Animal Fibres. Animal fibres, such as wool and silk, do not constitute raw material for paper-making. Wool is used for certain mottled papers in limited quantity, and silk is occasionally introduced in the form of thin threads into safety cheque papers. These fibres are easily detected by their peculiar form. NOTE. All fibres exhibit variations from the average dimensions given. Colour Reactions of Fibres.-The identification of fibres by means of reagents applied to the surface of the paper is practically limited to the detection of mechanical wood, esparto, or straw. The reagents are aniline sulphate and phloroglucine. Aniline sulphate is prepared by dissolving 4 parts of the crystallised salt in 100 parts of distilled water. Paper containing mechanical wood is stained yellow, more or less intense according to the amount of mechanical wood present. Paper containing esparto when gently warmed with a mixture of 10 parts of water and 1 part of aniline test solution turns a rose-red pink, the depth of colour being a rough measure of the amount of esparto. Straw cellulose gives a similar colour reaction with aniline sulphate. Phloroglucine is prepared by dissolving 4 parts of the crystalline salt in 100 parts of absolute alcohol and adding 50 parts of pure hydrochloric acid. This solution produces a reddish stain on papers containing mechanical wood, the depth of colour being a measure of the amount of wood present. In papers dyed with certain aniline colours, metanil yellow for example, this red coloration will be developed even in the complete absence of mechanical wood. It is, due, however, to the free hydrochloric acid in the reagent. If a paper gives a red colour with a few drops of hydrochloric acid, then some such dye is present. If the paper does not give a red colour with phloroglucine, mechanical wood is absent. The colour If the paper turns red, mechanical wood may be present. gradually develops and darkens slowly. Coarser particles of wood become deeply stained and give the effect of an uneven coloured surface. If the paper turns red, and the colour develops suddenly, producing a uniform shade with an absence of deeply stained particles, mechanical wood may not be present. In this case a few drops of hydrochloric acid, per se, will stain the paper red. The identification of fibres is more completely determined by reference to the microscope. In such cases the structure of the fibres may be rendered more definite by the use of certain staining reagents, as shown in Table XXVII., page 155. CHAPTER XIII ANALYSIS OF A SHEET OF PAPER · TYPICAL EXAMPLE OF A REPORT ON THE INVESTIGATION OF TWO HIGH-CLASS RAG PAPERS. THE extent to which a paper is examined for quality and value depends very largely upon the nature of the information required. In the majority of cases the information sought refers to Some comparatively simple constituent which is readily determined, or to some single defect which may be of great importance. Thus it may be necessary to report that the sample has a certain breaking strain, a factor easily expressed in simple numerical terms; or to determine accurately the nature of some defect, such as, for example, whether certain coarse fibres appearing in a sheet of news are derived from the pulp used in manufacture, or from odd pieces of string. Questions of the latter type are exceedingly varied in character, and are furthermore of the greatest importance, since the critical examination of the difficulty fixes the responsibility for any claim for damages. Of less frequent occurrence are investigations of a complete character, involving a careful measurement of all the normal qualities, physical and chemical, of the paper. As a typical example of such an investigation the following report will afford some insight into the work required. It is obvious that a complete report must take into account (1) General characteristics, and (2) Special qualities in reference to the purpose for which the paper is to be used. TABLE XXIX.-Report. This report deals with an investigation into the qualities of two high-class rag papers. The results are summarised in the table on page 174, the details being separately recorded. General Conclusion -The results of this investigation show that paper A is of better quality than paper B, having regard to the purpose for which the papers are intended. Samples submitted. The samples consisted of sheets marked respectively: A. 17 inches by 22 (480 sheets) 25 lbs. 221 (480 sheets) 26,, two sheets of each mark being supplied. |