T3 //75 
 
L(, 
 
 DEPARTMENT OF COMMERCE 
 
 Technologic Papers 
 
 OF THE 
 
 Bureau of Standards 
 
 S. W. STRATTON, Director 
 
 No. 189 
 
 METHOD FOR DIFFERENTIATING AND 
 
 ESTIMATING UNBLEACHED SULPHITE 
 
 AND SULPHATE PULPS IN PAPER 
 
 R. E. LOFTON, Associate Physicist 
 M. F. MERRITT, Laboratory Assistant 
 
 Bureau of Standards 
 
 APRIL 4, 1921 
 
 •Z 4, % ^ S" 
 
 PRICE, 5 CENTS 
 
 Sold only by the Superintendent of Documents, Government Printing OiEce, 
 Washington, D. C. 
 
 WASHINGTON 
 GOVERNMENT PRINTING OFFICE 
 
 1921 
 
LIBRARY OF CONGRESS 
 
 MAY 7^19^1 
 
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 V 
 
 1^ 
 
 ^<^ 
 
 A METHOD FOR DIFFERENTIATING AND ESTIMATING 
 UNBLEACHED SULPHITE AND SULPHATE PULPS IN 
 PAPER 
 
 By R. E. Lofton and M. F. Merritt 
 
 ABSTRACT 
 
 The purpose of this paper is to fill a need felt especially by paper chemists and ana- 
 lysts for a rapid and reliable method of distinguishing between and of making an ap- 
 proximately correct quantitative determination of mixtures of unbleached sulphite 
 and sulphate pulps. This paper gives briefly the basic differences in the manufactiu'e 
 of the two pulps, and contains a concise review of the methods that have been recom- 
 mended from time to time for distinguishing between unbleached sulphite and sul- 
 phate pulps. It gives the procediu-e followed in developing a new and comparatively 
 rapid method for distinguishing between these pulps, and also gives some of the more 
 important experiments carried out with various stains diuing this investigation. The 
 method of preparing the new stain and the method of procedure for differentiating be- 
 tween luibleached sulphite and sulphate fibers is described in detail, and tables show- 
 ing the results of quantitative microscopical analysis of mixtiu-es of these fibers stained 
 by the new method are given. 
 
 CONTENTS 
 
 Page 
 
 I. Introduction 3 
 
 II. Theoretical considerations involved 4 
 
 1 . Fundamental differences between the two pulps 4 
 
 2 . Possible bases of differentiation 5 
 
 3. Different affinities of pulps for dyes 6 
 
 III. Methods proposed by earlier experimenters 6 
 
 1 . Klemm 's methods 7 
 
 2. Schwalbe's methods g 
 
 3. Fannon's methods 10 
 
 IV. The malachite-green and fuchsine method 10 
 
 1 . Soitfces of materials used 10 
 
 2. Method of attack and earlier experiments 11 
 
 3. Detailed method of using 12 
 
 4. Estimating percentages 14 
 
 V. Summary of results 15 
 
 I. INTRODUCTION 
 
 The purpose of this pubHcation is to give a review of the various 
 methods proposed for distinguishing between unbleached sulphite 
 and sulphate fibers, and especially to describe the development 
 and application of a new method for accomplishing this result. 
 
 3 
 
 7'^-^ 
 
4 Technologic Papers of the Bureau of Standards 
 
 That there is and has existed for some time a demand for a quick 
 and certain method for differentiating between these two pulps is 
 indicated by the various attempts that have been made from time 
 to time to develop such a method. To be satisfactory, any method 
 proposed must be practical as well as certain — that is, it must not 
 require any expensive apparatus, or special experience, or tedious 
 and lengthy manipulation- — but it must be such as may be carried 
 out in a few minutes time by any one ordinarily familiar with the 
 microscopical examination of paper-making fibers. 
 
 Such a method would be of service to pulp manufacturers and 
 jobbers, to manufacturers of sulphite and sulphate papers, and to 
 the retailers and consumers of sulphite and sulphate papers in aid- 
 ing them to determine whether they are getting what they desire. 
 It is useless for a jobber or a consumer to specifically order an all 
 or part sulphate wrapping paper unless there is some means of de- 
 termining whether the article ordered is being furnished. 
 
 The authors acknowledge the assistance of M. B. Shaw, who 
 made a large number of fiber estimations, the results of which ap- 
 pear in Tables 3,4, and 5, and who gave assistance as to methods 
 of preparing the stains. 
 
 II. THEORETICAL CONSIDERATIONS INVOLVED 
 1. FUNDAMENTAL DIFFERENCES BETWEEN THE TWO PULPS 
 
 The difficulties to be overcome in developing a method for dis- 
 tinguishing between unbleached sulphite and sulphate pulps are 
 due to the similarity of the pulps. Both are made, for the most 
 part, from the same raw material, with but two or three exceptions. 
 Spruce, hemlock, balsam fir, yellow pine, tamarack, and white fir 
 are used in making both pulps. In addition to these woods, jack 
 pine and cypress are often used in the sulphate process. Yellow 
 pine is more generally used in the sulphate than in the sulphite 
 process, because the former process is better adapted to woods rich 
 in rosin and oil. The woods generally used in foreign countries 
 are of the same kinds as those used in the United States and Canada 
 except that black spruce is frequently used in Finland, Norway, 
 and Sweden. 
 
 Since the raw material from which these pulps are made is in 
 general the same, the only distinguishable differences between the 
 pulps are to be found in the two different digesting processes em- 
 ployed in their manufacture. 
 
