Boyle’s law: What is the deal with that? Did it support atomic theory of matter?

-Karthik Gurumurthy

The Irish Chemist Robert Boyle worked with his assistant Robert Hooke who developed a vacuum pump.  Boyle removed all of the air in a closed chamber and proved that air was necessary for transmission of sound and for candle light to burn. Boyle sealed the opening of the shorter leg of a J-shaped glass tube and then poured mercury into the longer leg.  This trapped the air in the short leg of the tube between the seal and the mercury. He continued to pour until the mercury in both the long and short legs of the tube was at the same level. Then Boyle poured thirty more inches of mercury int o the long end of the tube, in effect doubling the atmospheric pressure. The additional mercury compressed the air in the short leg of the tube to half its original volume. Thus Boyle had doubled the pressure on the trapped air and halved its volume.

Boyle’s law proved that the pressure and volume are inversely related. Decrease the volume of a gas and you increase its pressure, and vice versa. What was significant about this discovery was that this is the way a gas would behave if it were composed of a mass of freely moving particles, with empty spaces between those particles that allowed the gas to compress or expand. In other words, volume of a gas would be affected  by an increase or decrease in pressure if that gas were composed of atoms. The scientific observations behind Boyle’s law clearly supported the atomic theory of matter.