Stannous chloride solution:

Dissolve 120 g of stannous chloride (SnCl2.2H2O) in 400 ml of concentrated hydrochloric acid (p=1.18 g/ml) and make up to 1 litre with water. The solution must be perfectly clear and prepared immediately before use.

It is essential to check the reducing power of the stannous chloride: dissolve 0.5 g of stannous chloride in 2 ml of concentrated hydrochloric acid (p=1.18 g/ml) and make up to 50 ml with water. Then add 5 g of Rochelle salt (potassium sodium tartrate) and a sufficient quantity of sodium bicarbonate for the solution to be alkaline to litmus paper.

Titrate with 0.1 M iodine solution in the presence of a starch solution as an indicator.

1 ml of 0.1 M iodine solution corresponds to 0.01128 g of SnCl2.2H2O.

At least 80% of the total tin present in the solution thus prepared must be in bivalent form. For the titration, at least 35 ml of 0.1 M iodine solution must therefore be used.