Lynne Wong's PhD thesis

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6.9 FIBRE SATURATION POINT Berry and Roderick (2005) in their review on plant-water relations introduce the idea of fibre saturation point (FSP), well known and in routine practical use by engineers and material scientists for at least 50 years. Fibre saturation point is routinely used to estimate the volume fractions of solid, liquid and gas phases in bulk timber, it is based on the concept that a certain (and repeatable) amount of water is chemically bound to cellulose and other substances in wood. This water, also called bound water, exists in an integrated mixture of cell wall material and bound water, is recognized as a distinct phase called ‘solid solution’ by Stamm (1964), a separate phase from the adjacent water in either a pure liquid phase or a vapour phase. The following illustrates well the concept of fibre saturation point. When a small volume of liquid water is poured onto oven-dried timber, observations show that when equilibrium is attained, the added water is not visible in the voids, but it must be located inside the cell wall matrix; which will swell as a result and the strength of the timber will progressively decline as the moisture content increases. If the addition of water is continued, the moisture content increases further, and the system will reach a new equilibrium state when liquid water begins to accumulate in the voids. The moisture content at which this occurs is called the fibre saturation point, which has been described as the moisture content at which the cell walls are fully saturated with liquid moisture but the cell cavities contain no water. Water exists in timber in three phases: as vapour in the gas-filled voids, as ‘free’ or ‘bulk’ liquid water in the voids and as bound water in the cell wall matrix (Stamm, 1967a). The volume fraction of the three phases in timber can be estimated given its fresh volume, fresh mass, dry mass and the fibre saturation point. At the fibre saturation point, all of the liquid water is bound water, as it represents the maximum amount of water that can be taken up from the vapour phase by a unit mass of timber at a given temperature (Browning, 1963). If the fibre saturation point of timber is measured before and after pulverization to a larger surface area keeping the total mass the same, the results do not differ showing that there is a distinct number of binding sites for water in the timber, and the number of the binding sites is independent of the surface area of the sample (Stamm, 1964). The forces that hold the water preferentially in the cell walls are chemical bonding and/or capillary (i.e. surface) forces. The support of this statement comes from the fact that heat of wetting is evolved 19
when water is added to dry wood, which implies the existence of chemical reaction (Stamm, 1964). From the point of view of equilibrium thermodynamic, if EMC is plotted against relative humidity in absorption study of timber, when the relative humidity approaches 100%, the moisture content of the timber will be about 30%, which is usually the fibre saturation point of timber. With increase of temperature, the fibre saturation point of timber is expected to decrease since a larger proportion of the water molecules should then have sufficient kinetic energy to enter an adjacent gas phase (Berry and Roderick, 2005). The EMC data for the nine cane components of R 570 aged 52 weeks determined at 30, 45, 55 and 60 ºC (Tables 5.8 – 5.16) were plotted against relative humidity, taken as 100 multiplied by the water activity (Fig. 6.16). The fibre saturation point value of each component at each temperature was estimated and compared to the Brix-free water results determined at ambient temperature extracted from Tables 4.17 – 4.21 with 1.1 units added to correct for the residual moisture content (Table 6.9). Table 6.9. Brix-free water and fibre saturation point bound water in fibres of cane components of R 570. Sample Brix-free water/% Fibre saturation point value/% Ambient temperature 30 o C 45 o C 55 o C 60 o C Stalk fibre 12.37 20.18 24.61 27.74 28.62 Stalk pith 25.05 27.26 34.99 37.14 41.26 Rind fibre 12.02 22.02* 24.09* 26.58* 25.99 Rind fines 11.47 19.73 22.69 24.59 23.53* Top fibre 16.76 26.32 28.83 25.33 29.67 Dry leaf fibre 16.13 23.77 24.45 22.91 29.61 Dry leaf fines 18.17 23.22 28.14 27.61* 28.14 Green leaf fibre 13.77 23.18 28.83* 31.21* 27.04 Green leaf fines 14.79 25.63 28.04 28.13 28.26 Reconstituted cane stalk 15.13 22.05 27.27* 29.56 29.55 Reconstituted dry leaf 16.99 23.54 25.29 24.65 28.99 Reconstituted green leaf 14.11 23.98 30.55 30.20 27.68 * Fibre saturation point not yet attained. 20
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THE BRIX-FREE WATER CAPACITY AND SO
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dissolved and hydrated waters, and
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ACKNOWLEDGEMENTS I am particularly
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Page 1.5 THE DELETERIOUS EFFECTS OF
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Page 2.2 THE PHENOMENON OF BRIX-FRE
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Page 3.4.3.3 Cane tops 83 3.4.4 Cha
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4.3.3 Temperature at which Brix-fre
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4.6.1 Materials 143 4.6.1.1 Samples
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CHAPTER 6. PROPERTIES OF THE SORBED
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APPENDIX 3. CALCULATIONS LEADING TO
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LIST OF FIGURES Page Figure 1.1. Fi
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Figure 3.1. Glucose and fructose an
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Figure 5.11. Residual plots for the
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total adsorbed water (m) and the pr
