Elements (Robert Boyle)
The Greek concept of elements was popular for almost 2200 years and was the guiding force behind the alchemists' search for ways to turn cheap metals such as lead into gold. In 1661 the English scientist Robert Boyle raised an important objection to this model. In his book, The Sceptical Chymist, Boyle noted that it was impossible to combine the four Greek elements to form any substance and it was equally impossible to extract these elements from a substance. He therefore proposed a new definition of an element that became the basis for the modern definition of this concept
Boyle's definition of an element was based on the observation that many substances can be decomposed into simpler substances. Water, for example, decomposes into a mixture of hydrogen and oxygen when an electric current is passed through the liquid. Hydrogen and oxygen, on the other hand, cannot be decomposed into simpler substances. They are therefore the elementary, or simplest, chemical substances. Thus, as Boyle pointed out, an element is any substance that cannot be decomposd into a simpler substance.
Boyle's Law (Robert Boyle)
Torricelli's work with a vacuum caught the eye of the British scientist Robert Boyle. Boyle's most famous experiments with gases dealt with what he called the "spring of air." These experiments were based on the observation that gases are elastic. (They return to their original size and shape after being stretched or squeezed.) Boyle studied the elasticity of gases in a J-tube similar to the apparatus shown below. By adding mercury to the open end of the tube, he trapped a small volume of air in the sealed end.
Boyle's law is based on data obtained with a J-tube apparatus such as this.
Boyle studied what happened to the volume of the gas in the sealed end of the tube as he added mercury to the open end. The table below contains some of the experi- mental data he reported in his book, New Experiments Physico-Mechanicall, Touching the Spring of Air, and its Effects. . ., published in 1662. The first column is the volume of the gas in the sealed end of the J-tube, in arbitrary units. The second column is the difference between the height of the mercury in the sealed and open arms of the J-tube, to the nearest ±1/16th of an inch. The third column is the product of the volume of the gas times the pressure.
Boyle's Data on the Dependence of the Volume of a Gas on the Pressure of the Gas
|Volume||Pressure||P x V|
Boyle noticed that the product of the pressure times the volume for any measurement in this table was equal to the product of the pressure times the volume for any other measurement, within experimental error.
P1V1 = P2V2
This expression, or its equivalent,
P a 1/V
is now known as Boyle's Law.
|History of Chemistry|