118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. PART 11. THE FIBRE BALANCE. BY THOMAS BARRATT, D.Sc., F.INsT.P. (RESEARCH DEPARTMENT, WOOLWICH). Received May I 6th, I 9 2 4. An apparatus designed for the measurement of the breaking stress, extensibility, and recovery from strain of single textile fibres was described by the author in 1gz2.l A perspective view of an improved form of the ‘‘ Fibre Balance ” is given in Fig. I. The fibre A, whose properties are to be examined, is mounted by means of cycle cement between smalI paper squares, and one end of it clipped in a movable clamp C, hung from one of the knife edges of the balance.A second clamp BD, which can be moved up or down by means of a rack and pinion arrangement, grips the other end of the fibre. The extremities of these two clamps are of such a shape that the fibre is held quite tightly at points a definite distance apart. Suspended from the other knife edge of the balance is a solid rod K of very soft iron (“Lowmoor”), 11.3 crns. long, 0.63 cm. diameter, and of weight 28 gms. With the beam of the balance horizontal, 10-3 crns. of the length of this rod is inside a solenoid L of covered copper wire, through which an electric current can be sent so as to exert a pull on the fibre, owing to the attraction between the solenoid and the magnetised iron. The amount of this current can be varied by means of sliding rheostats, and measured by a sensitive milliammeter, suitably shunted.The weight of the rod is counterbalanced by an adjustable brass disc E. A thin brass rod H (dotted in the diagram), with a movable weight, serves to adjust the equilibrium of the balance beam to which it is attached. By this means it is arranged that the beam is very nearly in neutral equilibrium, so that the pull on the fibre is practically independent of the position of the beam. By hanging weights from 0.05 gm. to 15 gms. from the left-hand knife-edge, and observing the corresponding balancing currents as given by the milliammeter, a curve has been constiucted connecting the pull on the fibre with ‘‘ Readings on Ammeter.” I n order to measure the extension of the fibre at any given instant, two plane mirrors F and G are employed (see Figs.I and 2), F being attached to the moving beam and G to the central fixed pillar of the balance. A ray of light AB-GH (Fig. 2) is reflected three times from each mirror and then falls on a millimetre scale I 5 0 crns. away. I t can easily be seen that if the mirrors are at an angle a then the ray AB is turned through an angle 6a after the six reflections. I f then the mirror F is rotated through a small angle iSa, the ray GH rotates through an angle 68a. (See Fig. 3.) ’ ~ o u r n . Text. Inst. Proc., Jan. 1922. 274THE FIBRE BALANCE 2?5 A further magnification is given by the ratio (distance of mirror from scale)/(half length of balance arm), and the total manification is found to be 126 (see Table 11.).That is, an extension of I mm. in the fibre gives a movement of the spot of light of 120 mms. \ '- I / FIG. 1.-The fibre balance. The fibre experimented upon can be immersed in any required liquid by placing a beaker of the liquid in the position shown by the dotted lines. The clamp BD was given its '' U '' shape for this purpose. Some interest- ing measurements of the contraction of single cotton fibres in caustic soda solutions have been thus carried out.' 1 Willows, Barratt, and Parker, '+~nr. Text. Inst., XIII., 12, 1922.THE FIBRE BALANCE Calibration of the Balance. (I) Connection Between Reading of Ammeter and PuZZ on Pidre. The points investigated were :- ( a ) Reading of ammeter for various stresses with the balance beam horizontal (Fig.3). FIG. 2.-Double mirror arrangement for measuring extension or contraction of fibre. (6) The variation in these results when the soft iron armature is sucked (c) Variations due to hysteresis in the armature. further into the solenoid (Table I.). FIG. 3 . 