180 Mkcelhineous Intelligence. 



biquet admits, however, that the idea may be entertained of the 

 white compound being an union of the Prussian blue and sul- 

 phuric acid. 



On submitting Prussian blue (pure) to the action of sul- 

 phuretted hydrogen in solution for some time, small brilliant 

 crystals of a yellowish colour appeared, which became blue in 

 contact with the air, and were proto-prussiate of iron. 



M. Robiquet has succeeded in obtaining the acid of Prussian 

 blue in a solid crystalline state, by a process different to that 

 of Mr. Porrett's. Strong muriatic acid, in large quantity, is 

 mixed with Prussian blue (pure,) and, left for some time, the 

 sediment becomes of a green colour, and then yellow ; if water 

 be added to this mixture, it is again rendered blue, but if no 

 water be added, and it be allowed to stand in a narrow vessel, 

 the sediment falls to the bottom, and a deep red brown solu- 

 tion covers it ; this u an acid solution of muriate of iron, and 

 cannot be made to produce a blue by any method tried. The 

 sediment was allowed to contract itself for several days, and 

 the supernatent liquor drawn off by a little syphon, the wash- 

 ing was then repeated with concentrated muriatic acid as before, 

 antil the process was supposed complete. The magma was then 

 collected into a capsule, and placed in a receiver, containing 

 much lime, to dry. When dry, it was digested in alcohol, 

 filtered and evaporated spontaneously, and a number of small 

 crystals were obtained. These crystals were separated, washed 

 in fresh alcohol, dissolved, and again crystallized, and were 

 then the pure acid of Prussian blue, or the ferro chyazic acid 

 of M. Porrett. 



These crystals appear at times to be tetrahedral ; they are 

 white when pure, but become slightly blue by exposure to the 

 air. They have no odour, their taste is acid and peculiar, 

 without being like that of prussic acid. They are soluble in 

 water and alcohol. The colourless solution produces an immense 

 precipitate of Prussian blue in persulphate of iron. The acid 

 perfectly saturates potash, and produces the common triple prus- 

 siate of potash. If it be heated, a considerable quantity of 

 prussic acid first passes off, the remainder becomes of a deep 



