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INDUSTRIAL AND ENGINEERING CHEMISTRY
Herschel (4) defined oiliness as “the property that causes a difference in the friction when two lubricants of the same viscosity a t the temperature of the film are used under identical conditions.” If one adheres rigorously to this definition, it seems that no account can be taken of the change of viscosity with pressure but only of its change with temperature. If, however, oiliness be defined as “the property that causes a difference in the friction when two lubricants of the same viscosity a t the temperature and pressure of the film are used under identical conditions,” oiliness is made independent of viscosity and can be considered as a property of the system consisting of the lubricant and the rubbing surfaces. It must be remembered that, although no dimensions can be given for oiliness, it involves the physical state of the rubbing surfaces, and therefore the assignment of different values of oiliness to a number of oils would apply rigorously only for the machine with which the measurements were made. 0. C. Bridgeman, in December, 1933, before the Society of Rheology, said that oiliness was “that characteristic of liquids, which results in lowering of friction between surfaces moving relative to one another and which cannot be accounted for on the basis of viscosity.” We would probably have a still better definition of oiliness if the word “viscosity” were replaced by “known properties of these liquids.” The need for a word without inherent meaning such as “oiliness” has then disappeared in a measure as our knowledge of liquids increases. The fact that aP determines the temperature rise for all the oils studied in this investigation illustrates the meaning of the proposed definition of oiliness, for differences in friction that might be ascribed to oiliness can be accounted for by taking into account the variation of viscosity with pressure. It should also be pointed out here that the hydrodynamic nature of the lubrication is confirmed by the fact that the observed temperature rise is a function of viscosity only.
VOL. 31, NO. 9
*41though it appears that the variation of the viscosity over the bearing surface cannot be obtained, it is evident that, especially a t the higher loadings, the three oils will differ greatly. Similarly the value of G cannot be known, but it will evidently be greatest for the oil having the greatest value of a. This oil, having the greatest viscosity a t a given load, will then have the greatest hydrodynamic coefficient of friction but it should also have the thickest lubricant film. The fact that these thicker films would occur with oils showing the greater changes of viscosity with both pressure and temperature gives rise to interesting speculations on modern trends in lubricating oil refining. Further support to this theory of oiliness is given by the work of Needs (7) who studied the effect of change of viscosity with pressure in lubrication. He showed that in his experiments also effects that might be thought due to oiliness were, in reality, due to the increase of viscosity with pressure. Finally it should be stated that these results represent only a single set of measurements. The calculations given in this paper have supported Everett’s general conclusions but more experiments are required to confirm fully the theory advanced here.
Literature Cited (1) Bradford, L. J., and Vandergrift, C . G., Inst. Mech. Eng., Lubrication Discussion, Oct., 1937, Group I, 23-9. ( 2 ) Bradford, L. J., and Wetmiller, R. S.,Machine Design, Jan., 1937. (3) Everett, H. A., S . A . E . Journal, 41, 531 (1937). (4) Herschel, W. H., S. A. E . Trans., 17, part 1, 282 (1922). ( 5 ) Hersey, M. D., “Theory of Lubrication,” p. 92, New York, John Wiley & Sons, 1936. (6) McKee, S. A,, and McKee, T. R., 8. A. E. Journal, 31,371 (1936). (7) Needs, S.J., Trans. Am. SOC.Mech. Engrs., May, 1938, p. 347. PRESENTED before the Division of Petroleum Chemistry at t h e 96th Meeting of the S m e n c a n Chemical Society, Milwaukee, Wis.
Cation Exchange in
Cellulosic Materials T
HE concept of ionic exchange has been employed from time to time to aid in the interpretation of certain phenomena in cellulose chemistry. Kolthoff (11) in 1921 studied exchange reactions in filter paper, associating them entirely with the ash constituents. Since that time a number of references to exchange reactions in cellulosic materials have appeared in the literature, and in other cases phenomena have been described which are readily explained through use of the ionic exchange concept. Despite this attention, recent work in our laboratory has indicated that this concept is more valuable and more generally applicable than is usually supposed in elucidating the behavior of cellulosic materials. This work strongly indicates that exchange phenomena play so prominent a part in certain processes and tests that they should be kept in mind in practically all operations on cellulosic materials. Of particular importance in this regard are those operations involving treatment of the materials with solutions, such as in the cooking, washing, and dyeing of pulp and textiles, the rosin sizing of paper, and analytical measurements on pulp, paper, textiles, etc.
