FLUORINE IN SEA-WATER. 431 



of steamers, he obtained conclusive evidence 

 of the presence of this element, in the produc- 

 tion of hydrofluoric acid vapour, which has the 

 property of corroding glass almost instantly. 

 By properly treating the crust thus obtained, 

 he was able to etch several pictures on glass, 

 which were exhibited at the scientific meeting 

 before which his experiments were brought. 

 In all probability, as fluorine has been found 

 both in the waters of the German Ocean, of 

 the Firth of Forth, in the teeth of the walrus, 

 and in the ashes of marine plants, fluorine in 

 minute portions is one of the regular consti- 

 tuents of sea-water. Professor Forchhammer 

 states that he has examined many shells and 

 marine products from various localities, and they 

 all gave evidence of the presence of the same 

 body, the quantity being always greater in sea 

 than in land animals. 



The shields of many infusorial animalcules 

 found in sea-water are largely comp_osed of 

 silica; yet silica is not found as one of the 

 mineral ingredients of sea- water. In all pro- 

 bability they are able to obtain it even when it 

 exists merely in a state of mixture in water. 

 Dr. Smith discovered silicious-coated animal- 

 cules in the water of the Thames only in those 

 parts of it which receive the drainage of the 

 metropolis, and he ingeniously conceives the 

 silex to be derived from the decomposition of 