 Sulphite pulp is made by cooking wood chips in a solution of 
 bisulphite of calcium, or of calcium and magnesium. This solution 
 
Differentiating Unbleached Sulphite and Sulphite Pulps 5 
 
 has an acid reaction. The chips are cooked under a steam pressure 
 of from 60 to 80 pounds for from 8 to 20 hours. The process was 
 invented by B. C. Tilghman, of Philadelphia, who took out the 
 first United States patent in 1867. 
 
 Sulphate pulp, frequently called "Kraft" (a German word 
 meaning "strength"), is made by cooking wood chips in a solu- 
 tion the chief ingredient of which is sodium sulphide. The sodium 
 "sulphate" added from time to time is reduced to "sulphide" 
 during the preparation of the cooking Uquor. The reaction of 
 this solution is alkaline. In this process the chips are cooked 
 imder a steam pressure of about 100 pounds for from 2 to 7 hours. 
 This process was invented by Carl F. Dahl, of Danzig, Germany, 
 about 1883, and was introduced into America in 1907, when the 
 Brompton Pulp and Paper Co. set up a sulphate mill in Canada. 
 
 Unbleached sulphite pulp is used in the manufacttue of wrapping 
 paper and bag stock, of many so-called Kraft and manila papers, 
 of twines used in tying bundles and in making paper rugs, onion 
 and potato sacks, and in any pulp or paper product where strength 
 is the chief consideration. Sulphate pulp has a considerably 
 darker color than sulphite, for which reason the latter is often 
 colored in the process of being made into paper to resemble sulphate 
 pulp. In general, sulphate pulp may be used wherever it is per- 
 missible to use unbleached sulphite. In cases where the greatest 
 possible strength is required, sulphate is used instead of sulphite, 
 since it is somewhat stronger. The cost of sulphate, due to a 
 more expensive process of manufactiire, is somewhat more than 
 that of sulphite pulp. 
 
 2. POSSIBLE BASES OF DIFFERENTIATION 
 
 Commenting on the problem, C. \V. Schwalbe stated' in 191 4 
 that there was no simple method known at that time for distin- 
 guishing between unbleached sulphite and sulphate pulps; also, 
 that it is difficult to develop such a method because the pulps are 
 so closely related. Schwalbe recognized, too, as do others who 
 have made a study of the two pulps, that there are two differences 
 between them which may be used as a basis on which to develop 
 reactions which will differentiate them, namely, (i) the difference 
 in the amounts of incrusting or Ugneous material, and (2) the dif- 
 ferent chemical changes which have been brought about by the 
 different digesting processes. 
 
 1 Testing Methods for Sulphite and Sulphate Cellulose in Paper. Pulp and Paper Magazine, p. 21; Jan. 
 1. 1914- 
 
6 Technologic Papers of the Bureau of Standards 
 
 3. DIFFERENT AFFINITIES OF PULPS FOR DYES 
 
 It is pretty generally known by persons who have made any 
 analytic study at all of paper-making pulps that those pulps differ- 
 ing in the degree of cooking, or of bleaching, or both, usually have 
 quite different affinities for various dyes and stains. The dye 
 most generally used to show the properties of different pulps in 
 tliis respect is malachite green, a basic aniHne or coal-tar dye 
 which has a great affinity for highly lignified fibers and very little 
 or no affinity for pulps and fibers freed from incrusting matter. 
 The result of this property is that, when malachite green alone is 
 used to stain a pulp composed of a mixture of fibers having a high 
 content of lignin and of other fibers more thoroughly digested, one 
 gets a range of shades varying from deep green to very light green, 
 or, perhaps, to the entire absence of color in the case of fibers that 
 are completely freed from incrusting matter. Although there may 
 be no sharp color line of demarcation to set off any one group of 
 fibers against any other, results of this kind may serve the purpose 
 of determining the thoroughness or the uniformity of the cooking 
 or of the bleaching action. But if this or a similar dye or stain 
 is followed by one of a contrasting color, as recommended by 
 Siebert and Minor,- it will sometimes be found possible to separate 
 quite distinctly a mixture of two different pulps, as, for example, 
 a well-cooked from a slightly-cooked pulp, or a well-bleached from 
 a poorly-bleached pulp, or a chemical from a mechanical pulp. 
 These authors, however, recommend that malachite green be 
 followed by an acid dye, while in the method described below both 
 of the dyes used are basic. 
 
 Whether the different affinities of the two pulps for various dyes 
 and stains are due to different chemical properties of the pulps 
 brought about by the different cooking methods, or whether they 
 are due merely to the different amounts of incrusting matter 
 remaining in the sulphite and sulphate pulps, is a question on 
 which cellulose chemists do not agree. 
 
 III. METHODS PROPOSED BY EARLIER EXPERIMENTERS 
 
 In studying tliis problem the available methods proposed from 
 time to time by others who have experimented along tliis Une were 
 tried. Below is given a description of each method, together with 
 a brief statement of results obtained by the writers in trying the 
 method. 
 
 ^ The Differentiation of Sulphite Pulps, Paper, 25, No. 21; Jan. 2S, 1920. 
 
Differentiating Unbleached Sulphite and Sulphite Pulps 7 
 1. KXEMM'S METHODS 
 
 Klemm is given credit for developing two methods, in one of 
 which use is made of malachite green alone, and in the other use 
 is made of both malachite green and rosaniline sulphate. 
 
 Klemm's malachite green method is described by R. W. 
 Fannon ' as follows : 
 
 The reagent consists of a saturated solution of malachite green, a coal-tar dye, to 
 which 2 per cent acetic acid has been added. A portion of pulp is treated with a few 
 drops of the reagent sufficient to soak it, and the excess blotted up. The fiber is then 
 examined microscopically. Unbleached sulphite is colored full green; sulphate is 
 colored light green. 
 
