DISSERTATION ON PRUSSIAN BLUE. Part II. 1783. 



SECTION XL 



(a) The colouring liquid rectified as directed in the 

 preceding paragraph (p. 244) appears to be neither acid nor 

 alkaline ; for it neither reddens paper dyed with lacmus, nor 

 does it restore the colour of such paper after it has been 

 made red ; but it renders turbid the solutions of soap and 

 hepar sulphuris. (b) The same liquor, mixed with fixed 

 alkali, produces a compound which, though it contains a 

 superabundance of the colouring matter, restores the blue 

 colour of paper reddened by an acid. If this compound be 

 distilled to dry-ness, there goes as much of the colouring 

 matter over as can disengage itself from the alkali. The 

 residuum is soluble in water, and the solution has all the 

 properties of the best lixivium sanguinis. This solution is 

 decomposed by all acids, even by the aerial acid (Sec. in.). 

 (c) Combined with caustic volatile alkali, it forms a kind of 

 ammoniacal salt, which has the smell of volatile alkali, though 

 the colouring matter be superabundant in the compound. 

 This salt instantly rises by distillation, and there remains 

 nothing but pure water in the retort. I doubted at first 

 whether this matter could enter into a union with the 

 volatile alkali ; but was soon convinced, when I saw that the 

 solution of magnesia in the colouring matter was precipitated 

 by volatile alkali. Besides, this ammoniacal salt showed the 

 same phenomena in the precipitations as the pure lixivium 



