226 



NATURE 



[April 13, 191 1 



the same experience if he provided cither a similar valve or 

 a reservoir of air of sufTiriont capacity near the closed end 

 of the cul-de-sac (such as exists in the form of branch 

 workings in most mines), from which air could expand 

 :»nd thus wholly or partially destroy the vacuum. If he 

 arranged his experiment in this way, he would have no 

 difficulty in securing propagation by means of a firedamp 

 explosion ignited by a spark, much less by loo grammes of 

 dynamite. 



Many other points of importance mijjht be referred to 

 with advantage, but space would fail us were we to 

 attempt to go further in this place, and the final remark 

 we would make in regard to this series of experiments is 

 that the water employed in damping the dust, which forms 

 globules on the surface of the latter, does not appear to 

 have been applied in the form of an exceedingly fine spray, 

 repeated several times, in succession, with a short interval 

 between each application, and we venture to think that 

 if this had been done the results would have been different 

 from those actually experienced. 



The fourth series of experiments was made with the 

 gallery lengthened to 230 metres (251 J yards), although the 

 whole length was not always employed. For the first 

 32 i yards the form of the gallery was trapezoidal, with a 

 lining of cement, the remainder cylindrical, with a lining 

 of wood and with a floor. The coal dust was prepared from 

 Li^vin coal, with 2q to 31 per cent, of volatile matter and 

 6 to 12 per cent, of ash. The slate dust employed in some 

 of the experiments was obtained from the pit. It contained 

 per cent, of volatile matter and 87 per cent, of ash, and 

 was mi.xed with marly chalk, clay, siliceous sand, and 

 boiler-furnace cinders. Mixtures of coal dust and inert dust 

 were prepared by grinding them together. The mixture was 

 simply spread uniformly on the floor and not stirred up 

 mechanically before the explosion. The charge employed 

 in creating the explosions consisted of 240 grammes of 

 gelatine dynamite untamped and fired electrically, the axis 

 of the cannon being 15^ inches above the floor. 



Fine dust was spread to a distance of 16^ feet in front of 

 the cannon to insure ignition, but beyond that point coarser 

 dusts ground for a quarter or half hour and even grains 

 were employed. 



Some explosions effected with half-hour dust were very 

 violent, traversing the whole length of the gallery in 

 1^ seconds, with increasing velocity, which exceeded iioo 

 yards per second at the orifice, while the pressure, which 

 was 28^ lb. per square inch for most of the distance, 

 increased to between 42^ lb. to 71 lb. per square inch at 

 4.:; metres from the orifice, and to 1565 lb. per square inch 

 at II yards from the orifice. With 900 grammes per cubic 

 metre of quarter-hour dust, the flame traversed the gallery 

 in 1-23 seconds, and the pressure attained 224 lb. per square 

 inch at 10 metres from the orifice. 



With a deposit of coal dust containing up to 33 per cent, 

 of slate dust the coal dust was exploded, and the explosion 

 was capable of becoming violent. 



Passing over the experiments with dustless, watered 

 and shale dust zones, and those made with obstacles of 

 various heights, placed on the floor and on shelves at the 

 sides of the gallery, we come to what are the most novel, 

 and perhaps also the most interesting, of all the experi- 

 ments, namely, the efficient results obtained in the way of 

 arresting even violent explosions by placing loose, easily 

 displaced cinders, or, mutatis mutandis, half-round sheet- 

 iron tanks 40 inches long by 8 inches in diameter, filled 

 with water on transverse planks one metre apart just 

 under the roof of the gallery. It is to be hoped 

 that these two methods of arresting explosions will be the 

 object of further successful experiments, and it is not 

 improbable that, after all, we may owe to France a debt 

 of gratitude for pointing out a simple and efficacious means 

 of effecting the object which all of us are so anxious to 

 attain. May the present writer suggest in conclusion that 

 possibly appliances of the nature of extincteurs or fire 

 extinguishers, put into operation by the blast which pre- 

 cedes the flame of an explosion acting upon a movable vane 

 which would open the passage Tor the escape of their 

 contents, might be used instead of open troughs filled with 

 water? The former would possess the indubitable advantage 

 that they would retain their efficiencv intact for any length 

 of time ; whereas the latter would require constant attention in 

 the way of cleaning and refilling them. W. Gallow.ay. 