4 u r v e connecting ammeter reading with pull on fibre. Weights from 0.05 gm. to 15 gms. being suspended from the left-hand knife-edge, the reading of the ammeter was taken with the spot of light at 0, at 2 0 and at 60 cms. (The beam was horizontal with the spot at 2 0 , and the whole range from o to 60 corresponded to an extension of the fibre, or a movement downwards of the armature into the solenoid, ofTHE FIBRE BALANCE Pull in Gms. 0.05 0'70 0'20 1'00 277 Position of Spot. 20 20 20 0 20 0.5 cm.) case where the spot is at 2 0 (beam horizontal).The results given below (Table I.), are shown in Fig. 3 for the A reading 13.7 on the ammeter corresponds to a current of I ampere. Current Increasing. TABLE I. Current Decreasing. Current Increasing. 9'85 10'38 10.85 I 1-42 I I -85 12-38 12.80 Ammeter. 0.60 1-35 2-70 3-10 3.18 3'35 4'45 4'5 5 4-70 5'52 5-62 5'75 Current Decreasing. 9'72 10'25 10.73 I 1.28 11.70 12.65 12-22 Pull in Gms. 5-00 7-00 10'00 15.00 ?ositioa of Spot. I Ammeter. 0 20 60 -2 0 60 0 0 20 0 20 60 60 7.10 7.22 7'45 8'50 8.62 8.86 10.25 10.38 10.70 12.65 12.80 13-16 As most of the pulls measured were of the order 4 or 5 gms. it is fortunate, in this arrangement, that the ammeter is much more sensitive for small stresses than for larger ones.The position of the armature within the solenoid is seen to have some slight influence on the amount of the pull on it, but as this position seldom differed by more than I mm., it was not often necessary to take it into consideration. To measure the effects due to hysteresis in the armature, readings of the balancing current for various weights were taken ( I ) with increasing currents, (2) with decreasing currents. The results are given in Table IL, and it is clear that, owing to the extreme softness of the iron, only a small correction is necessary on account of hysteresis effects. TABLE 11. Pull in Grams. Ammeter Reading. 3-18 4'55 5-62 6'46 7-22 8-00 8-62 9-20 3-10 4'45 5'50 6'34 7-1 I 7'90 8-50 9-10 Pull in Grams. 9 I0 11 12 I3 I4 I5 Ammeter Reading.The method could easily be employed to give a rapid and accurate determination of the hysteresis curve of a sample of iron or steel. (2) Measurement 4th (( Magnsjfation " of l%re Exten&on. In order to measure the ratio of the movement of the spot of light on cathetometer microscope, reading to 0.002 cm. The following observations278 -- THE FIBRE BALANCE (Table III.), were made of simultaneous positions of the spot of light and readings on the cathetometer scale. Readings taken upwards and down- wards agreed within errors of observation. TABLE 111. Readings of Cathetometer. 1.084 0 ~ ~ 1 4 0'832 0.748 0.666 0.584 I'OOO 1 Differences, 1 Cms. 0.084 0.08 6 0.086 0'082 0.084 0.082 0-082 Readings of Spot, Cms. - I0 20 30 40 50 60 Differences, 1 Cms. I - I0 I0 I0 I0 I0 I0 Magnification.- 119 116 I22 I22 The mean magnification is 120. Measurements on Various Fibres. Stress-strain Diagrams. The method employed in obtaining stress-strain diagrams of single fibres is as follows :- The fibre, mounted as described above, is clipped in the upper clamp C . The lower clamp B is then adjusted by means of the rack and pinion ar- rangement so as to grip the upper part of the lower paper square. The beam is then set free by lowering the supports in the usual way, the current through the solenoid being sufficient to exert a small known pull (say 0.01 gm.) on the fibre. The lower clamp is moved by means of the rack and pinion until the spot is at a convenient pckt on the scale. The pull on the fibre is increased or decreased at will, and simulianeous readings taken of the ammeter and of the spot of light.From these readings (reduced to grams pull and percentage extension) the stress-strain diagram is easily constructed. Diagrams obtained in this way for various textile fibres are given in Figs. 4 to 11. The results found vary greatly from fibre to fibre, and those shown in the diagrams are chosen out of a large number as beihg roughly representative of average values. The properties exhibited by the curves are (I) breaking stress; (2) total extension; (3) recovery from strain. The last named property, which is taken as the percentage recovery in the length when the pull on the fibre is diminished by one gram, is easily obtained from the diagrams, being the tangent of the angle of slope of such a line as AB in Figs.4 and 5. Values obtained from Figs. 4 to 11 are given in Table IV. TABLE IV. Fibres. Cotton, Egyptian Sliver (unmercerised) Gun-cotton . . . . . Bog Cotton . . . . Artificial Silk (Viscose) . . . Linen . . . . . . Silk . . . . . . Wool (Merino top cap) . . . 