94 HISTORY Ot PRUSSIATES. 



ing attention to the conditions necessary to ensure success, 

 have found, that the base of the green sulphate might be, 

 come that of a prussiate different from the prussiate which 

 tendered blue nas f or ;t s b ase oxide at a maximum, But as the black ox- 

 tl'ie atinos- ide, ' n passing from one combination to another, never loses 

 phere. jt s disposition to acquire a surplus of oxigen, we perceive^ 



as soon as the matrass is removed from the fire, that the at- 

 mosphere reacts on the milky mixture, and rapidly produces 

 tints of colour, which gradually diffuse over the whole a 

 fine deep blue. 

 Another me- This product may be obtained in another way. Let fall 

 i'ngth^pru"- P^ ussiate of potash grain by grain into a very dilute boiling 

 siate. Bolution of green sulphate, and a precipitate will make its- 



appearance, the whiteness of which will resist the action of 

 the air somewhat longer. 



I shall add a few other processes, which, If they do not 

 increase conviction, may be interesting from the variety of 

 the means employed. 

 A third, Fill two glasses, one with nitrate of iron, and the other 



with green sulphate, each in a state of very dilute solution; 

 and drop into each a crystal of prussiate of potash. In the 

 former we shall see the crystal instantly coloured of so deep 

 a blue, that it resembles black velvet. In the latter it cracks, 

 separates, and falls into a white powder : but, as it had im- 

 bibed atmospheric air previous to the experiment, the pre- 

 cipitate is variegated like sage cheese. 

 A fourth. -kct * w0 g' asses De hUed with boiling water; add to each 



a few drops of prussiate of potash, and to one of them a, 

 few drops of hidrosulphuret of potash, or of ammonia, 

 likewise. Let fall into each a few drops of nitrate of iron; 

 and the former, as might be expected, will give a complete 

 blue; but the latter will exhibit the amusing appearance of 

 a precipitate, which, at first blue, will rapidly lose its co- 

 lour, and become white, The theory of these facts is so 

 obvious, that I shall pass it over: neither shall I here repeat 

 all the other experiments given in my first paper to establish 

 the existence of two prussiates of iron. If the prussiate at 

 a minimum have no colour when it is not acted upon by the 

 atmosphere, we see, that the dried green sulphate is equally 

 White prus» colourless. The absence of colour in one of these salts is^ 



surely 



