|Wisdom from grandma can help us to determine the freshness of eggs.
This is useful in selecting eggs when you are in the market.
Fresh eggs, when held to the light, the white will look clear, and the yellow distinct; if not good, they will have a clouded appearance.
The shell will be almost transparent.
When eggs are stale, the white will be thin and watery, and the yolk will not be a uniform color, when broken; if there is no mustiness, or disagreeable smell, eggs in this state are not unfit for making cakes, puddings, etc.
From "The National Farmer's & Housekeeper's Cyclopedia," 1888
You can use this method at home.
To determine the exact age of eggs, dissolve about four ounces of common salt in a quart of pure water and then immerse the egg. If it be only a day or so old, it will sink to the bottom of the vessel, but if it be three days old it will float in the liquid; if more than five it comes to the surface, and rises above in proportion to its increased age.
From the book, "The Hearthstone," 1887