| Show A brief history of Chemi chemistry written b by W tor for C the ebaugh min mining ing ph review D wa lei M wa 1101 I 1 continued from last issue the next advance was brought about by john dalton an english quaker dalton applied the ancient atomic theory of the t greeks to modern conditions and evolved i the atomic theory which is still taught in our schools and colleges in brief dalton asserted 1 that when substances unite to t form new substances they do so in definite 1 proportions by weight and 2 that a substance A may unite with a substance B to 1 form two or more substances if we consider the weight of substance A to be fixed then t I 1 the weights of substance B which will unite s with it bear to one another simple ratios I 1 1 thus one part by weight of carbon can unite with une one and a third or with two and two i thirds parts of oxygen these weights bear to each other the simple ratio 12 dalton explained this peculiar condition by saying that matter is not infinitely divisible but if the subdivision is carried out far enough there will be obtained a particle of the substance which resists all further efforts at division such a particle he called an atom every element consists of homogeneous atoms of constan constant c weight these simple atoms may unite with atoms of the same or different kinds but they always do so in the simplest conceivable proportions this would explain the laws above enunciated for since the atoms are indivisible and have constant weight and since they can unite in one or more ratios it follows that the compounds formed must have definite compositions and must obey the law of multiple proportions as daltons dalfons Dal tons second statement quoted above is usually called quite a controversy over these laws was waged by Bert hollet and the latter proving that they were true while the former tried to show that the relative masses of the reacting substances caused them to unite ad libi tum but dalton made no distinction between the atoms of elements and compounds this final step in we development of the atomic theory was left to avogadro professor of physics at the university of turin certain facts observed while studying the relations between tile the densities and the combining weights of gases led avogadro to the belief that the so called atoms of many elements contained two or more particles if this were granted the observed facts would become amenable to the laws aeration era tion cl consequently Ion avogadro called the smallest particle of a substance which could exist and retain the properties of the substance a molecule and the smallest particle of the substance that could enter into a chemical combination an atom mole cules therefore are made up of atoms more recent investigations have demonstrated that mercury the alkali metals zinc cadmium and some other elements contain one atom to ane molecule the elementary gases like hydrogen oxygen nitrogen chlorine etc have two atoms to the molecule while phosphorus and arsenic have four and sulphur in some of its forms six atoms in each molecule the size of some of the molecules of carbon compounds is enormous speaking from the chemists point of view but the question may be asked how flow large are they when compared with things familiar to our everyday every day experience from physical measurements made JOHN DALTON by several methods quite different in their nature lord kelvin recognized as the foremost authority on physics in our day has estimated that were a drop of water to be I 1 magnified until it was as large as the earth a molecule of water would be larger than a base ball and smaller than a football in one cubic inch of air at a temperature of melting ice and under a pressure of one atmosphere there are present about molecules when it is remembered that each of these molecules contain at least two atoms and that there may be much free or empty space between these atoms a taint faint conception of the size of an atom can be obtain obtained el are these the smallest particles of matter of which scientists take cognizance in the light of recent developments in the study of the roentgen ray the cathode ray and the newly discovered elements radium and polonium we must admit that it is very probable that there exist particles of mat ter many thousand times smaller than the atoms above referred t to J j J thompson of london introduced this conception within the past few years if this be true and we can cannot not reasonably deny it certain effects observed in studying by means of the spectroscope the light emitted by substances heated to exceedingly high temperatures temperature 3 come within the realm ot of explanation it is conjectured that the atoms ot of these substances break down into smaller corpus cles and that these corpuscles corpus cles are of the same size and can carry equal charges of electricity what would this indicate that the atoms as we know them are made up of condensed corpuscle corpuscles corpus cles s and hence all our seventy odd elements may ie DC only the condensation densa tion products of an original primordial subs sub rance lance we must confess that in this paper the reader has been led far into the domain of nebulous hypothesis but abut nothing has been said that is without the warrant of men high in scientific circles the oft quoted truth history repeats itself receives another confirmation in this instance the early philosophers dreamed that the uni i verse was simple in its ultimate structure and built I 1 up their cosmologies cosmo logies accordingly the alchemist hoped to be able to resolve a base metal into its primordial constituent and then reunite the portions of this constituent in such a way as to form a noble metal the chemists of the early part of the nineteenth century thought that certain relations that existed among the combining numbers of the elements pointed to their being merely condensations of hydrogen or of some substance one half as heavy as hydrogen jean servais stas by his pains taking work vork upon atomic weights over threw the notion but now fifty years later the same conception backed by experimental evidence reappears appears re and finds credence among many leaders of thought can it be true tit it all matters is but the same primal substance only in in various states of condensation who will be the genius to demonstrate by an crucis that such 1 ie the case until such a proof comes we are forced to acknowledge that the theory olf of the complexity of the creators work has on its side tho greater part of the evidence the I 1 he concep concepion jon ot of the ultimate simplicity of matter attracts us strongly nevertheless the end |
