--------------+----------------------------------------+--------------- Copper Taken. | Other Metal Added. | Copper Found. --------------+----------------------------------------+--------------- 0.1000 gram | 0.1000 gram of silver | 0.1800 0.1050 " | 0.1000 " " | 0.2000 0.1030 " | 0.1000 " mercury | 0.2010 0.1037 " | 0.1000 " " | 0.2015 0.1020 " | 0.1000 " lead | 0.1020 0.1030 " | 0.1000 " " | 0.1028 0.1010 " | 0.1000 " arsenic | 0.1010 0.1007 " | 0.1000 " " | 0.1022 0.1030 " | 0.1000 " antimony | 0.1050 0.1034 " | 0.1000 " " | 0.1057 0.0990 " | 0.1200 " tin | 0.0990 0.1014 " | 0.1000 " " | 0.1015 0.1000 " | 0.1000 " bismuth | 0.1662 0.1040 " | 0.1000 " cadmium | 0.1052 0.1009 " | 0.1300 " zinc | 0.1017 0.1014 " | 0.1000 " nickel | 0.1007 0.1079 " | 0.1200 " iron | 0.1089 0.1054 " | 0.1000 " chromium (Cr_{2}O_{3}) | 0.1035 0.1034 " | 0.1000 " " (K_{2}CrO_{4}) | 0.1010 0.1075 " | 0.1000 " aluminium | 0.1078 0.1010 " | 0.1000 " manganese | 0.0980 --------------+----------------------------------------+--------------- It will be seen from these that mercury, silver, and bismuth are the only metals which are precipitable[52] along with the copper under the conditions of the assay. Mercury, which if present would interfere, is separated because of the insolubility of its sulphide in nitric acid. Bismuth is precipitated only after the main portion of the copper is thrown down. It renders the copper obviously unsuitable for weighing. It darkens, or forms a greyish coating on, the copper; and this darkening is a delicate test for bismuth. In assaying ores containing about three and a half per cent. of copper, and known to contain bismuth in quantities scarcely detectable in ordinary analysis, the metal deposited was distinctly greyish in colour, and would not be mistaken for pure copper. Ten grams of this impure copper were collected and analysed, with the following results:-- Copper 99.46 per cent. Bismuth 00.30 " Iron 00.14 " Arsenic 00.10 " ------ 100.00 The quantity of copper got in each assay was 0.175 gram, and consequently the bismuth averaged 0.00053 gram.