June 29, 191 ij 



NATURE 



597 



zontal, if an_\-, the barrel of the mortar usually stands 

 when a charge is fired from it, or whether there are two 

 mortars, one in the explosion chamber, the other movable 

 to any other desired position. The only reference we can 

 find in this connection is to a mortar " on the floor of 

 the gallery," fired in this particular instance at a distance 

 of 20 m. from the explosion chamber (p. 2b). 



An attempt has been made to measure pressure by means 

 of a spring indicator. We say " attempt," because the 

 curves reproduced on pp. 19 and 22 are of identical con- 

 struction with, and indistinguishable in this respect from, 

 those obtained by the present writer with a similar con- 

 trivance in the small Royal Society gallery (1877-8). We 

 put these curves aside at the time (although we still possess 

 them) as altogether untrustworthy, as we were of opinion 

 that the first impulse given to the piston was due to the 

 initial explosion of firedamp, and its subsequent vibrations 

 to the combined action of the momentum of the moving 

 parts and the resilience of the spring, and not to those 

 of the air in the gallery ; and we consider the curves now 

 before us to be of quite as little value as our own. 



The length to which the flame extends is ascertained by 

 placing a series of sulphur matches set in wooden blocks 

 at intervals of i m. apart along the walls of the gallery, 

 and observing how many of them have been burnt. 



A bottle filled with water, suspended neck downwards 

 at a distance of 10 m. from the explosion chamber, with 

 its loosely fitting cork attached by a string to the nearest 

 hanging frame, serves the purpose of collecting a sample 

 of the afterdamp. When the hanging frame moves under 

 the impulse of the blast, the cork is displaced, the water 

 runs out, and the air and gases take its place. 



The audible and visible phenomena produced by an ex- 

 plosion are stated to be a shock " followed by a return 

 shock after an interval of not more than two seconds " ; 

 the shock expels a column of air from the terminal shaft 

 (the one farthest from the explosion chamber), opens the 

 door at the top of the intermediate shaft (when the door at 

 its bottom, which opens into the gallery, has been re- 

 moved), and expels a cloud of " smoke " (? dust-laden air), 

 followed, when the explosion is violent, by a flame several 

 yards in length ; the return shock opens the iron door at 

 the explosion chamber, closes the door at the top of the 

 intermediate shaft, and fresh air rushes in at the shafts 

 at both ends of the gallery. Immediately afterwards, 

 "thick, dense, blackish-grey afterdamp" is expelled from 

 the terminal shaft by the fan. The frames with shelves 

 aie usually torn away and shattered; and on one occasion 

 the door at the top of the intermediate shaft, together 

 with portions of its frame, was thrown to a distance of 

 30 ni. 



Passing over the accounts of tentative and preliminary 

 experiments, both with suspended cartridges of dynamite 

 and with black powder fired from the mortar, we may 

 take the following as fairly tyj)ic;il examples of the best 

 results with both kinds of f'xpl<>--ivi' : - 



(i) With suspended cartridges of dynamite. 



With 325 k. of dust strewn over a length of 00 m- 

 from the chamber, and with dust being disseminated in 

 the air by the distributing fan in the chamber and by 

 the revolving discs at 47-8 and 82-8 m. from the latter, 

 rhe length of flame in the gallery was 124 m. and that 

 in the intermediate shaft 24 m. 



In another explosion, with n strewing of qo m., con- 

 ducted, prcsiimalilv, iniflcr lli'- ^.-mv cdiirlii ioii^ ;ir~ the last, 

 but not so ^p'Tilii'd, (III- lrnL;ili <>f ll.-iiii- w.is iiS m. ; the 

 m.-ixinuiin pn-ssurf i- >l,-i!''(l Id hav lii"ii 1-38 atmo- 

 S|")!ii'|-.\ :m(l thi- diii-at ion of lli'- .■xpl. i^i.m (11.13 second. 



(2) With 3<ji) grams of l)la(k powder lir.d in \h<- mortar 

 witlioul tamping, when l)ol1i disc-, aiid_lh'' di^lrihid ing fan 

 wt>rr- ai work, and 30 k. of dust " i-m'plo\.'d " ('som-' of it 

 -Ir-wn on ill.- floor?), the lengili of ihi' fl.ani.^ 

 ni. (p. 23). 



v.ii tho finest dust, containing 2-2 to 4'5 per cent. 

 inr', onlv r(l,a(iv'd\- '-\\-j}\\ .xplosions and sliort 

 >ii!fl 1..' ohiain-'d wll'i ■■'\'A\'--\- dxti.aniiti' or bl.ack 

 luil wilh (-\-cn roa;--- diisl, i-otit.aining on!v 0-7 

 ■I'wn oV'i- a d'-; an.- of SS-2 m., flami-s 



prol,: 



was 

 W 

 of n 

 flam, 

 powc 



to 1-7 per (.-nt 

 up to 147 m. 



In tho s.M-oi 

 aftf'r a ivw ( 



NO. 2174 



that , 



, vol 



d ! 



