Re: NANFA-- ppt vs. specific gravity

Sajjad Lateef (
Sat, 28 Apr 2001 12:05:26 -0500 (CDT)

On Sat, 28 Apr 2001, Bob Bock wrote:

> Does anyone know how to relate parts per thousand of sodium to the specific
> gravity of sea water? What specific gravity would water with a salinity of
> six parts per thousand have?

I recall that full strength seawater has 35 grams of NaCl per 1000 grams
of water. That means that 6gm/1000gm is 1/5 strength seawater. (I can't
find my chem book right now but I think that's about right).

I looked into specific gravity of seawater and calibrating hygrometers for
Moontanman some time ago. Do you still have those emails, Michael?

Specific means "per gram of substance".

Specific Gravity is the ratio of density of a substance to the density of
some other substance (usually pure water for liquids).
Spec Gravity = density(subs)/density(water)

Density is mass/volume.
Pure Water is 1000 gm/1000 ml or 1gm/ml. This makes calculation simple.

Just weigh 1 ml of liquid and it's weight will be it's specific gravity.
Specific gravity = (mass of liq in grams/1 ml) / (1gm/1ml)
Therefore, specific gravity of 1 ml of liquid = mass in grams.

Your hygrometer ought to display 1.035 for full strength seawater (if my
memory serves me) and ought to display 1.006 when you add 6 gms of salt to
1 liter of water (a standard teaspoon is 5 gms of salt).


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