 The results obtained by using tliis method were not satisfactory, 
 since there is no sharp or distinct line of demarcation between 
 the two pulps, some of the more deeply colored sulphate fibers 
 showing a deeper green than some of the lighter colored sulphite 
 fibers. These results are in harmony with the statements made 
 above regarding the use of malachite green in staining various 
 pulps and fibers. 
 
 Schwalbe mentions another procedure,* a malachite green 
 and rosaniline-sulphate method, wliich he also calls Klemm's 
 method. No details as to making up the dye solutions or method 
 of applying them are given. 
 
 It was found, however, that a fairly good differentiation between 
 the two pulps is had if they are stained for about two minutes with 
 a one-half per cent aqueous solution of malachite green, rinsed 
 with water, then stained \\-ith a solution of rosaniline sulphate 
 acidified with sulphuric acid. The same results may also be 
 obtained if these two stains are compounded in the right pro- 
 portions before being applied to the pulps. 
 
 When the chemical composition of rosaniline sulphate is com- 
 pared with that of magenta, or fuchsine, one of the dyes recom- 
 mended below, it is evident that they are very closely related, 
 and that the color radical is the same in both. An insight into 
 the constitution of these compounds may be had from any good 
 treatise on organic chemistry. 
 
 Pararosaniline and rosaniline ^ are the bases of the fuchsine 
 dyes. Both are triacid bases, stronger than ammonia. The 
 basic fuchsine or magenta dyes are formed by treating these 
 bases with various acids, particularly hydrochloric and acetic, 
 
 * An effort to find a simple means of differentiation between sulphite and sulphate pulp. (.\ thesis 
 prepared at the University of Maine. June. 1916.) 
 
 * Pulp and Paper Magazine, p. 2i;Jan. 1. 1914. 
 
 ^ A. Bemthsen. Organic Cheinistr>*. translation by J. J. Sudborough; New York. 1912. 
 
Technologic Papers of the Bureau of Standards 
 
 water being eliminated during the reaction. The formula of 
 rosaniline is 
 
 <CeH,.NH3 
 CeH^.NH^ or C,„H,iN30. 
 
 C,H3(CH3).NH3 
 
 By treating with hydrochloric acid, the following reaction 
 takes place: 
 
 CjoHjiNjO + HCl = C2oH3„N3Cl + HjO. 
 
 Rosaniline Hydro- Rosaniline Water 
 
 chloric hydrochloride 
 
 acid 
 
 From analogy, it appears that a similar reaction takes place 
 when rosaniline is treated with sulphuric acid, and that rosaniline 
 sulphate is essentially a basic fuchsine or magenta dye, but \\4th 
 an add radical not usually found in dyes put out under this name. 
 
 (QoH^iNjO)^ + H,S04 = (CoH,„N,),SO, + 2H,0. 
 
 Rosaniline Sulphuric Rosaniline sul- Vater 
 
 acid phate 
 
 As the coloring power, however, of these dyes lies wholly in the 
 basic constituent, there can be no doubt but that rosaniline 
 sulphate is essentially basic fuchsine or magenta. 
 
 One authority " states that basic magenta is a mixtiu-e of the 
 hydrochloride and acetate of rosaniline and pararosaniline ; 
 according to another, it is a mixture of the hydrochlorides of 
 rosaniline and pararosaniHne. The formula of pararosaniline is 
 
 <CeH,.NH3 1 
 CeH^.NH,. or C^H.^NjO. 
 CaH,.NH, j 
 
 The reaction of this base with acids is like that of rosaniline. 
 
 The malachite-green and rosaniline-sulphate stain, however, 
 does not give as brilliant color contrast between the two kinds of 
 fibers. This advantage of the use of basic fuchsine over that of 
 rosaniline sulphate is probably explained by the greater solubility 
 of basic magenta as compared "with that of rosaniline sulphate, 
 since it was found by test that basic magenta is much more soluble 
 in water than is rosaniHne sulphate. Tliis fact is in harmony with 
 the known properties of the salts of these acids. 
 
 fl Thomas H. Norton artifical dyestuifs used in the United States, Special Asent Series. No. 121. Bureau 
 Foreign and Domestic Commerce. Washington D. C. Ira Remsen. Organic Chemistry. Fifth revision; 
 New York, 1909. 
 
Differentiating Unbleached Sulphite and Sulphite Pulps 9 
 2. SCHWALBE'S METHODS 
 
 Schwalbe also describes ' two methods of analysis, in one of 
 which aqueous solutions of ferric chloride and potassium ferro- 
 cyanide are used, and in the other solutions of a copper salt and 
 an organic dye. The former method is also briefly outlined by 
 Fannon." 
 
 The ferric-chloride and potassium-ferrocyanide method consists 
 in extracting the pulps for about 30 minutes in alcohol and ether 
 to remove rosin, treating with a 0.05 A'^ solution of ferric chloride 
 at from 60 to 80° C for about 30 minutes, or until all the fibers 
 settle to the bottom of the container, washing with distilled water, 
 and treating with a i per cent solution of sulphuric acid, to wliich 
 is then added from four to eight drops of a 2 per cent solution 
 of potassium ferrocyanide. The container and contents are then 
 placed on a water bath and kept at a temperature of from 60 to 
 80° C for from 5 to 10 minutes. The pulps are then washed and 
 examined under the microscope. Sulphite fibers are colored a 
 deep blue, and sulphate fibers a much lighter blue. 
 
 This method did not give results that would enable a distinction 
 to be made in all cases between the two pulps, nor to permit 
 estimations in any case. Moreover, the process is too long and 
 tedious to be practical. However, since Schwalbe so liighly 
 recommends this method, it is thought probable that better 
 results could be obtained if enough time should be spent in study- 
 ing and experimenting with it. 
 
