By PragyanSharma Polavarapu
INTRODUCTION
In the age of scientific discoveries which began about 600 years ago the scientists and philosophers like Copernicus, Kepler, Galelio and Sir Issac Newton made great discoveries in astronomy and mechanics with the aid of advanced mathematics. We may perhaps say that the later scientists turned their attention to other challenging branches –like science of heat energy and light energy and the vast new science of chemistry which tried to understand how the millions of substances on earth are formed.We are not discussing here the extraordinary discoveries in the life sciences of Biology,Botany and Medicine.
In the modern universities established in Europe 400,500 years back , serious and intensive studies in mathematics, literature and philosophy and in sciences were taken up. In addition lot of research in all sciences was carried out under guidance of great professors. There was always great respect for religion, spirituality and ancient philosophy among most of the scientists.
DEVELOPMENT OF PHYSICS AND CHEMISTRY DURING LAST 300 YEARS.
Let us concentrate on the progress of science during the last 300 years.In that time Dr Joseph Black(1728 – 1799) of Scotland was a famed scientist. He was professor of medicine and chemistry for ten years at University of Glasgow and after that for 30 years at University of Edinburg. He was a most famous physicians and was one of the founders of the Royal Society of Edinburgh and President of the Royal College of Physicians of Edinburgh. He was editor of the medical encyclopedia and was appointed as principal physician of the king .
It is said that students from other parts of Europe came to study under him and that students preserved his lecture notes for years to guide them and inspire them. He was not only a great professor but also was among the foremost inventors . His achievements are greatly respected in Scotland even today . The chemistry laboratories at the above two universities are named after him.
Though there was great scientific knowledge in those days the prevailing theories did not agree with modern views about matter and energy. There was no encompassing atomic theory to properly explain the the results of thousands of chemistry experiments being performed in the various university laboratories. There was no differentiation between chemical compounds and elements. Some very important chemical compounds were treated as elements. However many scientists generally believed in existence of atoms—the smallest unbreakable particles constituting all matter. Even ancient philosophers believed that only unbreakable minute particles created all matter in the world.
Scientists in Europe in those times believed in “five fundamental substances” which created all matter in the world. They named these fundamental substances as “Principles” . The five “Principles” were
(1)Water– considered as an element,
(2)Salts– the many salts found dissolved in sea water and some found also on land
(3) Earth–the mountains,hills and rocks,the sand and the vast land ,
(4) Fire, and
(5) Metals—the pure metallic substances of extreme purity and special metallic shine.
Scientists believed in “affinity” between some of these “principles” under certain conditions and due to this affinity different chemical compounds are formed
DR BLACK’S DISCOVERY OF LATENT HEAT AND SPECIFIC HEAT
Though a chemist Dr Black is more famous for his discovery of specific heat and latent heat in the field of physics . The invention of thermometer (the instrument to measure temperature) by the German scientist Fahrenheit in 1714 appears to have accelerated research in the science of heat.
Dr Black noted surprising facts in his two experiments (a) when ice changes to water and (b) when hot water changes to steam. He noted during several control experiments that
(1) When water/ice mixture in a vessel is heated the temperature of the mixture does not rise until entire ice is melted into water. We can observe that till all ice melts and changes into water , then only the temperature starts to increase. We now in modern science can guess the reason. Heat energy is used to lessen the attraction between the H2O molecules existing in solid state — to change their bonding to liquid state bonding. This utilization of heat energy cannot be noticed by thermometer as the energy is used as a kind of work to lessen the bonds between the billions of H2O molecules . The heat thus utilized in a hidden way is called “Latent heat of Fusion” of ice i.e. hidden heat energy used for melting ice.
(2) Similarly when already boiling water in , say a narrow neck bottle, is still heated for some more time— then also temperature of water does not increase above 100 degrees centigrade. The temperature, shown by thermometer, stays only at 100 degrees centigrade till entire water changes to steam. The heat energy being supplied is used for removing the mutual attraction between the H2O molecules and to convert all water into the free state of a gas. This hidden heat is called “Latent heat of Vaporization” of water.
