Mr. Denham Smith on Ferric Acid. 499 



curs in such minute quantities as to render its detection im- 

 practicable by the ordinary tests ; and partly from the solubi- 

 lity of sesquioxide of iron in potash under certain conditions, 

 — a fact noticed by M. Chodnew*. The first error occurs in 

 pp. 242—3, [Phil. Mag. S. 3. vol. xxiii. p. 220.] where it is 

 stated that chlorine gas passed into " the deep amethystine 

 solution of ferrate of potash, keeping the vessel cool during 

 the passage of the gas, gives a solution of a lighter colour 

 than the amethystine liquid." This solution proved to be a 

 very dilute solution of permanganate of potash. I do not 

 however find the intensity of colour altered by the gas, and 

 from the permanent nature of this solution I hope eventually 

 to succeed in isolating the potash salt. 



The second is the more serious error (p. 247), where I an- 

 nounced the existence of an oxide of iron forming a green salt 

 with potash ; such a salt I now believe does not exist. I pre- 

 pared a quantity of this green solution by boiling ferrate of 

 potash and rapidly filtering the clear green solution ; this 

 gradually decomposed, and the brown deposit was dissolved 

 in hydrochloric acid, affording a yellow solution, to which a 

 solution of hydrochlorate of ammonia was added, and then 

 caustic ammonia; a small quantity of a reddish-brown floccu- 

 lent precipitate, resembling sesquioxide of iron, fell ; this col- 

 lected, washed and redissolved in hydrochloric acid, gave a 

 yellow solution styptic to the taste, which, diluted and ren- 

 dered as neutral as possible, immediately struck the respective 

 colours blue and blood-red, with ferrocyanate and sulpho- 

 cyanate of potash, evidencing the presence of iron ; the am- 

 moniacal solution was evaporated to expel excess of ammonia, 

 and tested with ferrocyanate of potash, when the voluminous 

 flesh-coloured precipitate, characteristic of manganese, was 

 produced : potash added to another portion of this ammo- 

 niacal solution gave, on the application of heat, a small quan- 

 tity of the dark brown oxide of manganese. 



Having, in the paper referred to, satisfied myself that iron 

 did form a salt with potash, and also that the green salt con- 

 tained this metal, I was too hastily induced to imagine that 

 the colours, of the two solutions alluded to, arose from iron, 

 not anticipating the existence of manganese in the precipitated 

 sesquioxide of iron. Whether an oxide of iron, intermediate 

 to the sesqui and teroxide, and possessing the qualities of an 

 acid, really exists, I am at present unable to state, but hope 

 to be able to decide this point, as well as to communicate some 

 new facts respecting ferric acid and its combinations in a fu- 

 ture paper. 



* Journ.fur Prakt. Chemie, Band xxviii. 

 2 K2 



