specific gravity

Nov 01, 2004 4 Replies

I'm learning about specific gravity and I need a little help.



Say you have 5 bottles of saltwater solution. You know the percent of salt each bottle contains and it's specific gravity. For example:


5% = 1.050
10% = 1.080
15% = 1.120
20% = 1.150
25% = 1.200

Now what if you had a bottle that contained an x% of salt but it's specific gravity was 1.100. How would you calculate how much percent of salt the bottle contains?


Anything with a substance dissolved in water, be it salt, sugar, or whatever, that has a sg of 1.100 is always always always 10% by weight, not volume.

The engineer in me wants to plot a graph from sample points and then extrapolate the % for SG=1.100 from the chart. The numbers presented here are not consistent. Are these your real readings? If not, do you have real readings?

-- WB

Looks like 12.5% to me.

You could interpolate between the points. For example, taking the points either side of where SG 1.100 would appear you have:

10% = 1.080 15% = 1.120

Assuming a linear relationship, SG 1.100 is half way between SG 1.080 and 1.120, so the % salt would be half way between 10% and 15% - i.e. it would be 12.5%.

Of course, this only accounts for the two points and assumes a linear relationship. You could fit a curve or line to *all* your points (a better method) and then deduce the appropriate value. Fitting a line to your points and forcing it through the origin (0% salt should be SG

1.000) you get: SG = 0.0079*%salt + 1

Rearranging, %Salt = (SG - 1)/0.0079. So SG 1.100 should be 12.7% salt.

HTH, Ben

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