DOMAIN XI. DECOMPOSED. 21 Q 



contains a notable proportion of muriated 

 magnesia, and a small proportion of selenite. 

 From these data we may infer, that when 

 this stone is wetted by sea water, the sele- 

 nite is decomposed by the mild magnesia 

 contained in the stone, and intimately 

 mixed with the calcareous earth. Of this 

 decomposition, two results deserve atten- 

 tion : 1. the production of vitriolic Epsom. 

 2. the extrication of mephitic air; the 

 muriatic magnesia of the sea water serving, 

 during this extrication, the purpose of at- 

 tracting and detaining a sufficiency of 

 moisture. This air thus slowly generated, 

 and meeting the dry oxygen of the atmo- 

 sphere, forms nitrous acid, highly mephi- 

 tised ; but it soon acquires a due propor- 

 tion of oxygen, by deoxygenating the vi- 

 triolic contained in the Epsom salt, which, 

 by successive depredations of this sort, is 

 gradually destroyed. Part also must unite 

 to the mild calx, which in its turn is de- 

 composed by the remaining mild magnesia ; 

 more mephitic air is set loose, and more 

 nitrous acid is produced, until the stone is 