9 9 3 9 ,, (mercerised) Breaking Stress. Gms. 8.0 5'4 2-8 4'2 10.9 23-0 4'6 7'2 I Extension Per Cent. -I 8.0 13.6 2-6 5'1 21.7 38.0 6.4 12'2 Recovery from Strain. (Percent age per Gm.) 0.42 0.67 0-8s 0'47 0.42 1.4 1'7 0'12THE FIBRE BALANCE 279 The mercerised cotton (mercerised without tension) shows an increase in extensibility of 7 0 per cent., and an increased recovery from strain of 60 per cent., over the unmercerised cotton. The guncotton also shows a large increase in recovery from strain, but a decrease in extensibility and PULL ON FIBRE (GRAMS). WLL ON FIBRE (GRAMS).. FIG. 4. FIG. 5. in breaking stress. The guncotton fibre is more brittle, and the mercerised one less brittle, than the untreated cotton. The wild variety of cotton (bog-cotton) shows a decrease in strength and in extension, but a slight increase in recovery from strain. Artificial silk (viscous) is more extensible than (unmercerised) cotton, with a recovery about equal to that of cotton. PULL ON FIBRE (GRAMS). FIG. 6. FIG. 7. Its breaking stress per unit area is however less than that of cotton, as the mean sectional area of the viscose was four times that of cotton, while its breaking stress was not more than I* times as great. The most remarkable contrasts, however, which incidentally throw much light on the known pro- perties of the threads and fabrics concerned, are to be found in the fibres2 80 THE FIBRE BALANCE of linen, silk, and wool.Linen is strong, but of very small extensibility, while its recovery from strain is about a quarter that of cotton, and only one-fourteenth that of wool. Wool and silk-especially the former PULL ON FIBRE (GRAMS). FIG. 8. -have a very high extensibility and recovery from strain as is shown in Table IV. and in the stress-strain diagrams. The plasticity of all the fibres examined is another noteworthy property. For example, on stretching a wool fibre (see Fig. 11), 32 per cent. of its original length, and then removing the stress, the fibre regained only about g per cent. of its length.In the case of other fibres this property is even more marked. I t was remarked by E. A. Fisher1 that “the elongation produced in threads (worsted yarns) by tension is very largely a permanent elongation.” The author considered this elongation to be due to the ’yourn. Text. Inst., Oct. 1921.THE FIBRE BALANCE 281 slipping of the fibres, but the results above show that it can be explained just as well by the permanent increase in length which is undergone by the individual fibres. n 22 21 20 I9 18 17 16 15 ib 13 12 II '10 9 <a 87 2 6 25 00 & 4 b3 s2 E l z x w o 1 2 3 4 5 6 PULL ON FIBRE (GRAMS). FIG. 10. FIG. 11. Mercerisatlon of Single Cotton Fibres. Numerous variations in the process of mercerisation of cotton are em- ployed in practice. Some of these have been imitated on single fibres in the present series of experiments.I n order to obtain lustre the fibres com- prising the thread or fabric being mercerised must be stretched at some part of the process. The object of the experiments described below was to ascertain :282 THE FIBRE BALANCE (I) the force required to stretch the fibre to its original (dry) length after it had been allowed to contract during mercerisation (or, in one case, the force necessary to keep the fibre from contracting at all during mercerisation) ; (2) the force required to break the fibre under the same conditions as