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(subflood) wrote:

> Say you have 5 bottles of sal****er 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?

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