NO. 2163, VOL. 86] 



THE INSTITUTION OF NAVAL ARCHITECTS 

 'T'HK spring meetings of the Institution of Naval Archi 

 ■*• tccts 0|>ened on Wednesday, April 5, at the room* 

 the Royal .Society of Arts. Owing to the death of Eat 

 Cawdor, president of the institution, the chair was takfi 

 by Sir W. H. White, who announced that t! . 

 recommended the election of the Marquis of 



K resident. The grant of a Royal Charter <' '■ 

 as received the Royal assent. The eel- 

 jubilee of the institution, post|K)ned from . 

 take the form of an International Congress on Navi 

 Architecture and Marine Engineering, openmg on July 4. 



Fourteen papers were read and discusvd. The probici) 

 of size in l^attlcships was dealt with by Prof. J. J. Welch 

 Among other points raised in this paper is the ■ 

 that large dimensions expose a greater target t> 

 contention which must now be expanded to i 

 additional menace of missiles from dirigibles or . 

 Assuming tlie attack to be delivered from a hei. 

 mile, and therefore reasonably out of range of 

 fire, a hollow bomb carrying loolb. of explosive • 

 about twenty seconds to reach the water level, ana . 

 then have a striking velocity of about 500 feet per s< ^ : 

 In twenty seconds a ship would change position - 

 540 feet, supposing her to be proceeding at 16 knots. ! 

 the probabilities of such a vessel being struck from :• 

 would be decreased if, at the moment of discharge of ri 

 weapon, her helm were put hard over. The time, hov 

 would not suffice to allow the vessel to sweep clear o; 

 previous track before the missile reached water !• . i. 

 although the exposed area of deck in that track would U 

 very much smaller than before. The difficulties associated 

 with correctly judging speeds of battleships from the height 

 named, and making proper allowance for cross wind 

 currents, &c., combine to render a hit very uncertain if a 

 single missile only is employed. It is stated, however, th.it 

 arrangements are being made for dropping a number of 

 such missiles from a single dirigible, in which case t'r :* 

 form of attack would become a serious menace. It ^-^ r - 

 reasonable to suppose that the best protection from si;, h 

 attacks will be found in the counter-attacks by the same 

 type of air-ship, associated with high-angle gun fire from 

 (he vessel attacked. 



The Hon. C. A. Parsons and Mr. R. J. Walker gave the 

 tesults of twelve months' experience with the gcar<xl 

 turbines fitted to the cargo steamer Vespasian. In this 

 vessel, the reduction of speed ratio of 20 to i is obtaiii«'d 

 by means of a spur wheel and pinion having double helical 

 teeth. The vessel has now steamed 20,000 miles, and in- 

 spection shows that the wear in the teeth so far seems to 

 be a negligible quantity. With the view of experimenting 

 with dilTerent qualities of steel, a pinion of chrome nickel 

 steel of tensile strength 55 tons per square inch, elastic 

 limit 38 tons, and an elongation of 20 per cent, in a lengtf< 

 of two inches, was tried and removed after two voyages. 

 The corners of some of the teeth were found to be fractured. 

 probably owing to irregular machining and to the material I 

 being too brittle. The original pinions were of mild chrome 

 nickel steel of tensile strength 37 to 38 tons per square 

 inch, and an elastic limit of 32 tons per square inch. ThcM 

 were replaced and have now carried the vessel more than 

 18,000 miles. A very noticeatfle feature has been the absenee 

 of racing of the engines under conditions when the propeller 

 has been entirely out of the water. It is very difficult lo 

 observe any acceleration in the speed of the engines witheat 

 the aid of a sensitive tachometer. This is owing to the 

 very great angular momentum of the turbine. 



Mr. G. S. Baker contributed a fullv illustrated d€ 

 tion of the National Experimental Tank and its equipme 

 including the model-making apparatus. 



The whole of Thursday morning was taken up by a paper 

 on Diesel engines for sea-going vessels, by Mr. J. T. Milton, 

 of Lloyd's Register, a paper which provoked a very in- 

 teresting discussion. Inducement to forsake the steam 

 engine for ordinary sea-going vessels will be mainly the 

 question of fuel economy. Even this important point would 

 not of itself warrant a change to a new type of engine 

 unless equal certainty of continuous efficiency on the voyages 

 to be undertaken was provided, that is. as little risk of 

 accident to machinery and as great facility for usin^j 

 temporary expedients for reaching port in case of break- 



