Re: How do you calculate specific gravity?

Terri,

Specific gravity is simply the weight per unit volume expressed [usually] in 
grams/cubic centimeter.

In the laboratory we use a device called a pycnometer for determining the 
specific gravity of liquids and solids.

In testing a liquid, the pycnometer is a small flask fitted with a hollow 
stopper. The liquid under test is placed in the flask and the stopper inserted 
fully [which causes an overflow]. The weight difference [empty-full] divided by 
the volume [provided by the pycnometer manufacturer] is the sg. If the volume 
is not known, repeat the experiment with water as the reference liquid [at the 
same temperature, of course]. using the sg of water as 1.0 [or go to the CRC 
Handbook for exact values] you can calculate the volume.

For solids, the pycnometer is usually a fully automated instrument. Lacking 
one, you need,once again,the weight and volume. The first is no problem and the 
second [volume] is usually done with a displacement technique by  adding the 
known weight of an unknown substance to a known volume of a non-solvent and 
reading the new volume providing, of course, that the unknown sinks and does 
not float.

Specific gravity remains one of the most fundemental tools of an analyst.

Ken Johnsen