Atoms & Light

Part 3 - Chemists

The Greek philosopher, Empedocles, (492 – 432 BCE) argued that all matter was composed of fire, air, water, and earth in various proportions. He thought stone contained mostly earth, while a rabbit had a more of both fire and water thus giving it life. This was an important theory as it was one of the earliest suggestions that substances, like stone, were a combination of different "elements."

Later, Democritus (460 BCE - 370 BCE), noted that broken pieces of stone never resembled fire, air, water, or earth, and reasoned that cutting a stone into ever smaller pieces would eventual result in pieces too small to be cut. He suggested these infinitesimally small fragments were indestructible and unique for each material and he named them atomos meaning indivisible. Unfortunately, two of the most famous philosophers of Ancient Greece, Aristotle and Plato, rejected Democritus' idea and it was almost 2,000 years before it was rediscovered.

In 1660 Robert Boyle, in England, realized that earth, fire, air, and water were not elements and proposed a new definition. Elements were basic substances that could not be broken down by chemical means. In 1643, Evangelista Torricelli, Galileo's invention of the barometer proved that air was capable of pushing down on a column of liquid mercury. This was an amazing discovery. If air, an invisible, odourless substance capable of driving sailing ships and windmills, had weight, it must be made of something physical.

Daniel Bernoulli, (1700 – 1782) a Swiss mathematician, proposed that air, and other gases consisted of tiny particles too small to be seen. He imagined that they were loose collections of tiny billiard-ball-like particles that were continuously moving around and bouncing off one another. When a human body moved through them, the tiny particles were pushed aside. He reasoned that these particles must be in constant motion otherwise they would settle on the ground like dust particles. Methane gas was first scientifically identified in 1776, by Italian physicist Alessandro Volta after reading a paper written by Benjamin Franklin about "flammable air." He collected gas rising from the marshes of Lake Maggiore and by 1778 had isolated the pure gas. He also demonstrated that the gas could be ignited with an electric spark.

In 1754, a Scottish medical student, Joseph Black discovered the gas carbon dioxide. For the first time scientists realized that there was more than one kind of air and quickly discovering new gases like hydrogen and nitrogen.

The French scientist Antoine Lavoisier knew these discoveries could debunk the Phlogiston Theory which claimed that metals were formed by heating ores with charcoal, a rich source of phlogiston. When those metals rusted, they were supposed to release the phlogiston, turning it into a "calx." Chemists could supposedly turn the calx back into a metal by heating it with charcoal. By carefully measuring the weights of his experimental materials, Lavoisier noticed that iron gained weight as it rusted. Air, or some part of air, was absorbed into the metal as it rusted. This same "air" also seemed to be absorbed by objects as they burned.

By 1774, in England, Joseph Priestley was experimenting with red mercury calx, a red solid stone, that had been coveted for thousands of years because when heated, it turn into mercury. When Priestley heated the calx, with sunlight through a burning lens, he noticed that a strange gas was released with the mercury and he carefully collected the gas in glass jars. He found that a candle in the gas burned with a vigorous flame and that a mouse placed in a sealed container of this gas lived longer than a mouse placed in a sealed container of ordinary air. The process produce the metal without charcoal! No source of phlogiston was needed. So he called the gas "dephlogisticated air," Priestley's discovery demonstrated that new substances could be formed by combining or separating various components.

http://www.mysteryofmatter.net/Priestley.html

Includes a delightful video of his discovery (nature's restorative) that plants produce oxygen while animal consume it.  Unfortunately you will have to type it into the URL line.

For two years, Lavoisier had searched in vain for the identity of this mystery gas, and when Priestley described his discovery over dinner in Paris in October 1774, he wondered if this could be it. Lavoisier began his own experiments with red mercury calx. Priestley's new gas, which Lavoisier would name "oxygen," from the Greek words 'acid maker,' was, "more breathable, more combustible and more pure than even the common air in which we live." 

He announced his findings with great fanfare at the 1775 Easter meeting of the French Academy of Sciences without giving credit to Priestley.

Coincidentally, in 1766, in Britain, Henry Cavendish produced "inflammable air" (hydrogen) by the action of acids on some metals and discovered that two parts of hydrogen when burned with one part oxygen produced water. He also dissolved alkalis in acids to make "fixed air" (carbon dioxide), which he collected in bottles inverted over water or mercury.

Lavoisier knew that acids react with some metals to release another highly flammable gas called phlogiston and he mixed the two gases (phlogiston and oxygen) in a closed glass container and inserted a match. The phlogiston immediately burned, and afterwards he observed droplets of water on the glass container. After careful testing, Lavoisier realized that the water was formed by the reaction of phlogiston and oxygen, and so he renamed phlogiston hydrogen, from the Greek words for 'water maker'.

Lavoisier also burned phosphorus, sulfur and other substances in air, and showed that they combined with air to make new compounds which weighed more than the original substances, and the weight gained was lost from the air. From these observations, Lavoisier established the Law of Conservation of Mass, which says that mass is not lost or gained during a chemical reaction.

In 1789, he published a list of the 33 chemical elements known at that time, grouping them into gases, metals, nonmetals, and earths. During the French Revolution, on May 8, 1794, Antoine Lavoisier was executed by the guillotine in Paris . . . He was 50 years old.