IftO Mr Bald on the Fires tJiat take place in Collieries. 



wards, and, on the 21st May, the last day on which I have a 

 report of the temperature, the thermometer stood at 84°. 



As this subject is very interesting, the register of the tem- 

 perature as taken by Mr Dewar is annexed. 



We therefore conclude, that the fire is about extinguished, 

 and that our labours will be successful. We now expect that 

 the temperature will progressively lower by slow degrees, be- 

 cause there is a vast mass of heated rock, considerably above 

 the immediate contact of either water or steam. 



It has been a matter of physical investigation to show by what 

 chemical action spontaneous ignition is generated in those coals 

 where pyrites abound. Air and moisture seem to be indispensa- 

 bly necessary ; and it is also requisite that the coal rubbish be of 

 considerable thickness, — for, if it is only a foot or two in thick- 

 ness, the decomposition will take place with a very small degree 

 of heat, but fire will not be the consequence. In this case, it 

 appears that the heat is dissipated the instant it is formed ; 

 whereas, when the heap is of several feet in thickness, there is 

 a certain degree of pressure, and the heat, as it is formed, accu- 

 mulates. This accumulation of caloric hastens the more rapid 

 decomposition, when heat is also more rapidly generated, and 

 that to the point when actual ignition commences. The heat 

 and fire which are generated in wet hay, seem to depend on si- 

 milar circumstances ; for, without accumulation and pressure, 

 actual fire will not take place. As to the chemical action, seve- 

 ral principles may be acting, namely, the decomposition of at- 

 mospheric air, when the iron of the pyrites seizes the oxygen of 

 the air, and sets the latent caloric free ; the oxygen and hydro- 

 gen of the water may highly contribute to encrease the tempe- 

 rature ; and we know that it is a common occurrence for the 

 coal rubbish, which is mixed with pyrites, at the mouth of pits, 

 to take fire from the same causes ; but depth and pressure are 

 always necessary to produce the result. 



What I have thus narrated, and explained by diagrams, 

 shews the risk to which mines of coal and miners are exposed ; 

 in particular the latter, who are brought into the most trying 

 situations, surrounded with darkness and the pestilence, — where 

 the mind has full time to contemplate the danger, and the 

 approach of death ; and when the thought of home, of a wife, 

 and of children, touch the heart with the most painful and 