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Table 2.18. Moisture content in sug
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Page Table 4.4. Results of the dete
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Page Table 4.24. Analysis of varian
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Page Table 5.13. Table 5.14. Equili
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Table 6.3. Heat of sorption of the
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GLOSSARY OF TERMS Absorption is the
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Filterability of a raw sugar is mea
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Sorption is the generic term used w
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LIST OF MAIN SYMBOLS Symbol Descrip
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s c s Slope of Caurie I isotherm pl
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number of 255, and cane land covere
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Nouvelle Mon In Trésor ustrie and
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Figure 1.3. Cane sampling by core s
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In Mauritius, most of the sugar fac
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are: cane tops, dry and green leave
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1.4 TRENDS IN CANE QUALITY RECEIVED
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campaign was launched to encourage
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The level of extraneous matter in c
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In Australia (Cargill, 1976), cane
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The effect of soil on factory perfo
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leaves increased the level of impur
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• From 1976 to 1980, when the pro
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Clerget purity of molasses 40 Clerg
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CHAPTER 2. IMPACT OF EXTRANEOUS MAT
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Since the extrapolated purity of mo
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Figure 2.1. Jeffco cutter grinder.
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2.1.4 Results The analytical result
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Table 2.3. Analytical results of re
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Table 2.5. Composition of dry trash
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Table 2.7. Predicted factory perfor
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Boiling house recovery 91.0 89.8 89
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0 5 10 15 20 % EM in cane y = 0.572
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% EM in cane 0 5 10 15 20 0 -2 -4 -
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1 y = 0.020 (% D) R 2 = 1.00 = 0.03
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% EM in cane 0 5 10 15 20 0 -2 y =
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esulting in 0.015 unit sucrose loss
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2.2.1 Experimental procedure Cane m
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filter paper, rejecting the first f
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Table 2.9. Effect of increased addi
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Table 2.11. Effect of increased add
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Table 2.13. Effect of increased add
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various components such as stalk fi
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in the presence of dry leaves, if c
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Table 2.17. Moisture content in sug
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CHAPTER 3. SEPARATION OF THE SUGAR
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Table 3.1. It can be seen that the
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Table 3.2. Fibrous physical composi
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R 579 R 570 M 1557/70 M 1400/86 74
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loosen the fibre. The woody core is
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agitate the mixture in the pot, and
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Figure 3.7. Custom-built fibre-pith
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The extraction of fibres starting f
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pre-treatment in a Jeffco cutter-gr
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Figure 3.19. Stalk cake washed free
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not have many dry leaves attached t
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Table 3.5. Masses of cane samples a
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Table 3.7. Masses of cane samples a
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Table 3.9. Masses of cane component
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3 57.6 126.3 23.7 97.2 31.1 53.8 11
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Table 3.12. Material loss (%) from
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3.5.3 Fibre/pith ratios in cane com
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Table 3.15. Effect of extraneous ma
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Snow (1974) investigated the season
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from Figure 2.9 that the change in
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Table 3.18. Fibre % cane results by
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110
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(a). Dry leaf (b). Green leaf (c).
