COAL APPLES. 11 



the centre of a block of coal. These spheroidal bodies are not 

 nodules in the strict sense of the word, but are forms caused 

 by a system of jointing, producing overlapped joints after the 

 coal has acquired its ordinary jointing-, for some apples show 

 a concentric structure through which the ordinary cleavage of 

 the coal passes. The more brittle the specimen, the more in- 

 distinct the grain. Sometimes composite apples occur in 

 which a smaller apple becomes enveloped by a larger one. 

 Professor Liversidge, of the University of Sydney, gives the 

 following analyses of a nodule, and a sample of the seam en- 

 closing it : 



Coal apple. Seam. 



Carbon 83.828 81.06 



Hydrogen 5.437 5.81 



Oxygen 8.236 6.52 



Sulphur 190 1.14 



Nitrogen 530 1.23 



Ash 1.779 4.24 



100.000 100.00 



Sp. Grv .. 1.294 1.24 



The proximate analysis gave : 



Coal apple. Seam. 



Moisture 3.32 2.21 



Volatile Hydrocarbon 32.41 36.70 



Fixed Carbon .... 62.35 55.82 



Ash 1.72 4.15 



Sulphur 0.19 1.12 



The sample of the seam was that of the whole seam, and 

 as the composition of the several beds comprising it varied, 

 this may, to some extent, account for the difference in the 

 analysis. Anyhow, one cannot expect to draw fair conclusions 

 from one set of results. In other countries, the analysis of a 

 coal apple and the seam in which it was found appear to be 

 much the same; sometimes one being a little higher in carbon, 

 and sometimes the other. This looks as if the change was 

 purely physical, not chemical. 



Most coals contain gases occluded in them, which are 

 given off on exposure to the atmosphere, sometimes with con- 

 siderable force, when they are known as "blowers." In some 

 mines, one can hear the gases continuously fizzing out of the 

 face. The gases held by coal are methane, carbonic 

 dioxide, nitrogen, and oxygen. They are present in various 

 quantities and proportions. The quantity of occluded gases 

 in coal does not appear to influence its liability to explosions. 

 A dense coal may occlude more gas than a softer coal, but the 

 latter, on account of its more porous nature, may readily yield 

 up the gases contained in it. Sometimes the gases are 



