How to prepare potassium cyanide from potassium ferrocyanide

How do we prepare potassium cyanide from potassium ferrocyanide? 


It is something which I am curious about, but cannot find the answer. I am studying inorganic chemistry but this reaction cannot be found.




Until about 1900, potassium cyanide was produced by melting dry potassium carbonate with dry potassium hexacyanidoferrate(II):
$$\ce{K4[Fe(CN)6] + K2CO3 -> 6KCN + FeO + CO2}$$
However, the product contains potassium cyanate, which is approximately formed as follows:
$$\ce{K4[Fe(CN)6] + K2CO3 -> 5KCN + KOCN + Fe + CO2}$$


In a small scale, dry potassium hexacyanidoferrate(II) is melted in a covered porcelain crucible. It is heated as long as nitrogen escapes.
$$\ce{K4[Fe(CN)6] -> 4KCN + N2 +FeC2}$$
The iron carbide sinks to the bottom and the molten potassium cyanide can be poured off.


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In addition to Loong's excellent answer, I'm going to shed some light on the last process i.e. the decomposition reaction of potassium ferrocyanide. 


Actual reaction is this:


$$\ce{3K4[Fe(CN)6] ->[\Delta]12KCN + Fe3C + 5C + 3N2}$$



> 
> The thermal decomposition of potassium hexacyanoferrate(II) to produce
>  potassium cyanide, iron carbide, carbon and nitrogen. This reaction
>  takes place at a temperature near 650°C.([source](https://chemiday.com/en/reaction/3-1-0-5202))
> 
> 
> 


As always nitrogen gas escapes, iron carbide and carbon sinks to the bottom and the molten potassium cyanide can be poured off.


There is a [paper](http://akademiai.com/doi/abs/10.1007/BF01915163?journalCode=10973) which discuss the decomposition of potassium ferrocyanide trihydrate($\ce{K4[Fe(CN)6].3H2O}$) to give anhydrous potassium ferrocyanide. Further increase in heat gives various decomposition products like $\ce{α-Fe2O3, Fe3O4, Fe3C, Fe, FeO, KFeO2,\beta-FeOOH, KOCN, K2CO3}$ and $\ce{KCN}$.


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