812 THE COLLIERY GUARDIAN. Apbil 18, 1913. paraffins than is indicated by the analyses given above. No hydrogen was found in any sample analysed. We give, in Appendix II. to this report, methods of collecting gas-samples, and a method of analysing them. Differences of opinion, we are aware, exist as to methods of analysis of firedamp; the method in the Appendix is that which has been followed in the laboratory at Eskmeals. (2 ) The Influence of Incombustible Dusts in Suspension upon the Inflammation of Gaseous Mixtures. The question to be considered owes its importance to the proposal to use stone or other inert dust as a means of preventing the ignition of coaldust. It has arisen from an opinion expressed by the late Sir Frederick Abel* that he had proved experimentally that the presence of certain inert dusts in suspension renders inflammable mixtures of firedamp and air otherwise ■unin flammable. The importance of this opinion of course lies in the fact that, if it were correct, the causing inert dusts to mix with the air of a mine, though it might mitigate the danger of coaldust, would increase the danger of gas explosions. The idea that inert dusts might influence the explosion of weak mixtures of gas and air was first put forward during the enquiry which followed the Seaham explosion in September 1880. In consequence of testimony which seemed to render it probable that the presence of coal- dust had influenced the explosion, Mr. R. S. Wright suggested that Prof. Abel should experiment with a view to determining whether the ash-content of samples of dust taken from the mine indicated that coaldust suspended in the air had been burned. At that time it was not generally believed that coal- dust played any part in mine explosions, but Abel’s experiments, though they failed to convince him that coaldust alone could cause an explosion, proved that coaldust suspended in air containing very small propor- tions of firedamp, could propagate flame—a fact already established by Galloway. As a result of his experiments Abel was led to try to find out whether it was the carbonaceous nature of the coaldust that rendered the mixture of gas and air explosive, or whether non-combustible dusts possessed the same power. The apparatus used by Abel was similar to that employed by Galloway in his well-known experiments. The gallery or channel (1 ft. length of which had a capacity of about 1 cubic foot) was 28 ft. in length measured from the hopper or drum-sieve, used for delivering the dust, to the vertical shaft at the end, into which a steam jet passed, whereby the air current was established and maintained at the desired velocity. 'The air supply was drawn through heated boiler tubes and thus raised to a temperature of 75 to 85 degs. Fahr. With regard to the mixture of gas and air Abel states:—“ Special arrangements were made to secure accuracy in the intimacy and consequent uniformity of the mixture. The results of analyses of samples of the gas and air mixtures, collected from different places in the gallery, afforded most satisfactory proof of the attainment of these results.” The gas employed was, in the majority of the experi- ments, firedamp issuing as a blower from the Wigan Nine-foot seam at Garswood Hall Colliery, and is described by Abel as “ what is commonly called a sharp gas, of the kind known as silver gas” The main results that he obtained with this gas are given in the table that follows :— Experiments at Garswood Hall Colliery with Fire- damp. Ignition by a Naked Lamp Flame. Percentage of gas in Velocity of air- current. Result. mixture. 3'5 Feet per minute. ... 200 to 1,000 ... Feeble explosions, sometimes 3'0 100 immediately and sometimes after the gas mixture had been passing for 5 to 10 seconds, “the general igni- tion of the mixture being preceded by flares which travelled forward from the lamp flame.” Elongation of the lamp flame. 3*25 100 A very faint flickering flame 3’50 100 was observed. The “faint flickering flame” 3'75 100 was lengthened. The lamp flame became occa- 4'00 100 sionally prolonged into a lambent flame. The “lambent flame” increased 4'25 4'50 } 100 J I in size. “The flame increased in size rapidly, filling the gallery in front of the lamp flame, and finally a general ignition of the gas mixture in the whole gallery occurred.” In addition to the above, some experiments were made •at Woolwich in an apparatus arranged for the exposure * Report to the Secretary of State for the Home Depart- ment. March 23, 1881. of mixtures of coal gas and air, perfectly still, to the effect of flashes of flame (produced by igniting small quantities of gun-cotton electrically). No result was obtained