D. A. MCLEAN AND L. A. WOOTEN Bell Telephone Laboratories, New York, N. Y.
Since the interest in cellulosic materials in our laboratory is principally in the electrical grades of textiles and paper, we have considered exchange reactions from the viewpoint of their influence upon the performance and testing of such materials. I n previous papers (18, 19) from this laboratory, the existence of exchange reactions in cotton has been demonstrated and the bearing of such reactions upon the electrical behavior of washed cotton discussed. The present work deals principally with paper, although results on other materials are included. Methods of demonstrating and studying exchange reactions in cellulosic materials are given special attention, and the bearing of the results upon certain processes and tests is discussed. The exchange capacity is shown to vary markedly with the grade of the fiber, and strong in-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
dications are obtained that the exchange reactions are associated not so much with the cellulose itself as with the organic impurities present.
Colorimetric Experiments Certain types of cellulosic materials, particularly those employed as electrical insulation, receive such a thorough washing in their commercial preparation that a distilled water extract is sensibly neutral and contains but small amounts of inorganic materials. However, even after such extraction,
1139
While treating the samples with the acid, they were frequently squeezed and stirred with a stirring rod. Under these conditions the reactions are surDrisindv ranid. . , going to completion within 10 minutes as il1;strat:d by Table If In addition. Table I1 nrovides an idea as to the renroducibilitv of the determination since each value reporte; concerns la separate sample. A feature of the data given in Table I is the relatively high magnitude of the neutralizing action of the papers as compared to the alkalinity of the samples as determined upon a ~~
The results of experiments on cation exchange in cellulosic materials, particularly kraft and linen condenser tissues, are presented and discussed. The methods used were the colorimetric determination of the reduction of acidity of a dilute acid treated with the cellulosic material and the potentiometric titration of a pulped sample with acid or alkali. Water softening by properly activated jute is demonstrated as an example of exchange reactions. Potentiometric methods were used to prove that there is no anion exchange comparable in magnitude with the cation exchange. The
if the material is treated with a dilute acid, the acid is definitely neutralized. The degree of neutralization for such extracted samples is only slightly less than for materials as received from the manufacturer. (It will be evident from considerations discussed later in this paper that this is true only if the pH of the water used for extraction is nearly the same as that used to give the paper its final washing in the mill.) Table I shows a number of results obtained both on commercial materials and on materials which have received long extractions. In the experiments upon which Table I is based, 2-gram samples of each material were treated with 100 cc. of 0.0058-0.0059 N hydrochloric acid. Fifty cubic centimeters of this solution were then drawn off with a pipet and titrated in an atmosphere of nitrogen with a standard sodium hydroxide solution using phenolphthalein. The results are expressed in milliequivalents of acid neutralized per gram of dry sample. Although the effect does increase definitely with increase in strength of acid used, this dependence is not critical in the region of these particular tests.
cation exchange reactions are shown to be reversible and independent of the particular anion present. In a general way the exchange capacity is higher, the greater the /3- and y-cellulose content. It is suggested that the noncellulosic constituents (lignin, uronic acids, etc.) are chiefly responsible €or the exchange reactions. The role of exchange reactions in determining the ash content of insulating papers is pointed out. The importance of exchange reactions in analytical measurements on cellulosic materials is discussed.
water extract. In all cases where data were available, a water extract showed no alkalinity in excess of about one per cent of the tabulated acid neutralizing values. Another fact of importance shown by Table I is the large variation in acid neutralization from sample to sample. For example, the kraft papers consistently show larger neutralizing values
TABLE I. DECREASE IN ACIDITY OF HYDROCHLORIC ACID SOLUTION BY VARIOUS CELLULOSIC MATERIALS Sample NO. 1
la lb IC 2 3
4 5
5a 5b 5c 6 7 8 9 10 11 12
13 14
15 16
Acid Neutralization, MiIliesuivalent/Cm.
