88 Mr. F. A. Abel [April 28, 



WEEKLY EVENING MEETING, 



Friday, April 28, 1882. 



Sir Frederick Bramwell, F.R.S. Vice-President, in the Chair. 



F. A. Abel, C.B. F.R.S. 

 President of the Institute of Chemistry. 



Some of the Dangerous Properties of Dusts. 



When dealing with the subject of so-called accidental explosions, in 

 a discourse delivered to the Members of the Royal Institution, in 

 March 1875, the lecturer pointed out that combustible, and especially 

 inflammable substances, if sufficiently light and finely divided to 

 allow of their remaining for some time suspended in air in consider- 

 able quantity, so as to form an intimate mixture with it, may, when 

 ignited in this condition, produce explosive effects. The combustion 

 of the finely divided particles which, under such conditions, are first 

 inflamed, at once communicate flame to those in their immediate 

 vicinity, and combustion is thus transmitted by and through the sur- 

 rounding mixture of dust and air with a rapidity regulated by the 

 inflammability of the dust, and by the proportion and state of division 

 in which it is distributed through the air. If a rajndly burning 

 mixture of this kind is confined, its combustion will be attended by 

 explosive effects, the degree of violence of which is determined by 

 the combustibility of the dust, by the quantity of mixture ignited, 

 and the nature of its confinement. Its behaviour is indeed quite 

 similar to that of a mixture of inflammable gas or vapour and of air ; 

 at the instant of its ignition each dust-particle is to a more or less 

 considerable extent converted into inflammable vapour, or is, at any 

 rate, surrounded by an envelojDe of burning vapour, so that if the 

 particles are in sufficiently close proximity to each other, the rapidly 

 successive development of vapour from them as the flame spreads, gives 

 rise to a condition of things very like that which obtains when an 

 inflammable gas, or vapour, originally existing as such, is mixed 

 with air. 



Even the most inflammable solid, in the form of dust, must be 

 mixed in large proportion with air, must, indeed, be present in the 

 form of a dense cloud, in order that the transmission of flame may 

 proceed continuously from the portion first ignited to surrounding 

 parts of the mixture. A dense cloud of Lycopodium dust in air will 

 transmit flame with rapidity and violence throughout its whole extent, 

 but if the particles in the cloud be not in very close proximity, the 

 application of flame to it will only produce short flashes in the 



