For comparison, analyses of a few spring and river waters are given on [p. 89].
Analyses of various Waters.
| Thames, at Kew. | Thames, at London Bridge. | Severn, Wales. | Thirlmere. | Rhine, Basle. | Spring, Witley, Surrey. | Spring, Watford, Herts. | Artesian, Well Trafalgar Square. | Ripley's, Well Holbeck, Yorks. | Well, Council Acad., Vienna. | River Witham, Lincoln. | Beamhouse well, Lowlights. | |||||
| Total solids | 31·0 | 40·8 | 3·87 | 5·15 | 16·9 | 7·6 | 33·8 | 84·9 | 150·4 | 212·2 | 33·0 | .. | ||||
| Ca | 7·6 |  | 8·21 |  | ·3 | ·43 | 5·55 | ·81 | 11·0 | 1·56 | 1·22 | 19·6 | 6·08 | .. | ||
| Mg | ·47 | ·2 | ·12 | ·48 | ·18 | .. | ·84 | ·42 | 10·4 | .. | .. | |||||
| Na | ·87 | 1·43 | ·6 | ·49 | ·06 | ·64 | 1·1 | 29·4 | 58·1 | 41·1 | .. | .. | ||||
| K | ·39 | ·17 | ·1 | .. | .. | ·23 | .. | ·85 | ·83 | 10·5 | .. | .. | ||||
| CO3 | 10·53 | 6·94 | ·2 | 1·09 | 8·62 | trace | 15·6 | 11·3 | 39·8 | 97·6 | .. | .. | ||||
| SO4 | 3·95 | 3·22 | 1·3 | ·75 | 1·54 | 1·33 | ·68 | 20·6 | 1·03 | 26·7 | 7·59 | .. | ||||
| Cl | 1·21 | 6·36 | ·8 | 1·1 | ·15 | 1·28 | 1·21 | 16·5 | 45·2 | 3·5 | 2·60 | 21·8 | ||||
| SiO2 | ·63 | ·18 | ·2 | ·07 | ·21 | 1·23 | 1·16 | ·57 | 2·63 | ·3 | .. | .. | ||||
| Temporary Hardness | | 20·0 | .. | ·9 | ·7 | .. | 2·8 | .. | .. | .. | .. | | 8·0 | 39·7 | ||
| Permanent hardness | 8·4 | 48·0 | ||||||||||||||
[CHAPTER VI.]
METHODS OF CHEMICAL ANALYSIS FOR THE TANNERY.
It is assumed that the reader has an elementary knowledge of chemistry, and of the common manipulations of the laboratory; but at the risk of giving information which to many is already familiar, the principles that underlie those methods of testing which are most applicable to technical purposes must be briefly explained.
Standard Solutions.—If 40 grm. of pure caustic soda (NaHO) be dissolved in water, and a little tincture of litmus added, it will be coloured a bright blue. If hydrochloric acid be now added, drop by drop, the litmus will at last become purple, and a single drop more would turn it a bright red. At this point the liquid is neither acid nor alkaline, and if it be evaporated to dryness, nothing will be left but 58·5 grm. of common salt (NaCl), while 18 grm. of water will be formed and have escaped. We have therefore used exactly 36·5 grm. of pure HCl, and if we dissolve 40 grm. of caustic soda in 1 litre of water, and 36·5 grm. of pure HCl in another, equal parts of these liquids will always exactly neutralise each other, forming nothing but common salt and water. It will be obvious that if we have a soda solution of the strength named, we can find the amount of hydrochloric acid in any solution of unknown strength, by seeing how much of it is required to neutralise, say, 10 c.c. (= 0·4 grm. soda) of the known solution. Instead of 40 grm. of caustic soda, we may take 56 grm. of potash to the litre, and it will exactly neutralise an equal volume of the hydrochloric solution containing 36·5 grm. If, again, we make a solution containing 49 grm. of pure sulphuric acid (SO4H2) per litre, it will neutralise an exactly equal volume of either the soda or the potash solution, thus being precisely equivalent to the HCl solution. Such solutions are called normal, and any normal acid solution will neutralise an equal volume of any normal alkali, and vice versâ. For many purposes normal solutions are too strong, and solutions containing 1/10 of the quantities required for normal solution are preferable; such solutions are called decinormal. All solutions containing known quantities of chemicals, and intended for use in volumetric analysis, are called Standard solutions.