 By the copper method the pulps are boiled in a solution of a 
 copper salt such as copper sulphate, washed, then treated with a 
 solution of an organic dye such as benzopurpurine loB. The 
 benzopurpurine treatment develops in some classes of fibers an 
 intensely blue color, according to Schwalbe, due to the formation 
 of a so-called copper lake with the copper salt retained by the 
 fibers. 
 
 This method was not experimented with, since Schwalbe liimself 
 condemns it as being too involved and uncertain in results, 
 especially with pulps so similar in their properties as unbleached 
 sulphite and sulphate. 
 
 T Pulp and Paper Magazine, i). 21; Jan. i, 1914. 
 ^ Thesis referred to above. 
 
 34392°— 21 2 
 
lo Technologic Papers of the Bureau of Standards 
 
 3. FANNON'S METHODS 
 
 Fannon " found that a saturated aqueous solution of rosaniline 
 sulphate, to which is added i to 3 per cent of alcohol and enough 
 sulhpuric add to cause the solution to take on a violet shade, is 
 a satisfactory stain. He used two methods of applying this 
 stain and examining its staining action : 
 
 In the first method, two or three drops of the solution were 
 allowed to fall in the same spot onto the samples of sulphite and 
 sulphate pulps tested, and the color reactions observed \vith the 
 unaided eye. The unbleached sulphite pulps showed "a deep 
 bluish center with a yellow ring siurounding," while the sulphate 
 sample gave "a deep red coloration." "From 7 to 15 minutes 
 after the stain was dropped on, the distinctive colorings were 
 evident. After an hour or so the colors faded." 
 
 In the second method, " mixtures of sulphate fibers and sulpliite 
 fibers were made, stained with the last-named solution. The 
 different fibers developed their respective colorations, and under 
 the microscope estimations of each were possible." 
 
 This stain was not found satisfactory when used according to 
 either method recommended, because the color differences shown 
 by the two pulps are not sharp enough to enable one to detect 
 without doubt even the presence of small percentages of one pulp 
 when mixed with the other. 
 
 IV. THE MALACHITE-GREEN AND FUCHSINE METHOD 
 1. SOURCES OF MATERIALS USED 
 
 The samples of pulps and papers used in this investigation 
 consisted of 188 pieces collected from a number of different firms, 
 and represent pulps manufactured in all parts of this cormtry, 
 and in at least four foreign countries, Canada, Finland, Norway, 
 and Sweden. All possible information was obtained regarding 
 these samples, such as the kind of wood used and in what locaUty 
 grown, the degree of cooking, etc. 
 
 The dyes and stains used during the earlier part of this investi- 
 gation were obtained chiefly from the chemical di\dsion of this 
 Bureau. Most of them had been in stock for some time, and all, 
 or nearly all, were of German manufacture. But after the 
 method given below had been pretty thoroughly worked out, 
 samples of the two dyes used in this method were obtained from 
 different sources in this country in order to determine whether 
 the different makes of dyes were equally suitable for the purpose. 
 
 ^ Thesis rderred to above. 
 
V 
 
 Differentiating Unbleached Sulphite afid Sulphite Pulps 1 1 
 2. METHOD OF ATTACK AND EARLIER EXPERIMENTS 
 
 The method of conducting the investigation was to try out 
 on the two kinds of pulps the reaction of various biological stains 
 and dyes recommended by authorities on microscopical methods, 
 and also other stains and dyes that were suggested in one way or 
 another. Most of the experimenting was carried on with red, 
 green, and blue dyes, since dyes of these colors are usually the 
 most brilliant and positive in their coloring action. The few 
 yellow dyes that were tried did not give sufficiently brilliant 
 color effects on the fibers, and little work was done \vith them. 
 
 In making tliis investigation by what may be properly called 
 the empirical method, a great number of tests were necessarily 
 made that are relatively valueless and therefore are omitted 
 from this publication. Those which may be of value to others 
 who are experimenting along the same line are given in Table i . 
 
 TABLE 1. — Interesting Experiments Made and Stains Used with the Color Reactions 
 
 on Sulphate and Sulphite Fibers 
 
 [Ext. alc.= extracted with alcohol; aq.=> aqueous; so'.= soIutlon.] 
 
 How stained 
 
 Satranin in equal parts water and alcohol, 
 rinsed with water, Delafield's hema- 
 toxylin. 
 
 Ext. ale. boiled 1 minute. ^4 per cent aq. 
 sol. malachite green, rinsed with water, 
 rosanjline sulphate and little sulphuric 
 acid. 
 
 Ext. ale, boiled 1 minute. }.i per cent aq. 
 sol. malachite green, rinsed with water, 
 eosin in equal parts alcohol and water. 
 
 Ext. ale, heated to 100°C in }'i per cent aq. 
 sol. malachite green, rinsed with water, 
 1 per cent aq. ale. sot. safranin. 
 
 Boiled 1 minute in 1 part rosaniline sul- 
 phate sol., then 1 part 1 per cent aq. sol. 
 malachite green added, lightly rinsed 
 with water. 
 
 Ext. ale, boiled in water, acidified solu- 
 tion 50 per cent alcohol, Deiafield s 
 hematoxylin 10 to IS minutes, rinsed 
 with water, J 2 P" cent sol. congo red 1 
 minute, rinsed with water. 
 ; Ext. ale. boiled in water, acidified solu- 
 tion 5U per cent alcohol, Delafield's 
 hematoxylin left on until air dry, rinsed 
 with water, ^2 per cent sol. congo red I 
 minute, rinsed with water. 
 
