ANALYSES OF TYPICAL CLAYS
The samples were all dried at 105° C.
| Clay | China Clay | Ball Clay | Fireclay | Brick Clay | Boulder Clay | Marl |
| Locality | Cornwall | Dorset | Yorkshire | Midlands | Lancs. | Suffolk |
| Ultimate Analysis: | ||||||
| Silica | 47·1 | 49·1 | 68·9 | 57·7 | 63·7 | 43·7 |
| Alumina | 39·1 | 33·7 | 19·3 | 24·3 | 20·4 | 15·5 |
| Ferric oxide | ·6 | 1·2 | 1·0 | 5·0 | 3·0 | 5·2 |
| Titanium oxide | — | ·2 | 1·8 | ·1 | ·2 | — |
| Lime | ·4 | ·8 | ·9 | 3·7 | 4·3 | 16·3 |
| Magnesia | ·2 | ·3 | ·3 | 2·5 | 2·7 | 2·1 |
| Potash and Soda | ·3 | 2·5 | ·9 | 2·8 | 2·9 | ·7 |
| Carbon | 2·6 | 4·3 | 1·8 | 1·6 | ·4 | 1·6 |
| Water | 9·3 | 7·7 | 4·8 | 2·0 | 2·2 | 2·4 |
| Other Matter | ·4 | ·2 | ·3 | ·3 | ·2 | 12·5 |
| Total | 100·0 | 100·0 | 100·0 | 100·0 | 100·0 | 100·0 |
| Proximate Analysis: | ||||||
| Gravel and Sand | — | 8·4 | 4·6 | 22·1 | 23·1 | 9·2 |
| Silt | — | 4·8 | 9·0 | 3·1 | 8·4 | 16·0 |
| Felspar- and mica-dust | 5·2 | 15·4 | 10·3 | 24·3 | 18·5 | 8·9 |
| Silica-dust | 3·1 | 4·0 | 38·0 | 3·1 | 12·6 | 2·0 |
| Free calcium carbonate | — | — | — | 2·1 | ·2 | 28·4 |
| Free iron oxide and pyrites | ·4 | ·9 | ·7 | 4·2 | 1·6 | 3·9 |
| 'True clay' | 91·3 | 66·5 | 37·4 | 41·1 | 35·6 | 31·6 |
| Total | 100·0 | 100·0 | 100·0 | 100·0 | 100·0 | 100·0 |
For other analyses the books in the Bibliography at the end of the present volume should be consulted, particularly No. 2, i.e. British Clays, Shales and Sands.
The amount of mechanically mixed water will naturally vary with the conditions to which the clay has been subjected; it will be greatest in wet situations and will diminish as the clay is allowed to dry.
The 'combined water,' on the contrary, appears to be a function of the true clay present in the material, and reaches its highest proportions in the china clays and kaolins, which contain approximately 13 per cent. On heating a clay to 105° C. the moisture or mechanically mixed water is evaporated, but the combined water remains unaffected[4] until the temperature is raised to more than 600° C., when it is driven off and the clay is converted into a hard stone-like mass with properties entirely different from those it previously possessed (see [Chapter VI]).
[4] Strictly, there is a slight loss at lower temperatures, but it is too small to be important.
The Physical Characters of Clays.
The physical characters of clays are of far more interest and importance than their chemical ones, though the two are naturally connected in many ways, and just as the chemical composition of clays is a subject of extreme complexity so is a study of many of their physical properties. Hence only a few of the more important characteristics can be mentioned here: for further details the reader must consult a larger treatise ([2]).