Cookbook:Cold Water Candy Test
When sugar syrup is cooked, water boils away resulting in a high temperature sugar concentrate. Hence, as the temperature raises so does the concentration of sugar within the solution. The nifty thing about cooking sugar is that the highest temperature it reaches can tell you a little something about how it will turn out once it cools down to room temperature. Often it is practical to use a candy thermometer how ever using the cold water test can be more fun (and dangerous). Note that the following temperatures are listed at sea level, as they are listed in most cookbooks, because of this actually using the cold water test can be a more reliable gage when making candy. Each test is completed by dropping a dollop of the hot candy solution in cold water (not room temperature), and then extracting the candy formed. Be sure to allow for a moment for the candy to cool before handling it to avoid getting burnt.
Sugar Concentration at approximately 80%
At this point there is a lot of water left in the syrup. When cooled in water it will create a liquid thread than cannot be easily collected.
This stage is proper for making syrup such as Chocolate Syrup but is not technically a candy.
Soft Ball 
Sugar Concentration at approximately 85%
At this point the syrup dropped in to cold water can be formed in to a soft and flexible ball. At this point the candy cannot easily support itself and will begin to run if left out.
This stage is proper for making items such as Fudge.
Firm Ball 
Sugar Concentration at approximately 87%
A little syrup at this temperature dropped in to a cold water bath will create a firm chewy ball that can support its own weight and will remain chewy.
This stage is appropriate for making candies such as Caramel, but please note this in not the same thing as Caramelizing.
Hard Ball 
Sugar Concentration at approximately 92%
At this stage the syrup solution will form thick ropy threads when quenched in cooled water. If a large enough quantity is cooled it will form a hard ball with little moisture.
This temperature is best suited for recipes such as Rock Candy or
Soft Crack 
Sugar Concentration at approximately 95%
When the solution reaches this stage the bubbles will become obviously smaller and more concentrated. The candy at this stage has a low moisture point and will create small flexible threads when dropped in the cold water.
This stage is optimal for recipes such as Honey Taffy or Salt Water Taffy.
Hard Crack 
Sugar Concentration at approximately 99%
At this point the moisture levels are nearly non-existent, it is also the highest recipe that will be used in a standard candy recipe, after this point you enter the region of caramelizing. A small amount of syrup, when dropped in to cold water, will become brittle threads and easily break when bent or dropped.
This final stage is used for creating Toffee and Hard Candy.