92 



PR0CEEDINC4S OF THE ACADEMY OF 



[1892. 



originally taken by it chiefly from the atmosphere, and conversely, 

 the quantity that will be returned to the atmosphere on the com- 

 bustion of such coal, making a reasonable allowance in the last case 

 for such portion of the coal as is inaccessible to man and can there- 

 fore never be consumed through his agency. 



The following computations bearing on this point and graduated 

 to meet several difierent estimates of quantity, have been made Avith 

 the assistance of Mr. 'B. C. Tilghraan, an accomplished young 

 chemist of experience and capacity and a member of this Academy. 



The oxygen of the atmosphere, 23 per cent, by weight (or about 

 21 per cent by volume), if all burned into carbonic acid would pro- 

 duce 682*56 lbs. per square foot of earth surface. This would cor- 

 respond to a weight of 185"76 lbs. of carbon in suspension per 

 square foot of earth surface, and at a specific gravity of 95 lbs. per 

 cubic foot (the average for anthracite) would correspond to a 

 stratum of carbon 23*45 inches thick over the entire earth surface or 

 to 83'71 inches thick on the land surface, assumed at 28 per cent, 

 of the whole. With the aid of Mr. Tilghman the following tabular 

 statement has been constructed from these data, which are repeated 

 in its first horizontal line. 



The first horizontal line of the table represents, merely as a basis, 

 the theoretical results of a total absorption of all free oxygen by 

 carbonization, for which, however, all the available accumulations 

 of carbon that we know of are of course inadequate; for the 

 return to the atmosphere of the carbonic acid formerly subtracted 