W'T" mru 



;hr . ■ 



plosion, had been fixed at the bottom of the intermediate 

 shaft, and a third revolving disc placed at a distance of 

 120 m. from the chamber, a flame of 200 m. in length 

 was obtained in one of the experiments wiili a charge 

 of 250 grams of dynamite and with 129 grams of coal 

 dust per cubit metre (containing 13-3 per cent, of ash, 

 0-45 of moisture, and 19-2 of volatile matter), disseminated 

 over a distance of 120 yards. This coal dust left 12-2 per 

 cent, on a sieve with 3480 meshes per square centimetre. 



Under the sam.- conditions, except that the dust con- 

 tained 7-55 per i(iu. of moisture, no explosion took place. 



Coal dust <inuaining 14 per cent, of ash gave violent 

 explosions wiih llames 150 m. in length, whereas that 

 containing 47() per cent, did not explode. 



Coal dust mixed with increasing proportions of Roman 

 cement continued to explode until the mixture contained 

 63-3 per cent, of the latter. The suggested and highly 

 probable explanation of this apparent anomaly is that the 

 cement dust falls more quickly than the coal dust, and 

 leaves the mixture remaining suspended in the air purer 

 than it would otherwise be. 



The influence of wet zones, and what are designated 

 " water curtains," was also investigated. " The wet zones 

 were formed by sprinkling in the usual way just before 

 shot-firing, and were intensified at intervals by water 

 curtains " (p. 34). The " usual way " is probably that 

 described on p. 11, that is, by means of hose pipes attached 

 to branches of a supply pipe laid along the floor of the 

 gallery. The water curtains, which consist in sprays of 

 water issuing upwards, downwards, and across the gallerv 

 at right angles to its longer axis from perforations or 

 nozzles in pipes fixed on its periphery, are stated to have 

 produced little effect on the length of the flame (p. 35). 



A wet zone of 60 m. extinguishes an explosion even 

 when a dry-dust explosion produced under the same con- 

 ditions extends to 137 m. in the absence of the water. 

 " With wet zones 36 to 57 m. long, the flame projected 

 beyond them failed to ignite the dust in the immediately 

 adjoining second coal-dust zone in which the third atomiser 

 (revolving disc) was in operation." 



In comparing the foregoing results with those obtained 

 in the galleries at Altofts and Li^vin, it should be borne 

 in mind that the coal dust employed was collected at the 

 screens and in the workings, that it, consequently, con- 

 tained indefinite proportions of coarse and fine particles, 

 and that it is lower in volatile matter than the coals 

 employed in the two galleries named. 



These less favourable conditions seem to accoimt for its 

 apparenth' lower intl.anim.aliiJity and its gia'at.'r x-nsiiive- 

 ness with regard to increasing proportions ol uncombined 

 moisture. 



From a priori considerations as to the ti.ituro of com- 

 bustion, it might have been thouglit that th.' two follow- 

 ing propositions could have been accfpi.il as axioniatii-, 

 namely, that, caeteris paribus, (i) the finer the dust, the 

 greater the proportion of volatile combustible matter, the 

 drier the air and the higher its pressure and temperature, 

 and the less the proportion of miniial ni.ill.r and moisture 

 (coinbined and uncombined) the morr intlamniahli' tlie 

 dust; and (2) conversely, willi all the condition^ r.v.a-s.d. 

 As it is, most of them lia\.' h.-.n verified by th.' results of 

 all till' recent quantitative .'xperinients, including an e\c.d- 

 jent ■-ra-ii"^ on ih.' lal)oraIor\- seal.' li\- i'rof. iv^Kon ,nid 

 Mr. Widci.as.' 



The results of tli.' .xperinvnts mad.' Ii\- llv rriis-ian 

 Firedamp ( ■ounuission - v,.iaii.'d to eonlrailiet th.^ ^eccMul 

 condition as to lli.' intlmaic.- of inta-.-as.' in ill.' pr.tportlon 

 of volatil.' mailer, in r.-gard lo which tli.'X' niak- llie 

 following,' r. niark-s on p. 31 : 



(7,) " i')ei .-inian r'lidi.al! •■ ,an tlciehtierMi H.'-t a ndi li. ■: Lai \-oil 



1 8 



■n 



li.vnt 

 i., -1. 



d;.' I-'laniin.au.i-lanL^.'iaiiu 



('.)) '• Mit .0 

 th.'ilen tritt 

 l-'lannn.MiV'i'la 

 fvi., I ;, i|- I 



Wohl die-. " e 



Ml (''..'halt. 



]'..■-: 



in llcieh'i' 

 ent-eh;. d.'n.> Ahn ' 

 -illist li.'i ;;an/ f.'in.'ie 

 , .M, Jj). '" Fs hl.-ilen -l.i.'Il- 

 l.'ii olin.' Au-n.dini.' noeli sehr 



Iv. I'.a-I V. 



I Tr.Tiis.ictions of the Instiiution of Mining F-nginfers. \ 



ftOToV 



" \ ' if a't-Rerichte der Preussischen Sclihii;wriici -C 0111111 



VI. Pp. 35(1886). 



.S() 



