SEPTEMBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
of analysis. I n the dilute acid trckatment, 5 grams of each of the solids were treated with 40 ml. of 10 per cent nitric acid in the same manner as the concentrated acid Sreatment. A comparison of the results from the two treatments is given in Table I. These results show that a much greater yield is obtained by the use of concentrated than of dilute acid which is consistent with the low yields obtained by the action of concentrated nitric acid on evaporated liquors containing relatively high water contents. The initial reaction with the concentrated acid is much more violent and markedly exothermic as compared with the dilute acid. The smaller yields with the latter acid are due to the less complete decomposition of the lignin materials. When fuming nitric acid (specific gravity 1.56) was substituted for the concentrated acid, the yield of oxalic a.cid was not appreciably increased.
1135
Experiments with and without the addition of catalyst (0.1 per cent vanadium pentoxide) indicated that no significant increase in yield could be effected by its addition.
Acknowledgment The writers express their thanks to E. C. Sherrard of the U. S. Forest Products Laboratory, Madison, Wis., for suggesting the problem, and to T. F. Doumani for assistance in the study. Literature Cited (1) Heuser, E., Roesch, H., and Gunkel, L., Cellulosechem., 2, 13 (1921). ( 2 ) Howard, G., Canadian Patent 304,644(Oct. 7,1930). (3) Reed, H., U.S. Patent 1,217,218(Feb. 27,1917). (4) Sellers, J., thesis, Univ. Ill., 1929. ( 5 ) Webber, H.A , , Iowa Eng. Expt. Sta., Bull. 118,31(1934).
Effect of Pressure on Viscosity in Relation to Lubrication J
J. W. GIVENS Shell Development Company, Emeryville, Calif.
A n analysis has been made of data on the temperature rises in three oils while a partial bearing was being lubricated at high loadings. Using the pressure coefficients of viscosity of these oils, an operating variable was calculated that accounted for the observed temperature rises and that should be useful in studying lubrication. Differences in the frictional characteristics of these oils that might be ascribed to oiliness could be accounted for by known properties of the oils. The use of the term “oiliness” to account for such differences admits ignorance of the properties of liquids, and the need for this term will disappear proportionately as more exact information becomes available.
I
N BOTH the hydrodynamic and dimensional theories of
fluid lubrication, the viscosity of the lubricant has been shown to be of paramount importance. Evidently it is not the viscosity as ordinarily measured but the viscosity existing a t the working surfaces that is required for a mathematical treatment of the problem. The variation of viscosity with temperature has long been recognized and taken into account. There has, however, been some difficulty in getting the actual operating temperatures. The effect that the change of viscosity with pressure might have in lubrication has only recently been considered. We may expect a t the outset that owing to the small change of viscosity with pressure, the effect will be appreciable only
in experiments made a t very high loadings but again not a t loadings sufficiently high to cause boundary lubrication to occur. It will be recalled that under conditions of boundary lubrication viscosity plays no part. This paper gives calculations made on data recently published by Everett (3) that were obtained in such a way that the foregoing conditions are fulfilled. The results of these calculations obtained throw further light on the mechanism of lubrication in general, and in particular they demonstrate that one more effect previously ascribed to oiliness can be accounted for by known properties of the lubricants.
Data and Calculations Everett (3) described lubrication experiments made with a machine described by Bradford and co-workers ( I , 2 ) . I n these experiments the rubbing surfaces consisted of a large steel journal running against a small brass block accurately fitted to the shaft and carefully run in. The block subtended 8’ of arc on the journal and could tilt so that a wedge-shaped film could be formed. Lubrication was provided by a stream of oil flowing over the journal. The temperatures of the incoming and outgoing oil were measured by thermocouples. The temperature rises were measured a t various loads for an eastern, a mid-continent, and a western oil. The three oils had viscosities of about 215 Saybolt Universal seconds at 130’ F. and a t atmospheric pressure. Data were also given (3) relating viscosity to pressure for these oils over a range from atmospheric to 54,000 pounds per square inch. It was observed that the viscosity of the western oil increased most rapidly with pressure and that of the eastern oil least rapidly. It was pointed out that this result correlated with the observation that on the testing machine the western oil showed the greatest temperature rise for a given load, and the eastern oil the least.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Examination of the data relating viscosity to pressure showed that they could be represented in the region above 6000 pounds per square inch with reasonable accuracy by an equation of the form: 2 log,,- = 09 2" where 2 = viscosity at the applied pressure, P 20 = viscosity at atmospheric pressure a! = pressure coefficient of viscosity, which varies with nature of oil and with temperature
VOL. 31, NO. 9 WESTERN OIL
60 LL 5 0 -
a
Table I gives the values of a obtained from equation 1.