 Colorless te faint 
 
 reddish 
 
 brown. 
 Clear blue, 
 
 bundles 
 
 green. 
 
 Dark blue 
 
 Light to dark 
 
 Pink to light 
 magenta. 
 
 Color difierence 
 quite noticeable. 
 
 Pale gray to Differen t ia t i 
 lavender. good. 
 
 Colorless to 
 
 faint purple. 
 
 Light to dark 
 red. 
 
 Pits of sulphite 
 fibers colored 
 green. 
 
 Do. 
 
 Purple Good differentia- 
 tion. 
 
 Fair difierentia- 
 
 tion. 
 
 Purple with 
 litUe red. 
 
Technologic Papers of the Bureau of Standards 
 
 TABLE 1. — Interesting Experiments Made and Stains Used with the Color Reactions 
 on Sulphate and Sulphite Fibers — Continued 
 
 
 
 Action 
 
 on— 
 
 
 Serial 
 
 How stained 
 
 
 
 Remarks 
 
 No. 
 
 
 
 
 
 Sulphate 
 
 Sulphite 
 
 
 57 
 
 Ext. ale, washed with 1 per cent aq. sol. 
 tannic acid, then equal parts 1 per cent 
 
 Blue 
 
 Purple 
 
 Good differentia- 
 
 
 
 tion. 
 
 
 aq. solutions acid ftrchsine and malachite 
 
 
 
 
 
 green 3 minutes, rinsed with water. 
 
 
 
 
 79 
 
 Ext. ale, boiled in water, dried with filter 
 paper on slide, then 50 parts each o( 1 per 
 cent aq. solutions magenta and malachite 
 green and 1 part 1 per cent aq. sol. tannic 
 acid 2 minutes, quickly rinsed in 50-50 
 aq. ale. sol. slightly acidified with HCl, 
 rinsed with water. 
 
 Greenish blue.. 
 
 
 Differentiation ex- 
 cellent. 
 
 82 
 
 Boiled in water, i 2 per cent aq. sol. mala- 
 
 Blue 
 
 do 
 
 Color difference not 
 
 
 chite green and aq. sol. rosaniline sul- 
 
 
 
 as decisive as 
 
 
 phate and little HsSO,, all left on fibers 
 
 
 
 when magenta is 
 
 
 2 mhiutes, then rinsed with water. 
 
 
 
 used in place of 
 rosaniline s u 1 - 
 phate. 
 
 84 
 
 Slide as made up by No. 79 examined under 
 
 Various colors . 
 
 Various colors. 
 
 No distinguishing 
 
 1 microscope in polarized light, wiUi both 
 
 
 
 properties 
 
 parallel and crossed nicols. 
 
 
 
 appeared. 
 
 85 Boiled In water, pulped and examined 
 
 Yellow, orange. 
 
 Yellow, orange, 
 
 Do. 
 
 under microscope in polarized light with 
 
 and blue. 
 
 and blue. 
 
 
 
 both parallel and crossed nicols. 
 
 
 
 
 Some of the pulps were extracted with alcohol to remove 
 resins, and this fact is indicated in each case in the table. The 
 pulps were then rinsed and cooked, at first, in clear water, and 
 pulped, no chemical being used in the cooking process, as it was 
 thought that any chemical treatment might possibly interfere 
 with the staining action to follow. Experiments that were con- 
 ducted later, however, indicated that cooking the sample of 
 paper in a one-half per cent aqueous solution of caustic soda 
 does not have any effect on the action of the dyes. The alcohol 
 used at various times and for various pvu-poses, as indicated, 
 was in all cases ethyl alcohol. The color appearances and other 
 characteristics noted are those which appeared under the micro- 
 scope. 
 
 3. DETAILED METHOD OF USING 
 
 The stain which was found to be most satisfactory in diflfer- 
 entiating between unbleached sulphite and sulphate pulps or 
 fibers was a mixture of one part of a 2 per cent aqueous solution of 
 malachite green and two parts of a i per cent aqueous solution of 
 
Differentiating Unbleached Sulphite and Sulphite Pulps 13 
 
 basic fuchsine, or magenta. The solutions were made up accord- 
 ing to the following formulas, kept in tightly stoppered separate 
 bottles, and mixed only when wanted for use : 
 
 A — Malachite green 2 g 
 
 Distilled water .;:.... 100 cm* 
 
 B — Basic fuchsine i g 
 
 Distilled water 100 cm ^ 
 
 Since there is considerable variation in the quality of dyes from 
 various sources, it is not to be expected that any given combina- 
 tion of dyes or method of procedure will best fit all cases; it is, 
 indeed, more than probable that the compovmd stain will have to 
 be modified somewhat as to its two components, depending on the 
 source of the dyes. 
 
 After this stain, therefore, has been made up according to 
 formula, it will be necessary to test it out on samples of sulphite 
 and sulphate fibers. To do this, samples of unbleached sulphite 
 and sulphate pulps should be prepared and a few fibers of each 
 placed on a slide, care being taken not to get the two samples 
 mixed. The fibers are then dried and stained, as directed below, 
 and then examined under the microscope. All the sulphate fibers 
 should have a blue or blue-green color, and all the sulphite fibers 
 should have a purple or lavender color. If any purple fibers 
 appear in the sulphate pulp this indicates that too much fuchsine 
 is present in the combination, and a little more malachite green 
 solution must be added to coimteract this effect. If, on the other 
 hand, some of the sulphite fibers show green or blue, there is too 
 much malachite green in the combination, and more fuchsine 
 solution must be added. Of course the analyst must be sure that 
 he is using authentic samples of the two pulps for this test. When 
 tested out in this manner and the proper combination found, the 
 stain is ready to be used on unknown combinations of fibers con- 
 taining either imbleached sulphite or sulphate, or both. 
 
