llISfORY OP PilUSSlATESi 91 



blue. We shall examine the particular mixture of these two 

 salts farther on : but if the residuum have been washed with 

 care, acids will not give rise to more blue. This washing not easily re- 

 is very tedious, it is true; for I have been obliged to pour ™° sn e - y 

 boiling water at" least twenty times following on a single 

 drachm of residuum, before I could obtain it completely 

 free ; but when this is at length accomplished, acids will 

 dissolve it, without any blue being produced. 



When these residuums effervesce with acids, they contain Effervescence 

 carbonate of potash or of lime. The former may be carried botiate. 

 off by ablution ; and the second will be detected by vinegar 

 after the washing. It is not the red oxide therefore, that Red oxide of 



occasions this effervescencs: it cannot indeed combine with ' r0 " 0( r» /> ot 



unite with car- 



the carbonic acid, consequently cannot take it from the bonic acid. 

 potash, in exchange for the prussic acid, which it cedes toih 

 In nature, as in art, it is only the oxide of iron at a mini- 

 mum, that can combine with the carbonic acid. 



A pound of Prussian blue of the shops of fine quality, Prussian blue 



has afforded as much as nine ounces and half of crystallized a ° Tx 



, . •'of prussiate of 



prussiate of potash. It is by no means uncommon, to find potash. 



in the mother water left to itself truncated octacdra an inch 



in diameter. If the blue be contaminated with sulphuric 



acid, at least four crystallizations will be requisite, to free 



the prussiate entirely from sulphate of potash. The mother Lixivia not 



water contains alumine, sometimes in abundance, sulphate pure ' 



and phosphate of potash, ferruginous alkaline carbonate, 



&c. Hence may be inferred the importance of employing the crystals 



crystallized prussiate of potash in analyses, and not simple 1 ' ere .j 01 ^ j 



lixivia of Prussian blue, as was formerly done. Prussiate as a test. 



of potash'is unalterable in the air, whether dry or damp: Characters of 

 r ' . tne prussiate, 



boiling it for any length of time does not alter its nature : 



its taste is sweetish, and slightly saline, leaving after it a 

 faint impression of bitterness. It is insoluble in alcohol ; 

 which separates it from its aqueous solution in a white snow 

 with the lustre of mother-of-pearl ; and this lustre it retains 

 when dry, so that it might be mistaken for the argentine 

 gauze of acetate of mercury. Redissolved in water it re- 

 produces a common solution of triple prussiate. 



This salt r which I shall term a triple salt, or trisule, in- which is a tri- 

 discriminately, to distinguish it from the simple prussiate of p e sa ?* 

 H 2 potash, 



