The History of Physics from 2000BCE to 1945. Sheldon J.D. Cohen

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СКАЧАТЬ 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.

      ATOMS ELEMENTS COMPOUNDS

      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. Napoleon’s invasion of Spain forced him back to France where he did his most important work.

      Chemists of the time were trying to determine the proportion of elements within each compound. 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 different atomic masses, and it was these masses that differentiated one element from another. Dalton also said that atoms combine with each other in whole number ratios. As example 1:1, 1:2, 1:3, 2:4, etc. Since atoms were indivisible, it was impossible for a fraction of an atom to combine to form a compound.

      William Nicholson (1753-1815) was an English chemist who determined that the composition of a water molecule was two parts hydrogen and one part oxygen (molecule is from the Latin meaning small mass). When he passed an electric current through water, oxygen and hydrogen bubbled out. The mass of the oxygen was eight times the mass of the two hydrogen atoms. Since there were two hydrogen atoms in every water molecule, it meant that a single oxygen atom had sixteen times more mass then a single hydrogen atom. Dalton had actually referred to this as weight, but weight refers to the gravitational pull of a body by the earth and mass refers to the amount of matter contained in the individual atoms. Mass is the preferable term, but Dalton’s calling it weight has stuck and to this day we refer to atomic weights.

      Jons Jacob Berzelius (1799-1848) was a Swedish chemist who worked out atomic weights for hydrogen and many other elements. He confirmed that every element had a different atomic weight.

      Dmitri Ivanovich Mendeleev (1834-1907) was a Russian chemist who developed a table of elements with increasing atomic weights. He demonstrated that some properties of the elements repeat themselves in an orderly fashion, and these elements fall into the same column. This method of arrangement caused gaps in the columns that Mendeleev felt represented undiscovered elements. Time would prove him right.

      WHAT IS THIS ATTRACTIVE FORCE?

      Scientists continued to do work on the attractive force discovered by the Greeks (static electricity). Charles Francois Dufay (1698-1739) was the gardener to the king of France. In his spare time, he produced two types of electric charges when he rubbed different substances together. Working with glass, he discovered that some charged pieces would either attract or repel other charged pieces of glass. He called these two types of effects resinous and vitreous. He theorized that matter contained two fluids in a definite balance that was disturbed during the act of rubbing; each body acquiring either an excess or a deficiency of the fluids. Subsequently the terminology of resinous and vitreous for this unknowm mysterious force became negative and positive. The use of the word fluid would remain for about one hundred-fifty years, or until the exact nature of this mysterious force was discovered.

      In the mid 1700s, Pieter van Musschenbroek (1692-1761) a Dutch physicist from the University of Leyden, developed a means of storing static electricity. He half filled a glass container with water and sealed the top with a cork. He then pierced the cork with a nail that extended into the water. The exposed nail subjected to friction caused static electricity to be stored within the glass container. Discontinuing the friction, then touching the exposed nail, resulted in a shock. This was the earliest form of what would be known as the Leyden jar. It eventually consisted of a jar coated inside and out with tin foil. The outer tin foil connected to the earth; the inner tin foil connected to a brass rod projecting through the mouth of the jar. Charging one of the tin foils with an electrostatic machine would produce a severe shock if both tin foils were touched at the same time.

      It was possible to force a large amount of electric charge into the Leyden jar. In fact, if the jar carried a sufficiently large amount, even approaching a nearby object could discharge it and a spark would force its way through the air to the other object. When it did this, there were those who saw a resemblance to lightening. From this primitive beginning, natural philosophers developed numerous devices that created electric current.

      Benjamin Franklin (1706-1790) the great American politician, statesman, inventor, and natural philosopher, used a metal conductor to discharge the inner and outer layers of tin foil in a Leyden jar creating the clearly visible and audible spark. He was one of those who speculated about the similarity of the visible and audible spark to lightening. Could lightening be an electric discharge similar to the spark produced within the Leyden jar?

      To prove this hypothesis he flew a kite with a metal tip in a thunderstorm. He used wet hemp line, a conductor of electricity, to fly the kite and attached a metal key to the end of the line. From the key he attached a non-conducting silk line that he held in his hand. When he held his other hand near the key he drew sparks from it, thus proving that lightening was an electrical phenomenon with the same properties as the electric spark produced with the Leyden jar. Franklin was fortunate: the next two men who tried to duplicate Franklin’s experiments died of electric shock.

      The lightening experiments brought great fame to Franklin. Much of his success as a diplomat in France was due to his reputation as a natural philosopher. For the French knew that they were receiving one of the world’s leading scientific figures, and not just an American patriot.

      Franklin showed that the electrical experiments performed in a laboratory are related to the natural events of our world---lightening. Therefore, future natural philosophic studies of nature could not be divorced СКАЧАТЬ