The Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991

Solution of stannous chloride:

4.11  dissolve 120 g of stannous chloride (SnC1₂.2H₂O), in 400 ml concentrated hydrochloric acid (d = 1.18 g/ml) and make up to 1 litre with water. The solution must be completely 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 concentrated hydrochloric acid (d = 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 show an alkaline reaction to a litmus paper test.

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

1 ml of iodine solution 0.1 N corresponds to 0.01128 g SnC1₂.2H₂O.

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