Chevruel's Salt

Chevreul's Salt.
 Found this interesting article in another old School Science review Sep 1986.
 boiling solutions of Sodium metabisulphite Na2S2O5 ( sodium disulphate iv) added to boiling CuSO4 soln , and boiled for 4 mins gives Chevreuls salt, Cu3(SO3)2.2H2O)
This is a red solid , which evolves a little Sulphur Dioxide.
 Copper (I) chloride will be obtained by dissolving chevreuls salt in dilute HCL, with some SO2 present. 

3S2O52- + 3Cu2+ + %H2O -----> Cu3(SO3)2.2H2O + 3So2 + 2H3O+ + SO42-

 Says dissolve 6g of the metabisulphite in 30ml hot water.
 Dissolve 7g copper sulphate in another beaker in 100 ml water, asnd heat this to boiling.
With stirring as the metabisulphite is added, and boil for about 4 mins.
The precipitate if filtered off, and washed with several portions water.
This is the chevreuls salt.
 Dssolving this in some dilute HCL will provide a white precip, within a greeny / blue solution.
This white precip turns green slowly of exposure to air .
The CuCl. Addition of excess HCL redissolved the precip. Addition of ammonia gives the intense blue copper tetraammine (ii) complex.