Grease a large cookie sheet, set aside
In a heavy 2 quart saucepain, over medium heat, bring to boil sugar, corn syrup, salt, and water, Stir until sugar is disssolved.
Stir in peanuts
Set candy thermometer in place and continue cooking. Stir frequently until temperature reaches 300 degrees F or until a small amount of mixture dropped into very cold water separates into hard and brittle threads.
Remove from heat, immediately stir in butter and baking soda.
Pour at once onto the cookie sheet.
With 2 forks, lift and pull peanut brittle mixture into rectangle about 14x12 inches
Snap candy into pieces.