188 EXPERIMENTS ON MOLYBDEffi. 



since these pieces were thrown from the focus of the vol- 

 cano, at the very moment when its contents were in the 

 highest fusion. 



shoukibecom- selves, to solve so many difficulties," says Mr. Fl. de Bel- 



p:ired wUh levue at the outset, «' must be carefully to compare the 

 those of art. •' ^ 



products ot volcanoes, and the cn-cumstances in which they 



are found, with the results of those large bodies of fire, by 

 means of which man separates, dissolves, brings together, 

 and combines minerals, and produces in them a change of 

 Tlilsdoiie. form." This I have just done. I have compared the pro- 

 ducts of our glass-house furnaces with those included in 

 lava, and the result of my comparison is, that they are to- 

 tally different. 



f To be concluded in our next. J 



Experiments on Molybdena : by Christian Frederic 



BUCHOLZ. 



{Continued from p. 13%.) 



VI. Phenomena presented by molybdena exposed to the action 

 of Jire in contact with atmospheric air. 



l^oTybdeiia Jt^xp. 22. xa. Piece of molybdena in the metallic state, 

 calcuicd. weighing fifty-three grains, of a moderate consistency, and 



an ashen gray colour, was put into a Hessian crucible, and 

 the beat raised gradually. Scarcely had the heat reached a 

 deep red, when the surface of the metal became of a brown- 

 ish yellow, and soon changed to a fine violet, inclining to 

 indigo. The metal being withdrawn from the fire and 

 broken, its central part was still gray, and had undergone 

 Oxided in dif- no alteration. From this nucleus to the surface the colour 

 rent degrees. pro^jee^Jefi Jn gradation through a yellow and brownish yel- 

 low to blue. The metal having been again exposed to the 

 same degree of fire for a sufficient time, it became entirely 



blue: 



