In determining antimony in ore, weigh up 0.5 to 1 gram, and dissolve in hydrochloric acid with, if necessary, the help of chlorate of potash. The antimony is separated as sulphide, redissolved in hydrochloric acid, and oxidised with a crystal of chlorate of potash. Chlorine is boiled off, and the solution diluted with an equal bulk of water. To the clear cold solution potassium iodide is added, and after a few minutes the liberated iodine is titrated with "hypo," as already described. The method only yields satisfactory results when the standard and assay are carried out alike. FOOTNOTES: [50] "Modern American Methods of Copper Smelting" (Dr. Peters). [51] "Journal of the Society of Chemical Industry," vol. v. No. 2. [52] Lead when present is precipitated on the _spiral_ in the form of a dark powder of dioxide (PbO_{2}). Manganese is also thrown down on the spiral as dioxide (MnO_{2}), the solution at the same time becomes violet from the formation of permanganic acid. [53] See the method given under _Examination of Commercial Copper_. [54] CuSO_{4} + 4KCy = 2KCy.CuCy_{2} + K_{2}SO_{4}. [55] 2CuSO_{4} + 3KCy + Am_{2}O = Cu_{2}Cy_{2} + Am_{2}SO_(4) + K_{2}SO_{4} + KCyO. [56] 2CuSO_{4} + 4KI = Cn_{2}I_{2} + 2I + 2K_{2}SO_{4}. [57] 2Na_{2}S_{2}O_{3} + 2I = 2NaI + Na_{2}S_{4}O_{6}. [58] For further information, see Appendix B., and a paper by J.W. Westmoreland, _Journal of the Society of Chemical Industry_, vol. v. p. 48. [59] 3Cu_{2}O + 6AgNO_{3} + 3H_{2}O = 2Cu_{2}H_{3}O_{3}NO_{3} + 2Cu(NO_{3})_{2} + 6Ag. (Insoluble basic salt.) [60] K_{2}CrO_{4} + Pb(NO_{3})_{2} = PbCrO_{4} + 2KNO_{3} [61] Made by dissolving 12 grams of tartaric acid and 4 grams of stannous chloride in water, and adding potash solution till it is alkaline. The solution should remain clear on heating to 60° or 70° C. [62] It must be remembered that arsenate of bismuth is completely insoluble in this acid. [63] SbCl_{5} + 2KI = I_{2} + SbCl_{3} + 2KCl. CHAPTER XI. IRON--NICKEL--COBALT--ZINC--CADMIUM. IRON. Iron rusts or oxidises very readily, and, consequently, is rarely found in the metallic state in nature; such native iron as is found being generally of meteoric origin or imbedded in basalt and other igneous rocks. It chiefly occurs as oxide, as in magnetite, hæmatite, and in the brown iron ores and ochres. Chalybite, which is carbonate of iron, is an ore of great importance. Iron is found combined with sulphur in pyrrhotine and pyrites, and together with arsenic in mispickel. It is a common constituent of most rocks, imparting to them a green, black, or brown colour; and is present, either as an essential part or as an impurity, in most substances.