MR. J. B. DANCER ON COAL-ASH OR DUST. 293 



heit. The other thermometer is not so sensitive, having 

 less than four divisions to the degree. The total rise of 

 its freezing-point has been only •6 of a degree; but this is 

 probably owing to the time which elapsed between its con- 

 struction and the first observation being rather greater 

 than in the case of the other thermometer. The rise of 

 the two thermometers has been almost identical during the 

 last nineteen years. 



A projection of the observations given above is shown 

 in the following diagram : — 



!?< r* § 5^ JO qt OJ eS 



XXVI. On the Microscopical Examination of Coal- Ash or 

 Dust from the Flue of a Furnace, illustrated by the Mi- 

 croscope. By J. B. Dancer, F.R.A.S. 



^ead April 2nd, 1867. 



When coal is burnt in a furnace to which atmospheric air 

 has free access, a portion is converted into gaseous and 

 volatile matter, and the incombustible substance which 

 remains is the ash. The amount of ash in coals from dif- 

 ferent localities is very variable ; it is said to range from 



