DIFFICULTY OF OBTAINING MAGNESIUM. 135 



senses, is sufficient to move the heaviest stones, to lift and 

 tear up pavements, and to push up and sustain the materi- 

 als of which the branches and leaves of the tree are com- 

 posed, hundreds of feet into the air. 



It is by a force somewhat analogous to these in respect to 

 the minuteness of the limits through which it operates, and 

 the vastness of the power which it exerts within those lim- 

 its, that the particles of the metallic magnesium are held 

 in combination with those of oxygen in all the substances 

 in which it is found in a state of nature. And so firmly is 

 it held by this force, that, though innumerable experiments 

 were made with the substances in which it was combined, 

 it was a very long time before the existence of the hidden 

 metal in these substances was discovered. The discovery 

 was at length made in 1827. Small portions were separa- 

 ted, and the metal, as a metal, brought to view ; but it was 

 not until quite recently that methods were devised by 

 which any great quantities could be produced. 



Of course, in these attempts, the substance of the magne- 

 sium could be brought into its metallic form only by sep- 

 arating the oxygen from it, and this could be done only by 

 applying a greater force to the oxygen than that by which 

 it was united with the magnesium. This force was, as has 

 already been said, very great. Indeed, the eagerness with 

 which it returns to the combination, and which is the cause 

 of the great development of heat and light, is the measure 

 of this force. Thus the chemist, in separating the magne- 

 sium from its oxygen in its natural combinations, forces 

 the substances apart for the sake of witnessing the effects 

 produced by the violence with which they come together 

 again. The operation is very analogous to that of lifting 

 a stone high into the air in order to observe the force of 

 the concussion with which it strikes the ground in falling. 



