How to Make Stearic Acid

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Stearic acid is used in the production of paraffin candles to make them burn longer.
Stearic acid is used in the production of paraffin candles to make them burn longer. (Image: Photos.com/Photos.com/Getty Images)

Stearic acid, or stearin, is a derivative of animal and vegetable fats and is often used in the manufacture of candles, among many other uses. It is a waxy and very hard solid. Prior to its development around 1811, candles were made from tallow and were notoriously soft, smoky and smelly. By the middle of the 19th century, stearin was being mixed with paraffin to produce hard, long-lasting mass-produced candles that burned clean with no odor. Stearin can be made at home, but it is a lengthy process that may also be dangerous.

Things You'll Need

  • Tallow, usually beef
  • Large glass or enameled iron pot
  • Glass spoon or stirrer
  • Slaked lime
  • Sulfuric acid
  • Goggles
  • Plastic face mask
  • Heavy-rubber work gloves

Weigh beef tallow and add to the pot, then heat to a low boil. You'll need a total weight to measure other ingredients. Other types of tallow can by used, but animal fat has far more stearin content than vegetable fats. Stir occasionally until the fat is completely melted.

Add 3 oz. of slaked lime per 1 1/4 lbs. of tallow. Stir until mixed thoroughly and continue to heat gently until it thickens into lime soap.

Add 4 oz. of sulfuric acid to the mix, again per 1 1/4 lbs. of tallow. Be very careful with sulfuric acid and be sure to wear eye and hand protection. Stir gently and continuously until the fat separates from the tallow and rises to the top. Turn off the heat.

Once the stearin has cooled, it will be a solid cake floating on the liquid underneath. Carefully remove from pot.

Place the stearin cake into another pan and melt over low heat. Stir gently until all moisture has been removed.

Tips & Warnings

  • Beef tallow can be purchased at any butcher shop and many grocery stores that cut their own meat. Slaked lime, also called hydrated lime or food-grade lime, can be purchased at Mexican grocery stores (it's used to make tortillas) or garden-supply stores. Sulfuric acid, because of its dangers, must be purchased from an authorized chemical-supply retailer. It can also be found in household products, such as drain cleaners.
  • Sulfuric acid is very dangerous and can cause severe burns. It is highly toxic. Do not add water to sulfuric acid. Always wear protection when handling the substance. Dispense and dispose of according to manufacturer's directions.

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