Scientific Method and Chemistry Help (page 2)

By — McGraw-Hill Professional
Updated on Aug 28, 2011

Melanosis, Leukosis, And Xanthosis

Alchemists thought color was a basic property of a metal. In their attempts to make gold, they decided that they had to first get the golden color. To do this, they performed a three-step color changing method called melanosis, leukosis , and xanthosis . These three steps in the method worked to bring a yellow-gold color to base metals of very different colors.

Melanosis, leukosis, and xanthosis alchemy procedures were performed in a device called a kerotakis . Figure 1.1 shows how a kerotakis might have looked. In the kerotakis, a metal sample like copper was placed on a screen in a tall container. Sulfur was added and the entire container heated by a small fire in the base. When the sulfur was hot, it acted on the metal. Condensing sulfur-containing sulfides settled out. A sieve, like a spaghetti strainer only flat, held back pieces of unreacted metal, while a black compound collected at the kerotakis bottom. This mixture was heated in an open container to remove any extra sulfur.

Scientific Method and Chemistry Melanosis, Leukosis, And Xanthosis

Fig. 1.1. A kerotakis device used a divided chamber with a furnace to provide heat.

The metal blackening was the first step in the process of melanosis. It was thought that a metal’s original color was removed through this process. Since, melanosis darkened the metal’s original color, alchemists thought they had banished it.

Following the blackening stage, another compound like arsenic sulfide was added to whiten the copper. This second step was called leukosis.

The third and final color-changing step, xanthosis, called for the addition of a calcium polysulfide solution (usually made of lime, sulfur, and vinegar). Mixed with the whitened copper, the solution was heated until the metal’s surface took on a tinted, yellow color. This step gave the golden color that alchemists bragged was the newly formed gold.

Alchemists thought that heating base metals with sulfur caused the freeing of gold from a metal. They thought that when they got the golden color, they had gold. Since a lot of the rulers didn’t know any better, the newly made gold gained alchemists acceptance for a while.

Other alchemists, eager to please those in power, thought they could create gold from other base metals such as lead and zinc. Ambitious rulers, looking for ways to fund their war machines, sponsored many of these early attempts.

Alchemists became the new superstars. Those who made wild claims they couldn’t deliver, were permanently benched. Others made progress. Crystallization and distillation of solutions began to be understood and used as standard practice. Many previously unknown elements and compounds were discovered.

Alchemists often used the image of a serpent catching its own tail as a way to symbolize the unity and convertibility of the elements. Early alchemists used the signs of the planets, to which they thought the elements were connected, as symbols for metals. This is illustrated in Figure 1.2 .

Scientific Method and Chemistry Melanosis, Leukosis, And Xanthosis

Fig. 1.2. Symbols of the planets were used to identify metals.

Other Areas of Science

Other areas of science were advancing now, and in 1543 Nicolas Copernicus made a hypothesis based on his observations of the planets. He thought that the Earth and planets rotated through space around the Sun, not the Earth, as was commonly believed at that time.

 A hypothesis is a statement or idea that describes or attempts to explain observable information.

Copernicus believed that from the Sun outwards rotated Mercury, Venus, Earth (with the moon rotating around it), Mars, Jupiter, and Saturn. This strange, new hypothesis wasn’t well accepted since everyone knew that the Sun revolved around the Earth. Even the alchemists wondered how different metals might be affected.

 An experiment is a controlled testing of the properties of a substance or system through carefully recorded measurements.

In 1609, Galileo Galilei tested Copernicus’ hypothesis with a home-built telescope (there were no factories then). He took measurements and recorded data that confirmed Copernicus’ hypothesis. Galileo discovered the key to valid research, experimentation . Curious about how things worked, he recorded his observations with respect to changing factors such as time, angle in the sky, and position of the Moon, Sun, and stars. His observations and calculations led to the discovery of the four satellites of Jupiter in 1610. As a result of his experiments, Galileo is thought of as the founder of the scientific method .

Antoine Lavoisier (1743–94) insisted on accurate measurements (which we will discuss more in Chapter 2) and developed a theory of combustion. He determined that combustion results from a chemical bonding between a burning substance and a component of the air (which he named oxygen), to form something new.

 A theory is the result of thorough testing and confirmation of a hypothesis. A theory predicts the outcome of new testing based on past experimental data.

Lavoisier found that liquid mercury when burned in the air became a red-orange substance with a greater mass than that of the original mercury. He also showed that the original mass of mercury could be regained when the new substance was heated.

mercury + oxygen ⇒ mercuric oxide

Along with experiments by Joseph Priestly, Lavoisier discovered that the air was composed of several different components, including nitrogen, instead of one all-purpose gas. Curious about what was in the air that added to combustion, he performed experiments with other gases. These experiments showed that nitrogen did not support combustion even though it was a component of “air.”

In experiments with water, Lavoisier found that water contains hydrogen and oxygen. He was also the first person to arrange chemicals into family groups and to try to explain why some chemicals form new compounds when mixed. Due to his experiments, Lavoisier is said to be the father of modern chemistry .

Following experimentation in many fields such as astronomy, electricity, mathematics, biology, chemistry, and medicine, data were recorded that showed how nearly everything could be studied and predicted through a series of successive observations and calculations. When the same results were repeatedly obtained by a variety of experimenters in different laboratories in various countries, a particular hypothesis or theory became a law .

 A law is a hypothesis or theory that is tested time after time with the same resulting data and thought to be without exception.

John Dalton developed the law of partial pressures in 1803. Dalton, interested in the Earth’s atmosphere, recorded more than 200,000 atmospheric findings in his notebooks. These observations prompted Dalton to study gases and from the results of his experiments explained the condensation of dew and developed a table of the vapor pressures of water at different temperatures.

By extending these experiments, Dalton proved that the total pressure of a gas in a system is equal to the sum of the partial pressures of each constituent gas ( P total = P 1 + P 2 + P 3 + ...). He was also the first to publish the generalization that all gases, initially at the same temperature, expand equally as they increase in temperature.

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