EFFECTS OF AIR UPON MUD, ETC. 459 



water and air, and a definite fixedness of com- 

 position is attained by the compounds thus 

 situated, preparatory to their removal and sub- 

 mergence beneath the waters of the great deep. 



In our own mild climate these decompositions 

 are so slight, though constant, as to be without 

 any perceptible effect upon the air of their vici- 

 nity, and it is well known that the air near the 

 sea-coast is generally highly pure and salu- 

 brious. But in tropical countries the case is 

 widely different. The full influence of the 

 tropic's sun favours all these decompositions to 

 a fearful extent, and the most subtile and deadly 

 poisons are produced upon the sea-coast. 



It was until recently considered that the 

 fearful mortality on the coast of Western Africa, 

 was due to the development of sulphuretted 

 hydrogen gas as a result of the mutual reaction 

 of vegetable matter and the sulphates in sea- 

 water. But Dr. Me William, in the Medical 

 History of the Niger Expedition, has shown 

 that it is erroneous to believe the sea on 

 the African coast to be impregnated with this 

 gas. A large number of experiments failed to 

 indicate the slightest trace of this gas in the sea- 

 water. It was most probably produced in the 

 bottles submitted to Professor Daniell, who first 

 proposed this theory, by a decomposition subse- 

 quent to the time of the collection of the water. 



