# Boyles law pressures?

## Main Question or Discussion Point

Hi, I'm doing a question about Boyles law, and I don't understand some of the units they are giving.

Initial pressure = 20kN/m^2 (gauge) = 20kPa (gauge)
Initial volume = 47 volumetric units

Final pressure = 120kN/m^2 = 120kPa
Final volume = ?

(The barometric pressure was 762mm Hg)

I don't understand the units 762 mm Hg, and why they say (gauge) in brackets. I think it has something to do with a manometer, but I'm only used to working with Pa so far.

I'm guessing volumetric units could be anything, because the units probably cancel out when you put them into the equation, so only the ratio between the initial and final volumes is significant?

Thanks

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I don't know about gauge, but 1 mm Hg indicates pressure exerted by pure and dry liquid mercury of 1mm high in a tube at 273Kelvin temperature. That tube is to be placed on 45 degree latitude of sea level.

101.325 kPa = 760 mm Hg pressure. It means that mercury column of 760 mm high will exert that much pressure under those above stated conditions. It's just describing pressure in term of the height of mercury column in the tube, nothing else.

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