of permitted explosive from a well-known British manufactory which cost ,£1,250 was destroyed owing to the above defect. In other parts of the Dominion permitted explosive gave satisfaction. At the Taupiri Extended_ Colliery during the year 35,783 shots, containing 30,4811b. of Viking Powder or Cambrite, were fired, 'and in no case where the detonator exploded did the charge inissfire. ft is therefore reasonable to conclude that either the atmospheric conditions on the West Coast, or the transport thereto from the chief ports, is responsible for the defective condition of the explosive, some of the ingredients of which, such as nitrate of ammonium, sodium nitrate, or chloride of sodium, are exceedingly hydroscopic. In addition to more careful transport, handling, and storage, it appears advisable, that the ends of the cartridges for use in New Zealand shall be completely closed by dipping in wax before they leave the manufactory. It was found at the Dominion Laboratory, where numerous tests were carried out by the Chief Inspector of Explosives, that, the ends of defective cartridges were frequently insufficiently closed by their waxed cartels. Support of Roof and Sides. —There has been considerable improvement in the observance of the regulations as regards systematic timbering, and. to this must be credited the reduction in the number of accidents by falls—the most prolific cause of mining accidents throughout the world. The importance of a thorough observance of systematic timbering cannot be overestimated or too frequently instilled into miners and deputies. I generally find that where there has been failure in this respect the timber is available in the working-place, but the miners have delayed putting it up after firing until they have " filled their coal," or were " just going to put it up " when I came along. The workmen's inspectors in their reports after inspection, which are otherwise fair, seldom or never refer to failure by workmen to erect timber as required, and I will be glad if they will do so in future. Supply of Materials. —The supply of material produced in the Dominion has been equal to the demand at no considerable increase in cost, but new material manufactured abroad, except, explosives, has been practically unobtainable, such items as steel ropes, rails, tubs, wheels, axles, and electrical supplies being offered only at prohibitive prices. As a result shortages have been made good from installations at inoperative mines and works. Bathhouses. —ln accordance with the provisions of the Coal-mines Act, mine-owners have erected or are erecting bathhouses at such mines where by a vote of the workmen they are desired. The first colliery bathhouses were erected at the State collieries near Greymouth, from a design by Mr. I. A. James, the chief mine-manager; these proving a success, the design has been followed at the principal mines. The building consists of a changing-room with parallel rows of seats, above which clothing is elevated by cords and pulleys, where they are suspended and dried by heat from steam-pipes. Hot and cold showers, also fixed hand-basins, are contained in cabinets built as lean-tos of the changing-house, from which they are entered. The concrete floor is graded and drained, the floor-space in the change-room being not, less than 12 square feet for each person. The bathhouses in use have proved an unqualified success, and are very popular with the miners. At some mines they are made use of by more persons than voted for their erection. In all cases bathhouses are erected and maintained at the expense of the mine-owners. Electricity at Collieries. —During 1917 there has been practically no increase in the number or capacity of electrical installations. The following is a summary of the annual returns in accordance, with Regulation 160 (c) regarding electrical apparatus at collieries : — Number of collieries at which electrical apparatus is installed ... 13 continuous-current installations ... ... ... 10 ~ alternating-current installations ... ... ... 2 ~ collieries electrically lighted ... ... ... ... 12 ~ collieries using electrical ventilating-machines ... ... 7 ~ ~ pumping plants ... ... 5 ~ ~ haulage plants ... ... 7 ~ screening plants ... ... 2 ~ ~ miscellaneous plants ... ... 3 ~ ~ locomotives ... ... ... 1 Total horse-power employed from motors on surface ... ... ... 1,740 ~ ~ underground ... ... 671 I have, &c,, Frank Reko, Inspecting Engineer and Chief Inspector of Mines,