$F{{e}^{+2}}+\underset{\text{Ferricyanide}}{\mathop{{{[Fe{{(CN)}_{6}}]}^{3-}}}}\,\to F{{e}^{+3}}+\underset{\text{Ferrocyanide}}{\mathop{{{[Fe{{(CN)}_{6}}]}^{4-}}}}\,$

$F{{e}^{+3}}+{{[Fe{{(CN)}_{6}}]}^{4-}}\to {{\{Fe[Fe{{(CN)}_{6}}]\}}^{-}}$

$F{{e}^{+3}}+{{[Fe{{(CN)}_{6}}]}^{4-}}+{{K}^{+}}\to \underset{\begin{smallmatrix} 
 \text{Pot}\text{. ferric ferro cyanide} \\ 
 \text{or Tumbull }\!\!'\!\!\text{ s blue } 
\end{smallmatrix}}{\mathop{K\{Fe[Fe{{(CN)}_{6}}]\}}}\,$Ferric ions react with potassium thiocyanate to give blood red colouration due to the formation of ferric thiocyanate

$FeC{{l}_{3}}+3KCNS\to \underset{\begin{smallmatrix} 
 \text{Ferric}\,\text{thiocyanate} \\ 
 \,\,\,\,\,\,\,\text{(Blood}\,\text{red)} 
\end{smallmatrix}}{\mathop{Fe{{(CNS)}_{3}}+3KCl}}\,$