iMaterial
Bleached linen paper Sample 1, extd. 16 hr. with distd. HzO in Soxhlet Sample 1, extd. 6 hr. with abs. alcohol i n Soxhlet Sample 1, extd. 2 hr. with benzene in Soxhlet Bleached linen paper Unbleached linen paper Unbleached linen imuer Unbleached kraft aber Sample 5, extd. 1 6 9 r . with distd. Hz0 in Soxhlet Sample 5, extd. 6 hrs. with abs. aloohol in Soxhlet Sample 5, extd. 2 hr. with benzene in Soxhlet Unbleached kraft paper unbleached kraft paper Unbleached kraft paper Unbleached kraft paper Unbleached kraft paper Partly bleached kraft uauer Absorbent cotton Filter paper Raw jute extd. with HzO and ether Raw ‘ute cooked in dilute NaOH and extd. with Hzb Unbleached Manila hemp ~
TOTAL A S H IN
PER
CENT
FIGVRE 1. RELATION BETWEEN ACIDNEUTRALIZATION AND TOTAL ASHOF SIXPAPERS Numbers correspond t o sample numbers of Table I.
~
0.020 0,017 0,024 0,020 0.012 0.018 0.033 0.100
0.098 0.106 0.102 0.098 0.091 0.064 0.154 0.111 0.067 0.002 0.012
0.132
0.145 0.178
~~
than do the linen papers; the effect for absorbent cotton is virtually negligible, and for jute and manila hemp very large. It should be pointed out that the absorbent cotton and filter paper are not strictly comparable with the other samples employed, since they undoubtedly had received an acid wash in the course of their preparation.
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It has been demonstrated in several ways that this decrease in acidity of dilute acid by paper is unquestionably of an exchange nature. In the first place, Edge (6) and others have found that this acidity reduction is closely related to the ash of the sample. This relation closely approximates proportionality as shown in Figure 1, where determinations on six papers are involved-samples 3, 4, 5 , 7, 9, and 11. TABLE 11. EFFECTOF TIMEOF TREATMENT ON SAMPLE 5 (KRAFTPAPER) Acid Neutralization Millieqmvslent/Cm:
Time of Treatment 10 min. 23 min. 40 min. 1 hr. 6 min. 3 hr.
0.100 0.100
0,099
0.101 0.101
The significance of this relation from the ion exchange point of view is evident from the following interpretation: Even after complete washing of cellulosic materials, metal ions are held in some insoluble combination, the extent of retention of such ions varying markedly with type of fiber. Such ions can be replaced readily by hydrogen ions from dilute acid solutions; neutralization results as indicated in Table I. It is interesting that the constant of proportionality calculated from Figure 1 gives a value of 52 for the equivalent weight of the ash; considering the probable presence of a certain amount of neutral salts in the ash, this value checks fairly closely the equivalent weight of magnesium and calcium carbonates in which form most of the ash is probably weighed. The extent to which ash constituents are removed by a dilute acid from 7
#-FILTER 6
-WATER
PAPER W I T H 0.01N H C l CURVE
Ip5
4
3 I
2
3
4
5
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capacity of paper. In this section “linen paper” will refer to sample 1 of Table I, “kraft paper” will refer to sample 5. In the first tests 1-gram samples of the paper were pulped by means of a high-speed beater in 100 cc. of distilled water, The resulting mixture of pulp and water was titrated with standard 0.01 N hydrochloric acid in a glass-saturated calomel electrode system. Back-titrations were carried out with standard 0.01 N potassium or sodium hydroxide solution. Plots of the titration data are shown in Figures 2 and 3; curves on distilled water are shown for comparison. In one titration 0.01 N sulfuric acid was substituted for hydrochloric acid. In another case 0.01 barium hydroxide was employed in the back-titration, and the titration was extended over the pH range of 3 to 9.5 (Figure 3). I t was recognized that the presence of potassium ions in the solution, resulting from diffusion from the salt bridge of the calomel half cell, might tend to shift the equilibrium point of the ion-exchange reaction. (Previous work in this and other laboratories had shown that more hydrogen ions can be extracted from certain papers with potassium chloride solution than with water.) To test the effect of potassium ions on the exchange reaction, a titration of kraft prtper in 1 M potassium chloride solution was made. A plot of the data is shown in Figure 4. It is evident from the curves that the presence of 1 mole of potassium chloride shifts the exchange equilibrium in the expected direction by a large amount. In order to estimate the magnitude of the effect of diffusion of potassium chloride from the salt bridge during titration, several tests were made in which acid of various concentrations was added and the solutions were decanted off for pH determination; contact of the salt bridge with solutions containing the paper was thus eliminated. The results indicated that the exchange capacities of both kraft and linen papers are higher than the titration curves of Figures 2 and 3 show, but the relative order of the two papers is not altered appreciably. The error appears larger at the lower hydrogen-ion concentrations. If we eliminate this error for the moment as being unimportant in a qualitative study of the exchange reaction, the potentiometric data confirm amply the coloriaetric data discussed previously. The potentiometric results indicate that the exchange capacity of kraft paper is much greater than that of linen, and that the capacity of linen exceeds that of filter paper. The approach of the linen curve to the kraft
