USP34-NF29 <621> 粘度 <911> VISCOSITY

Viscosity is a property of liquids that is closely related to the resistance to flow. It is defined in terms of the force required to move one plane surface continuously past another under specified steady-state conditions when the space between is filled by the liquid in question. It is defined as the shear stress divided by the rate of shear strain. The basic unit is the poise; however, viscosities commonly encountered represent fractions of the poise, so that the centipoise (1 poise = 100 centipoises) proves to be the more convenient unit. The specifying of temperature is important because viscosity changes with temperature; in general, viscosity decreases as temperature is raised. While on the absolute scale viscosity is measured in poises or centipoises, for convenience the kinematic scale, in which the units are stokes and centistokes (1 stoke = 100 centistokes) commonly is used. To obtain the kinematic viscosity from the absolute viscosity, the latter is divided by the density of the liquid at the same temperature, i.e., kinematic viscosity = (absolute viscosity)/(density). The sizes of the units are such that viscosities in the ordinary ranges are conveniently expressed in centistokes. The approximate viscosity in centistokes at room temperature of ether is 0.2; of water, 1; of kerosene, 2.5; of mineral oil, 20 to 70; and of honey, 10,000.

粘度是液体的属性之一，它与流动阻力紧密相关。在规定的条件下，待测液体充满平面间的空隙，在不断转动过程中，所产生的力定义为粘度。该粘度等于剪切应力除以剪切应变率。基本单位是泊；但是经常遇到泊的分数表示的粘度，因此厘泊（1泊=100厘泊）是更常用的单位。由于粘度随温度变化明显，需指明温度。通常情况下，粘度随温度的升高而减小。尽管粘度的测量是以绝对粘度形式表示，其常用单位是泊或厘泊，但为方便期间常常得到的是运动粘度，常用单位是司和厘司（1司=100厘司）。为了从绝对粘度得到运动粘度，绝对粘度需要除以同温度下的液体密度。如，运动粘度=绝对粘度/密度。单位的大小便于表示常规范围内的粘度为厘司。在室温情况下，以厘司估计的粘度，醚为0.2；水为1；煤油为2.5；矿物油为20～70；蜂蜜为10,000。

Absolute viscosity can be measured directly if accurate dimensions of the measuring instruments are known, but it is more common practice to calibrate the instrument with a liquid of known viscosity and to determine the viscosity of the unknown fluid by comparison with that of the known.

如果已知测量仪器的准确尺寸，可以直接测得绝对粘度。但是更常用的做法是使用已知粘度的液体校准仪器，通过与已知粘度的液体相对比，测定未知粘度的液体。

Many substances, such as the gums employed in pharmacy, have variable viscosity, and most of them are less resistant to flow at higher flow rates. In such cases, a given set of conditions is selected for measurement, and the measurement obtained is considered to be an apparent viscosity. Since a change in the conditions of measurement would yield a different value for the apparent viscosity of such substances, the instrument dimensions and conditions for measurement must be closely adhered to by the operator.

许多物质，如制药中用到的胶，具有可变粘度。它们中的大多数在高流速的情况下，流动阻力较低。在这种情况下，为了测量粘度选定一个特定条件，得到的测量值被认为是表观粘度。因此测量条件的改变会造成这类物质的表观粘度值的不同。操作者必须严格遵守测量时的仪器尺寸和条件。

Measurement of Viscosity— The usual method for measurement of viscosity involves the determination of the time required for a given volume of liquid to flow through a capillary. Many capillary-tube viscosimeters have been devised, but Ostwald and Ubbelohde viscosimeters are among the most frequently used. Several types are described, with directions for their use, by the American Society for Testing and Materials (ASTM, D-445). The viscosity of oils is expressed on arbitrary scales that vary from one country to another, there being several

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USP34-NF29 <621> 粘度

corresponding instruments. The most widely used are the Redwood No. I and No. II, the Engler, the Saybolt Universal, and the Saybolt Furol. Each of these instruments uses arbitrary units that bear the name of the instrument. Standard temperatures are adopted as a matter of convenience with these instruments. For the Saybolt instruments, measurements usually are made at 100°F and 210F; Redwood instruments may be used at several temperatures up to 250°F; and values obtained on the Engler instrument usually are reported at 20°C and 50°C. A particularly convenient and rapid type of instrument is a rotational viscosimeter, which utilizes a bob or spindle immersed in the test specimen and measures the resistance to movement of the rotating part. Different spindles are available for given viscosity ranges, and several rotational speeds generally are available. Other rotational instruments may have a stationary bob and a rotating cup. The Brookfield, Rotouisco, and Stormer viscosimeters are examples of rotating-bob instruments, and the MacMichael is an example of the rotating-cup instrument. Numerous other rotational instruments of advanced design with special devices for reading or recording, and with wide ranges of rotational speed, have been devised.

