What's the chemical formula of "Everitt's salt"? According to my school textbook (which is notorious, for being in possession of several errors), a certain "Everitt's salt" is a complex that results from the reduction of Prussian Blue.

Everitt's salt (according to our inglorious textbook)  has the chemical formula $\ce{K2[Fe(CN)6]}$... which I straightaway dismissed as nonsense, because it would mean it's got $\ce{Fe^{4+}}$ (ferryl ion). From my (very limited) knowledge of the subject, the ferryl ion doesn't look like something that would occur in any reasonably stable compound; since Everitt's salt is, well, a "salt" (and since salts can usually be crystallized into stable solids).

Google wasn't much help in this regard,


  
  
  I've no idea how to interpret the formula that is supposedly that of Everitt's salt 




Questions:

1) Is there really something called "Everitt's salt"? Is it produced by the reduction of Prussian Blue?

2) What's its chemical formula?
According to various sources Everitt's Salt has the formula $\ce{K2Fe[Fe(CN)6]}$, where both $\ce{Fe}$ are in the $+2$ Oxidation State. Everitt described it as a yellow precipitate, resulting from the reaction:

$$\ce{2 K4Fe(CN)6(aq) + 6 H2SO4(aq) \to 6 HCN(g) + 6 KHSO4(aq) + K2Fe[Fe(CN)6](s)}$$

Acc. Everitt, the wet salt can be oxidised to Prussian Blue by the action of air (oxygen).

Source.