0
VOLUME OF REAGENT IN M I L L I L I T E R S
FIGURE 2. TITRATION OF WATER AND PAPERWATERMIXTURESWITH 0.01 N ACID P B A C K - T I T R A T I O N WITH K OH
paper containing very little water-soluble ash is illustrated by the following experiment: Two portions of paper ‘sample 5 were treated with cold 0.01 N hydrochloric acid and 1 per cent hydrochloric acid. The ash values of these samples after treatment were 0.069 and 0.039 per cent, respectively, in contrast with the 0.50 per cent of the original. The alkalinity of the ash is nearly equivalent to the acidneutralizing power of the paper, provided the latter test is carried out in such a way that the final equilibrium pH of the acid solution in contact with the paper is 2-2.5. However, it should be noted that upon potentiometric titration the ash behaves as a strong base, whereas the paper behaves as a typical exchange material, as will become evident in the next section.
I
31
Potentiometric Experiments Interesting confirmatory results have been obtained by using potentiometric methods in the study of ion-exchange
5
4
3
I
I
I
I
I
I
2
1
0
1
2
3
I 4
5
VOLUME OF REAGENT IN MILLILITERS
FIGURE 3. TITRATION OF WATERAND PAPER-WATER MIXTURES WITH 0.01 N HYDROCHLORIC ACID AND 0.01 N BASES
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1141
0.30 12 curve a t the higher p H values may be due in part to the slightly higher alkalinity of the 11 0.28 linen paper. The titration in which sulfuric acid was 0.26 lo substituted for hydrochloric furnishes evidence 0.24 that the anion does not play an important role 9 in the exchange reaction. Conclusive evidence 8 0.22 that the hydrogen ion (or oxonium ion, HzO +) 0 alone enters into the exchange reaction is fur5 0.20 O 7 nished by the titration curves in Figure 5. > 0 They demonstrate that no detectable change 6 0.18 TER T R E A T M in chloride-ion concentration occurs when kraft 5 0.1 6 paper is treated with 0.001 N hydrochloric acid, whereas the pH changes from 3.0 to 4.2, 4 0.14 a decrease in hydrogen-ion concentration by a factor of approximately 1/12. 3 0.1 2 In this particular test, a 100-cc. portion of 0.1 0 0.001 N hydrochloric acid was added to 2 grams 2O 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 of kraft paper. It was well mixed and allowed M I L L I L I T E R S OF 0.01 N KOH M I L L I L I T E R S OF 0.01N AgNO3 to stand for 4 hours. A 50-cc. Portion Of the FIGURE 5. (Left) CHANGE IN HYDROGEN-ION TITRATION CURVEPRODUCED solution was withdrawn with a pipet and BY TREATING KRAFTPAPERWITH DILUTE HYDROCHLORIC ACID. (Right) NEGLIGIBLE CHANGE IN CHLORIDE-ION TITRATION CURVE titrated with 0.01 N silver nitrate solution: the silver electrode was used as indicator, and a saturated calomel system, connected by means of a potassium with dilute acid, washed, soaked in 2 M sodium chloride, and nitrate-agar-agar bridge, was employed as a reference half cell. then washed with distilled water until the wash water showed A 50-cc. portion of the original 0,001 N hydrochloric acid was no trace of chlorides. A 12-gram sample was formed into a titrated in the same way to determine the chloride-ion con6-inch column in a glass tube, through which a solution of centration of the same solution. A similar test was carried calcium sulfate containing 233 parts per million of calcium was out in which the solutions were titrated with potassium hyallowed to drip. Successive 25-cc. samples were tested for hardness with the result shown in Figure 6. The first 100 cc. droxide, the pH being measured with the glass electrode syswere almost completely softened, the efficiency for softening tem previously described. The data obtained in both tests water being entirely lost after 175 cc. had passed through. are plotted in Figure 5. To the left is shown the large change However, it was demonstrated that this jute could be comin pH brought about by contact with the sample, to the right, the negligible change in chloride ions. pletely reactivated by treatment with a strong sodium chloride solution, exactly as in commercial water softeners employing the exchange principle. @-KRAFT W I T H H C 1 IN WATER b
