Ostwald measurements

The basic design is that of the Ostwald viscometer a U-tube with two reservoir bulbs separated by a capillary, as shown in Figure 24a. The Hquid is added to the viscometer, pulled into the upper reservoir by suction, and then allowed to drain by gravity back into the lower reservoir. The time that it takes for the Hquid to pass between two etched marks, one above and one below the upper reservoir, is a measure of the viscosity. In U-tube viscometers, the effective pressure head and therefore the flow time depend on the volume of Hquid in the instmment. Hence, the conditions must be the same for each measurement. 

Measured ia 95% ethanol at 25°C usiag an Ostwald-Cannon-Fenske viscometer. 

In Nature, however, we always have a contiiinous distribution of particles. This means that we have all sizes, even those of fractional parentage, i.e.-18.56n, 18.57p, 18.58 p, etc. (supposing that we can measure 0.01 p differences). The reason for this is that the mecheuiisms for particle formation, i.e.- precipitation, embryo and nucleation growth, Ostwald ripening, and sintering, are random processes. Thus, while we may speak of the "statistical variation of diameters", and while we use whole numbers for the particle diameters, the actuality is that the diameters are fractional in nature. Very few particle-size" specialists seem to recognize this fact. Since the processes are random in nature, we can use statistics to describe the... 

Pectin lyase (PNL) activity was measured spectrophotometrically by the increase in absorbance at 235 nm of the 4,5-unsaturated reaction products. Reaction mixtures containing 0.25 ml of culture filtrate, 0.25 ml of distilled water and 2.0 ml of 0.24% pectin from apple (Fluka) in 0.05M tris-HCl buffer (pH 8.0) with ImM CaCl2, were incubated at 37 C for 10 minutes. One unit of enzyme is defined as the amount of enzyme which forms Ipmol of 4,5-unsaturated product per minute under the conditions of the assay. The molar extinction coefficients of the unsaturated products is 5550 M cm [25]. Also viscosity measurements were made using Cannon-Fenske viscometers or Ostwald micro-viscosimeter, at 37°C. Reaction mixtures consisted of enzyme solution and 0.75% pectin in 0.05 M tris-HCl buffer (pH 8.0) with 0.5 mM CaCl2. One unit is defined as the amount of enzyme required to change the inverse specific viscosity by 0.001 min under the conditions of reaction. Specific viscosity (n p) is (t/to)-l, where t is the flow time (sec) of the reaction mixture and t is the flow time of the buffer. The inverse pecific viscosity (n p ) is proportional to the incubation time and the amount of enzyme used [26]. Units of enzyme activity were determined for 10 min of reaction. 

Figure 8.7 Temperature dependences of viscosity for several solvents measured with conventional Ostwald viscometers. Markers exhibit experimental results. Data points were interpolated by polynomial function the calculated curves are drawn with lines.

The measurements were performed in an Ostwald Cannon-Fenske viscometer (No. J-627-25) using the method described by Silberberg and Klein Ci). This involves determining the time of flow as a function of the amount of liquid in the viscometer. Amounts between 7 and 8 g are chosen and the viscometer weighed to determine the exact amount. Buffer replacements were undertaken by dilution. 

For Molecular weight determination by viscometry we do not need absolute h value, viscosity measurements may be carried out in simple Ostwald Viscometer. Because of (the non-Newtonian behaviour of most macromolecular solutions at high velocity gradients in the capillary, the viscometer dimensions are chosen in such a manner that the viscosity gradient is the smallest possible. 

Fig Capillary viscometers commonly used for measurement of polymer solution viscosities (i) Ostwald-Fenske and (ii) Ubbelohde. 

For chemists, the problem of affinity, or what Meyer called variable valence, was the central problem of chemistry, one in which, Ostwald claimed, chemists made no progress while seeking to measure chemical "forces." Meyer, who often is identified with the tradition of physical chemistry and theoretical chemistry, as noted in chapter 3, was confident that the answer to affinity lay in theories of motion, not in species or types, just as Nemst later was to identify the end of affinity theory with its reduction to physical causes. 

Measurements of the dissociation constants of m-nitrobenzoic acid and p-nitrobenzoic acid began with Ostwald in 1889114. However, the first reasonably precise values were obtained by Dippy and coworkers in the nineteen-thirties, as part of an extensive study of the ionization of carboxylic acids by conductimetric methods115. The pKa values in water at 25 °C of m-nitrobenzoic acid and p-nitrobenzoic acid were found to be 3.493 and 3.425, respectively, compared with 4.203 for benzoic acid itself. On the basis of these values Hammett28,116 proposed 0 values of 0.710 for m-NOy and 0.778 for p-NOy (see Section II.A). These a values have commonly been used thereafter, often rounded to 0.71 and 0.78, respectively. 

Quantitative measurements of simple and enzyme-catalyzed reaction rates were under way by the 1850s. In that year Wilhelmy derived first order equations for acid-catalyzed hydrolysis of sucrose which he could follow by the inversion of rotation of plane polarized light. Berthellot (1862) derived second-order equations for the rates of ester formation and, shortly after, Harcourt observed that rates of reaction doubled for each 10 °C rise in temperature. Guldberg and Waage (1864-67) demonstrated that the equilibrium of the reaction was affected by the concentration ) of the reacting substance(s). By 1877 Arrhenius had derived the definition of the equilbrium constant for a reaction from the rate constants of the forward and backward reactions. Ostwald in 1884 showed that sucrose and ester hydrolyses were affected by H+ concentration (pH). 

IL. Dilute solution viscosity measurements were done at 30 with the appropriate Ostwald-Fenske capillary viscometers. The water content of all organic solvents, used as the liquid phase in solid-liquid PTC runs was analyzed by potentiometric Karl Fischer titration using a Metrohm AG CH 9100 model automatic titrator. 

Ostwald coefficient physchem A measure of the solubility of a gas in a liquid, equal to the volume of gas that can be dissolved in a given volume of liquid divided by the volume of liquid. ast.valt, ko-3,fish-ant ... 

An Ostwald viscometer is similar to an Ubbelohde-type rheometer except that it is simpler in design and is less expensive. A schematic of an Ostwald viscometer is shown in Fig 3.6(b). It is characterized by a lower bulb that acts as a solution reservoir. A solution of known polymer concentration is placed in the lower bulb. A single capillary tube in which the measurement is taken is connected to the bottom of the bulb and to two small bulbs at the top of the capillary. Fluid is forced from the lower bulb through the capillary into the two small bulbs attached to the top of the capillary. There is a line between the two bulbs and at the exit of the lower bulb. The fluid is then allowed to drain back into the lower bulb through the capillary, and the time for the fluid to travel between the two lines is recorded. The time, if there were no end effects, is proportional to the kinematic viscosity (/j/p). 

Bebahani, Gh.R.R., Hogan, P., and Waghorne, W.E. Ostwald concentration coefficients of acetonitrile in aqueous mixed solvents a new, rapid method for measuring the solubilities of volatile solutes, J. Chem. Eng. Data, 47 (5) 1290-1292,2002. 

The Ostwald coefficient Lg is the ratio between volume of adsorbed gas and volume of solvent, measured at the same temperature ... 

A monomolecular film is resistant to shear stress in the plane of the surface, as is also the case in the bulk phase a liquid is retarded in its flow by viscous forces. The viscosity of the monolayer may indeed be measured in two dimensions by flow through a canal on a surface or by its drag on a ring in the surface, corresponding to the Ostwald and Couette instruments for the study of bulk viscosities. The surface viscosity, r s, is defined by the relation... 

---