Block Gambier.
Effect of Different Temperatures.
| Temperature of Extraction. | Tanning Matters absorbed by Hide. | Soluble Non- Tanning Matters. | Per cent. of Tannin on Maximum Yield. | Colour of 1⁄2 per cent. Solutionin 1⁄2 inch Cell. | Per cent. of Colour on Maximum Yield. | ||
|---|---|---|---|---|---|---|---|
| Red. | Yellow. | Total. | |||||
| °C. | per cent. | per cent. | deg. | deg. | |||
| 15 | 30·1 | 27·4 | 50·1 | 2·6 | 8·1 | 10·7 | 33·5 |
| 15-30 | 34·8 | 26·2 | 69·6 | 2·4 | 8·0 | 10·4 | 34·0 |
| 30-40 | 40·8 | 27·2 | 81·6 | 2·0 | 9·0 | 11·0 | 55·0 |
| 40-50 | 44·8 | 27·6 | 89·6 | 2·4 | 9·8 | 12·2 | 61·0 |
| 50-60 | 46·8 | 27·8 | 93·6 | 2·4 | 10·1 | 12·5 | 62·5 |
| 60-70 | 47·3 | 27·6 | 94·6 | 2·5 | 10·6 | 13·2 | 66·0 |
| 70-80 | 47·4 | 27·6 | 94·7 | 2·8 | 10·9 | 13·7 | 63·5 |
| 80-90 | 47·6 | 27·3 | 95·2 | 3·2 | 11·6 | 14·8 | 74·0 |
| 90-100 | 48·2 | 27·1 | 96·4 | 3·8 | 12·8 | 16·6 | 83·0 |
| Boiled 1⁄2 hour | 50·2 | 26·4 | 100·0 | 5·0 | 15·0 | 20·0 | 100·0 |
CHAPTER XXIII.
FATS, SOAPS, OILS AND WAXES.
Fats and oils constitute a large class of substances, of animal or vegetable origin, which may be solid, pasty or more or less viscous liquids, but which in the latter case are commonly known as “fixed” or fatty oils, to distinguish them from the volatile, or essential oils, which may be distilled without decomposition, and which are the source of most of the odours of plants, and of quite different chemical constitution. The term “oil” is also applied to various products of mineral origin, and especially to those derived from petroleum, on account of their similarity in appearance and physical properties to the fixed oils, though, chemically, they form a very distinct class. The waxes are another group somewhat closely allied to the fats; and there are certain fixed oils, such as sperm oil, which though very similar in appearance and properties to the fatty oils, are chemically members of the group of waxes.
As it is obvious that there is no chemical distinction between the fats and fatty oils, except that of melting-point, it will be convenient to treat them together; especially as what is a solid fat in one climate may be an oil in another. Palm and cocoa-nut oils are cases in point, as the first is buttery, and the second a hard fat in this country, though they are both liquid in tropical climates.
For more detailed information on the chemistry of fats and oils, the reader must be referred to the ‘Leather Industries Laboratory Book,’ sect. xviii., or to the larger manuals devoted specially to the subject by Lewkowitsch, Jean, and others, or the very excellent section on oils in Allen’s ‘Commercial Organic Analysis,’ vol. ii.; but a few general facts must be recapitulated.
The true fats contain carbon, hydrogen and oxygen, but no nitrogen. They are all compounds of glycerin with organic acids which are generally termed “fatty acids,” and which resemble in many of their characteristics the fats themselves. Glycerin is a very weak base, of the nature of an alcohol, and consequently, when a fat is heated with a solution of one of the caustic alkalis, the fatty acid combines with the latter, and the glycerin is set free. The salts thus formed are denominated “soaps.” The reaction with stearin (glycerin stearate), the principal constituent of hard animal fats, is shown in the following equation.
| Stearin | Sodium hydrate | Sodium stearate | Glycerin | |||
| (C17H35CO.O)3C3H5 | + | 3NaOH | = | 3C17H35CO.ONa | + | C3H5(OH)3. |