0-KRAFT WITH H C 1 IN I M K C l *-$M K C l SOLUTION W I T H H C l
2 5
4
0
I VOLUME OF REAGENT I N M I L L I L I T E R S
FIGURE 4. EFFECTOF POTASSIUM CHLORIDE OR THE TITRATION CURVE OF KRAFT PAPERWATERMIXTURE(0.01 N ACID)
Another important fact established by the potentiometric titration data is that the reaction is reversible with sodium, potassium, or barium hydroxides; this indicated that in the region of acid and salt concentrations studied, the equilibrium in the paper is controlled principally by the hydrogen-ion concentration. This result is in agreement with those of Figure 4 and shows that a large excess of potassium ions is required to reduce markedly the quantity of hydrogen ion taken up.
Water Softening Another experiment demonstrates that exchange reactions exist in cellulosic materials, and that in such materials metal ions are mutually exchangeable in much the same manner as in zeolite minerals. This experiment consisted of softening water by properly activated jute. The jute was treated
Relation to Beta- and Gamma-Cellulases In the work done to date, we have been interested principally in a qualitative and relative study of the phenomena rather than in precise determinations of absolute values of exchange capacities. However, since the samples listed in Table I, with the exception of absorbent cotton and filter paper, have in their preparation been washed to neutrality from their natural state or from an alkaline condition, it appears that with these exceptions the acid-neutralizing values of Table I can be taken as an approximate measure of the exchange capacities of the various materials. That this is only an approximation derives from several sources, principally that the result will be influenced by the electrolyte content and pH of the water used in the final washing of the pulp in the mill and that the papers are likely to retain small quantities of residual free alkalies. We note at once that if the various fibers are rated according to this exchange capacity, the resulting order a t least approximates the inverse of that obtained by rating in the order of grade of fiber as regards a-cellulose content. In a more refined test of this apparent relation, data were obtained from which Figure 7 is plotted. There appears to be at least some functional relation between the percentage of /3and y-cellulose and the exchange capacity, although this relation may not be linear as suggested by the data. The p- and y-cellulose determination is somewhat arbitrary and subject to appreciable errors. For example, the linen papers (samples 3 and 4) indicated 100 per cent a-cellulose in the alkali solubility test; yet this is actually unlikely, and, in fact, a pentosan test showed 0.5 t o 0.8 per cent pentosans in these papers.
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1142
It is doubtful if the data justify the conclusion which one is tempted to make-namely, that the materials ordinarily determined as 0-and y-celluloses are alone responsible for the exchange reactions. The explanation is probably more complex and possibly involves functional groups associated with the lignin in the kraft paper and other lignocelluloses as well as the materials which show up in the 0-and y-cellulose determination. In the latter category would be included the carboxyl groups of uronic acids. In either class of compounds it is conceivable that phenolic hydroxyl groups play an important role. 3An
simple pentoses and hexoses have no buffer action approaching that required to explain the exchange reactions in cellulosic materials; whereas gum arabic, known to contain uronic acids (S), has a strong buffering action. I n this connection the recent publication of Stuewer (17) is of interest since it shows that pectins are capable of exchange reactions. The present data allow one to draw only the following definite conclusions: The evidence is very strong that, as pure a-cellulose is more and more closely approached, exchange reactions become less pronounced. This indicates that the exchange reactions are not a property of the cellulose itself but rather of the associated organic impurities. A point of importance in this connection is the rapidity of the exchange reactions as shown in Table 11; this indicates that the active groups are readily accessible as they would be in the cell wall where pectic substances (Y), lignin, and other noncellulosic constituents are most likely to occur. Wurz (10)recently gave evidence of the presence of insoluble metal pectates in wood pulps. The view that noncellulosic materials are responsible for exchange reactions finds support in the work of Khinchin (IO), who ascribes the absorption of aluminum by paper to salts of organic acids and who states that such impurities in cellulose give it its apparent amphoteric properties.
