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Hydrometer used in laboratory

1. What is hydrometer?
    1.1 Working principle of hydrometer
    1.2 Range of hydrometer
2. Type of hydrometer
3. Use of hydrometer
    3.1 Precaution on hydrometer
4. How to buy hydrometer?

What is hydrometer?

Hydrometer is made according to Archimedes' law and the condition that the object floats in equilibrium on the liquid surface, and is an instrument for determining the density of liquids. It is a closed glass tube, one end of uniform thickness, the inner wall is attached to the scale paper, the scale is not uniform, on the sparse under the dense, the other end is slightly inflated in the shape of a bubble, the bubble is equipped with small lead particles or mercury, so that the glass tube can be tested in the liquid vertical immersion to a sufficient depth, and can be stable floating in the liquid, that is, when it is subjected to any shaking, can automatically return to a vertical stationary position. When the hydrometer floats in the liquid, its own gravity is equal to the gravity of the liquid it is discharged. So, the pressure is different in different liquids immersed in different depths, and the specific gravity meter is used for this relationship scale.

A specific gravity hydrometer is a thin glass or plastic tube sealed at both ends, with graduated or printed scales, and calibrated to the specific gravity. One end of the tube is spherical and weighted with ballast made of fine lead or steel pellets. The ballast causes the instrument to float upright in the liquid like a fish float. A second glass or plastic cylinder, called a hydrometer tank, is filled with the measured liquid. The hydrometer is then placed in the hydrometer jar containing the sample liquid. The specific gravity of the sample liquid is indicated when the sample liquid level in the wide-mouth jar is aligned with a point on the scale of the hydrometer.

Working principle of hydrometer

The long tube of a liquid-specific gravity meter is often marked with the following numerical scales, such as 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 ....... When the hydrometer sinks in the liquid to the scale of 0.9, it is immediately known that the density of the liquid measured is 0.9. With this instrument, the object will only sink to the depth where the weight of the liquid excluded by it is exactly equal to its own weight. Therefore, the specific gravity meter in the lighter specific gravity of the liquid, than in the heavier liquid to sink more deeply. For example, it will sink deeper in alcohol than in alcohol mixed with water; shallower in pure milk than in milk mixed with water. The specific gravity meter will be inserted into various liquids with decreasing specific gravity, such as sulfuric acid (1.8), water (1.0), ether (0.717), etc., and the depth of sinking is gradually deepened. Therefore, the larger specific gravity must be located in the lower part of the scale, and the smaller specific gravity is located in its upper part. The scale itself must of course be calibrated first, and also in accordance with the specific gravity of various liquids, or directly in accordance with the specific properties of the liquid being measured, such as the alcohol content of wine, the fat content of milk, the pure acid content of sulfuric acid, etc. to calibrate.

Range of hydrometer

The hydrometers sink deeper when used in lower-density liquids such as kerosene, gasoline, and alcohol, and sink shallower in denser liquids such as salt water, milk, and acids. Typically, specific gravity meters for dense liquids have the 1.000 (water) mark near the top of the stem, while those for lighter liquids have 1.000 near the bottom. in many industries, a set of specific gravity meters (1.0-0.95, 0.95-.) is used to allow the instrument to cover the range of specific gravity that may be encountered.

Type of hydrometer

Hydrometer is a laboratory instrument used to measure the specific gravity of a liquid. Gravity is defined as the relative density obtained by dividing the density of that liquid by the density of water. The specific gravity meter is made of glass material and includes a long cylindrical rod. The bottom has a bulb weighted with lead or mercury to allow it to float upright and provide stability in water. It also has a scale printed on its side for measuring specific gravity. To ensure better accuracy, the reading must be adjusted to the temperature of the liquid at the time of measurement.

There are two types of hydrometers in common use. One is used to measure the density of a liquid with a density greater than 1, called a "heavy meter". It’s the lower end of the lead pellets or mercury loaded more. The smallest scale of this specific gravity meter is "1", it is at the top of the scale line, from top to bottom, in order, 1.1, 1.2, 1.3 ...... put this specific gravity meter in the water, it is greater than 1 scale line, all under the surface of the water.

Another kind of density used to measure the density of liquids less than 1, is called the "light meter". Its lower part of the lead pellets or mercury less, the maximum scale line of this specific gravity meter is "1", this scale line is at the lowest, from the bottom up, 0.9, 0.8, 0.7 ...... put this specific gravity meter in the water, it is less than 1 scale line all over the water surface. When using, should pay attention to whether the density of the liquid is greater than 1 or less than 1 to choose this weight meter. At present, secondary school textbooks no longer talk about specific gravity units but density units, but still use the specific gravity meter when measuring density, the measured value is no big difference.

The scale of a specific gravity meter varies depending on the industry’s application. For example, the petroleum industry uses API-specific gravity, the chemical and pharmacology industry uses Boehmey, and the brewing and winemaking industry uses Plato and Bailey's Brix for the sugar-based liquids industry.

Specific gravity meters are specifically designed to measure low-density liquids such as gasoline, alcohol, and kerosene, as well as high-density liquids such as acids, brines, and milk. The only difference is that high densities will be darker, while low densities will not be darker. In use, it is placed in a container containing the liquid. The value of the surface of the liquid actually provides the specific gravity of the liquid.

There are different types of specialized specific gravity meters named after their purpose.

a. Lactometers

b. Alcohol meters for wine and alcohol

c. Sugar meters

d. Barometer for tanning liquor in tanning

e. Urine meter for urine analysis

f. Acidity meter

g. Specific gravity meter for lead-acid battery cells

h. Salinity meter for salt-containing liquids

i. Temperature-specific gravity meter for fuel oil such as petroleum

Specific gravity meters are even used in soil analysis - a process for classifying fine-grained soils, clays, and silts.

For any type of liquid involved, the uses of a hydrometer are varied. Choose a hydrometer according to the industry laboratory in which you work.

Use of hydrometer

a. Check whether the specific gravity meter and the glass casing are broken, the rubber is not damaged, and the positioning hole is not loose before use, and confirm that it is good before carrying out the following steps.

b. Put the hydrometer into the glass tube and put the pipette in place. Note that the end with the scale is placed upward.

c. Squeeze the top rubber flat, then vertically put the tube in the measured liquid slowly relax the squeezed rubber hand, and the liquid is sucked into the glass tube.

d. When the liquid in the tube exceeds 1cm of the positioning hole of the specific gravity meter, stop absorbing liquid.

e. The scale of the current horizontal surface hydrometer is the specific gravity of the measured liquid.

f. If the specific gravity of the measured liquid is greater than or less than the specified value, we must re-compare the specific gravity of the liquid according to the ratio, and then measure again until it meets the specified value.

g. After the measurement is completed, clean the hydrometer with alcohol and store it well for the next measurement.

Precaution on hydrometer

a. When introducing the liquid, pay attention to the injection volume to prevent overflow.

b. After one year of use, the specific gravity meter should be calibrated by a third party before use.

c. Specific gravity reading, the general data range of each specific gravity meter is 0.100. specific gravity is related to temperature, the higher the temperature, the smaller the specific gravity, and vice versa, the specific gravity increases.

How to buy hydrometer?

ANTITECK provide lab equipment, lab consumable, manufacturing equipment in life sciences sector.
If you are interested in our hydrometer or have any questions, please write an e-mail to, we will reply to you as soon as possible.

    AntiTeck Life Sciences Limited

    A1-519, XingGang GuoJi, Yingbin Road, Huadu, Guangzhou, China, 510810
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