Daniel Emery, age 13, of Jersey Shore, Pa., for his question:

WHAT IS NITROGLYCERIN?

Nitroglycerin is a very powerful explosive. It is the principal ingredient of dynamite. In its pure form, it is a heavy, oily liquid as clear as water.

When nitroglycerin explodes, it expands to form gases that take up more than 3,000 times as much space as the liquid.

The explosion of nitroglycerin is about three times as powerful as that of an equal amount of gunpowder, and the explosion speed is 25 times as fast as that of gunpowder.

The explosive is made by slowly adding glycerin to concentrated nitric and sulfuric acids. It was discovered in 1846 by an Italian chemist named Ascanio Sobrero. At first it could not be depended upon, but in 1864 a Swedish chemist named Alfred Nobel came up with a detonating cap.