~Potassium Bisulphate~ (KHSO_{4}) is used as a dry reagent for opening up minerals. It fuses; and at a much higher temperature is converted into potassium sulphate with loss of sulphuric acid. ~Potassium Sulphocyanate~ (KCNS) is used for the detection and determination of traces of ferric iron; as also in the separation of silver and copper from some of the other metals. Make a 10 per cent. solution. It should show no colour on the addition of hydrochloric acid. "~Red Lead~" (Pb_{3}O_{4}) is used in the dry assay as a flux instead of litharge, from which it differs in containing a little more oxygen. When acted on by nitric acid a brown residue of lead dioxide is left, nitrate of lead going into solution. Like litharge it always carries silver; about 2 milligrams in 100 grams. ~Silver~, Ag.--Pure silver in foil is required as a standard. It may be prepared as follows:--Dissolve scrap silver in dilute nitric acid and decant off from any residue; dilute the solution with hot water and add hydrochloric acid until there is no further precipitate, stir; allow the precipitate to settle; decant and wash; dry the precipitate, mix it with twice its bulk of carbonate of soda and fuse the mixture in a crucible until tranquil; clean the button and roll or hammer it into foil. ~Sodium Acetate~, NaC_{2}H_{3}O_{2}.3H_{2}O.--The crystals may be purchased sufficiently pure. Make a 20 per cent. solution in water. It is used for replacing mineral acids by acetic acid.[7] ~Sodium Acetate and Acetic Acid.~--A solution is used in the determination of phosphates and arsenates; 100 grams of the salt is dissolved in 500 c.c. of acetic acid, and diluted with water to one litre. ~Sodium Bicarbonate~ (NaHCO_{3})is used as a flux in dry methods. On ignition it leaves the carbonate (Na_{2}CO_{3}), which is used as a standard reagent. Make a 20 per cent. solution of the carbonate for use. It should be free from chlorides or sulphates, or if impure the amount of impurities must be determined. ~Sodium Hydrate~, NaHO. It may be purchased in sticks, which should be kept in a well-corked bottle. It is sometimes called "caustic soda." It is a strong alkali. It is used for neutralizing acid solutions and for separations where ammonia is unsuitable. Make a 5 per cent. solution for use. ~Sodium Hyposulphite~, Na_{2}S_{2}O_{8}.5H_{2}O.--It may be purchased pure. It is generally known as "hypo." It is used as a standard. ~Sodium Sulphite~ (Na_{2}SO_{3}.7H_{2}O) is used as a reducing agent. ~Sodium Phosphate~, Na_{2}HPO_{4}.12H_{2}O. The crystals may be purchased pure, but they effloresce in dry air with loss of water. It is used as a standard and for precipitating magnesia, &c. Make a 10 per cent. solution.