[Farid]

 Hi,
Could you have look?

When we add iron chloride solution into a test tube with benzoic acid the solid will get precipitated. And my question is: what this solid is ? is it a salt (iron salt) of benzoic acid?

And if i add FeCl3 to salicylic acid, what will be product of this reaction? The solution changes colour to puple.

[UnintentionalChaos]

You are referring to ferric chloride, correct?
When combined with benzoic acid, you should precipitate ferric benzoate.
When you add salicylic acid, which has a phenol group, the complex discussed briefly here http://www.nature.com/nature/journal/v165/n4208/abs/1651012b0.html
Except of course, there is a carboxylic acid group thrown in there.

[Babcock_Hall]

SNIP

And if i add FeCl3 to salicylic acid, what will be product of this reaction? The solution changes colour to puple.

The purple complex is ferric chloride complexed with salicylic acid, and my understanding (which is poor) is that there is some sort of charge-transfer going on.  The formation of this complex was the basis for a test for aspirin poisoning using a commercial strip called Phenistix.^TM  IIRC Phenistix were made by Miles Laboratories, and they were manufactured originally to form a complex between ferric iron and phenylpyruvate.