Conclusions
H20 C O L L E C T E D IN M I L L I L I T E R S
FIGURE 6. SOFTENING OF WATERBY BASEExCHANGE IN JUTE FIBERS Determinations were made on consecutive 25-cc. samples.
Kullgren and Du Reitz (4, 6, 12, IS) ascribe the exchange reactions in sulfite pulps entirely to residual lignosulfonic acid. When such a material exists in the pulp, it can probably account for cation exchange. However, our work shows that the sulfonic acid group is not essential to exchange reactions. I n fact, raw spruce sawdust which has had no chemical treatment exhibits exchange reactions to a marked degree (Figure 8). Furthermore, materials such as filter paper which show relatively small exchange capacity can be given a high exchange capacity by being converted into oxycellulose with nitric acid, according to the method of Nastjukoff (16); this process is known to produce uronic acids. Furthermore, the ash of a sample in vrrhich metal ions were held by sulfonyl groups should not have an alkalinity equal to the exchange capacity; our work indicates that this is a t least approximately true. Hence, the hypothesis of exchange reactions based upon sulfonyl groups is untenable for the materials used in this work. Actually it appears that Kullgren and Du Reita intended their theory to apply only to sulfite pulps. Our tests have shown that the 0-and y-cellulose in the papers represented in Figure 7 contains little or none of the beta fraction, and that the gamma fraction is only 1030 per cent higher than the pentosan content, calculated on the basis of furfural yielded by boiling with 12 per cent hydrochloric acid. Since uronic acids as well as pentoses and pentosans yield furfural, it seems possible that pectic or related substances containing uronic acids play a part in exchange reactions in cellulosic materials. Exchange a t the carboxyl group of a uronic acid is more plausible than at the relatively inactive hydroxyls of a simple pentosan or of cellulose. Tests in this laboratory have shown that the available
The concepts of ionic exchange appear to explain satisfactorily a number of phenomena associated with cellulosic fibers in commercial form. They explain adequately the tenacity with which cellulosic fibers retain the last traces of ash constituents. For example, the higher ash contents of the unbleached kraft papers made from thoroughly washed fibers as compared to similarly treated linen papers correspond to the higher exchange capacities of the former. Although much work remains to be done on this problem, a
0.02
I
I
I
1
I
I
'
'
1
FIGURE 7. RELATION BETWEEN ACID NEUTRALIZATION AND p- AND y-CELLULOSE CONTENT OF PAPERSAMPLES
reasonable conclusion on the basis of the present available data is that the ash constituents which are ordinarily weighed as oxides or carbonates in an ash determination exist in the paper as metalorganic compounds, of which the organic portion contains acidic groups associated with the noncellulosic impurities. The results also indicate that the electrolyte content and pH of the water used in the final washing of pulp in the mill will have an important bearing upon the ash content of the paper and upon the quantity of hydrogen ions which the resulting paper can take up from acid solution. These results have certain obvious bearings upon the analysis of cellulosic materials. They emphasize the importance of using water of a high and constant degree of purity in extracting paper for the purpose of making acidity and con-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1143
11
respectively, being equivalent. This is in complete agreement with the theory of exchange of cations and the principle of mass action. ALKALI-COOKED, 9 Gavoret (8), in attempts to determine the isoelectric point of cellulose, recently showed that the tendency of cellulosic e materials to take up lead ions from a lead chloride solution 7 depends upon the pH; it is greater, the higher the pH. I n I addition she showed, as have we, that very little chloride ion 6 is taken up. The explanation of these results on the basis of exchange reactions is obvious. Since these exchange reac5 tions are a property of the noncellulosic constituents of cellu4 losic materials, such measurements can have little actual bearing upon the isoelectric point of cellulose. 3 In view of the recent work of Adams and Holmes (1) and of Burrell ( 2 ) on the high base-exchange capacity of resins 54 1 2 1 0 8 6 4 2 0 2 4 6 8 10 1 2 1 4 VOLUME OF REAGENT IN MILLILITERS made from wood extracts, it is scarcely surprising that fibers FIGURE8. TITRATION OF RAWAND ALKALI-COOKED SPRUCE purified by commercial processes can display base exchange phenomena to the degree indicated in the foregoing. WITH HYDROCHLORIC ACIDAND POTASSIUM HYDROXIDE Reagents 0.01 N 10
