# How can I obtain an apparent specific gravity, of a plastic bag?

I need to verify an Apparent Specific gravity of a plastic bag- like the type used for a food vacuum sealer. I'm not sure how to go about it. I think I have all the needed items; scale, water bath, even a vacuum sealer if needed. I just can't find the method, or the formula used to calculate. I even called the manufacturer of the bag I'm using, and they had no idea how they came up with their data.
Thank you for any ideas you can share with me.
Jodie

"Apparent" specific gravity means you're dealing with something that has trapped air, and so the bulk density of the object is lower than the density of small samples of the raw material.

the easiest way to do something like this would be to seal up your bag, getting "as much" air out as is possible/reasonable. Weigh the sealed bag on a precision scale (i.e., down to milligrams if possible). Use Archimedes' method -- submersion in a water tank, e.g. by anchoring it with a fine thread to the bottom -- to get the volume, then just divide to find the density.

This technique will be subject to substantial measurement uncertainty, so you should to several trials with the same sealed bag and average the results, and you should also probably make several samples and do (multiple) measurements on each one.