Why does adding salt remove a blood stain

Why does adding salt remove a blood stain  

Haemoglobin is an essential component of the blood. The central, active part of the molecule comprises a haem ring (as above) at the centre of which lies an iron ion. We call it a charge transfer couple, since it requires two constituents, both the iron and the haem. 

An old-fashioned way of removing the stain caused by blood is to place the stained item in a fairly concentrated solution of salt, and is usually performed by sprinkling table salt on the bloodied cloth after dampening it under a tap. 

After a while, sodium ions from the salt swap for the iron ion at the centre of the haem ring. There is no longer a couple (one component is lost), and consequently no scope for an MLCT transition, so the red colour of the blood fades. 

It is likely that the haem remains incorporated in the cloth, but it is not involved in a charge-transfer type of process and is now invisible. 

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