WHAT IS LIGHT?
The Greeks were also responsible for the first enlightened discussion on the subject of light. Prior to their serious evaluation of this phenomenon, the world was content to accept God’s pronouncement: Let there be light: and there was light. Light was the antithesis of dark. Because of it, all life on earth was given the gift of sight. But what was it that caused our eyes to perceive the world around us when the sun or the moon or fire allowed us to see? What did our eyes do that allowed us to visualize distant objects? Did our eyes emit something that sped rapidly to a distant or nearby object, and once having struck the object caused us to see it, or did light issue forth from any luminous object and reach our eyes, and in doing so give us a visible world?
Pythagoras (582-500BCE)
championed this latter thought many years in the past.
These conflicting theories only served to raise many more questions. If light entered our eyes enabling us to see, or if something left our eyes giving us the same ability, what was it that entered or left? What about its size? What does it weigh? Very little, no doubt, if it has weight at all? What is its speed? Why does it pass through some objects and not others? Why does cloth block light and thick glass allow it to pass through?
These questions would remain unanswered for centuries, and the solution would be intimately connected with the development of the atom theory that the Greeks so brilliantly propounded.
THERE ARE ATOMS AFTER ALL
Boyle (1627-1691)
was born in Ireland with a silver spoon in his mouth. His father was the richest man in the British Isles. Boyle, to his credit, put this financial blessing to good use and took advantage of the opportunities that money opened up for him by becoming a renaissance man. The combination of brilliance and financial resources allowed him to pursue a full time “hobby” studying religion, philosophy, mathematics, languages, and the physics of such pioneers as Descartes and Galileo.
Descartes (1596-1650)
is considered the father of modern science when he refused to accept any ideas that could not be proven by experimental proof as opposed to the assumptions and emotions that served early scientists. He is remembered for his mathematical approach to physics helping to establish it as a firm discipline requiring proof as opposed to conjecture.
Galileo (1564-1642)
was an Italian scientist who concentrated his work on the physics of motion and astronomy. He postulated that the planets of the solar system did not rotate about the earth, but rather rotated around the sun raising the ire of the church in Rome who pronounced him a heretic and forced him to renounce his theories publically.
Back to Boyle
His natural philosophic work included an improved vacuum pump that allowed him to make excellent vacuums; and in so doing he demonstrated that air was necessary to sustain life, that sound would disappear in a vacuum, and a candle would stop burning as the air was evacuated.
His main triumph, so familiar to all students of chemistry, was the volume-pressure inverse relationship. Boyle used a J shaped glass tube closed at the shorter end and opened at the long end. When he poured mercury in the tube, air trapped in the closed short end. The more mercury he poured in, the less air seemed to be trapped. He made many measurements at atmospheric pressure and also at lower and higher then atmospheric pressure. He determined that when the pressure on the air was increased by the addition of more mercury, the volume of the air decreased, and when the pressure on the air was decreased the volume of air increased.
This was the pressure-volume inverse relationship and it lent credence to the atomistic theory; if air is made up of widely separated atoms, suggested by Democritus, this would explain the fact that air was lighter than solids where the atoms were closer together. Placing the atoms of air under pressure would push the atoms closer together, thus decreasing the volume of the air.
It all made sense under the atomistic theory. Others could easily reproduce Boyle’s experiments, and the concept of atoms gained the upper hand, finally vindicating the Greek philosophers.
Boyle’s work also laid the foundation for ending the concept of air, fire, earth, and water as the basic four elements. Boyle said speculation as to the basic elements served no purpose and an element was anything that could not be broken down further by chemical manipulation. Chemists then started on the trail of elements and eventually it was determined that gases, such as oxygen and nitrogen were elements, and iron, copper, gold, silver, and the mercury used in Boyle’s experiments were elements.
This led to the definition of a compound (latin meaning put together), which was any substance put together by a combination of elements.
Joseph Louis Proust (1754-1826)
was born in France and trained as a pharmacist. He taught and did research in Spain for twenty years until Napoleon’s invasion of Spain forced him back to France where he did his most important work. He was an analytical chemist and defined the law of definite proportions stating that substances only truly combine to form small numbers of compounds each of which uses components that combine in fixed proportions by weight. Chemists of the time were trying to determine the proportion of elements within each compound. Proust experimented with copper carbonate and separated it into copper, carbon, and oxygen in a ratio of five to one to four. No matter how he did the experiment this was the result. If he added more of one of the elements in a greater proportion then there ordinarily would be in the compound, he founded some of the element left over. He found the same thing to be true for other compounds he worked with. They always had a fixed amount of elements in a definite proportion. He named this the law of definite proportions, and other chemists confirmed his work. Berthollet (see below) eventually had to admit that his concept was wrong and Proust’s was right.
Proust’s work supported the concept of the indivisibility of atoms.
The French chemist…
Claude Berthollet (1748-1822)
stated that the compounds could vary in composition depending upon the amount and proportion of the reactants used in the formation of the compounds.
Proust experimented with copper carbonate and separated it into copper, carbon, and oxygen in a ratio of five to one to four. No matter how he did the experiment this was the result. If he added more of one of the elements in a greater proportion then there ordinarily would be in the compound, he founded some of the element left over. He found the same thing to be true for other compounds he worked with. They always had a fixed amount of elements in a definite proportion. He named this the law of definite proportions, and other chemists confirmed his work. Berthollet eventually had to admit that his concept was wrong and Proust’s was right.
Proust’s work supported the concept of the indivisibility of atoms.
John Dalton (1766-1844)
was an English chemist who worked with gases and discovered that different gases could have different proportions of the same elements. For instance, the substance carbon monoxide had one part carbon and one part oxygen, while the compound carbon dioxide had one part carbon and two parts oxygen. (mon is a Greek word for one and di is a Greek word for two). He called this the law of multiple proportions, although each compound followed the law of definite proportions. He agreed that all chemical elements were composed of atoms, and each atom of an element had the same mass, whereas different elements had