DICKSON ESTIMATION OF HEMP AND WOOD FIBRES I N PAPER PULP 373 The Quantitative Estimation of Hemp and Wood Fibres in Paper Pulp. BY W. DICKSON F.I.C. (Read at the Meeting May 2 1923.) INTRoDUCTION.-h examining papers of any new make and origin it is very necessary that the analyst should be able to estimate with a reasonable degree of accuracy the proportion of different kinds of fibre in a given sample of paper. Generally speaking there is little help to be obtained from the literature on this subject. Some authors state that a great deal of experience is required to estimate with any approach to accuracy the quantity of various fibres contained in paper 374 DICKSON ESTIMATION OF HEMP AND WOOD FIBRES I N PAPER PULP and that the experienced man can judge the amounts from a cursory examination of a slide under the microscope more accurately than an inexperienced person from elaborate counts of the fibres.Differential staining with iodine and zinc chloride etc. is not of much service in bringing out the different Elasses of fibres because differential staining depends upon the sensitiveness of the cellulose to hydration. This sensitiveness depends to some extent on the treatment to which the fibre has been subjected as well as on its origin. As regards these staining methods the author agrees with Clapperton (Practical Paper Making p. 163) and holds that micro-structure is the only safe criterion upon which to base a diagnosis of the constituents of paper pulp. The difference in micro-structure of the various fibres is often very difficult to recognise and undoubtedly a very great deal of experience is required in order to make reliable diagnosis of the types of fibres present in the mixtures.There is no difficulty in recognising the majority of woody cells under the microscope. There are however in pure wood fibre a number of cells (see Figs. 3 and 4) which are decidedly difficult to distinguish from fibres say of hemp and manilla and it is the presence of these fibres which makes the quantitative estimation of the amount of hemp and wood in a mixture so very difficult. It will be readily understood that in order to make a quantitative estimation of these two fibres it is necessary to count the number of fibres of each kind in a large number of fields and unless the operator can decide definitely on each fibre examined results are liable to be very doubtful, IDENTIFICATIOE; OF FIBRES IN PAPER PuLP.-The first step towards a quanti-tative estimation of fibres therefore is to ensure a quick and certain recognition of different fibres under the microscope.It was found that Cross and Bevan’s double staining method in which malachite green and Congo red are used brought out structural details very well and it was adopted. Generally the whole of the fibre is dyed a deep reddish brown but there appear occasional green fibres. I t is concluded that these fibres have been highly lignified and have therefore taken the nialachite green most readily. This stain probably gives an idea of the completeness or otherwise of the bleaching of the fibres but no attention is paid to these different colours as a means of identification of the fibres.The stain was adopted simply because it appeared to bring out the detail in the micro-structure very well. In making slides for examination it is necessary to ensure that the fibres shall be well spread out over the cover slip so that individuals may be easily seen and counted. To do this it was found best to work with a dilute mixture of pulp and water. The concentration 0-02 to 0.03 per cent. recommended by Spence and Krauss ( W ~ l d ’ s Paper Trade Reiliew Dec. 18th 1917) was found very suitable. The stained pulp in the proper concentration is placed in a cylindrical glass vessel and stirred with a microscopic teasing needle. The needle is held stationary near the side of the glass for a minute or two with the result that the fibre attaches itself to the needle and a good representative sample can b FIG.1 x 320 diams. FIG. 2. x 2 2 7 diams. FIG. 5. x 63 diams. FIG 6. x63 diams. l’lnle W . Dickson’s Pn;her. FIG. 3. x 67 diams. FIG. 4. x 67 diams. FIG. 7. x 67 diams. FIG. 8. x 67 diam DICKSON ESTIMATION OF HEMP AND WOOD FIBRES I N PAPER PULP 375 withdrawn. The sample is placed on a cover slip and ~ e l l teased out so that the individual fibres can be seen and counted. During the teasing part of the sample is rejected and care is taken to make this rejection uniform throughout so that a good representative sample is retained on the cover slip. The slip is dried with alcohol and mounted in Canada balsam in the usual way.The slide is examined under a microscope fitted with the ysual Nicol prisms to provide polarised light. In examining fibres with a view to determining their kind it was found most useful to examine both by ordinary light and polarised light. From the photo-micrographs shown in this paper it will be seen that certain characteristic markings of different fibres are brought out best in ordinary light, and certain others in polarised light. For example the cross markings in hemp (Fig. 5) are most readily seen by ordinary light but there is a peculiar characteristic appearance of hemp fibres which is best brought out by polarised light (see Fig. 6). With practice the operator becomes very expert in noting these different ap-pearances on rotating the Nicol prisms attached to the sub-stage polariser of the microscope.As far as the author is aware examination by means of polarised light has not previously been utilised for the identification of fibres in paper pulp. For purposes of identification of fibres it is useful to employ two magnifica-tions say 100 diam. and 400 diam. With practice 100 diam. is sufficient but for purposes of confirmation the higher magnification is convenient. Figs. 1 and 2 show photo-micrographs of characteristic hemp fibres under the high