粘度的测量方法- 测量粘度的常用方法涉及测定指定体积的液体流经毛细管所需的时间。已经定制了许多毛细管粘度计，但是奥斯特瓦尔德和乌氏粘度计是最常用的。美国测试与材料协会(ASTM, D-445)描述了几种类型的粘度计及其应用方向。针对油粘度的表述比较是随意，不同的国家之间因使用的仪器不同而有所差异。其中，广为使用的是红木1号和2号、恩格勒、赛波特通用和赛波特重油仪。每种仪器使用代表仪器名称的单位。为方便起见，这些仪器采用标准的温度。对赛波特仪，测量时的温度通常是100°F和210°F；红木仪有几个温度可用，最高250°F。恩格勒仪测得的事值通常报告温度为20°C和50°C。一种极其方便快捷的仪器是旋转粘度计，它利用浸没在待测物中的浮子和转子，测量旋转运动的阻力。不同的转子对应不同的粘度范围，有几个不同的转速可选择。其它的旋转装置有一个固定的浮子和旋转杯。Brookfield粘度计，Rotouisco，斯托默粘度计是浮子旋转仪器的例子。MacMichael是旋转杯仪器的例子。许多配有特殊的阅读或记录装置，和宽的转速范围的先进旋转仪已定制。

Where only a particular type of instrument is suitable, the individual monograph so indicates. 然而只有一种特定类型的仪器是合适的，在各个专论中有指示。

For measurement of viscosity or apparent viscosity, the temperature of the substance being measured must be accurately controlled, since small temperature changes may lead to marked changes in viscosity. For usual pharmaceutical purposes, the temperature should be held to within ±0.1°.

粘度或表观粘度的测量，必须准确控制被测物质的温度，由于小的温度变化可能导致粘度的显著变化。通常制药用途，温度应当控制在±0.1°。

Procedure for Cellulose Derivatives— Measurement of the viscosity of solutions of the high-viscosity types of methylcellulose is a special case, since they are too viscous for the commonly available viscosimeters. The Ubbelohde viscosimeter may be adapted (cf. ASTM, D-1347) to the measurement of the ranges of viscosity encountered in methylcellulose solutions.

纤维素衍生物程序 – 高粘度的甲基纤维素溶液的粘度测量是特殊情况，对常规可用的粘度计而言，它们太粘了。可采用乌氏粘度计(cf. ASTM, D-1347)测量甲基纤维素溶液的粘度范围。

Calibration of Capillary-Type Viscosimeters— Determine the viscosimeter constant, k, for each viscosimeter by the use of an oil of known viscosity.*

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USP34-NF29 <621> 粘度

毛细管类型粘度计的校准 – 通过使用已知粘度的油测定每个粘度计的粘度计常数，K。

Ostwald-Type Viscosimeter— Fill the tube with the exact amount of oil (adjusted to 20.0 ± 0.1°) as specified by the manufacturer. Adjust the meniscus of the column of liquid in the capillary tube to the level of the top graduation line with the aid of either pressure or suction. Open both the filling and capillary tubes in order to permit the liquid to flow into the reservoir against atmospheric pressure. [Note—Failure to open either of these tubes will yield false values. ] Record the time, in seconds, for liquid to flow from the upper mark to the lower mark in the capillary tube.

奥斯特瓦尔德型粘度计划- 根据生产商的指导，填装确切数量的油（调整至20.0 ± 0.1°）至填充管。在压力或吸力的帮助下，调节毛细管内液柱的半月面至与顶端刻度线相切。打开填充管和毛细管，使液体在大气压的作用流入储液器。[注意事项- 任何一个管不打开，都会得出错误的值。]记录液体在毛细管内，从上刻度线至下刻度线的流出时间，以秒为单位。

Ubbelohde-Type Viscosimeter— Place a quantity of the oil (adjusted to 20.0 ± 0.1°) in the filling tube, and transfer to the capillary tube by gentle suction, taking care to prevent bubble formation in the liquid by keeping the air vent tube closed. Adjust the meniscus of the column of liquid in the capillary tube to the level of the top graduation line. Open both the vent and capillary tubes in order to permit the liquid to flow into the reservoir against atmospheric pressure. [Note—Failure to open the vent tube before releasing the capillary tube will yield false values. ] Record the time, in seconds, for the liquid to flow from the upper mark to the lower mark in the capillary tube.

乌氏粘度计 – 在填充管内，加入一定量的油（调整至20.0 ± 0.1°），并稍加吸力转移至毛细管内，通过保持空气排空管处于关闭状态，防止液体中产生气泡，调节毛细管内液柱的半月面至与顶端刻度线相切。打开填充管和毛细管，使液体在大气压的作用流入储液器。[注意事项- 任何一个管不打开，都会得出错误的值。]记录液体在毛细管内，从上刻度线至下刻度线的流出时间，以秒为单位。 Calculations— 计算 –

Calculate the viscosimeter constant, k, from the equation: 根据以下公式计算粘度计常数，K k = v/d t

in which v is the known viscosity of the liquid in centipoises, d is the specific gravity of the liquid tested at 20°/20°, and t is the time in seconds for the liquid to pass from the upper mark to the lower mark.

其中，v是已知液体的粘度，厘司；d在20°/20°情况下测得的液体的比重；t是液体从上刻度线至下刻度线的流出时间，秒

If a viscosimeter is repaired, it must be recalibrated, since even minor repairs frequently cause significant changes in the value of its constant, k.

如果粘度计经过维修必须进行校准，由于即使是小的维修经常会造成粘度计常数，k，的显著变化。

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