Specific Gravity

[jordan102]

Hi all,

Specific Gravity is defined as (density of fluid) / (density of water @ 4degC & at 1atm).

Does the 'density of the fluid' of interest have to be at the same temperature of that of water (i.e. 4degC) to get an accurate specific gravity figure. I think it does and my calcs kinda prove it, but the internet is full of contradictions, just just wanted to check here if anyone knows for certain

Sames goes for specific density of gas .... whether the density of gas has to be at the same temp and pressure as the reference density of air at STP

 

[3DDave]

Answer to the last question - it does not. That's what allows warmer air to rise - it's specific density is lowered by the increase in temperature.

But - it depends on your use. If you means does is specific density is a reference density that is at Standard Temperature and Pressure or if it is the specific density at the instant of interest. The first will be in a text or other reference book, the second will not.

 

[IRstuff]

For the purposes of bulk selling, all liquids and gases are sold by normalized quantities; otherwise, you'd get a better deal on some days than others.

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[rb1957]

wouldn't specific gravity be for the same conditions ? It could be that the density of water is "unaffected" by temperature, so then the change to other conditions would depend only on your fluid.

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