TABLE I. VISCOSITY PRESSURE COEFFICIENTS (a)CALCULATED BY EQUATION 1 FROM THE DATAOF EVERETT" Oil 100' F. 130' F. 210° F. 5.4 X 10-6 3.6 X 10-6 Eastern 6.4 X 10-6 6.0 X 10-6 4.4 X 10-5 7.0 X 10-6 Mid-continent 8.4 x 10-6 4.4 x 10-5 9.1 x 10-6 Western a Units used, pounds per square inch and centipoises.
500
1000
I50C
FIGURE 1. TEMPERATURE RISEAS A FUNCTION OF EQUIVALENT VISCOSITY
ation due to temperature, and a t the highest loads the viscosity may be increased by a factor of 75. Applying the classical operating variable G, defined as the product of viscosity and angular velocity divided by load It is seen that the variation of a with temperature is such per unit area of bearing surface, is valid owing to the constant that at intermediate temperatures linear interpolation may be mechanical conditions and should be able to indicate what used without great inaccuracy. It was found that the devikind of lubrication is occurring. The data of Table I1 show ations from Equation l were greatest a t the lowest pressures. that in calculating G the equivalent viscosity rather than the For this reason the values of a given in Table I and used in viscosity a t atmospheric pressure should be used. Values of G subsequent calculations were obtained from data obtained a t calculated from the equivalent viscosity are given in Table I11 pressures of 6000 pounds per square inch and greater. and are comaared with the values for the same oils, neglectiig the pressure variation of viscosity. The relation between G and AT obtained in TABLE11. EQUIVALENT VISCOSITY (2,) AT VARIOUS LOADSCOMPARED WITH this way is shown in Figure 2. It is Seen at Once PRESSURE (2,) IN CENTIPOISES TOGETHER WITH VISCOSITIES AT ATMOSPHERIC that the correction of G for the pressure effect of OBSERVED TEMPERATURE RISES( A T ) CORRECTED FOR CONDUCTION, ETC. viscosity makes large differences. The most Load, Ib./sq. in. of 6000 8000 IO,OOO 12,000 14,000 16,000 18,000 20,000 fundamental difference is evident from Table 111. .Drojeoted . area Eastern oil: 23 31 When G is not corrected for pressure, i t de1 2 6 9 13 AT' F. 28 25 creases with increasing load, but when the 37 37 35 33 31 zo ZE 87 127 173 240 320 420 514 614 change of viscosity with pressure is taken into Mid-continent oil: 5 9 12 15 20 25 34 44 account, G actually increases with increasing AT' F. zo 40 36 35 32 30 28 26 23 load for these experiments. Comparison of these 87 133 207 280 394 494 ZE 747 curves with others in the literature (6) shows Western oil: A T o F. 10 15 20 24 31 38 49 64 that by this criterion the operating conditions, Za 167 38 24, 36 380 34 560 32 788 31 1067 30 13$: instead of being in the region of unstable or parZE tial film lubrication, were in the region of incipient hydrodynamic lubrication. In examining G curves given in the literature, great caution must be exercised in drawing concluI n attempting to relate observed temperature rises to viscosity, it seemed that a calculation of an equivalent viscosity over the bearing surface for these experiments might be useful. To do this, certain simplifying assumptions about presCURVESFOR 0 UNCORRECTED WESTERN OIL sure distribution over the bearing surface must be made. It 6 0 : FOR PRESSURE EFFECT will be assumed that the maximum pressure is one and a half LL times the average pressure or loading, and that the equivalent MID-CONTINENT AND viscosity is two thirds the viscosity a t the maximum pressure. EASTERN OILS The mean temperature was taken as the average of the temperatures of the incoming and outgoing oil. Calculations based on these assumptions are given in Table 11, where equivalent viscosities obtained from the data of Table I are compared with temperature rises. The viscosities corrected for temperature but not for pressure are given for comparison. I n Figure 1 the relation of observed temperature rise to calculated equivalent viscosities is given. These curves show that for a given viscosity the temperature rise is less with the western oil than with either of the others a t high loads. 10 20 30 Table I1 shows that in these experiments the variation of FIGURE 2. TEMPERATURE RISE AS A FUNCTION OF G viscosity due to pressure is very large compared to the vari-
i:
14i$
INDUSTRIAL AND ENGINEERING CHEMISTRY
SEPTEMBER, 1939
TABLE111. VALUESOF Ga FROM VISCOSITIES CORRECTED FOR PRESSURE COMPARED WITH VALUES(Go) FROM VISCOSITIES AT ATMOSPHERIC PRESSURE Load, lb./sq. in. of projeoted area, Eastern oil:
Go G
6000
2.9 6.7
8000
10,000 12,000 14,000
2.2 7.4
1.6 8.1
1.3 9.3
1.0 10.6
16,000
18,000
0.87 12.2
20,000
0.58 14.3
0.72 13.3
Mid-continent oil:
GO G
3.1 6.7
2.1 7.7
1.6 9.6
1.2 10.9
1.0 13.1
0.81 14.4
0.67 16.2
0.54 17.4
2.9 13.0
2.1 14.4
1.6 17.7
1.2 21.7
1.0 26.2
0.87 31.0
0.72 33.6
0.56 34.6
60
so
J
#
w’ 40
w a
3
$30
Western oil:
Go G
0
1137
w 3 t- 20
In (oentipoises) (r. p. m.)(pounds per square inch).