Aclsnowledgment
ductivity measurements and water-soluble determinations on the extract. When free of carbon dioxide, the distilled water used should have a p H close to 7. In applying potentiometric methods to the measurement of exchange capacity of paper, it is important to introduce as little metal ion as possible in making the measurement. Haug (9) suggested the use of an extract with a potassium chloride solution for measuring the acidity of papers. Obviously, higher acidity values will usually result from such extractions. However, if the sample to be tested is in such a condition as to be essentially neutral to water, a measurement of acidity on an extract made with a salt solution is associated more with the exchange capacity of the material than with the harmful free acid present. It is also quite possible, though unlikely to occur frequently in practice, to have a paper which is neutral as far as the water extract is concerned, is acid in the sense that it gives an acid extract with a neutral salt solution, and yet is alkaline in the sense that it has a neutralizing action on aqueous acid solution. It is easy to prepare such a sample b y washing an ordinary paper with an acid of such strength and volume that it will exchange only a portion of the metal ions, and then by a thorough washing with distilled water. Although the use of a salt solution for extracting in acidity work must be approached with caution, the concept of ionic exchange does seem capable of providing valuable auxiliary tests on rellulosic materials. Several. such tests are suggested by the work reported in the foregoing section. I n the first place the good correlation between acidity reduction and percentage ash in unfilled unsized papers such as those employed for electrical insulation purposes suggests the use of a test based on the neutralizing action of such papers as a simple and rapid means of estimating the ash of the sample. It is further quite possible that measurement of the exchange capacity of a cellulosic material can be ubed to estimate the purity of the material as regards a-cellulose content. More extensive research is required on these possibilities. The results of Oman (16) and of Masters (14) can be fully explained by the exchange reaction concept. The former noted that cellulosic materials are capable of neutralizing both dilute acids and dilute alkalies. This is in accord with Figure 3 and can be explained on the grounds that the equilibrium between the hydrogen ions and metal ions in the cellulosic material is driven in the predicted direction in each case. Masters found that repeated alternate extractions with water and sodium chloride solutions gave alkaline water extracts and acid sodium chloride extracts, the alkalinity and acidity,
The authors wish to acknowledge the aid of H. A. Birdsal in carrying out the potentiometric titrations.
Literature Cited Adams, B. A., and Holmes, E . L., J . Sac. Chem. I n d . , 54, 1 T (1935). Burrell, Harry, IXD. ENG.CHEX,30, 358 (1938). Butler, C. L., and Cretcher, L. H., J. Am. Chem. SOC.,51, 1519 (1929). Du Reitz, Carl, Svensk Kern Tids., 45, 185 (1933). Ibid., 49, 52 (1937). Edge, S. A., J . SOC.Chem. I n d . , 48, 118T (1929). Farr, W. K., J . Phvs. Chem., 41, 987 (1937). Gavoret, Juliette, Compt. rend., 204, 1643 (1937). Haug, Kaare, Papir-J., 21, 184 (1933). Khinchin, Ya. G., Bumazhnaya Prom., 15, No. 9, 15 (1937). Kolthoff, I. M., Pharm. Weekblad, 58, 233 (1921). Kullgren, Carl, Svensk Kern. Tids., 42, 179 (1930). Kullgren, Carl, and Du Reitz, Carl, Svensk Papperstid., 34, 433 (1933). Masters, Helen, J. Chem. SOC.,121, 2026 (1922). Nastjukoff, A., Ber., 34, 3589 (1901). Oman, H., Papir-J., 15, 91, 107, 116 (1927). Steuwer, R. F., J . P h v s . Chem., 42, 305 (1938). Walker, A. C., and Quell, M. H., J. TextiZe Inst., 34, T131 (1933). Ibid., 34, T123 (1933). Wurz, Otto, Papier-Fabr., 35, 184 (1937). PRESENTED before t h e Division of Cellulose Chemistry a t t h e 96th Meeting of the American Chemical Society, Milwaukee, Wls.
Courtesy, C I B A
