Лако-красочные материалы — производство

In principle, a known amount of ferrous iron is oxidized to ferric iron, and this is reduced with titanium trichloride using potassium thiocyan­ate as an indicator.

As the ferrous salt, Knecht used iron ammonium sulfate (Mohr salt) and oxidized this to ferric sulfate with 0.02 N potassium permanganate in sulfuric acid solution. The resulting ferric salt was then back-titrated with titanium trichloride solution. The other, equally simple method consists in dissolving pure iron wire in pure hydrochloric acid and oxidizing the ferrous chloride solution with a few drops of bromine. The excess bromine is removed by boiling and the solution is titrated with the titanium trichloride solution.

The commercial titanium trichloride solution (about 15 per cent) is diluted by mixing 100 cc. with 100 cc. pure 30 per cent hydrochloric acid. The mixture is heated to boiling and then made up to 1 liter at 18°C. This solution can be held unchanged by storing under carbon dioxide or hydrogen, but it should be restandardized at regular inter­vals.

To standardize the solution with iron, an iron solution containing exactly 2 grams of iron per liter is used. This solution should contain 5 per cent hydrochloric acid or sulfuric acid. As an example, it is found that 6.85 cc. of a titanium trichloride solution corresponds to 25 cc. of the iron chloride solution, using potassium thiocyanate as the in­dicator (spot test). Since the iron solution contains 2 grams of iron per liter, 1 cc. TiCl3 solution corresponds to 0.05/6.85 or 0.007299 grams of iron.