# What are some common mistakes students make when measuring gas pressure?

Jul 5, 2018

Given the plethora of gas pressure units...mistakes are routine and inevitable...

#### Explanation:

One of the things I cannot account for is the persistence of the $\text{psi}$...$\text{pounds per square inch}$. What the f... is that? And there is also an issue with $\text{psi}$, and $\text{psig}$; the latter is $\text{pounds per square inch gauge}$, and the ZERO reading on this scale is $1 \cdot a t m$ or $\text{32 psi}$...And so a reading of $1 - 2 \cdot \text{psig}$ is a bit over one atmosphere.

I think these days the preferred pressure measurement is $\text{1 bar}$, where $\text{1 bar}$ is almost an atmosphere... Chemists traditionally used the $\text{atmosphere}$, an accessible and meaningful unit...especially so as a mercury manometer could be set up to measure pressure AT or below $\text{1 atmosphere...}$

And $1 \cdot a t m \equiv 760 \cdot m m \cdot H g$... Of course, these days the mercury manometer and the McLeod gauge have all but disappeared from modern laboratories. At least we won't die now!