SU1286949A1 - Method of determining liquid capillary constant - Google Patents

Abstract

The method relates to the measurement of the physicochemical properties of liquids. The purpose of the invention is to improve the accuracy of determination. The determination of capillary constant and surface tension coefficient is carried out using a tee-shaped capillary, one branch of which with a known hole size in its end part is introduced through the bottom of the cell with plane-parallel transparent edges into which the liquid under study is poured, and the lower expanded part of the capillary tube introduces a light guide that provides a light indication of the moving upper boundary of the bubble, which is formed as a result of gas blowing through the sides A branch of the capillary tube. High contrast, resulting from varying degrees of absorption and scattering of light by the liquid and gas phases and reflection of light at the gas-liquid interface, makes it possible to follow the movement of the upper boundary of the bubble during its growth. When the bubble is detached, a merge of points A and A of the isthmus, which is formed in its lower part, occurs, and light, in its upper part, is excluded. With each new bubble growth, the process repeats, and the maximum movement of the light indication in the vertical direction contributes to the tearing height of the bubble, which is evaluated by the microscope by placing the sighting line at the maximum movement of the light indication. The values of capillary constant and surface tension coefficient S are determined by the formulas a hl, b h / 12gRp, where p is the density of the liquid; h - bubble height at the moment of separation; R is the radius of the capillary in the end part; g - free fall acceleration. 1 il. (P

Description

The invention relates to measuring technique and can be used in the study of the physicochemical properties of a liquid to determine their surface properties in scientific research practice.

The purpose of the invention is to increase the accuracy of determination by eliminating errors that occur when determining the geometric parameters of a gas bubble.

The drawing shows a diagram of the device for implementing the method.

A capillary tube 1 is used, having the shape of a tee, one branch of which with a calibrated radius of the hole in the end part is passed through a rubber stopper 2, which acts as a sealant, through an opening made in the bottom of the cuvette 3 with flat parallel transparent edges that prevent geometric distortion a bubble, and a light guide 5 is inserted through the seal 4 into the lower expanded part of the capillary tube. Investigated liquid 6 is poured into the cuvette 3, and the side branch 7 of the capillary tube is connected to the source gas, by regulating the flow rate of which it is possible to ensure quasistatic growth of the bubble 8 in the end part of the capillary 1 introduced into the cuvette 3. The light introduced into the cavity of the bubble 8 by means of the light guide 5 results in a much lower absorption and scattering of the gas phase compared to liquid and as a result of reflection from the upper interface (gas-to-liquid) it is possible to monitor with the aid of a microscope 9 the movement of the upper boundary of the bubble.

performed as follows.

After the cuvette 3 is filled with the test liquid 6, a beam of light is directed into the light guide 5 and the gas is passed through the side branch 7 of the capillary tube 1 to form the bubbling bubbles 8. Using a microscope 9, they observe the light pattern near the capillary end. Before the moment of bubble removal, an isthmus AL is formed in its lower part. When the points A and A merge, the path of the light flux into the upper cavity of the bubble and the process of alternation (e

five

0

Neither the light boundary in the vertical direction is repeated with each new bubble growth.

The maximum displacement of the light boundary in the vertical direction, measured from the upper edge of the capillary, corresponds to the height of the bubble hg at the moment of its separation.

Thus, the bubble itself is an automatic controller for the maximum movement of the light indication in the vertical direction, in which the value is determined using a microscope, by setting the sighting line to the maximum movement of the light indication.

I

By the measured value of h and iz,

the known radius of the capillary opening R, the capillary constant is calculated

a lz / 12T.

Since the capillary constant at low pressures is determined by the expression

b

 i pa lg

where b is the surface tension; p is the density of the liquid; g - free fall acceleration,

then the surface tension coefficient using the parameters R and h is determined by the equation

b - 12gRp

Example. The capillary constant and surface tension of distilled water at a temperature of 20 ° C were determined. The radius of the capillary opening was R 0.206 mm. Measured height hp 2.64 + 0.01 mm. The calculated value of a is 2.73 ± 0.04 mm. Relative error of determination

and equal to 1.6%, which is 4 times less than in the method prototype.

Claims (1)

Invention Formula The method for determining the capillary constant of a liquid, which consists in passing a gas through a vertical calibrated capillary, the end of which is located in the liquid, and measuring the geometrical parameter pA, characterizing the position of the liquid-gas boundary, characterized in that, in order to increase the determination accuracy, the gas is passed through the capillary upwards and along the length of the glowing line near the capillary end observed in the process of blowing a bubble, the parameter characterizing the position of the liquid-gas boundary is the height of the gas puff at the moment its separation from the capillary, after which the capillary constant of the liquid is calculated using the expression o h3 / 12R where a is the capillary constant of the fluid, cm; hg is the height of the gas bubble, cm; R is the radius of the capillary opening in the end part, see