 A mixture of one-haif sulpliite and one-half sulphate may also 
 be used to test out the stain, the proper combination for the stain 
 being indicated when one-half of the fibers are colored blue, and 
 the other half purple. 
 
 The stain should not be used for more than a few hours after 
 being compounded and should be made up anew at least each 
 day. 
 
14 Technologic Papers of the Bureau of Standards 
 
 The method of preparing the samples of pulps or papers for 
 staining, and of applying the stain, is as follows: 
 
 The sample is boiled for a few minutes in water or in a one- 
 half per cent aqueous solution of sodium hydroxide, and the fibers 
 are thoroughly disintegrated by shaking in a test tube or other 
 receptacle about half filled with water, glass beads being added 
 if the fibers can not otherwise be separated. Several fibers are 
 then removed by means of a teasing needle, or preferably by 
 means of a glass tube " about seven thirty-seconds of an inch in 
 diameter, placed on a microscope slide, and dried by the use 
 of hard filter or blotting paper. Two or three drops of the com- 
 pound stain are then placed on the fibers by means of a suitable 
 dropper or a pipette and allowed to remain 2 minutes, during 
 which time the fibers are being teased apart and moved about in 
 the stain on the slide. This teasing is necessary in order that 
 the stain may have equal opportunity to act on all the fibers. 
 At the end of 2 minutes the excess stain is removed with three 
 or four thicknesses of hard filter paper, and the fibers treated with 
 three or four drops of a weak aqueous solution of hydrochloric 
 add, made by adding i cm' of concentrated acid (sp. gr. 1.19; 
 HCl 37 per cent) to i liter of distilled water. The acid solution 
 is allowed to remain on the slide for from 10 to 30 seconds, during 
 which time the fibers are teased and moved about rapidly. Fol- 
 lowing this, the excess acid solution is removed with filter paper, 
 three or four drops of distilled water applied, the fibers quickly 
 teased about, and the water absorbed with filter paper. If all the 
 excess stain has been removed from the sHde at this point, a drop 
 or two of water may be added, the fibers spread about on the slide, 
 and a cover glass placed over them. But if too much stain 
 remains on the slide at this point, it will be necessary to rinse 
 again wth distilled water before applying the cover glass. After 
 the cover glass has been placed in position the fibers are ready for 
 examination imder the microscope. 
 
 4. ESTIMATING PERCENTAGES 
 
 The color contrast not only enables one to detect the presence 
 of one or both of these fibers, but is sharp enough to enable one, 
 after some practice, to make an approximately correct estimate 
 of the percentages of each of these fibers present. 
 
 "> F. C. Clark, Paper Testing Methods, Tappi Publishing Corp., New York. N, Y.; 1920. 
 
Differentiating Unbleached Sulphite and Sulphite Pulps 15 
 
 In order to get a practical idea as to what could be accomplished 
 in estimating the percentages of sulphite and sulphate fibers when 
 stained as directed, three persons, all of whom had had experience 
 in estimating the percentages of fibers stained with the zinc- 
 chloride and iodine stain, made a number of estimations on known 
 mixtures of these two pulps. 
 
 Seven mixtures, made from representative samples of sulpliite 
 and sulphate pulps, were prepared by weighing on a chemical 
 balance the proper proportions of each pulp, the weights of the 
 two components totaling 30 g in each case. The pulps were then 
 thoroughly mixed by agitating in a tight container with consid- 
 erable water. The series made up contained 20, 25, 40, 50, 60, 
 75, and 80 per cent of unbleached sulphite. A representative 
 portion of each member of this series was placed in a container 
 and labeled. Microscope slides were then made up from each 
 of the seven samples, each slide being given an unknown mark 
 of identification, and handed over to the analysts for their esti- 
 mations. Four different series of estimates were made, in each 
 of which a different make of American dyes was used. 
 
 V. SUMMARY OF RESULTS 
 
 In the tables below are given the results of estimates on the 
 seven fiber mixtures, each table showing the results obtained by 
 using dyes from one of the four sources. 
 
 TABLE 2. — Results of Analyses, Using Dyes from First Source 
 
 
 Ob- 
 server 
 
 Percentage sulphite in mixture 
 
 Error 
 
 o( 
 aver- 
 age 
 
 Prob- 
 able 
 error 
 
 <r) 
 
 
 Number of 
 estimations 
 
 Estimated 
 
 Actual 
 
 Huge 
 error 
 
 (u) 
 
 
 Maxi- 
 mum 
 
 Mini- 
 
 Aver- 
 age 
 
 16 
 
 A 
 
 C 
 A 
 C 
 A 
 
 C 
 A 
 C 
 A 
 C 
 A 
 C 
 A 
 C 
 
 40 
 50 
 50 
 50 
 60 
 90 
 75 
 80 
 80 
 90 
 90 
 80 
 95 
 90 
 
 20 
 10 
 20 
 20 
 25 
 25 
 40 
 40 
 60 
 60 
 25 
 40 
 75 
 25 
 
 23.8 
 27.9 
 33.1 
 33.9 
 41.6 
 50.7 
 51.6 
 57.1 
 67.2 
 69.6 
 73.7 
 72.9 
 
 80.6 
 76.4 
 
 20 
 20 
 25 
 25 
 40 
 40 
 50 
 50 
 60 
 60 
 75 
 75 
 80 
 80 
 
 Per cent 
 
 +3.8 
 + 7.9 
 +8.1 
 +8.9 
 
 + 1.6 
 + 10.7 
 
 + 1.6 
 + 7.1 
 + 7.2 
 + 9.6 
 -1.3 
 -2.1 
 +0.6 
 -3.6 
 
 Per cent 
 5. 1 
 8.8 
 8.2 
 
 8.7 
 7.1 
 
 12.7 
 5.4 
 9.5 
 7.1 
 8.7 
 9.6 
 7.8 
 3.4 
 
 10.1 
 
 Per cent 
 
 12.3 
 
 
 21.6 
 
 16.. . 
 
