276 NOTE ON THE UNDERGROUND FIRE. 



bromine and iodine. These refuse products, together with waste 

 salt, and furnace debris, were carried away to the rubbish heaps. 

 The quantity of coals required for effecting the evaporation was 

 very large ; but, as fuel was cheap and abundant, not much 

 regard, therefore, seems to have been paid to its economic con- 

 sumption, for a very considerable proportion of the pan rubbish 

 consists of coals and imperfectly consumed cinders, the combus- 

 tion of which forms the present underground fire. 



The first indications of a fire smouldering beneath the surface 

 about Carpenter's Hill was observed in February, 1872, and 

 in the following month the ground was discovered to be much 

 heated, and smoke was seen issuing from it in several places. 

 Iron rods were thrust down at various points to depths varying 

 from six to fifteen feet, and after remaining a few minutes were 

 found to be very hot. The fire extended to the streets and 

 courts about the hill, and up to the present time about twenty 

 houses have been destroyed, while many more are imperilled by 

 its threatened extension. 



A careful examination of a section of the rubbish deposit will 

 remove any difficulty that may be felt with reference to the re- 

 quisite supply of oxygen for sustaining the combustion. Some 

 layers consist of fine granulated compact ash, but the greater 

 mass is coarse and open, having numerous connected and ramified 

 interstices and cavities filled with atmospheric air. Through 

 these the gaseous products of combustion and vapours find their 

 way to the surface, and the cavities containing air highly rarified 

 by decomposition, and a hot temperature, obtain a continuous 

 fresh supply by atmospheric pressure. With reference to the 

 origin of the fire some persons think it has arisen from sponta- 

 neous combustion, or that a small smouldering fire has remained 

 until now dormant in the pan rubbish since its first deposit; 

 while on the other hand it is maintained that it originated from 

 a strong fire applied externally to the heap. 



From the chemical nature of the refuse deposit, the scattered 

 position of its unconsumed coal, and the considerable time that 

 has elapsed since its deposition, the conditions are entirely want- 

 ing to render at all probable the spontaneous combustion theory. 