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dry fibre, or a factor, is used in
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Steuerwald (1912) applied sucrose s
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solution/fibre ratio was lowered fr
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leave some residual moisture on the
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instead of 150 g of 10° Brix sucro
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Table 4.2. Determination of Brix-fr
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Table 4.3. Comparison of Brix-free
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Table 4.4. Results of the determina
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In order to test for homogeneity of
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Table 4.7. Results of the repeat de
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The experiment was repeated with th
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e any residual moisture in the samp
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By means of the same technique, Won
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was still hot. Since the filter was
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value determined could be corrected
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Qin and White’s finding was confi
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A sample size of 3.5 g with 75 g co
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Figure 4.4. Fibre samples drying in
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- One large fibre sample (rind) of
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Table 4.18. Brix-free water values/
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Table 4.20. Brix-free water values/
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4.7.3 Statistical analysis It is es
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Table 4.23. Analysis of variance (B
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pointing out that at 52 weeks old,
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The crop of R 570 sampled in 2001 w
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4.7.4. Estimated Brix-free water co
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The main difference in the two sets
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Table 4.27. Predicted Brix-free wat
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4.8 SUMMARY AND CONCLUSIONS An anal
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component parts, and verify the Bri
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3) Thermodynamic, water in equilibr
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Langmuir (1916, 1917, 1918) propose
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to determine the moisture sorption
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Table 5.1. Some commonly used isoth
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Lomauro et al. (1985) found that wi
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and on agricultural products such a
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Bruijn (1963) studied the mass incr
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After measuring the EMC of dry corn
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approached, that is, either by adso
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Table 5.4. Water activity (a w ) of
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5.6.3 Procedure to determine equili
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5.6.4 Results and discussion An exa
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Table 5.8. Equilibrium moisture con
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Table 5.10. Equilibrium moisture co
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Table 5.12. Equilibrium moisture co
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30 o C 45 o C 55 o C 60 o C Water w
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m/m of 96% activity, a w (g/100g dr
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vaporisation generally decreases fr
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30 o C isotherm 45 o C isotherm 55
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4 0 Stalk fibre 5 0 Stalk pith 5 0
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5.6.4.4 Fitting of sorption models
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Table 5.19. Parameters of the sorpt
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Modified GAB Kuhn Iglesias - Chirif
Page 277 and 278: Table 5.28. Classification of resid
Page 279 and 280: Stalk fibre Stalk pith Rind fibre 4
Page 281 and 282: 5.6.4.5 Calculated EMC values of re
Page 283 and 284: Table 5.30. Calculated equilibrium
Page 285 and 286: m/m of 96% Table 5.32. Calculated e
Page 287 and 288: Table 5.33. Parameters of the Hailw
Page 289 and 290: CHAPTER 6. PROPERTIES OF THE SORBED
Page 291 and 292: where m is the equilibrium moisture
Page 297 and 298: 6.2 THE NUMBER OF ADSORBED MONOLAYE
Page 299 and 300: 6.3 TOTAL SOLID SURFACE AREA AVAILA
Page 301 and 302: Thus, for each cane component of ea
Page 303 and 304: abscissa. For each moisture level (
Page 307 and 308: A similar procedure was followed to
Page 309 and 310: 10 0 Stalk fibre Stalk pith Rind fi
Page 311 and 312: Moreover, if T β > T hm the proces
Page 313 and 314: Table 6.5. Characteristic parameter
Page 315 and 316: Binding energy/kJ (kg mol) -1 2 0 0
Page 317 and 318: 6.8 CALCULATION OF BOUND WATER AND
Page 319 and 320: The values of K 1 , K 2 and W were
Page 321 and 322: Table 6.7. Separation of the total
Page 323 and 324: Table 6.7. (Contd.) Sample 30 o C 4
Page 325 and 326: 3 0 S talk fibre 4 0 Stalk pith 3 0
Page 327: 3 0 Reconstituted cane at 30 o C 3
Page 331 and 332: It is evident that in some cases ma
Page 333 and 334: The number of adsorbed monolayers,
Page 335 and 336: Data in Tables 2.9 and 2.11 show th
Page 337 and 338: particular fibre is systematically
Page 339 and 340: Anon. (1985b). Laboratory manual fo
Page 341 and 342: Blanchi R.H. and A.G. Keller (1952)
Page 343 and 344: Day D.L. and G.L. Nelson (1965). De
Page 345 and 346: Heyrovsky J. (1970). Determination
Page 347 and 348: Kuhn I.J. (1964). A new theoretical
Page 349 and 350: Madamba P.S., R.H. Driscoll and K.A
Page 351 and 352: Prinsen Geerligs, H.C. (1897). Stud
Page 353 and 354: Sing K.S.W., D.H. Everett, R.A.W. H
Page 355 and 356: Van der Pol C., C.M. Young and K. D
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Lynne Wong's PhD thesis

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