176 



DUST-PARTICLES OF WHEAT AND COAL. 



copist to observe what variations or similarity in the size of the 

 dust-particles of the two substances, wheat and coal, there appears 

 to be. 



I have been unable to gather the dust required for my purpose, 

 either in the coal-mine or in the flour-mill, and,_ therefore, have had 

 to content myself with a simple mode of collection. In the case of 

 coal, I have collected the dust on shelves placed at fixed distances 

 from the coal-trap of a large cellar, during the unloading of several 

 tons of coal ; and in the case of wheat-flour, in a similar manner 

 during the sifting of flour in a confined space. After collecting 

 the samples of dust, I have, by gentle tappings, transferred minute 

 portions to glass sUps for examination, taking care that the par- 

 ticles have been evenly distributed on the surface. The micros- 

 copical examinations have been made with a i-inch objective, 

 A eye-piece, and stage micrometer, and by reflected light. In 

 cases where variation in the diameters of particles (which in both 

 cases are very rugged) has been observed, as, e.g., of an oblong 

 spheroid, I have recorded the smaller diameter. I have chosen for 

 examination groups of about 250 particles, evenly distributed over 

 the field, and have endeavoured to secure the same conditions of 

 observation in each case. 



Wheat-Flour. — I have examined three samples: — (i) fine 

 household flour, (2) dust from it collected 4 feet off, and (3) dust 

 from it collected 6 feet off". 



I. — Flour. 



No. of Fraction 

 particles, of inch. 



3=-oo25o 



6=*ooi5o 

 I i = -ooioo 

 3o=-ooo75 

 50= -00050 

 5o='ooo25 

 5o='oooi5 

 5o='oooio (&less) 



2. — Dust at 4 ft. 



No. of Fraction 

 particles, of inch. 

 2 = '00250 



5=:-ooi5o 



8="ooioo 

 2o=*ooo75 

 3o='ooo5o 

 4o="ooo2 5 

 55=-oooi5 

 90='oooiO(&less) 



3. — Dust at 6 ft. 



No, of Fraction 



particles, of inch. 



0=*00250 



o=*ooi5o 



4=-ooioo 



8="ooo75 



i3="ooo5o 



25 = '00025 



45=-oooi5 



I55="OOOIO ^& less) 



2sO 



250 250 



CoAL-DusT. — I have examined also three samples from Welsh 

 coal, collected at distances of 4, 6, and 1 1 feet. 



I. — Dust at 4 ft. 2. — Dust at 6 ft. 3. — Dust at 11 ft. 



No. of Fraction No. of Fraction No. of Fraction 



particles, of inch. particles, of inch. particles, of inch. 



9=-00250 2 = '00250 0='00250 



i6=-ooi5o 8=*ooi5o 4=-ooi5o 



