952 A TREATISE ON METAMORPHISM. 



metals united with, sulphur, iron of course dominates over all others com- 

 bined. We may therefore use FeS 2 , the most common sulphide, to illustrate 

 the process. If the iron were changed to the ferric oxide and the sulphur 

 to sulphuric acid, the reaction may be represented by the equation — 



2FeS., -(-150 +4H,0 = Fe 2 3 +4H 2 S0 4 . 



Since sulphates are not known in the original igneous rocks, nor in 

 meteorites, it is to be presumed that practically all the sulphates which now 

 exist are a result of the oxidation of the sulphur of the sulphides by oxygen. 

 The total amount of sulphates in the ocean is vast. The amount of 

 sulphur present as sulphates in the ocean is estimated by Dittmar to be 

 1,187,000,000,000,000 metric tons. The oxygen derived from the atmos- 

 phere to unite with this sulphur in order to produce sulphuric acid is 

 1,777,200,000,000,000 metric tons, or 145.25 per cent of that now in the 

 atmosphere. If the sulphur in the sulphate deposits be estimated as equal 

 to one-tenth that in the ocean, the amount of oxygen required for the 

 production of all the sulphates would be 159.77 per cent of that now in 

 the atmosphere. As shown by the above equation, to oxidize the iron of 

 sulphides to the ferric oxide requires one-fourth as much oxygen as the 

 oxidation of the sulphur to sulphuric acid. Thus for this part of the 

 process 39.94 per cent of the amount of oxygen in the atmosphere would 

 be required. Summing all these amounts we find that for the oxidation of 

 the sulphides 2,443,473,000,000,000 metric tons of oxygen, or 199.91 per 

 cent (i. e., twice), that now in the atmosphere, has been consumed. (See 

 p. 1003 for possible modification.) 



It is shown elsewhere that sulphates produced b}?- oxidation of the 

 sulphides are extensively reduced to sulphides by carbonaceous material, 

 and this cycle of reproduction of sulphates and sulphides for some of the 

 material doubtless has been repeated many times. The above is a first 

 attempt to roughly estimate the amount of oxygen required to produce the 

 present existing sulphates, not the total amount of oxygen which has been 

 consumed in the oxidation of the sulphides to sulphates through geological 

 time. So far as the sulphides have been changed to sulphates and reduced 

 again to sulphides by organic matter, a consideration of the amount of 

 oxygen which is drawn from the atmosphere by this process has already 

 been accounted for in considering the relations of oxygen and carbon. 



