C.—4

5

Some attention is devoted to the subject of illuminants, the danger being noted of using the very volatile derivative of petroleum called " colzaline," the vapour of which forms with air an explosivo mixture. As, however, this illuminant is not employed in the colony, it is unnecessary to give the remarks in extenso. The Commissioners note that they have made experiments with over 250 lamps ; but, as only four are recommended for use, it will not be necessary to describe the rest. The " tin-can Davy " or common Davy lamp, surrounded by a case or can provided with a glass window, or constructed partially of glass, is highly commended in the report, which states that the addition " converts the Davy lamp, from one of the most dangerous, into one of the safest of the lamps in common use. The result of our earlier experiments," continues the report, " made it more generally known that the Davy and Clanny lamps, and, under special circumstances, the Mueseler lamp, are almost certain to cause an explosion when placed in a current of air sufficiently charged with firedamp, even if the velocity of the current is only from 6ft. to 10ft. per second," while no explosion is caused at a much higher velocity by a cased Davy. It may be useful, as giving an idea of how the testing of safety-lamps was carried out, to describe shortly the apparatus used by the Commission in conducting their very complete experiments. A wooden box, 20ft. long, and measuring 13'75in. by lOin. in section, was fixed with its sides horizontal and vertical. Near one end is an opening in the sides communicating with a small wooden chamber, on the top of which is placed an iron cylinder containing a nozzle (a Kortings blower), by which a jet of steam issues from a large boiler, and escapes by a trumpet-shaped opening into the air. This steam-blast, on the principle of an injector, causes a steady current of air to pass along the box from the open end towards the steam-jet, and by experiment any required velocity of current was found to be attainable. Thus, with an adjustable tap, an explosive current of any desired composition could be directed at any required velocity against the lamp under trial. Windows were also inserted into the box, so that the behaviour of the lamps under various conditions could be carefully noted. In some cases the conditions were varied so that the lamps weie inclined at a measured angle to the horizon; and in others screens were inserted in the box so that the explosive mixture impinged on the gauze at various angles; and in other cases the lamps were exposed to ascending or descending currents. "With this apparatus an enormou3 number of experiments were carried out and recorded. In view of the number of Davy lamps existing in this colony, the following decision of the Commission becomes very interesting : "It will be seen that in an explosive current with the very moderate velocity of 400ft. per minute the ordinary Davy lamp ceases to afford protection for more than a few seconds, unless the diameter of the gauze is very small The Davy lamp enclosed in a case of any form which completely shields the gauze from the direct action of the current may apparently be trusted in currents not exceeding in velocity 2,000ft. per minute, but for higher velocities the greatest care is necessary in designing the case and its relations to the enclosed lamp." The common Clanny lamp is found to offer very little more security than the Davy lamp, and is almost certain to ignite an explosive mixture in a velocity of 600ft. per minute ; it was found by experiment that if the percentage of marsh gas in the atmosphere bo reduced to 4-25 or thereabouts, Clanny lamps are extinguished, while Davy lamps are still liable to cause explosion. Like the Davy, the Clanny lamp is rendered much more safe when the gauze is protected from the direct action of the current by an external metal jacket or bonnet; and lamps thus protected did not appear dangerous in velocities of 1,500ft. per minute, or oven 1,900ft. per minute, but tin explosion was produced by a velocity of 2,857ft. per minute. The four lamps which are considered by the Commission to combine the quality of safety in a pre-eminent degree with simplicity of construction, and with illuminating power at least equal to that of any of the lamps at present in general use, are—(l) Gray's lamp, (2) Marsaut's lamp, (3) Evan Thomas's (No. 7) lamp, (4) the bonneted Mueseler lamp. In Gray's lamp (see C, Appendix I.) the air to feed the flame is brought down from near the top of the lamp by four tubes communicating with a small annular chamber surrounding a cylindrical strip of gauze under the glass. The exit-tube or chimney terminates at its upper end in a short cone, which is closed by a gauze diaphragm, having an area about double that of the section of the chimney. It is covered by a dome, through large perforations in which the products of combustion mainly escape. This lamp has a flat wick. The flame is not much affected by swinging the lamp through considerable angles, or by rapid motion up and down in a vertical direction. Three modifications of Gray's lamp have been tried: in the first, a horizontal gauze ring, extending from the neck of the oil-cup to the flange under the glass, has been added ; the second modification differs from the first only in the omission of the cylindrical strip of gauze which protects the inlet to the original Gray's lamp ; the third modification was merely experimental. In Marsaut's lamp (see B, Appendix I.), which is of the bonneted Clanny type, the inventor has taken an additional step in the direction of safety by the introduction of three gauzes in place of the single gauze cap of the ordinary Clanny. With these safeguards, the, lamp has not exploded in any current which could be produced. The illuminating-power also is good, being equal (with three gauzes) to about half a standard candle. Another bonneted Clanny lamp, the invention of Mr. Evan Thomas, is said to be, on the whole, the most satisfactory lamp tested by the Commissioners. (See A, Appendix I.) The following is a description : Inside the bonnet a brass tube lin. high fits the main gauze cylinder closely. To the upper end'of this tube is attached a horizontal brass flange extending nearly to the bonnet, so that an annular space only J & in. wide is left between the edge of the flange and the bonnet. The air, having entered the bomiet through horizontal slits near its lower end, passes through this annular space into the gauze cylinder and descends to the flame. The products of combustion escape through holes near the top of the bonnet, which are protected by a