Preface To Chemistry (1953)

like the elixir of life to cure all sickness and make men these early predecessors of our chemists were called Alchemists and their profession if we can call it that was Alchemy some of the Alchemists can their procedures were crude so very little of lasting value has come down to us from their work Alchemists were often bewildered by the outcomes of their experiments but such outcomes are easily understood by modern chemist one of the founders of modern chemistry was many discoveries have perpetuated his name but one of his most famous experiments was conducted with a simple piece of equipment a large burning glass with the glass he focused the heat from the sun's Rays on a tube containing some red powder floating on Mercury metal the heat decomposed the red powder briefly discovered that a gas had formed as the red powder decomposed he tested some of the properties of the gas he was thrilled to find that a glowing Ember held in the gas burst into flame and burned with unusual intensity Priestly had discovered one of the most important gases in nature but it remained for a Frenchman to offer an acceptation of priestley's observations it was Antoine Lavoisier who repeated priestley's experiments and conducted others he sealed some tin and air inside a glass flask and measured the total weight then he heated the flask containing the tin and air for several hours a coating of white powder formed on the surface of the tin during the heating Lavoisier reasoned that the tin must have combined with something out of the air that was in the flas if so there should be no change in the total weight to check his reasoning he again weighed the flask and found that the total weight had not changed laier explained that oxygen an element from the air had combined with another element in this case tin to form a compound this combining of an element with oxygen is called oxidation only a few elements were known in lavoisier's time today we know of nearly a 100 here in this periodic table the elements are listed each element has a symbol like o for oxy oxygen to stand for its name in this table there is much information such as the relative weights of atoms of the different elements teachers and technicians of today have a vast store of chemical information and experience to guide their work and the young people of today are learning the fundamentals from which may emerge new chemical discoveries tomorrow to them each new chemical experiment is a further step in learning to apply chemistry to practical problems every chemical compound is the product of a chemical change and chemical changes are involved in most chemical work the EXP prly and laier involves such changes here is another striking example the structor has placed some iodent crystals in a porcelain dish next he adds a piece of another element called phosphorus when the two elements iodin and phosphorus are brought together a chemical change occurs the compound phosphorus iodide forms this compound has characteristics that are different than either the phosphorus or iodin used originally problems about the compositions and uses of substances have led to specialization in chemistry here are three important fields of specialization that have developed inorganic chemistry originally dealt with the chemistry of minerals organic chemistry originally referred to the study of plant and animal products today the scope of these fields has broadened physical chemistry deals with the phys rely upon the chemical techniques of synthesis decomposition and Analysis let's look at some applications of chemistry synthesis for example takes place when two or more elements react to produce a compound as in the iodin and phosphorus experiment synthesis may also take place in nature minerals are compounds formed by synthesis to release the iron in this ore decomposition the opposite of synthesis has to take place in this smelter such a chemical decomposition is going on the metal is being separated from the ore chemists have different methods of decomposing a compound the instructor is demonstrating a method using an electric current I have these two tubes filled with an acid solution it's a common kind called hydrochloric acid now the the electrodes in the in the tubes are connected with a direct current power supply and when the current is turned on Phil would you mind turning that current on please the tubes fill fill up with gas like that because the current decomposes or breaks up the acid solution into its two elements hydrogen on this side and chlorine on this you can see that each part of the u tube is filling with gas at the same rate that's because the hydrochloric acid is made of equal unit parts of hydrogen and chlorine it's formula HCL H for Hy and cl for Chlor chemists build up and decompose many inorganic substances to produce materials that are more useful will you please shut down test us gas hydrogen now if I smell the gas I can tell by the very disagreeable odor that this is chlorine hydrogen on the other hand is an odorless gas besides color odor and taste there are other tests used in chemical analysis for example does this colorless solution contain any dissolved compound of silver we can find out if a white solid forms when hydrochloric acid is mixed with the solution and if the white solid dissolves when an excess of ammonium hydroxide is added silver is present there is the white solid when ammonium hydroxide is added the solid dissolves a compound of silver is present chemists long ago discovered the silver test in addition they have discovered hundreds of other tests which because of some color change or the formation of some characteristic solid tell the chemist which substance is dealing with this is qualitative analysis a chemist May however want to measure how much of a substance he has as well as find out what it contains an analysis to determine how much is called quantitative analysis to measure quantity in liquids graduated containers may be used like this tube called a buet some burettes measure as little as a fraction of a drop of liquid for measuring quantity in solids different kinds of balances may be used this is an especially delicate balance it can measure the pencil Le used to write this dot over the letter I the weight of any substance is just one characteristic property that may be measured every element or compound has many characteristic properties for example boiling point is an important property of liquid in this distillation equipment one liquid is being separated from another this is possible because the two liquids do not boil at exactly the same temperature the one with a lower boiling point is separated from the one with a higher boiling point by this process of distillation some compounds when dissolved in water have the property of conducting electricity here's an electric lamp that's all wired and plugged into an outlet right here now the lamp doesn't go on because there's no connection here when I make a connection the lamp glows here's some pure water in the glass I put the wires in the water the lamp do doesn't go on pure water does not conduct electricity now I'll add some table salt I'll stir it to make a solution out of it the lab glows a table salt solution does conduct electricity a solution of an acid will also conduct electricity acids have other interesting properties for example acids in solution turn blue litmus red here a solution of litmus is added to an acid solution the color changes immediately another group of substances called bases also conducts electricity when dissolved in water ordinary household lie as a base bases feel slippery to the a touch and they turn red litmus blue substances that cause red litmus to turn blue Are alkaline all bases and some salts Are alkaline and are called alkalis all bases contain one part called hydroxide this part consists of one atom of oxygen and one atom of hydrogen since all bases contain at least one part of hydroxide they're often called hydroxides alkalis have applications in industry and in Everyday Life Solutions of alkalis are used in the photographic laboratory for developing negatives and prints so far we've considered inorganic substances another large group of substances consists of organic compounds all of these contain the element carbon the first carbon compounds that chemists happen to study were associated with living things hence the name organ organic compounds all living things contain organic compounds chemists also produce organic compounds in the laboratory the preparation here is an organic compound called aetl salicylic acid its common name is aspirin the formula of any compound tells a chemist which elements are present and in what proportions the work of some organic chemists is especially concerned with Biology since their work combined biology and chemistry they are often called biochemists chemists produce many different useful products from the materials available to them plastics for example are made mostly from organic substances coal tar petroleum and cellulose Plastics are used in place of metals wood and other materials the industrial organic chemist makes gasoline synthetic Rubber and other useful products from petroleum synthetic fibers lead to improv textiles and increase the variety of our wearing apparel synthetic dyes brighten our surroundings some of the products of chemical research are used to condition and enrich the soil applied organic chemistry produces explosives that do the work of many men in obtaining materials from the earth and achieving other practical purposes further industrial uses of atomic energy depend upon learning more about the chemical elements formed formed as a result of changes in the nuclei of atoms chemists are helping discover more and more facts about these radioactive elements through such work the symbol of atomic energy is becoming a symbol of our age and all the while research in chemistry continues to point out New Horizons and new applications that may prove to be more important than any yet known by Looking Backward Through the Ages at the chemical work of other time s we can appreciate more fully the progress that has been made progress made possible by men like Priestly whose discovery of oxygen led to an understanding of chemical change and by laier who discovered the fundamentals of combustion through the relatively few intervening years chemists have learned how to analyze and synthesize vast numbers of substances and through discovery of more secrets of the elements and compounds our chemists of the future will provide products and procedures as yet undreamed of that will still further increase our standard of living in these ways we will achieve more of the values that lead to health and happiness