with mixtures of 3 and 4 per cent, of gas, but a “ feeble explosion ” was obtained with a mixture con- taining 4*25 per cent. Having made experiments with gaseous mixtures with no dust present, Abel next proceeded to test those mixtures with additions of coaldust, using for this purpose the dusts that had been collected at Seaham Colliery. He found that when such dusts were present in suspension, only 2'5 per cent, of firedamp was necessary to form an explosive mixture, and he records that “while the richness of a dust in coal, or its greater inflammability, influenced the rapidity and consequent violence of the explosion of dust- and gas-mixtures containing corresponding .quantities of firedamp, the physical characters and mechanical condition (lightness, porosity and state of division) evidently contribute more than the richness in coal or combustibility of the dust-sample, to determine the comparative readiness with which it brings about the inflammation of a gas- mixture not susceptible of ignition per se under otherwise similar conditions, and to regulate the proportion of gas required to produce, with it, a mixture which will ignite and convey flame, when coming into contact with flame.” For example, he found that the sample of Seaham dust containing the smallest proportion of coal, and containing, indeed, half its weight of non-combustible matter, ranked next in sensitiveness to the samples which consisted almost entirely of coal. This result led him to try whether the ignition by a lamp flame of a mixture of firedamp and air, not inflammable per se, would be brought about by suspending in it a fine readily floating dust which was quite non-combustible. The following experiments were therefore made with calcined magnesia:— “ A gas mixture having 3 per cent, of firedamp was allowed to pass a lamp flame at a velocity of 600 ft. per minute for some time ; no result was produced, but on causing it to convey calcined magnesia in suspension, long flares of flame were produced within a few seconds of the mixture first passing the lamp, and the inflam- mation speedily spread throughout the gallery with feeble explosive effect. With only 2'75 per cent, of gas, results quite similar were produced, the general ignition following, however, less rapidly after the first production of the flares in front of the lamp flame. With another sample of calcined magnesia, which was not quite so light as the first one, a corresponding result was obtained with a mixture containing 3 per cent, of firedamp.” The report continues :— “ These remarkable results led to the trial of a number of other non-combustible powders or dusts, which are not chemically affected by such heat as they would be exposed to in the flame of a lamp (such as kaolin, powdered flint and other forms of silica, pumice, slatedust, &c.) with results similar to those furnished by the magnesia dust, but more or less affected by varia- tions in the density and other physical properties of the dusts. In experiments with currents of 1,000 ft. velocity, the effect of any one of the powders being deposited on the bottom and sides of the gallery, was to cause the instantaneous ignition of a 3'5 per cent, gas- mixture on its reaching the lamp-flame through the influence of dust-particles carried along by the current, and in some instances a like result was obtained with 3'25 and 3 per cent, gas mixtures.” In summarising his report, Abel says :— “ One of the Seaham dusts which ranked high (third) in order of sensitiveness contained the lowest proportion of coal of all the samples, and consisted of non-combus- tible matter to the extent of nearly half its weight.” Special experiments, which were instituted in conse- quence of the behaviour of this sample, demonstrated that some perfectly non-combustible powders, which are also not susceptible of any chemical change when exposed to the action of flame, are very little inferior to the most inflammable or sensitive of the Seaham dust samples in their power to bring about the ignition of an otherwise uninflammable mixture of firedamp and air. Mixtures of firedamp and air, in proportions bordering on those which will ignite on the approach of flame, are inflamed instantaneously if they contain in suspension only few particles of such non-combustible dusts, or of the Seaham or other dusts from coalpits. This effect appears ascribable, at any rate in part, to the fact that these dust particles, when they pass through a lamp flame, immediately become incan- descent, and thereby localise and intensify the heat at those points, and thus bring about the ignition of the mixture of air and firedamp by which they are surrounded. But