This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1878 Excerpt: ...cellulose, and are flexible and tough, but if their colour is yellow, it indicates that they are more or less lignified or impregnated with nitrogenous substances which render them more or less stiff and brittle. If the iodine solution and the sulphuric acid have been properly prepared, the fibres are not in the least ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1878 Excerpt: ...cellulose, and are flexible and tough, but if their colour is yellow, it indicates that they are more or less lignified or impregnated with nitrogenous substances which render them more or less stiff and brittle. If the iodine solution and the sulphuric acid have been properly prepared, the fibres are not in the least altered in their forms, and the colorations obtained allow the most delicate characters of form and texture to be visible, and strike the eye more clearly than when a neutral liquid is used. The thickness of the walls of the cells, their dimensions, and the form of their central cavity, can likewise be more easily appreciated. It is possible then to know if this cavity is empty (Figs. 2 and 3, Plate I.), or if it contains a foreign substance, which appears then with a yellow or brown colour (Fig. 1, Plate I, Figs. 1 and 2, Plate II, Fig. 3, Plate III.) It happens sometimes that the cellulose of the cells is so close or hardened, that the fibres do not take any colour at all. In that case a few drops of caustic potash (10) are placed on a slide, and the refractory fibres, in a dry state, well impregnated with the liquid, and immediately dried with several folds of blotting paper. Iodine is then applied. It loses its colour at first, but fresh drops are added till the yellow tint of the iodine neither fades nor disappears. If this operation be performed with care, the colour will appear as soon as sulphuric acid is applied. If the colour is too deep, or if the cells seem to swell and lose their characters, a new preparation should be made, taking care to add a little water to the caustic potash on the slide before introducing the fibres. A little practice will soon show how this operation should be conducted. The characters thus observed are gen...
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