Manganous and alkaline potassium iodide solution was added immediately with 1 ml of each. Insert the stopper and mixed by inverting the bottle several times. Allow the precipitated to the settle halfway and mixed again and 1 ml of concentrated sulfuric acid was added and remained with 5 minutes. 100 ml of that solution was transferred into a conical flask and 0.025N sodium thiosulfate was added immediately drop by drop from a burette until the yellow colour almost disappears