some phenomena observed in the course of the experiments with non-combustible powders favour the belief that finely divided solids of particular descriptions may exert another quite distinct kind of action when heated in firedamp mixtures, which may at least contribute importantly in determining the ignition of gas-mixtures which are not susceptible of inflammation by the application of flame alone. This subject is about to receive complete investigation.” In his evidence at the adjourned Seaham inquest* Abel gave what seemed to him a “ satisfactory explana- tion” of these observations:— “ A finely-divided solid, especially if it be slightly warmed or heated as it passes the flame of a lamp, when brought into contact with a gaseous mixture—a mixture, for example, of firedamp and air containing only very small quantities of firedamp, which would remain in an inactive condition for any length of time—may at once establish an action of this kind; it may bring about an immediate combination between the two that will develop heat; and in this way in a very short space of time the solid body is raised to the temperature at which it will inflame this mixture, and action of this kind has been exhibited by the particular descriptions of various mineral powders with which I have experimented.” In the following year (1882) Abel delivered a lecture at the Royal Institution “ On Some of the Dangerous Properties of Dusts,” and in this lecture he lays emphasis on the view that the dust “ exerts a contact or catalytic action upon gas mixtures similar to that known to be possessed by platinum.” Just as platinum brought into contact with mixtures of oxygen with hydrogen or hydrocarbon gases sets up an oxidation whereby heat is developed, raising the temperature of the metal and increasing its activity until the surrounding mixture explodes, so magnesia acts catalytically on the air and firedamp. “ In many of the experiments with calcined magnesia,” he says, “ it was distinctly noticed that a dark space intervened between the gas flame used as the source of heat and the flare produced by the ignition of the gas mixture through the influence of the dust cloud suspended in it, which would seem to indicate that the dust particles, immediately on passing through the flame, establish some amount of oxidation of the fire- damp, which proceeded with increased rapidity as the dust became more highly heated through the chemical action developed, so that within a short distance from the point where the heating commenced the dust became incandescent, and the ignition of the gas mixture followed.” In this lecture Abel evidently leans to the catalytic theory of the influence of non-combustible dusts which constitute “ one element of the dangers arising from the presence of dust in the air of a mine which contains a small proportion of firedamp.” . In the Final Report of the Royal Commission on Accidents in Mines, published in 1886, the words of Abel’s lecture (quoted above) are embodied in the report, and the experiments of Mallard andLe Chatelier (1882) are referred to as “ quite confirmatory ” of those arrived at by Abel. (To be continued.} THE TIH-PLATE TRADE. Liverpool. There is no material change in the position. Stocks are still heavy, and are being sold at exceedingly low figures. Makers are also anxious sellers for quick specification, but are not desirous of booking ahead unless at higher prices. Buyers are proceeding cautiously, and as a rule are only covering their requirements over the next few weeks. Quotations for coke tins for shipment first half of the year may be called:—I C 14 x 20 (112 sh. 108 lb.), 14s. per box; IC 28 x 20 (112 sh. 216 lb.), 28s. to 28s. 3d. per box; IC 28 x 20 (56 sh. 108 lb.), 14s. 4|d. to 14s. 6d. per box; I C 14 x 19| (120 sh. 110 lb.), 14s. 3d. to 14s. 6d. per box ; I C 14 x 18| (124 sh. 110 lb.), 14s. 3d. to 14s. 6d. per box; I C 20 x 10 (225 sh. 1561b.), 19s. to 19s. 6d. per box; I C squares and odd sizes, 14s. 3d. to 14s. 6d. for usual specifications* Charcoal tins are in a little better demand owing to the rise in block tin. Quotations for I C 14 x 20 run 16s. 6d. to 17s. and upwards according to finish, Coke wasters: The demand is moderate and quotations are :—C W 14 x 20, 13s. per box; C W 28 x 20, 25s. 9d. per box ; C W 14 x 18|, 12s. 7>d. per box; C W 20 x 10,18s. per box—all f.o.b. Wales, less 4 per cent. <• The Trade of Hull,” published by the Eastern Morning and Hull News (price Id.) gives an interesting account of the commercial activities of the Humber port. There is a plan of the new joint dock and photographs of the Albert Dock coal hoists and the discharging belts at the Victoria Dock.