92 Dr. Thomson on the Composition of [Aug.- 



that of the azotic gas evolved, we shall find the former rather 

 more than 1 1 times as great as the latter. From this, it follows 

 that the number of atoms of carbon in the coal bear the ratio to 

 that of the azote of 11 to 1. 



The weight of an atom of oxygen is to that of an atom of 

 hydrogen as 8 to 1 ; but the numbers 437 and 416 are to each 

 other nearly in the ratio of equality. Hence it follows, that the 

 number of atoms of hydrogen is eight times as great in the coal 

 as those of the oxygen. 



From these data, it is obvious that the smallest number of 

 atoms of which caking coal can be composed is the following : 



33 atoms carbon = 24-750 75-28 



1 1 atoms hydrogen . .. = 1-375 4-18 



3 atoms azote = 2-250 15-96 



1-5 atom oxygen = 1-500 9*58 



32-875 100-00 



So that the weight of an integrant particle of caking coal cannot 

 be less than 32-875 ; and it must be either that number, or a 

 multiple of it. 



What I consider as constituting the important part of this 

 analysis is the establishment of the fact that caking coal con- 

 tains three times as many atoms of carbon as it does of 

 hydrogen. 



2. Splint Coal. 



This species is not so easily decomposed when heated along 

 with peroxide of copper as the other species. The copper tube 

 must be kept for several hours in a strong red heat. We found 

 it necessary to urge the charcoal fire during the whole conti- 

 nuance of the experiment by means of bellows, otherwise the 

 evolution of gas immediately stopped. 



The mean of the trials made to determine the composition of 

 this coal gave the following results : 



From one grain of the coal, there were evolved 4-492 cubic 

 inches of carbonic acid gas and 0- 144 cubic inch of azotic gas, 

 reduced both to the mean temperature and pressure. The water 

 extricated during the experiment weighed 0-4 gr. equivalent to 

 0-044 gr. of hydrogen. 



Hence the constituents of a grain of splint coal are as follows : 



Carbon 0-568 



Hydrogen 0-044 



Azote 0-043 



Ashes. 0-100 



0-755 

 Oxygen 0-245, 



1-000 



