THE BURSTING-POINT OF SOME STARCH-CELLS. 177 



40="OOIOO I2=*OOIOO 7='00I00 



7o='ooo75 28='ooo75 9=='ooo75 



45='ooo5o 4o=*ooo5o 2o='ooo5o 



25=-ooo25 55="ooo25 35=-ooo25 



2o="oooi5 45==*oooi5 75='oooi5 



25='oooio(&less) 6o='oooio(&less) Ioo='oooio(&less) 



250 250 250 



The results, we can see, express what might have been 

 expected, especially the greater absence of the larger particles at 

 the longer distances. To secure accuracy, I have modified my 

 first results by fresh examinations. It has been impossible to 

 estimate exactly the number of particles of the smaller sizes, but 

 the numbers expressed may, I think, be taken as approximately 

 correct. The question, " What are the smallest sizes in the 

 two dusts ? " I will not enter upon now ; I have observed particles 

 of -00003= ^^^^^^^ inch, even with a low power, and no doubt such 

 as travel great distances will seldom exceed "00005. 



Another question that I cannot at the present time discuss, is 

 the reason why such dust as that of wheat and coal should be so 

 explosive. I will therefore conclude this hasty sketch with a 

 quotation from a special report on the subject, prepared for the 

 Board of Trade, which gives a forcible explanation of the matter: — 

 ^' The finely-divided dust-particles being diffused in the air, are 

 each brought into intimate contact with the oxygen which is 

 necessary for their combustion, and consequently, when ignition 

 occurs, it is very rapid. The particles near the flame are ignited, 

 and in their turn ignite the neighbouring particles, which again 

 ignite the adjacent ones, until the whole chamber is a body of 

 flame." It seems to be a matter of extensive surface, and there- 

 fore of rapid combustion. 



1Rote6 on tbe Bursting^lpoint of 0ome 

 Starcb:==(reU0* 



By W. J. DiBDiN, F.I.C., F.C.S. Plate 17. 



THE following record of a series of experiments, conducted 

 with a view of ascertaining whether any reliable informa- 

 tion could be obtained from the bursting-point of various 

 Starch-cells as a means of assisting in their identification, may 

 probably be of interest, although the results are not of the analy- 

 tical value that it was hoped they would have been. 



The arrangement used for ascertaining the temperature was 



