The antimony must be in solution as antimonious chloride, and must not be accompanied by an excess of hydrochloric acid. To ensure these conditions, the solution is treated with potassium iodide until no more iodine is evolved, and is then evaporated to remove the excess of hydrochloric acid. To the concentrated, and nearly neutral, solution a freshly-prepared solution of gallic acid is added in slight excess. A bulky white precipitate is formed that settles rapidly. The solution is diluted with hot water and washed by decantation. Then the precipitate is collected on a weighed double filter, washed once or twice with hot water, and dried at 100° C. The dried substance is antimony bigallate, and contains 40.85 per cent. of antimony. It should be completely soluble in ammonium sulphide. The solution in which the antimony is precipitated need not be quite free from other metals. VOLUMETRIC METHOD. This is based on the reduction of antimonic chloride (SbCl_{5}) to antimonious (SbCl_{3}) by the action of potassium iodide in strong hydrochloric acid solution.[63] Iodine is at the same time liberated, and the amount of antimony reduced is got at by titrating with sodium hyposulphite, which measures the iodine set free. The standard solution of sodium hyposulphite is made by dissolving 41.32 grams of the salt (Na_{2}S_{2}O_{3}.5H_{2}O) in water, and diluting to 1 litre. One hundred c.c. will be equivalent to about 1 gram of antimony. It is standardised with the help of a solution of antimony made as follows:--Weigh up 5 grams of powdered antimony, transfer to a flask, and cover with 50 c.c. of hydrochloric acid; boil, and add nitric acid (5 or 10 drops at a time) until the metal is dissolved. Allow the action of the nitric acid to cease before adding more. Boil down to a small bulk, add 250 c.c. of hydrochloric acid, and dilute to nearly 1 litre. Warm until any precipitate which has formed is redissolved; allow to cool slowly, and run in from a pipette a weak solution of permanganate until a faint brown colour is produced. Dilute to exactly 1 litre; 100 c.c. contain 0.5 gram of antimony as antimonic chloride. In standardising, take 50 c.c. of the antimony solution, and transfer to a flask; add 2 grams of potassium iodide crystals, and when dissolved, after standing a few minutes, run in the solution of "hypo" from an ordinary burette until the greater part of the iodine has been reduced. Add a few drops of starch solution, and continue the addition of the "hypo" until the muddy-green colour changes to a clear brownish-yellow. The solution must be shaken after each addition of the "hypo."