Although it was invented 400 years ago by Sanctorius, the thermometer has been a common household appliance for only a few decades. Beginning in the 16th century and continuing to this day, confectioners have used a more direct means of sampling the syrup’s fitness for different candies: they scoop out a small amount, cool it quickly, and note its behavior. Thin syrups will simply form a thread in the air. Somewhat more concentrated syrups form a ball when dropped into cold water, and the ball will be soft and malleable between the fingers; as the concentration increases, the cooled ball becomes harder. The most concentrated syrups make a cracking sound as they turn into hard, brittle threads. Each of these stages indicates a particular temperature range and suitability for a particular kind of candy (see box).