294 MR. J. B. DANCER ON COAL-ASH OR DUST 



I to 35 per cent. The ash or dust which is the subject of 

 this paper was collected from the flue of my steam-boiler 

 furnace, in which common engine coal is used as fael. 

 This coal leaves a considerable amount of incombustible 

 matter. A specimen of the dust is now before you ; it is 

 of a reddish-brown colour, and free from soot or carbona- 

 ceous particles*. When this dust is examined under the 

 microscope with a power of 40 or 50 diameters, it is found 

 to consist of ferruginous matter and crystallized substances, 

 some particles transparent, others white and red. It con- 

 tains also a number of curious-looking objects, which vary 

 considerably in size and 'colour; the majority of these 

 bodies are spherical, and when separated from the irre- 

 gularly shaped particles forming the bulk of the dust, they 

 become interesting objects for the microscope. I shaU 

 confine my remarks more especially to these globular 

 bodies. Some of these are as perfect in form as the most 

 carefully turned billiard-balls, and have a brilliant polish. 

 The various colours which these globules exhibit give ad- 

 ditional interest to their examination. Some are trans- 

 parent crystal spheres, others are opaque white, many are 

 yellow and broAvn, and variegated like polished agates or 

 carnelian of different shades. The most abundant of the 

 highly polished balls are black : there are others which 

 look like rusty cannon-baUs ; some of these have an aper- 

 ture in them like a bomb-shell, and many are perforated 

 in all directions. To obtain these objects the dust should 

 be washed in a bowl and all the lightest particles allowed 

 to float away ; the remainder consists of fragmentary crys- 

 talline and ferruginous substances ; mixed with these are 

 the polished balls described, which, under the micro- 

 scope, by a brilliant reflected light, look like little gems. 

 To separate the spherical bodies from the irregular ones it 



* My attention was drawn to this subject by Mr. Johnson, of Wigan, in 

 November 1866. 