 20.0 
 
 
 21.2 
 
 16 
 
 17.3 
 
 
 30.9 
 
 16 
 
 13.2 
 
 
 23.1 
 
 16 
 
 17.3 
 
 
 21.2 
 
 16 . . .. 
 
 23.4 
 
 
 18.9 
 
 
 8.2 
 
 
 24.7 
 
 
 
1 6 Technologic Papers of the Bureau of Standards 
 
 TABLE 3. — Results of Analyses, Using Dyes £rom Second Source 
 
 
 Ob- 
 server 
 
 Percentage sulphite in mixture 
 
 Error 
 
 ol 
 aver- 
 age 
 
 Prob- 
 able 
 error 
 
 (r) 
 
 
 Number ol 
 estimations 
 
 Estimated 
 
 Actual 
 
 Huge 
 error 
 
 (u) 
 
 
 Maii- 
 
 Mini- 
 
 Aver- 
 age 
 
 16 
 
 A 
 
 B 
 C 
 A 
 B 
 C 
 A 
 B 
 C 
 A 
 B 
 C 
 A 
 B 
 C 
 A 
 B 
 C 
 A 
 B 
 C 
 
 40 
 25 
 40 
 50 
 40 
 25 
 75 
 60 
 75 
 
 75 
 60 
 60 
 80 
 75 
 60 
 80 
 80 
 80 
 80 
 80 
 80 
 
 20 
 25 
 20 
 
 20 
 25 
 20 
 25 
 50 
 30 
 50 
 60 
 40 
 50 
 50 
 50 
 60 
 80 
 70 
 75 
 75 
 70 
 
 24.7 
 25.0 
 24.0 
 37.2 
 35.0 
 24.0 
 50.0 
 53.3 
 47.5 
 54.1 
 60.0 
 51.7 
 65.0 
 66.7 
 56.0 
 
 75.6 
 80.0 
 77.0 
 
 78.4 
 78.3 
 73.7 
 
 20 
 20 
 20 
 
 25 
 25 
 25 
 40 
 40 
 40 
 50 
 50 
 50 
 60 
 60 
 60 
 75 
 75 
 75 
 80 
 80 
 80 
 
 Per cent 
 
 +4.7 
 +5.0 
 +4.0 
 
 + 12.2 
 + 10.0 
 -1.0 
 + 10.0 
 + 13.3 
 + 7.5 
 +4.1 
 + 10.0 
 +1.7 
 +5.0 
 +6.7 
 -4.0 
 +0.6 
 +5.0 
 + 2.0 
 
 -1.6 
 -1.7 
 -6.3 
 
 Per cent 
 6.0 
 3.4 
 6.0 
 
 10.0 
 8.3 
 1.5 
 
 10.5 
 9.5 
 
 10.8 
 5.4 
 6.7 
 6.2 
 7.6 
 9.1 
 4.3 
 4.3 
 3.4 
 3.0 
 1.9 
 2.0 
 5.1 
 
 Per cent 
 
 2 
 
 
 5 
 
 
 16 
 
 
 3 
 
 20.2 
 
 5 
 
 16 
 
 
 3 
 
 23.3 
 
 26.3 
 
 e 
 
 16 
 
 3 
 
 
 6 
 
 
 16 
 
 18.6 
 
 3 
 
 5 
 
 10.4 
 
 16 
 
 3 
 
 8.2 
 
 5 
 
 16 
 
 
 3 
 
 
 4 
 
 
 
 
 TABLE 4. — Results of Analyses, Using Dyes from Third Source 
 
 
 Ob- 
 server 
 
 Percentage sulphite In mixture 
 
 Error 
 
 ol 
 aver- 
 age 
 
 Prob- 
 able 
 error 
 
 (r) 
 
 
 Number of 
 estimations 
 
 Estimated 
 
 Actual 
 
 Hugo 
 error 
 (u) 
 
 
 Maxi- 
 mum 
 
 Mini- 
 mum 
 
 Aver- 
 age 
 
 16 
 
 A 
 B 
 
 A 
 B 
 A 
 B 
 A 
 B 
 
 A 
 B 
 
 A 
 B 
 A 
 B 
 
 50 
 40 
 75 
 50 
 60 
 75 
 60 
 75 
 75 
 80 
 80 
 80 
 80 
 80 
 
 20 
 20 
 
 20 
 20 
 25 
 25 
 20 
 40 
 25 
 40 
 60 
 50 
 50 
 70 
 
 27.5 
 26.9 
 32.5 
 37.2 
 43.1 
 48.4 
 45.3 
 55.3 
 55.0 
 63.8 
 74.4 
 70.9 
 
 75.3 
 78.4 
 
 20 
 20 
 25 
 25 
 40 
 40 
 50 
 50 
 60 
 60 
 75 
 75 
 80 
 80 
 
 Per cent 
 
 + 7.5 
 + 6.9 
 + 7.5 
 +12.2 
 + 3.1 
 + 8.4 
 
 - 4.7 
 + 5.3 
 
 - 5.0 
 + 3.8 
 
 - 0.6 
 
 - 4.1 
 
 - 4.7 
 
 - 1.6 
 
 Per cent 
 
 8.8 
 7.1 
 10.6 
 11.0 
 8.0 
 9.9 
 8.1 
 7.6 
 8.0 
 8.1 
 4.9 
 6.3 
 6.4 
 2.2 
 
 Per cent 
 
 16 / 
 
 17.2 
 
 16 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 15.5 
 
 16. . . . 
 