those used in stretching it in ( I ) ; (3) the total percentage extension of the fibre before breaking. The following variations in the method of mercerisation were tried : 1st Method:-The fibre was mercerised loose, and the contraction The fibre remaining in the mercerising solution, was stretched to 2nd Method ;-Fibre mercerised loose, and contraction noted.Fibre 3rd Method :-Fibre placed in mercerising liquor (NaOH 35’ Tw.), I t was It (the NaOH solution being of density 35’ Tw. in every case). noted. its original length, and then further stretched until it broke. then placed in water, and stretched. and the pull on it so adjusted as to keep the fibre at its dry length. then stretched until it broke, as in the other methods. was then placed in one of the following :- 4th Methud:-Fibre mercerised loose, washed, and allowed to dry. (a) Air. (6) Water. (c) Caustic soda 3 5 ’ 3 ’ ~ . (d) Absolute alcohol. ( e ) Benzene.cf) Ether. and stretched as before. The fourth method described above is that of Dollfus, Mieg et Cie, F.P. 267459/1897. “The yarn is mercerised loose, washed, dried, and if necessary stored, when it loses 20 per cent. in length.” (N.B.-This shrinkage is due not only to fibre shrinkage, which is only about 5 to 7 per cent., but also to increase in fibre section, and consequent shrinkage of yarn,) “While dry the yarn can only be stretched without rupture 5 to 7 per cent., but if the yarn is treated with water, steam, alcohol, ether, or benzene, the original may easily be regained.” The following results were obtained in the cases mentioned above, each figure given being the mean of only about twenty measurements, so that no great degree of accuracy can be claimed.The three results given in each case refer to ( I ) The force required to stretch the fibre to its original (dry) length ; ( 2 ) The force required to break the fibre ; (3) The total percentage extension of the fibre. 1st Mefhud:-0-30 gm. ; 3.8 gm. ; 12-4 per cent. 2nd Mefhod:-o-85 gm. ; 5-6 gm. ; I I -3 per cent. 3rd Method:-o.17 gm. ; 4-6 gm. ; 12.1 per cent. 4th Method :-2 (a) 3-20 gm. ; 5-7 gm. ; 13.3 per cent. (b) 0.975 gm. ; 5-6 gm. ; 23-8 per cent. (c) 0.30 gm. ; 4-2 gm.; 26-5 per cent. (d) 2.78 gm. ; 4.4 gm.; 6.6 per cent. (e) 2.89 gm. ; 5.9 gm. ; 13-0 per cent. v) 3.7 gm. ; 5-7 gm. ; 10.4 per cent. 1 Clibbens, Shivlejf Inst. Memoirs, Aug. 1923, p. 161. 2 The percentage extensions given in the fourth method are rather exaggerated, as they are reckoned from the length of the dried fibre after shrinkage in the mercerising soh tion.THE FIBRE BALANCE 283 The most interesting results brought out in this series of measurements are : (I) The comparatively small force (0-17 gm.) required to keep the fibre stretched while being mercerised. Nearly double this force is required when the fibre is allowed to contract in the mercerising solution. ( 2 ) The increase in the pull required to stretch the fibre when the stretching is postponed until the washing operation. (3) The comparatively enormous pull required when the fibre is placed in air, alcohol, benzene, or ether. (4) The large percentage extension of the fibre before breaking when immersed in the caustic soda solution. The results would appear to indicate that for lustre effects in yarns or fabrics the stretching should be done in caustic soda solution. This would give the required fibre extension with the least possible amount of force, and would therefore not involve so much displacement of the fibres by tearing them apart from each other. I t would also permit a greater total extension, with consequent increase of lustre due to a more circular section of the individual fibres. Another obvious advantage of the greater total extension is the increase in the length or breadth (or both) of the yarn or fabric concerned. My thanks are due to the Director of Artillery, who has kindly given his permission for the publication of this paper. Physico- Chmical LaJoratory, Research Department, Woolwich.