[Kahl207]

I tried to make magnetite using an online procedure I found:
Mix 30mL 40% Ferric Chloride solution and 30 mL distilled water
React with a piece of steel wool creating a green solution (FeCl2) and filter
Add 60mL 40% Ferric Chloride making a solution containing FeCl3 and FeCl2 in 2:1 ratio
Add 450mL Ammonia to precipitate Fe3O4.

This is where I think I have a problem. Once I aded the Ammonia a black precipitant started dropping out of solution until I started mixing. Once I mixed there was a reaction (beaker became hot and there was a sudden color change) and I now have a brown homogenous solution.
What'd I make? What could I have done wrong?

[Kahl207]

Ok, someone help me check my calculation:
40%wt Ferric Chloride aqueous solution is what Molarity?