Viscometer Ostwald

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. 

The original Ostwald viscometer has been modified in many ways, and a number of different versions are on the market (Table 4) (21). Most are available with a wide choice of capillary diameters and therefore a number of viscosity ranges. A number of viscometers are described in ASTM D445, which also Hsts detailed recommendations on dimensions and methods of use. 

Enzyme Assay The activity was assayed by the determination of substrate viscosity diminishing using Ostwald viscometer (10). The enz5une reaction was done at 37°C in 0.05 N acetate buffer pH 5.25. One unit of enzyme was defined as the amount of enzyme that could reduce the viscosity of 2% pectin by 50% in 10 min. 

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.

When proteins are "irreversibly" adsorbed in layers thicker than 1000 A it becomes possible to use an ordinary Ostwald viscometer (time of flow about 700 sec) to determine the layer thickness precisely. 

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. 

In the Ostwald viscometer, the solution is introduced through the tube a and is then sucked through the tube 7/ until its level is above mark C, the efflux time of the solution from mark c to mark d is then noted. 

When Ostwald viscometer is used, and equal volume of the solution should be taken for each determination. 

The error in the determination of the efflux time because of the deflection of the viscometer from the vertical is much larger in Ostwald viscometer than in Ubbelohde viscometer. 

Capillary viscometers that have this design are called Ostwald viscometers. There are many specific designs of Ostwald viscometers. The most frequently used are the Cannon-Fenske viscometer... 

The Ostwald viscometer is the general name given to a capillary viscometer. 

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). 

Figure 3.6 Solution capillary rheometers a) Ubbelohde-type rheometer (courtesy of Cannon Instrument Company, USA), and b) a schematic of an Ostwald viscometer...

Viscosity of the Serum. Provided the apparatus is available, this is a rather simple test to perform and the information obtained helps to establish the condition. Using an Ostwald viscometer at 20.0°C and 37.5°C in thermostatically controlled water baths, it was found that patients with macroglobulinemia had scrum with relative viscosity of 2.40-15.80. The normal is 1.54r-1.80. 

Fig. 2.15a. Ostwald viscometer Total length 25 cm capillary length 10 cm bulb 3 diameter 1.3 cm, bulb 4 diameter 2.2 cm, filling level 2 or 3 ml, flow volume 0.5 ml a, b head pieces c sintered glass filter for filtration of solvent and polymer solution...

Fig. 2.15b. Thermostatted hath and mounting for Ostwald viscometer 1 rubber bulb 2 drying tube 3 thermometer 4 heating coil 5 thermo indicator 6 cooling coil 7 stirrer 8 power and controlling unit...

The oxidative degradation of polyfvinyl alcohol) is followed at 25 °C by viscosity measurements in an Ostwald viscometer (capillary diameter 0.4 mm). One proceeds as follows ... 

Ostwald viscometer (capillary diameter, 0.5 mm e.g., Fisher Scientific) Constant-temperature mechanism (e.g., appropriate water bath)... 

Characterization of the Copolymer. The SO- content in the copolymer was calculated from the sulfur content determined by the Schoniger method. The reduced viscosity of the copolymer was determined at 30 °C with an Ostwald viscometer. DMF containing 0.1% LiCl was used as solvent at 0.2 gram/100 ml. The melting point of the terpolymer was measured by a hot-stage microscope. 

Figure 4. Decrease in specific viscosity during the hydrolysis of CMC solution by E-3-1, E-3-2, E-3-3, E-3-4, and E-3-5. Reaction mixture consists of 3.0 mL 1% CMC, 7.0 mL 0.1M sodium acetate buffer, pH 4.0, and 2.0 mL enzyme solution containing an amount of protein equivalent to an optical density of 0.05 at 280 nm. The reaction mixture was carried out at 30°C in an Ostwald viscometer.

With the viscosity of a liquid we mean the resistance to flow of that particular liquid. This resistance is caused by internal friction and other interactions between the particles. Among other things, viscosity is dependent on temperature, the solid volume fraction and the properties of the particles. The viscosity of normal liquids, solutions and lyophobic colloids which are not too concentrated and contain symmetrical particles is measured by allowing a certain volume to flow through a capillary and measuring the time required by the liquid to flow through it. In figure 5.10 you can see the instrument which is used for this measurement the Ostwald viscometer. 

The capillary method is simple to operate and precise (c. 0.01-0.1 per cent) in its results, but suffers from the disadvantage that the rate of shear varies from zero at the centre of the capillary to a maximum (which decreases throughout the determination) at the wall. Thus, with asymmetric particles a viscosity determination in an Ostwald viscometer could cover various states of orientation and the measured viscosity, although reproducible, would have little theoretical significance. 

Figure 6.3 Illustration of (a) an Ostwald viscometer and (b) a co-ordinate system showing the position of concentric flow layers.

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