"Smeckler" wrote in message
...
It says "Bordeaux mixture" on the pack.
It says it contains copper sulphate BUT the powder inside and the
deposit left on the plants is white. I also thought it would be blue.
Perhaps someone can explain!

I vaguely recall my first ever chemistry lesson at secondary school...

"Copper sulphate crystals were placed in a test tube and heated over a
bunsen flame. A crackling sound was heard and steam was seen escaping.
A white substance remained in the test tube."

The white stuff was "anhydrous copper sulphate", i.e. with all the water
removed...

Unless my memory is letting me down, the anhydrous copper sulphate is
hygroscopic and absorbs its water of crystallisation from moisture in the
air, thus re-acquiring its colour.

[Franz Heymann]