Beside lime and magnesia salts, water may contain sulphates and chlorides of soda and potash; but not carbonates of these bases in presence of permanent hardness. In soft waters carbonates are sometimes present, and form carbonate of lime in limed hides. Hides are said to soften rapidly in such water. Alkaline sulphates are not known to have any injurious action, and chlorides have already been spoken of. Iron may be present in solution as bicarbonate, but not in any other form in presence of bicarbonate of lime. It is removed completely with the temporary hardness by Clark's process, or boiling. Iron is much more common merely in suspension, as mud, but is always objectionable. Most waters contain a little silicic acid and alumina, and some few considerable quantities. Such waters are said to harden leather, but the writer knows of no case where they are in use in England; and their occurrence is comparatively rare. For comparison, analyses of a few spring and river waters are given on p. 89. Analyses of various Waters. ────────────┬───────┬─────────┬───────┬───────────┬─────────┬──────────┐ │Thames,│ Thames, │Severn,│ Thirlmere.│ Rhine, │ Spring, │ │at Kew.│ at │Wales. │ │ Basle. │ Witley, │ │ │ London │ │ │ │ Surrey. │ │ │ Bridge. │ │ │ │ │ ────────────┼───────┼─────────┼───────┼───────────┼─────────┼──────────┤ Total solids│ 31·0 │ 40·8 │ 3·87 │ 5·15 │ 16·9 │ 7·6 │ Ca │ 7·6 │} 8·21 │{ ·3 │ ·43 │ 5·55 │ ·81 │ Mg │ ·47 │} │{ ·2 │ ·12 │ ·48 │ ·18 │ Na │ ·87 │ 1·43 │ ·6 │ ·49 │ ·06 │ ·64 │ K │ ·39 │ ·17 │ ·1 │ .. │ .. │ ·23 │ CO_{3} │ 10·53 │ 6·94 │ ·2 │ 1·09 │ 8·62 │ trace │ SO_{4} │ 3·95 │ 3·22 │ 1·3 │ ·75 │ 1·54 │ 1·33 │ Cl │ 1·21 │ 6·36 │ ·8 │ 1·1 │ ·15 │ 1·28 │ SiO_{2} │ ·63 │ ·18 │ ·2 │ ·07 │ ·21 │ 1·23 │ Temporary │} │ │ │ │ │ │ Hardness │}20·0 │ .. │ ·9 │ ·7 │ .. │ 2·8 │ Permanent │} │ │ │ │ │ │ hardness │ │ │ │ │ │ │ ────────────┴───────┴─────────┴───────┴───────────┴─────────┴──────────┘