power with and without polarised light. Figs. 5 and 6 show hemp fibres under the low power with and without polarised light. Figs. 7 and 8 show mixtures of 80 per cent. of hemp and 20 per cent. wood. These figures illustrate very well the structure of the hemp and wood and it will be readily seen how the different fibres can be picked out when necessary.The photomicrographs shown were all made from pulp prepared in the laboratory from known raw materials. The method of preparation of the pulp was as follows:-A quantity of the raw material say 50 grms. of hemp rope was boiled with 10 per cent. sodium hydroxide solution for several hours the liquid filtered through a Biichner funnel and the residue pulped in a mortar. The resulting mixture was boiled up with an acid sodium sulphite solution and again filtered pulped and thoroughly washed. The pulp was then in a fairly well disintegrated condition ready for bleaching which was done by warming with sodium hypochlorite. This solution was acidified and the warming continued for a short time.By this means the pulp was bleached to a completely white substance resembling paper-maker’s ‘‘ half -stuff .” The making of pulp from wood was rather difficult because the shavings which were used as a starting point had to be ground up to some extent in a coffee mill before treatment with caustic soda. This treatment had to be repeated several times as had also the intermediate hand-pulping in order to get the material reduced to a sufficiently fine state for the next process. The sulphite treatment and final bleaching were conducted in exactly the same manner as described under hemp 376 DICKSON ESTIMATION OF HEMP AND WOOD FIBRES IN PAPER PULP THE QUANTITATIVE ESTIMATION OF FIBRES.-For the purpose of counting and thus estimating the proportion of fibre present the low power (100 diani.) is quite sufficient.In the paper by Spence and J. M. Krauss; previously cited a method of counting fibres is elaborated. This method depends on counting the number of diameters and fractions of a diameter represented by each of the fibres under examination. The diameter taken as a unit is the diameter of a field examined under the microscope. Sp'ence and Krauss deal mainly with woody fibres of various kinds and with rag. They find that equal weights of wood and rag when mixed and examined under the microscope by their method, do not give equal numbers of diameters and this they attribute to the fact that equal lengths of fibres do not represent equal weights; in order therefore to make correct estimations it is necessary to elaborate a correction which will convert the count expressed in diameters into weights.In the present work the object was to estimate hemp in the presence of wood. To do this various synthetic mixtures were made up containing different proportions of hemp and wood. Three slides were made from each mixture and the number of diameters of hemp and wood determined in about twenty fields taken from each slide. The average of the whole was taken to represent the proportions of the two fibres present. When this was done it was found that it was unnecessary to introduce any correction such as that described by Spence and Krauss because the results obtained by the diameters were sufficiently near the known proportions by weight. Sometimes the proportion of hemp was lower than the truth and at other times it was higher to about the same extent and therefore no advantage could be obtained by introducing the correction for the relationship between diameter and weight.The following table shows the results obtained with synthetic mixtures of hemp and wood. TABLE. Qzcantitative Estimation of the Percentage of Hemp present in Mixtures of Hemp and Wood PULP. Per cent. Per cent. Percentage errors Taken Found 50 Hemp. 50.9 + l a 8 33 *3 29 - 13 33.3 37.7 +13 80 80.3 + -4 25 30 +20 5 16 + 60 10 9.3 - 7 It will be seen that when the percentage of hemp is fairly high say above 10 per cent. the results are sufficiently good for practical purposes. The figures shown under percentage errors may appear at first high but if the significance of the percentage error is realised it will be seen that the accuracy of this method is probably rather better than that usually claimed by analysts experienced in paper analysis.Generally speaking the claim is accuracy within about 5 per cent. This 5 per cent. of course is not percentage error and is for that reason rathe DICKSON ESTIMATION O F HEMP AND WOOD FIBRES I N PAPER PULP 377 vague. The high percentage error shown in the table when only 5 per cent. of hemp is present is due to the enormous number of wood fibres to be counted. This naturally introduces cumulative errors. The accuracy of the method was also confirmed by examining a paper containing hemp and wood, the composition of which was unknown to the author. The results were found to correspond almost exactly with the composition as afterwards stated by the makers.The detailed method of carrying out the estimation of hemp is as follows: METHOD.