sions with respect to the so-called region of unstable lubrication, the region between the minimum and the ordinate axis. In experiments where the loadings are high, the assumed viscosities may be so much less than the actual viscosities that values for G, in which the pressure effect is ignored, may have no significance whatever.
5
FIGURE4. TEMPERATURE RISEAS TION OF (ap)
i
Load, Lb./ Sq. In. of Projeoted Area
Eastern Oil
AT
aP
0,324 0.432 0.530 0.636 0.728 0.832 0.918
1.000
5,000
LOADING, LB. IN? I 10,000
A
FUNC-
TABLEIV. VALUES OF THE PRODUCT OF THE PRESSURE COEFFICIENT OF VISCOSITY BY THE PRESSURE (&) AND OBSERVED TEMPERATURE RISES
WESTERN OIL
35
E
I
I
15,000
20,000
OF F I G U R8. ~ G AS A FUNCTION LOADING
Figure 2 shows further that there is a marked difference in behavior hetween the western oil and either of the others. For a given value of the operating variable, the temperature rise was less for this oil than for either of the others, although for a given load the temperature rise was greatest. It is also seen that the variations shown by these curves are similar to those in Figure 1, the plots relating temperature rise to equivalent viscosity. In Figure 3 the applied loading of the bearing is related to G. For a given loading the western oil shows the highest value of G, the mid-continent oil next, and the eastern oil the lowest. The foregoing calculations have been based on an assumed pressure distribution over the bearing surface. Therefore, it would be desirable to consider other possible variables which do not involve such an assumption. Hersey (6) showed that for thin films under high loads the coefficient of friction may be a function of various dimensionless products other than G. One such product is a P , the product of the pressure coefficient of viscosity by the applied pressure. This variable can evidently be calculated for these experiments without making any simplifying assumptions. Values of this product have been calculated for these experiments and are given in Table IV. Figure 4 shows the relation between crP and AT for the data of Table IV. The data for all oils fall on the same curve. Small deviations are observed for each oil, but they are nearly within the limits of experimental error. The form of the curve suggests that the temperature rise should be proportional to In Figure 5 the temperature rise varies directly as ( C X P )over ~ , the range of the experiments. Thus a single
Mid-oontinent Oil
AT 5 9 12 15 20 25 34 44
aP
0.360 0.472 0.590 0.696 0.812 0.912 1.05 1.25
1
2 6 9
13 17 23 31
Western Oil
aP
1.19 1.30 1.36
AT 10 15 20 24 31 38 49 64
variable has been found that will account for the results obtained for the different oils and that involves no assumptions regarding pressure distribution.
Theory of “Oiliness” The value of finding a variable by means of which the behavior of different lubricants in a set of experiments can be determined is well known. Although additional experimental data to test the wider application of the variable aP are necessary, it is possible to consider these results in the light of two well-known definitions of oiliness. I
I
I
I
EASTERN OIL 6 MID-CONTINENT OIL -WESTERN OIL
I
0
60
i
I
I /I
I
o
20
I
0.5
u
a
I
1.5
lo ( O P f
FIGURE 5. TEMPERATURE RISEAS
A
2.0
FUNCTION OF (aP)z
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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-
