Understanding Specific Gravity
Breathe. This write up is intended to help those who are frustrated by volume versus weight issues. You do not need to be a math wiz or have a 4 year degree to understand specific gravity. It is actually a very fun science experiment that your kids will ask to repeat time and time again.
Tools you will need to do the physical tests include clear glass jars, water, various other ingredients and a little time.
Most people have heard the phrase "A pint is a pound, the world round." This is a flawed rhyme because it is only true for water and other items that have a specific gravity of 1. You are probably wondering what that means.
Here are some examples of various products and their specific gravity:
- Water has a specific gravity of 1.
- Orange essential oil has an approximate specific gravity of .89
- Glycerin has an approximate specific gravity of 1.21
- Sweet Almond oil has an approximate specific gravity of .92
Specific gravity can be defined as 1 fluid ounce of product has a weight of (insert numbers here) ounces. Please remember that when ounces are listed it means weight, not volume. Some authors do not understand this so you will see confusing information. Let's take our examples and figure the specific gravity.
Water has a specific gravity of 1 which means 1 fluid ounce weighs 1 ounce. Orange essential oil has a specific gravity of .89 which means 1 fluid ounce weighs .89 ounce. Glycerin has a specific gravity of 1.21 which means 1 fluid ounce weighs 1.21 ounces. Sweet Almond has a specific gravity of .92 which means 1 fluid ounce weighs .92 ounce.
When you purchase, or use, a product and the label says 16 oz, by law, it means 1 pound. If the label says 16 FL OZ then the product is sold by volume. If the product label says NET WT 16 OZ then this company is really with it! The label has told you the product was weighed, not just filled to a "fill line." If you purchase a bottle that appears partially full, check the label. You may find out the product was sold by weight not by volume.
To get a general idea if the product you want to test has a specific gravity of more than 1 or less than 1 you need a clear jar (mayo jar or canning jar), water and the item you wish to test. Fill the clear jar with water to about 3/4 full. Add a small amount of the product you want to test. If the product floats on top of the water the specific gravity is less than 1, if the product sinks to the bottom the specific gravity is more than 1. If the product disperses and you can't tell then the product is water soluble and not a great candidate for this test.
Try some syrup, a drop of fragrance, and other items. Do not mix multiple ingredients into the same jar of water.