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1819.] some neu) Combinations of Prussia Acid 445 



still moist. The process is the same as in the preceding experi- 

 ment, excepting that the prussiate of potash must be added to 

 the mixture before introducing the muriatic acid. 



X. Blue Prussiate of Copper. 



Copper presents the singular phenomenon of being able to 

 furnish two permanent prussiates of different colours. 



If we pour a strong solution of prussiate of potash on pure 

 copper tilings, and then add a sufficient quantity of muriatic acid 

 to decompose the prussiate, and to dissolve a portion of the 

 copper, the metal dissolved in presence of the prussic acid forms 

 a very beautiful blue prussiate. This combination does not, like 

 the preceding, depend upon the temperature. Heat merely 

 increases the rapidity of its formation, 



When we treat granulated tin in the same manner, we obtain 

 likewise a blue prussiate, but we must employ nitroinuriauc acid 

 and heat. 



XI. Blue Prussiate of Mercury. 



To form the blue prussiate of mercury, the red oxide of that 

 metal is boiled in water, and a solution of prussiate of potash 

 previously decomposed by muriatic acid is added to it. The iron 

 contained in the prussic acid changes its condition so as to 

 become proper for forming the blue insoluble prussiate of mer- 

 cury ; while the acid without iron forms a colourless soluble 

 prussiate. This proves sufficiently that iron is a constituent part, 

 of the prussic acid employed in these experiments. The blue 

 prussiate of mercury, when first formed, is light green, and 

 passes slowly to blue by exposure to the air. 



XII. Prussiate of Iodine. 



If we boil iodine in a solution of prussiate of potash, adding 

 muriatic acid, we obtain a blue prussiate with a shade of purple 

 of the greatest beauty. When first formed, it is light green, 

 and requires a long exposure to the air to give it a blue colour. 



XIII. Prussiate of Alumina. 



The opinion that alumina forms no combination with prussic 

 acid is so generally established that when 1 began my trials with 

 this earth, I had little expectation of success. In fact the sul- 

 phate of alumina precipitated by prussiate of potash gives no 

 colour either when cold or hot. However, I observed that when 

 the salts in the mixture were concentrated, the alumina, after 

 long boiling, assumed a very distinct blue colour. The following 

 trial furnished me with a more complete combination. 



I pulverized together equal parts of sulphate of alumina and 

 prussiate of potash. I introduced them into a small matrass 

 without water, and heated them over a spirit of wine lamp to 

 cause them to melt in their water of crystallization. The mix- 

 ture became blue as soon as it began to swell. I regulated tin 



