3-16 Materials for a History of the Prussiates. 



kaline prussiates or earthy triples should not for the future en- 

 ter into the class of reagents useful in analyses, for this plain 

 reason, that' they cannot discover the iron in any solution, 

 without, at the same moment, adding their own : they 

 ought only to he allowed to, make a figure among those 

 which, like turnsole gall-nuts, &c, are confined to the class 

 of reagents proper for indicating merely if such and such 

 a principle be presented. 



Diluted sulphuric acid, when applied to the triple prus- 

 siate, furnishes similar results with the muriatic. 100 parts 

 of prussiate restore by this method from 115 to 116 of 

 sulphate of potash. If we knew exactly how much al- 

 kali there is in the sulphate, we might infer from the esti- 

 mate the base of the prussiate of potash. 100 parts of 

 crystals of prussiate lose ten of water by distillation. 



Tn order to complete its decomposition by the acids, the 

 ebullition must be kept up at least half an hour, in order to 

 dissipate the gas entirely, and to obtain the complete sepa- 

 ration of the white prussiate which is formed during the 

 operation. 



The prussiate of potash is dissolved cold in the muriatic 

 acid, without being decomposed. This mixture requires, 

 according to Berthollet, the assistance of light or of heat. 



Vinegar assisted by ebullition also decomposes it : the 

 prus^ic gas escapes, and the white prussiate is formed; it 

 does not become blueish so rapidly as with the foregoing 

 acids : in short, this prussiate, which does not appear ex- 

 cept at the very moment when the ternary combination be- 

 gins to be disorganized, strongly confirms by its whiteness 

 that it is really the oxide at the minimum oxi\y , which has the 

 privilege of entering into the formation of the triple prus- 

 siate : this is one of those truths which Scheele has com- 

 pletely established. Notwithstanding this, however, the 

 distinction of the oxides in these circumstances is a point 

 to which subsequent chemists have not paid proper at- 

 tention. 



Black Oxide Element of Prussian Blue. — We shall now 

 prove that this oxide, in an invariable dose, is an essential 

 principle in the constitution of the triple prussiate ; but it 



is 



