Page:Paper and Its Uses.djvu/119

Rh present, the microscope should be used for confirmation. Papers containing straw or esparto fibre are coloured pink, pale or deep according to the quantity of these fibres present, when heated in a weak solution of aniline sulphate. Strips of paper treated at the same time will afford comparative tests. Bamboo paper gives a pink reaction in the heated aniline sulphate solution, but some grasses, such as delta grass, are not affected. Microscopical Examination.—Colour reactions reveal the presence of mechanical wood, straw, and esparto in papers, but the reagents used do not reveal the presence of chemical wood or rag fibres, nor do they distinguish between cotton and linen fibres. In order to obtain more exact conclusions the microscope is employed. Although a powerful microscope is a valuable possession, a moderate instrument is preferable; a microscope equal to the "London," with a combination of eye-pieces and objectives to give magnifications of 59 to 270 diameters, will be found excellent for the examination of fibres. A supply of slips, 3 inches by 1 inch, and half an ounce of cover glasses 1 inch diameter will be required.

The fibres in most cases are securely fastened with the sizing materials, and to remove these the paper is boiled in a weak solution of caustic soda. After boiling, the paper is washed, and, with teasing needles, little pieces of paper picked out and placed on a glass slip. Or the paper is placed in a test tube with a little water, the thumb placed over the mouth of the tube, and by shaking violently the paper is soon reduced to pulp. A very small portion of pulp is placed on the slide, and superfluous moisture carefully removed with filter paper. A stain makes the markings