318 Mr. J. Stevenson on the Chemical and 



seams less than one foot in thickness and other thinly dis- 

 tributed carbonaceous matter amount to 100,000,000,000 

 (100 thousand million) tons. The total amount of coal and 

 other mineral carbonaceous matter in the United Kingdom 

 would then be 300,000,000,000 (300 thousand million) tons. 

 If we now suppose that the whole surface of the earth, 

 whether dry land or covered by sea, contains on the average 

 the same amount as the United Kingdom, then the total 

 quantity on the earth will be 300,000,000,000x1630, or 

 489,000,000,000,000 (489 million million) tons— an amount 

 which is practically equivalent to the total free oxygen of the 

 atmosphere. 



The total weight of the atmosphere is 5,200,000,000,000,000 

 (5200 million million) tons, as may be readily calculated 

 from the data that it is equal to the weight of a layer of 

 mercury 30 inches deep, or the weight of a layer of water 

 34 feet deep over the whole surface of the earth. And as 

 23 per cent, by weight of the atmosphere consists of free 

 oxygen, the total free oxygen weighs very nearly 1,200,000, 

 000,000,000 (1200 million million) tons. The amount of 

 pure carbon that would be required to convert this quantity 

 of oxygen into carbonic acid is 450,000,000,000,000 (450 

 million million) tons. Now if we suppose that the average 

 amount of combustible matter in coal is equal to 90 per cent, 

 of carbon (at least so far as its requirements of oxygen for 

 combustion are concerned), then the amount of coal equi- 

 valent to the above figures would be 500,000,000,000,000 

 (500 million million) tons ; a figure which is very similar to 

 the estimate of the coal and other carbonaceous matter in the 

 world which we have just made on the assumption that the 

 amount present in the United Kingdom is something like the 

 average for the whole world. It should also be noted that 

 the above quantity is equal to a layer of coal 2|- feet thick 

 and of 1*3 specific gravity over the entire surface of the globe, 

 or a layer 5 feet thick over the whole " continental " and 

 " transitional " areas. 



Of course the objections will be at once made that the 

 United Kingdom is probably very much richer in coal than 

 the rest of the world, and also that we should leave the water- 

 covered areas out of account altogether in making such a 

 calculation. As for the first objection, we can only say that 

 it may be a strong and vital one, but we have no definite 

 proof as yet. We may of course be quite sure that many 

 large areas of the world are very much poorer in coal than 

 the United Kingdom, but then again we know that other: 

 districts are very rich, perhaps even richer than the United 



