42 Materials for a History of the Prussiates. 



coat of aqueous vapour, and the scale then expressed the 

 degree of expansive capacity of the water-gas of the air with 

 the greatest precision possible. This kind of hygrometer, 

 besides the nicety of its results, also has the advantage that 

 an experiment may be made without loss of time and trouble, 

 and does not lire the observator like the former methods. 



JX. Materials for a History of the Prussiates, 

 By Af. Proust*. 



Part Second. 

 Some Precipitations by the simple Prussiate. 



J- ins prussiate yields, with metallic solutions, results dif- 

 ferent from those of the triple prussiate. Scheele had already 

 remarked some of them, and the following came under my 

 observation : 



Silver. Triple prussiate : a white precipitate which soon 

 became blue, on account of the white prussiate of iron 

 which is mixed with that of silver. 



Silver. Simple prussiate : a white curd which does not 

 change. 



Gold. Triple prussiate : nothing. 



Gold. Simple : white precipitate, which becomes of a fine 

 yellow. 



If we heat the mixture, this precipitate, when heated, 

 does not fulminate ; it is a true prussiate of gold. When 

 heated in a retort, it gives water, abundance of empyreu- 

 matic oil, carbonic acid gas, which burns with a blue flame, 

 and a residue of gold mixed with chareoal powder. Upon 

 looking over my notes I do not find ammonia mentioned, 

 perhaps from neglect. 



Molybdic Acid and Oxide of Tungsten. — The two prus- 

 siates yielded nothing in either of these cases. 



Titanium. Triple prussiate : Prussian blue proceeding 

 from the iron always retained by this oxide. 



• From Annates de Chimie, tome Ix. p. 225. — For M, Proust's first paper, 

 H t the preceding volume. 



Titanium* 



