ON MOLYBD^NA 171 



SECTION VIIT. 



(a) Concentrated vitriolic acid dissolves, with the assist- 

 ance of heat, a great quantity of this kind of earth. The 

 solution acquires a very fine blue colour, and becomes thick 

 on cooling; the colour disappears on the application of heat, 

 but returns again when it grows a little cool; as also in 

 water (Sec. in.). In a stronger heat the earth parts with 

 the vitriolic acid, and remains behind unaltered. (6) The 

 nitrous acid has no effect upon it ; (c) but when boiled with 

 muriatic acid it dissolves in considerable quantity ; and when 

 this mixture is distilled to dryness, there remains a dark 

 blue residuum. If the heat be increased, there arise white 

 flowers with a little blue sublimate, and in the receiver is 

 found smoking muriatic acid. The residuum is grey. The 

 sublimate and the flowers moisten in the open air, stain 

 metals wetted with the solution blue, and are only earth of 

 molybdama volatilised by muriatic acid, (d) If one part of 

 this earth be distilled with two parts of vitriolated tartar, 

 there goes over at last, when the heat is very strong, a 

 little vitriolic acid. The remaining earth is more soluble in 

 water than before, (e) Distilled with two parts of nitre, it 

 expels smoking nitrous acid. The residuum dissolved in 

 water is a neutral salt which precipitates all metallic 

 solutions, and resembles the salt of Sec. vn. (g). (/) When 

 it is distilled with two parts of pure common salt, the acid 

 is expelled in a fuming state, and there arise into the neck 

 of the retort white, yellow, and violet - coloured flowers, 

 which become moist in the air ; and when sprinkled on 

 metals give them a blue colour (c). 