 
 
 
Differentiating Unbleached Stdphite and Sulphite Pulps 1 7 
 TABLE 5. — Results of Analyses, Using Dyes from Foiuth Source 
 
 
 Percentage sulphite in mixture 
 
 Error 
 
 of 
 aver- 
 age 
 
 Prob- 
 able 
 error 
 
 (r) 
 
 Ob- 
 server 
 
 Estimated 
 
 Actual 
 
 
 Maxi- 
 mum 
 
 Mlni- 
 
 Aver- 
 age 
 
 A 
 
 B 
 
 25 
 25 
 
 20 
 20 
 
 20.6 
 20.6 
 
 20 
 20 
 
 Per cent 
 
 -1-0.5 
 +0.6 
 
 Per cent 
 
 1.2 
 1.2 
 
 A 
 B 
 
 40 
 50 
 
 20 
 20 
 
 28.2 
 27.1 
 
 25 
 25 
 
 -1-3.2 
 +2.1- 
 
 5.0 
 4.8 
 
 A 
 
 B 
 
 60 
 50 
 
 25 
 25 
 
 40.6 
 39.7 
 
 40 
 40 
 
 -HO. 6 
 -0.3 
 
 5.3 
 3.0 
 
 A 
 B 
 
 60 
 75 
 
 10 
 40 
 
 48.8 
 50.9 
 
 50 
 50 
 
 -1.2 
 -fO.9 
 
 3.3 
 5.5 
 
 A 
 B 
 
 75 
 75 
 
 25 
 50 
 
 58.8 
 59.4 
 
 60 
 60 
 
 -1.2 
 —0.6 
 
 7.7 
 4.8 
 
 A 
 B 
 
 80 
 80 
 
 60 
 60 
 
 74.1 
 74.1 
 
 75 
 75 
 
 —0.9 
 —0.9 
 
 4.7 
 4.7 
 
 A 
 
 B 
 
 80 
 80 
 
 75 
 75 
 
 78.2 
 78.5 
 
 80 
 80 
 
 -l.B 
 —1.5 
 
 2.0 
 1.8 
 
 Huge 
 error 
 
 (u) 
 
 The analysts, or persons who made the estimations, are referred 
 to as "A," "B," and "C." 
 
 The error of averages is the difference between the average of all 
 estimations for that particular case and the actual percentage of 
 sulphite in the mixture. The average result is computed from a 
 number of estimations in most cases ; the exact number of estima- 
 tions in each case is given in the tables. 
 
 The most probable error is an error of such magnitude that a 
 single estimation has an equal chance of being either within the 
 error or outside of it. The given errors are computed by the 
 method of least squares according to the formula 
 
 
 r = 0.6745 
 
 in which r is the most probable error, K is the error of one estima- 
 tion, 2X- is the sum of the squares of all errors of n estimations, 
 and n is the total number of estimations made on that particular 
 mixture by the given analyst. 
 
 The huge error is an error of such magnitude that the chances are 
 equal that 9 estimations out of 10 will be within the error, and 
 only I in 10 greater than it. These results are computed by the 
 method of least squares, according to the formula 
 
 1.65 
 
 
 or M = 2.44r, 
 
 in which u is the huge error. 
 
l8 Technologic Papers of the Bureau of Standards 
 
 In no case did an individual analyst make more than one estima- 
 tion on the same miscroscope slide or the same field of fibers. 
 
 It is noteworthy that the errors in the last series, or table, are 
 much less than those in the first three series. This is no doubt due 
 in large part to the differences between the dyes used in the first 
 three series and those used in Table 5, since those used in the last 
 series gave much more satisfactory' color effects than those used in 
 the first three series. This result is also certainly due in part to the 
 greater familiarity and experience the analysts had with the stain 
 at the time the last series was run. 
 
 There are at least two criticisms that may be offered against 
 these estimations. The first is that the results given may not 
 quite represent estimates on wholly unknown mixtures, since each 
 analyst knew in what proportion each of the seven combinations 
 in the series was made up; although, as stated above, each sample 
 was marked in code so that the analyst could not know what com- 
 bination was being examined. When a study of the individual 
 estimates is made, it appears that this circumstance did have an 
 appreciable influence on the estimates on the mixtures near either 
 end of the series. But since o per cent and 100 per cent are limits 
 in all mixtures, it seems probable that estimates on mixtures near 
 these limits will always be more nearly correct than estimates on 
 mixtures containing a higher percentage of the smaller constituent. 
 
 The second criticism is that it is not practical in most cases to 
 make 1 6 or 18 different estimates on the same sample of pulp or 
 paper. This criticism is valid, especially as applied to mill condi- 
 tions ; for the paper-mill chemist is usually too busy to give so much 
 time to the study of one sample of pulp or paper. It is necessary, 
 however, that anyone, whether novice or expert, doing work of tliis 
 kind, shall become famiHar by actual experience with the use and 
 properties of any stain before reliable results in estimating per- 
 centages can be had. To get best results in estimating, it is also 
 necessary that one keep constantly in practice, and refer often to 
 standard or known mixtures, accurately made up, and kept always 
 at hand. When the analyst becomes familiar with the character- 
 istics and use of the stain described above, it is probable that esti- 
 mates can be made by its use as quickly and with as much accu- 
 racy as with the zinc-chloride and iodine stain. 
 
 Washington, November 27, 1920. 
 
018 374 065 9 
 
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