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Smokes: Part II.— A method of determining the size of the particles in smokes

1923; Royal Society; Volume: 102; Issue: 718 Linguagem: Inglês

10.1098/rspa.1923.0019

2053-9150

R. Whytlaw-Gray, J. B. Speakman,

Fire dynamics and safety research

In Part I (1) an ultra-microscopic method of counting the particles in dilute and highly disperse solid-gas systems was described, and whilst the number was found to decrease as the cloud aged, a concurrent growth in size of the individual units was observed to take place. These changes in the case of non-volatile oxide smokes were proved to be caused by the aggregating of the smaller particles to form larger complexes. Now, in order to follow this process in a quantitative manner, it is necessary to determine the average mass of a particle at different periods in the age of the smoke. That is to say, some method must be used which can be carried out quickly, so that the particles have not time to increase appreciably in size. Now, none of the usual methods which deal with the movement of individual particles are suitable, because, apart from the validity of the Stokes-Cunningham equation (2), on which the majority of them are based, they are in practice too slow, and require the mean of a large number of observations if a representative value for the average size is to be obtained. This objection applies even more strongly to methods based on Einstein’s (3) equation of the mean displacement of a particle by molecular bombardment along a given axis in a definite time.