^i Addiiional praclknl Observalions on the 



scintillations. It appears that the miners were at first alarmed 

 by an effect of this kind prodtsccd by the dust naturally raised 

 during the working of the coals. I have made a number of ex- 

 periments on this subject; but thongh I have repeatedly thrown 

 coal dust, powdered rosin, and witch meal, througii lamjis burn- 

 ing in more explosive mixtures than evjr occur in coal mines, 

 and though I have kept these substances floating in the explo- 

 sive atmosphere, and heaped them upon the top of the lamp when 

 it was red hot, yet I never could communicate explosion by means 

 of them. Phosphorus or sulphur are the only substances which 

 can produce explosion by being applied to the outside of the lamp ; 

 and sulphur, to produce the efl'ect, must be applied in large quan- 

 titips and blown upon by a curren.t of fresh air. 



It will be unnecessarv to caution the workmen against heap- 

 ing sulphur, or gunpowder, or pyrites, vvbich afford sulphur by 

 distillation, upon their lamps ; and such dust from these sub- 

 stances as can float in the atmosphere cannot produce inflam- 

 mation; for miriute particles of ignited solid matter have no power 

 of inflaming the lire-damp ; and I have repeatedly blown fine 

 coal dust mixed with minute quantities of the finest dust of gun- 

 powder through the lanij) burning in explosive mixtures without 

 any communication of explosion :- and supposing danger u'ith re- 

 spect to gunpowder, the steel-mill must be nuich more liable to 

 inflame that substance than the wire-gauze lamp : and the dou- 

 ble cylinder lamp offers perfect security against the inflammation 

 of any matter that can ever exist in coal mines. 



In adopting from 30 to 26 apertures to the inch (from 900 to 

 676 in the square inch) and wires of from J„ to -^\ of an inch 

 in thickness, even single lamps are secure in all atmospheres of 

 fire-damp ; and double cylinder lamps are perfectly safe under all 

 circumstances even in atmospheres made explosive by cor.l gas, 

 which, from the quantity of olefiant gas it contains, is much more 

 inflammable than fire-damp. When indeed a strong current of 

 coal gas is driven from a blow- pine, so as to make v,-ire-gauze of 

 676 apertures strongly red hot in the atmosphere, the flame from 

 this pipe may be passed through it whilst it is strongly red hot ; 

 but this is owing to the power which wires strongly ignited pos- 

 sess of inflaming coal gas '^ ; and they have no such effect on ge- 

 nuine fire-damp ; and a stre^jn of gas burning in the atmosphere 

 acting on a small cjuantity of matter, is entirely different from an 

 explosive mixture, which is uniform within the lamp. 



* Olefiant gas contains twice as muc!i cliarcf)al as lif:iir carliui'cttcd Iiy- 

 •Irogen, and is mjcti more easilv dt'ciunpo^cd by heat; the dcnsitv of its 

 flame, as I sliall show on a future occasion, rlppends upon solid matter pro- 

 duced by its (ieconiposition in the (irocess of combustion, and which be- 

 comes ignited; and tlie same cir^iuinsluucc iioldbgood ol'uU flames afTord- 

 iiij; iutfiibc liijlit. 



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