-Half a grm. of dry paper is weighed out and boiled with 100 C.C. of 10 per cent. sodium hydroxide to remove sizing materials. The paper is then pulped in a mortar until most of the paper structure has disappeared after which the pulp is transferred to a cylindrical glass vessel (A) 5 in. high by 34 in. in diameter and thoroughly pulped by means of a hand egg-switch. When the pulp is thoroughly disintegrated it is transferred to a Winchester quart bottle which is filled up with water and shaken thoroughly. The resulting mixture contains 0.02 per cent. of pulp which is the concentration recommended by Spence and Krauss.A cylindrical vessel (B) about 6 in. high and 2 in. in diameter is filled with this mixture care being taken that the pulp is completely suspended in the water when the mixture is being pouied out from the Winchester quart bottle. The quantity of pulp in the cylindrical vessel is now collected on a Gooch crucible fitted with a small piece of filter paper and after washcng the pulp is carefully separated from the filter paper and transferred to a test tube. I t is now stained by Cross and Bevan’s differential method malachite green and Congo red being used in the following manner:-A small quantity of a 0-5 per cent. solution of malachite green containing a little acetic acid is added to the test tube and the mixture boiled for a few minutes.The pulp is again filtered off in a Gooch crucible under suction and thoroughly washed. It is next transferred to another test tube, stained with a small quantity of a 0.5 per cent. solution of Congo red containing a little sodium carbonate and filtered as before. The pulp so stained is transferred to the glass vessel (A) and the necessary amount of water added to bring it back to a concentration of 0.02 per cent. This is best done by filling the glass vessel (B) with water and adding it to (A). The pulp is now brought into complete suspension by pulping it with a hand egg-switch and the contents of vessel (A) are added to vessel (B). A microscopic teasing needle is taken and the pulp thoroughly stirred up with it. When the mixture has been made to rotate fairly quickly by stirring the needle is held stationary near the side of the glass for a few minutes; the pulp will now be found to have twined itself round the needle and a good average sample is obtained simply by withdrawing the needle from the mixture.Three micro-cover glasses, 2 in. square are taken a small portion of the mixture is placed upon each and very carefully teased out so that individual fibres are subsequently seen under the microscope. The cover glasses are dried by pressure with a small piece of filter paper. A little alcohol is added to each and the excess again removed by means of filter paper. A few drops of Canada balsam are placed on a micro-slide; an 378 DICKSON ESTIMATION OF HEMP AND WOOD FIBRES IN PAPER PULP one of the cover slips placed in position on the top of the Canada balsam in the usual way.The excess of Canada balsam is removed by means of a little benzene. The Nicol prism is put into position and an objective eye piece and tube length are so chosen as to give a magnification of 100 diams. The polariser Nicol prisni is fixed to the under side of the sub-stage condenser. The slide is now examined both by ordinary and polarised light the polariser Nicol prism being rotated in such a manner as to give either polarised or ordinary light as required. The examination of the slide is begun on the top left hand corner and suc-cessive fields are examined down the left hand side of the slide. The slide is then moved so that practically the centre of it comes under the objective and fields are examined right up the middle of the slide.It is then moved to the right hand corner and fields examined right down the right hand side of the slide. The proportions of the fibres to be estimated are expressed in diameters and fractions of diameters of the field. The total number of diameters of each fibre counted in the three slides is averaged and the proportions of the fibres present calculated to percentages in the usual way. As an example:-Suppose the total diameters of wood fibres to be 92.1 and those of the hemp to be 18.6. The total number of dian-ieters will be 110.7. Hence 110.7 diameters contain 18.6 diameters of hemp. One hundred parts will therefore contain : The slide so prepared is placed on the stage of the microscope. loo = 16.8 per cent. 110.7 The author desires to express his thanks to Messrs.Eley Bros. for permission to publish the results given in this paper. DISCUSSION. Mr. V. COFMAN asked whether the author could explain the reason for the difference in the appearance of the specimens when seen by polarised light and whether if the specimens had not been treated with the chemical reagents referred to the appearance by polarised light would have been the same. Mr. A. CHASTON CHAPMAN pointed out that monochromatic and ultra-violet light had been found capable of revealing differences in structures in the case of yeast and other organisms and suggested that possibly the same methods of illumination might bring out differences in such fibres as those with which the authors had dealt. He also wondered whether the readiness with which certain easily reducible metals could be deposited on the fibres could be made use of in ascertaining their origin.He did not remember having seen any account of work on these lines although the method had been usefully employed in other directions DICKSON ESTIMATION OF HEMP AND WOOD FIBRES IN PAPER PULP 379 Mr. R. G. PELLY enquired whether the author’s remarks applied only to true hemp (Cannabis species) or whether other kinds of hemp (such as Manilla and sisal hemp) were also referred to. He also asked how the fibre had been pulped; whether a model paper beater had been used for the purpose as beating might have some effect on the microscopic appearance of the fibres. Mr. DICKSON replying to the first speaker said he was unable to explain why hemp or any other fibre behaved as it did under polarised light. He was interested in the remarks on the possible effect of chemical treatment on the microscopic appearance of the fibre; in his experience the more one bleached the fibre the more apparent were the characteristic markings. He had not tried the application of monochromatic light. He was interested in the suggestion of the deposition of metals on fibre which would doubtless be a fruitful field of research hitherto not explored. As regards different kinds of hemp he had examined a few different kinds-sunn hemp and ordinary Italian hemp ; these were microscopically similar. Manilla hemp on the other hand was different but he had not studied it from the quantitative point of view