+ Submit your article here

What are Hydrometers?

11/18/2013 8:12:09 AM | by Anonymous


Hydrometers are scientific instruments used to measure the density of liquid as well as the specific gravity. The specific gravity is usually based on the Archimedes' principle of buoyancy. It is composed with a sealed glass bulb together with a long tube that is skinny and connected to only one end. After which, it is weighted with mercury or lead shot under the bulb in order for it to float upright. The tube portion is later labeled with the scale so that whenever it is placed in the liquid, the measured gravity will then be seen. The instrument will typically be calibrated for use with liquids at various temperatures. The scale on it will also vary depending on its intended use and function.


The Archimedes' principle of buoyancy states that whenever as object stays afloat on liquid, it is being lifted up by the force that is equal to the weight of the liquid that is displaced by the object. This means that the lower density will cause the hydrometer to sink in the liquid sample more. Similarly, when an object with higher density would mean that there is a greater force to lift the bulb higher in the liquid.


In order to use the hydrometer, the first thing that needs to be done is to pour the liquid sample into a glass cylinder that is tall enough to contain the capacity or a similar container. The hydrometer is then lowered and placed vertically into the liquid with the bulb end facing down so that it will bob and float in the sample. The depth of the bulb floatation is then measured with the scale on the neck of the tube. The reading should be taken at the plane of the water level and not at where the liquid would cling up at the side of the neck. The scale is typically measured in terms of specific gravity, with the range not falling below 1 to a little above such as ranging from 0.95 to 1.05


The ratio of the specific gravity of a liquid is the liquids mass to an equal volume of pure water. In simpler terms, it is measured by how many times lighter or heavier the liquid is when being compared to water. Since the ratio is measured in terms of mass, the specific gravity will then have no units. For example, the specific gravity of 1 would infer that the liquid would have the same mass and density as the same volume of pure water. If the measurement is however less than 1, the liquid is considered to have a lower specific gravity and is generally less dense.


Since the density of liquid changes with temperature, it is now know that the hydrometer will be typically calibrated to be used with liquids only at the specific temperatures. Traditionally, a hydrometer will also be calibrated to measure the specific gravity. This is done by the use of density of the water at 4 degree Celsius. This is due to the fact that it is at the point where the pure water reaches the maximum density.

In recent times however, it is generally more common these days for the hydrometers to the calibrated at temperatures such as 15.5 degrees Celsius or even 20 degree Celsius. The calibration will then be labeled on the neck of the tube and the liquid sample will then be at the calibration temperature whenever the measurement is taken.


On top of that, there are various different types of hydrometers. They have different scales that vary depending on their uses and functions. A typical hydrometer that has heavy liquids will usually have scales that start at approximately 1 or slightly above. For liquids that are lighter, they might have scales that start well below 1. The battery operated hydrometers also often comes as digital models that measure the specific gravity of battery liquids. They can be utilized to determine the condition and charges of a specific battery. Other types of hydrometers would also include alcoholometers. They are used to measure the terms of proof of alcohol. Saccharometers are also present in the measurement of density of sugar in a sugar solution.


Are you sourcing for a product or service?

Do you need a quotation?