The concepts of “Latent heat of Fusion”(ice to water) and “Latent heat of Vaporization”(hot water to steam) helped organize heat science into a highly organized mathematics-based discipline called Thermodynamics.
SPECIFIC HEAT
Dr Black proved that different substances( like metals, wood, rubber, stone ) require different amounts of heat energy to heat them in the same range of temperature . Suppose we take same weight of all these substances and heat them carefully and accurately in same temperature range ( say from 20 degrees centigrade to 40 degrees centigrade ).
It can be seen from such experiments that each substance requires a different amount of heat energy for the same increase in temperature. This individual heat energy requirement of different substances is a constant quantity and is called “specific heat” of that substance.
Dr Black like all great scientists of his time must have believed that all matter is made up of indivisible minute particles called atoms . The billions of atoms/molecules in a substance are held together by mutual attraction. The specific heat of a substance helps in exactly calculating the heat energy required by it to raise its temperature from one initial temperature to a required high temperature very accurately.
DR BLACK’S OTHER FAMOUS EXPERIMENTS .
(a) CARBON DIOXIDE.
Dr black realized that the common air all around us is also to be treated as a “principle” substance just like the other five principles–water, salt,earth, fire,metal.
He found that air contains very pure gases. He is the inventor of carbon dioxide which he called “fixed air”. The modern system of nomenclature for chemical compounds did not exist then. He obtained CO2 gas by strong heating of sea shells or by heating chalk(calcium carbonate) with dilute acid .CO2 gas had special properties— turning lime water milky and putting out a burning candle. He found that the air we exhale during breathing process also shows exactly the same property(of turning lime water milky and extinguishing flame). Thus he discovered existence of pure CO2 which he called “Fixed Air”.
(b) INVENTION OF MODERN LABORATORY BALANCE
In 1750, while still a student, Dr Joseph Black developed the highly sensitive “modern laboratory balance” (the analytical balance). It is a small sized laboratory weighing scale made of most delicate and clean metal parts. It had a metal beam balanced on a wedge-shaped fulcrum with metal pans hanging at the two ends of the beam. The balance was enclosed in a glass box .It had standardized metal weights. Everything was made of shining metal and manufactured with great accuracy. The balance could weigh even a grain of sand and because of its high accuracy this model of the balance immediately began to be used in almost all chemical laboratories of the world!
( c )HE WAS ALSO INVENTOR OF THE ELEMENT MAGNESIUM .
THE CONDITION OF CHEMISTRY IN THE TIME OF DR JOSEPH BLACK
At that time scientists were still unable to differentiate between elements and chemical compounds. They treated even some “pure chemical compounds” as elements. We can call those times age of “old science” as compared to our new science existing after discovery of electron!
But the incessant search for “pure chemical compounds” led to the discovery of more and more “elements”. Electricity was not yet discovered . All the following discoveries/inventions came only later—the atomic theory of Dalton, Avogadro’s theory of molecules, Mandeliev’s table of chemical elements,the modern system of Nomenclature of chemical compounds as per acidic/basic or metal/nonmetal radicals.
The gas laws and absolute temperature scale were not invented. The electrical cell, Ohm’s law , Faraday’s magnetic lines of force, Dynamo and Motor, Electrical nature of chemical reactions, Faraday’s laws of electrolysis, Discovery of spectroscopy and electromagnetic spectrum, Electrolysis of water—all these were not known and only came later.
Medieval scientists treated water and air as elements. We now know that water is a chemical compound called H2O and that air is a mixture of O2 and N2 –oxygen and nitrogen molecules. We know that in nature many pure gaseous chemical compounds like CO2, NO2, CO, SO2, SO3 exist.
Medieval scientists could not understand what combustion scientifically meant —from viewpoint of science of chemistry.They did not know the chemistry of candle flame, big fire, burning of dry wood or paper , burning of oil soaked cloth etc . They could not understand that flame was only a very hot region of visible chemical reaction of very hot gases reacting chemically.
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