A variety of scales exist, and are used depending on the context. Hydrometers may be calibrated for different uses, such as a lactometer for measuring the density creaminess of milk, a saccharometer for measuring the density of sugar in a liquid, or an alcoholometer for measuring higher levels of alcohol in spirits. Operation of the hydrometer is based on Archimedes' principle that a solid suspended in a fluid will be buoyed up by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid.
Thus, the lower the density of the substance, the farther the hydrometer will sink. See also Relative density and hydrometers. An early description of a hydrometer appears in a letter from Synesius of Cyrene to the Greek scholar Hypatia of Alexandria.
In Synesius' fifteenth letter, he requests Hypatia to make a hydrometer for him. Hypatia is given credit for inventing the hydrometer or hydroscope sometime in the late 4th century or early 5th century. The instrument in question is a cylindrical tube, which has the shape of a flute and is about the same size. It has notches in a perpendicular line, by means of which we are able to test the weight of the waters.
A cone forms a lid at one of the extremities, closely fitted to the tube. The cone and the tube have one base only. This is called the baryllium. Whenever you place the tube in water, it remains erect. You can then count the notches at your ease, and in this way ascertain the weight of the water. In low-density liquids such as kerosene , gasoline , and alcohol , the hydrometer will sink deeper, and in high-density liquids such as brine , milk , and acids it will not sink so far.
In fact, it is usual to have two separate instruments, one for heavy liquids, on which the mark 1. In many industries a set of hydrometers is used — covering specific gravity ranges of 1. Modern hydrometers usually measure specific gravity but different scales were and sometimes still are used in certain industries.
Examples include:. Specialized hydrometers are frequently named for their use: a lactometer, for example, is a hydrometer designed especially for use with dairy products.
A lactometer or galactometer is a hydrometer used to test milk. The specific gravity of milk does not give a conclusive indication of its composition since milk contains a variety of substances that are either heavier or lighter than water. Additional tests for fat content are necessary to determine overall composition. The instrument is graduated into a hundred parts.
Milk is poured in and allowed to stand until the cream has formed, then the depth of the cream deposit in degrees determines the quality of the milk. An alcoholometer is a hydrometer which is used for determining the alcoholic strength of liquids. It is also known as a proof and Tralles hydrometer named after Johann Georg Tralles , but commonly misspelled as traille and tralle. It only measures the density of the fluid. This category of devices is designed to measure the quality of gasoline, kerosene, diesel fuel and other petroleum products.
The device allows you to determine the presence of impurities that reduce the quality of the fuel. They are used not only in industrial enterprises. An ordinary motorist can also purchase such a device to make it easier to determine at which gas station it is worth refueling your car. Refractometers are used in the food industry mainly in enterprises engaged in the preparation of juices.
The device allows you to check the ripeness of the fruit. With its help, the concentration of sugar in the test medium is measured. Motorists use hydrometers to measure the density of antifreeze and electrolyte. Less commonly used to measure brake fluid and gasoline. In the case of models for testing acidic liquids, the instrument is slightly modified.
Additionally, it has a large hollow flask, inside which a glass float with an appropriate scale is placed. On the one hand, such a device is narrowed or with a rubber nozzle like a pipette , and on the other, a rubber bulb is put on it to take a portion of the electrolyte. This design is the safest, since contact of acidic and toxic substances with the skin is undesirable.
Most car models are universal and are used to measure the density of different liquids. Since the float in a separate medium dives to its depth, the parameters corresponding to a particular liquid are plotted at different levels of the scale.
In addition to the above modifications, hydrometers are also used in medicine for measuring the density of some biological materials of humans , in cooking, in the food industry for example, a lactometer measures the fat content of milk, and a salimeter helps determine the suitability of water for food purposes and its hardness , as well as enterprises producing chemical products.
The device is a flask sealed at both ends. Inside it there is a metal fraction. Its amount is determined by the purpose of the device each liquid has its own density. A scale is applied to the flask, which allows you to accurately determine the desired parameter. Some hydrometers are additionally placed in a large hollow tube as is the case with the model for electrolyte. An additional flask is used to measure some hazardous liquids.
It is designed to take portions for example, car hydrometers make it possible to accurately take a small amount of electrolyte. This design prevents electrolyte or other toxic material from getting on the skin. Depending on the design and purpose, the second flask can be made in the form of a bottle with a long neck or in the form of a thick test tube with a scale applied.
Some models are made of dense transparent plastic that is resistant to aggressive acid and alkaline solutions. One of the drawbacks of glass hydrometers is that they are fragile, so a collapsible model must be properly stored in a case with separate cells for each bulb.
In this case, the float must be removed from the large flask and stored in special packaging so that it does not break. When purchasing the same type hydrometer, you should pay attention to the error it is indicated in percent. Most often, this parameter is very important for accurate measurements in the workplace. Also an important factor is the graduation of the scale. The longer it is, the more accurate it will be. Cheap hydrometers most often have a small scale, so the determination of the exact density indicator of electrolyte or antifreeze is complicated.
In order to make it easier for the motorist to determine whether the indicator complies with the norm, marks on the scale are marked with the minimum acceptable value red mark. The optimal indicator is marked in green.
Using the device is very easy. To determine the required parameter, the float is placed in a container with a solution. He should calm down, which will give the most accurate indicator. Homebrewing Stack Exchange is a question and answer site for dedicated home brewers and serious enthusiasts.
It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. I know how to use my hydrometer, and I know what numbers to look at and write down on my brewing sheets, but I'm not sure what those numbers actually represent, or even what units I should use to label those readings. What's the science behind the hydrometer? How are they calibrated? What else should I know about the theory of using one to make better beer?
In other words, if you put a ball, with volume 1 litre completely under water, there is an upwards force on the ball buoyancy or flotation equal to the weight of 1 litre of water. If we place a floating object of mass 1 kilo, it will displace exactly 1 kilo of water, or 1 litre of water. If the volume of our object is greater than 1 litre i.
So, with a Hydrometer, it is weighted such that the weight of the submerged volume at the 1. If we dissolve solids into the water sugar that volume of water is heavier, and less of it needs to be displaced in order for the hydrometer's weight to be matched, and the Hydrometer floats higher. The general principle is based on density. That is, less dense things will float on top of denser things. By analogy, imagine a human floating in a pool of water.
Now imagine a human floating in a pool of salt water- the human will float higher in the salt water, since the density of the salt water is higher. A hydrometer works similarly- it's just a marked glass tube that's weighted such that in water, it'll sit at 1. If you put it in something denser than water like wort, which is water with stuff in it , it'll sit a little higher out of the liquid, so it's at something like 1.
If your liquid is not that temperature, you want to run your measurement through a conversion chart to account for the change in density of liquids based on temperature. Heavy ships can float because of the principles of buoyancy.
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