Hydrometer: use and types

Hydrometer: use and types

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Density meter, also called an hydrometer, but the first term gives a better idea of ​​what this instrument is used for, which is said to have been invented by Archimedes (287-212 BC) or by Hypatia itself. What is certain is that in 1612 it already existed, because it describes it Galileo in one of his letters to Nozzolini and in 1648 he still appears in the lines of Raffaello Magiotti who describes him a Lorenzo de 'Medici. The hydrometer it is not a modern tool but it has been able to evolve and remains useful, let's see what to do.

Hydrometer: use

Also called hydrometer from the Greek ἀραιός which means little dense / diluted, combined with "-meter" hydrometer is used to measure the density of a liquid and is based on the thrust of Archimedes, you can hear it also called gravimeter but among the three, the latter is the least used term.

To imagine the appearance of hydrometers, let's imagine gods floats that must be immersed in the liquid whose density is to be examined. In this way, Archimedes' thrust is exploited to obtain the desired measurement. Let's remember what he discovered Archimedes: "Each body partially or completely immersed in a fluid receives a vertical thrust from the bottom up, equal in intensity to the weight of the fluid displaced".

At this point, therefore, blindly trusting this principle, we can determine the specific weight of the liquid reading the portion emerging from the liquid on the scale above the float or by evaluating the weights that contribute to floating the hydrometer at a level defined by a reference notch.

Going into the specifics is not possible here, because the densimeter can have various shapes, depending on the use but also on the era in which it was built. The Cimento academics, for example, they were made of glass with a graduated torch, with saucers or baskets hanging from threads and chains, or in a sphere, but we find other types of hydrometer that have little rings to add or remove depending on the liquid in which the instrument is immersed.

From second half of the eighteenth century onwards, more models of densimeter have sprung up from time to time designed for a specific purpose or liquid, in the manufacturing sector, for example, these instruments were often used to measure the specific gravity and concentration of liquids in different solutions. We needed to do it quickly, accurately and effectively. Among the experts in density meters we mention a Antoine Baumé (1728-1804) and a William Nicholson (1753-1815).

Density meter: types

We can divide the density meters in two main categories, based on their operating principle that can be at constant weight or volume, in the first case we have simpler and more immediate tools to use but certainly less precise than the second ones

A constant weight density meter it has a swollen and weighted lower part in the bottom while in the upper part there is a rod where we can read the density value, indicated by the level of the liquid marked at the point where it intersects the hydrometer rod. Obviously it is necessary to wait for it to stabilize to record the measurement.

The models at constant volume, more precise and complex, consist of a glass vial with a ballast on the bottom and a plate on top, which emerges. The density measurement can be read on the stem that connects the plate to the immersed body, there is a notch that must come to correspond with the level of the liquid by adding or removing weights. In this case the concept is that the density measurement is obtained from the ratio between the weights which we add to bring the meniscus level plus that of the saucer and the known and constant volume of the immersed part.

Optical density meter

The optical density meter is one precision tool which is used in specific areas where an estimate of the density is not needed but a precise evaluation. Its operation is based on the refraction of light and it is often used for measuring the salt concentration in the marine aquarium and for its relative density.

Density meter for beer

Also to measure the density of a welcome liquid such as beer, we use density meters often designed specifically for this purpose. They can also be found on the market, online, for those who produce craft beer. At 16 euros on Amazon we find a densimeter with precise double scale of density and alcohol content which can do for those who not only love beer but also make it at home.

Density meter with thermometer

There are devices that do not only do from densimeters but also by thermometers, especially convenient for aquariums because they allow you to evaluate the parameters that interest us in a single shot. At 15 euros on Amazon we find a hydrometer thermometer of good quality for those who want to monitor the density and temperature of the water in which their fish wallow without having to maneuver an instrument that is too complex.

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