CHAPTEE XIV 



THE SULPHUR CYCLE 

 EVERYONE who has been confronted with a bad egg is aware 



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of the unpleasant character of the final decomposition products 

 of albumin. The product most easily recognised chemically 

 is sulphuretted hydrogen or hydrogen sulphide, H 2 S, whose 

 presence is easily demonstrated by holding a paper soaked in 

 a solution of lead acetate in its vicinity. The smell of a rotten 

 egg is mainly due to this gas. Hydrogen sulphide is there- 

 fore often described as having a smell like rotten eggs. 



It has been shown in Chapter XII that most varieties of albu- 

 min contain sulphur in greater or less proportion, and they are 

 capable, like egg-albumin, when undergoing putrefaction, of 

 liberating this sulphur as hydrogen sulphide. It is easily seen, 

 therefore, that decomposing albuminous matter is capable of 

 causing considerable nuisance from this source. 



Sulphur appears to be an essential constituent of both 

 animal and vegetable life, and a knowledge of its transforma- 

 tions as it passes from one to the other is of the greatest im- 

 portance, especially in view of the possibility of nuisance being 

 produced during the process. 



The transformations which sulphur compounds undergo 

 bear a rough analogy to the transformations of nitrogen con- 

 sidered in Chapter XIII. Just as the plant takes up nitrate 

 to furnish the nitrogen for vegetable albumin, which nitrogen 

 ultimately reappears, after passage through the animal 

 organism, as urea and ammonia, to be finally again oxidised 



