![calculate volume of gas in a tank calculate volume of gas in a tank](https://i.ytimg.com/vi/5rK0nPWdGk4/maxresdefault.jpg)
![calculate volume of gas in a tank calculate volume of gas in a tank](https://media.nagwa.com/156176784184/en/thumbnail_l.jpeg)
The two numbers in blood pressures are in units of mm Hg. In case you're curious one of the places where it's used is to measure blood pressure. But since it's just measuring pressure we can use mm of Hg as a pressure unit for other things, not just barometers. So the height of mercury, read in millimeters, in a mercury barometer tells us the amount of pressure applied by the atmosphere. Torricelli chose mercury instead because its density was much greater than that of water which required a much smaller barometer whose height would amount to less than 10 centimeters at atmospheric pressure. However the density of water is so low that it would result in such a high liquid height that it would make the barometer impractical to use. So if you're designing a barometer the most convenient liquid would probably be water. Without getting too much into the math, the greater the density of the liquid the smaller the height of the liquid in the tube. The actual numerical height is determined by Jurin's law. Now the type of liquid you choose also determines how high the liquid level rises to specifically it depends on its density. So what the barometer is really doing is measuring atmospheric pressure based on the height of that liquid. The more force applied to the liquid's surface, the higher the level inside the tube rises. Essentially what happens is that the liquid is forced into the tube by the pressure of the atmosphere pushing on the liquid's surface.
![calculate volume of gas in a tank calculate volume of gas in a tank](https://www.hagra.nl/glossary/convertors/horizontal-tank-level-volume-calculation-theory.gif)
Placing that tube with the open air into a body liquid will result in some of the liquid flowing into the tube and reaching a certain height above the rest of the liquid's surface. The way a barometer works is if you have a thin tube closed at one end with all the air evacuated from it so that it is a vacuum inside. The definition itself it based on the mercury barometer which measures atmospheric pressure. It's also called a Torr after Italian scientist Evangelista Torricelli who invented the barometer. Yeah mm Hg (millimeters of mercury) is a unit of pressure.