Show 1 I J EXPERIMENTAL L CHEMIS TR 2 I I t ter r r IU First Year Chemistry r It is is is' often orten's orten s said id and anCl by those who hold the place of teachers i in their com community coni- coni corri- corri that the criterion of truth is the combined opinion of the majority t N Never ever was any opinion more erroneous and h d never was any stu study d y more calculated to dissipate this erroneous view than the study of chemical analysis and synthesis All the members members' of a a given community are surrounded by a avery r. r very complex heterogeneous environment yet one that is essentially the same f for an any given section Each person during his growth from childhood to tor r F r maturity gets certain fixed and definite impressions from the forms of matter which constitute his environment and as aSa a large arge number themselves find-themselves subject subject sub sub- t. t to s substantially y the same surroundings their impressions will in ill the main i ree ao agree with each other b v But our impressions received thus passively are not to be relied upon We become se seemingly familiar with the outside e forms of objects which seem fixed and unchangeable and wholly unlike each other there seems to be no relation for for- example between a piece of marble and nd a piece of chalk between a a piece of charcoal al and the diamond glittering on a la ladys lady's ys y's finger or between a shining silver coin and the dull ore from which it is extracted Yet even a superficial study of the analysis and synthesis of substances will show the existence existence existence ex ex- of such relations will even show that some of these substances are are almost identical in composition differing only in the manners of the combination combination tion of their constituent elements the time required and the amount of heat present at such combination The study of experimental chemistry shows that all known matter is made up of about seventy elements which combine in various ways to produce producer the various forms of matter with which we are more or less familiar These r elements unite with each other in definite proportions which for any two of them bear simple relations to each other This seems very simple yet it is exceedingly wonderful considering the multitudinous forms of matter which surround us This knowledge has been arrived at by means of operations many of which appear exceedingly simple but operations whose significance has become known only through years of patient application o on the part of the brightest minds the world has produced The old alchemists performed many of f these operations and obtained in many cases the same reactions which h x 3 w I Lila L c have become so familiar and so useful to modern science But they were under the false impression that had they actually produced b by y sue such h reactions t. t Ions J entirely new substances instead of only n new w combinations of the elements of Yi those with which they began To illustrate how these operations are performed and and the re results obtained obtained let us consider some simple and well well- well known substances First First st w water ter which has been een found as s every very schoolboy knows to to consist of oxygen and hydrogen hydrogen hydrogen hydro hydro- gen in m the proportions ns by volume of one part oxygen to tw two of hydrogen and by weight of eight parts oxygen to one ne of hydrogen By inverting two glass tubes over an open ope vessel of water with their mouths dipping below beloY the surface of the water in m the vessel and placing the electrodes of a an electric battery in the water beneath the tubes and then passing a current we may decompose the water the hydrogen collecting in one of the tubes and the oxygen in the other By measuring and weighing these gasses they are found to be in the proportions given above This is represented by the equation 0 O 0 which means that from one molecule of water we have obtained one of oxygen and two of hydrogen i. i e. e the two atoms of hydrogen hydrogen hydrogen hydro hydro- gen are equal in valence to the one atom of oxygen i Thus by analysis we have haye determined the composition of water We may now by the reverse process produce the water by effecting a combination combination combination tion of the two gasses This may be done by heating zinc with an n acid such suchY Y as hydrochloric or sulphuric and igniting the escaping hydrogen gas by means of a jet or by passing g a stream of hydrogen gas over heated copper coppert X t oxide The latter reaction is represented by the equation Cu 0 04 O Cu the products being water and copper Thus Thu by analysis and synthesis r we have hav proved roved that water is composed of the two elements ts oxygen and hydrogen in the given proportions and by numerous similar operations the law can be proved to hold throughout all the realm of matter We may take another example By dissolving calcium carbonate 4 limestone or m marble maible in hydrochloric acid we get a gas known as carbon diK dioxide dioxide di di- K oxide and compound a of calcium and chlorine and water Ca J Cl Ca Car r I Ithe In this operation the CO 02 escapes and by y bringing into r the solution of Ca ammonium carbonate we obtain again the calcium i carbonate But this product is not identical in form with the original marble t or limestone It is the same substance made up of exactly the same elements but under very different conditions The marble is the crystalline form of f the substance Ages of slow growth under favora favorable b Ie con conditions d h have ave b been een required to produce this beautiful material and these conditions are indispensable ble to its f formation Limestone and chalk are other forms produced by th thame the same ame combination of the same elements but under widely diverse conditions In this latter example it will be seen th that t we have taken only three of the 7 70 elementary substances so when we remember the multitudinous forms of limestone marble and chalk with which we are acquainted saying nothing about the fact that these ele elements unite with others in almost numberless ss ways 0 we can readily perceive how such v variety in nature results from the he combination combination tion of these 70 elements And we see also that only by the aid of experimental experimental mental chemistry J can we arrive at any knowledge of such combinations W. W G. G R. R |