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Les cartas, planches, tableaux, etc.. peuvent ttre film«s A des tsux de reduction diffArents. Lorsqus le document est trop grand pour Atra reproduit en un seul clichA. ii est filmA A partir de I'angia supArieur gauche, de gauche A droite. et de haut an bas. en prenant la nombra d'images nAcessaira. 4.es diagrammes suivants illustrant la mAthode. 2 3 5 6 A^/tr a^jits:;^ / » ^-J *".u*- Sntietiitu of torottto. -H,:':- PAPERS nan •'»» CHEMICAL LABORATORY. "-'-'-■I'V'- ■ ^i-;: ^Wi'./^/ . , No 20.— Chemical and Physical Reactions. ■BY W. LASH MILLER. Ph.D ^.C. ■U: Hcsri?n«4 from " Jo»r*»J of the omai.o EdnonttonsI Asuoctation, April, 1904. ■ " «»V ', - TORO'^TO, 1902. .ii&^m 'a ' ■ i..lf. m r ■^■i ' CIIKMICAL AND PHYSICAL KEACTIONS. By W. Lash Miller, Ph.D., F.R.S.f, Tokoxth. .V I'liiK-r llMul HefoiT lhi>. .Viiril Jml. V.f'i. Ill tl.f last few years it lmn bocoiin' .|iiili! tlic I'liHliion for phywi- cista aii'l chemists to write lM)oks on tlie pliiiosopliy of their resnect've scii^iiccs, and hwt year tlie climax was reacheil when •[ the Iwst known of tlie Oerman 1'rofes.sors of ("lieniistry. in ic, havinj; been ;;rante utely on the .s,.le of the .,| agnir.Ht he new_,„en who Koruinely M,evc .„ the theory in which they have lH..en brought up. and who nmy Jm, relied ufK)u to a.lvancu and defend any absurdity if only .t affonl a chance of e«;ape from the l.gic of their opponent. An excellent ex,u„ple is afforded by th- contest In^tween the Ihogiston theory ,i„.l th- present theory of combustion, which t.>ok place at the end of the eighteenth century. In spite of the n-lvanUges o the n.odern view, obvious enough now. the Phloj^is- ton theory d.ed hard. Some of its adherents pooh-poohed all arg..n.ent.s based on the use of the Ulance. on the ground that this WHS a "physical ' instrument, and ought not to be bro *. i,„o •i purely chenncal controversy Others endowed I'hlogistoi. with negative gravity, others again identified it with hydrogen-anv- Inng bu. give it ..p. Priestly, the discoverer of oxygenrremained steadnu.t o h.. last ; a I'hiogistonist he was bom. a^d « Phlogi,- tonist hi' ilied. " The secmd point made by .,ur philosopher is: That the order of .l..seovery, on which so much .lepends. though settle.l in some ca.ses by chance, and,,, many cases by pecuniary and economic condi- ons. in general o lows this law. namely, that the most striking Ueiaost wonderful, phenomena are tvken up first; the common pluce and the uninteresting have to wait. Of all chemical phenomena the most striking are certainly those ocomhastion with the evolution of flames, light and heal; and .«cord,ngly, we hnd that the first chemical theory w,vs the Phlo-' g.s,.,n theory, or Flame theory. Its downfall was' brought alt b^jn.. study ot comparatively obscure reactions of me^ury and After combustion, the reaction between acids and bases has attracted the attention of chemists perhaps more than anTleT nth.s,arl have a mixture of .sulphuric aci.l and water, some l.tmus, a sturer, and the bulb of a thermometer ; in the burette is ^1 l"^«.arptaseof the ,^id .lisappear: the thermometer rise.s. the l„,u,d e.xpands (two pints do not make a ,,uart when one is t on ,.s tak.ncr pkee. .S.Jdenly the red color of the litmus dianges to blue, the .smell of ammonia is noticeable, and the th r mometer ceases to rise, although ammonia is still flowin.. into the cylinder— the reaction is over. " ,-j-,^,.i-A;'r^. 3 Tlir iiiori! thin I'L'iictioii wiin Htililicii tlif more wiirnlcrs wrvv iUh- covtTfil. We lit-^iui witli aininoiiiit ;;u.-i nml wattT, iiml (lii|iiiil| Biilphuric acid mill water ; if watiT In' rfiiiovcii I't'oiii tlit- cniiti'iitH uf tliL- cyiiniler a Holiil will reiiiAiii. Mcasiiri'iiu-iit of tlic >|uaiiti- tie.s of ociils and alkaiios wtiioli react toj,'etlicr led to tlie law of coinbiiiatioii in rccipnical pro|Hjrti<)'is: tliu law of coniliiiiation in multiple pro|iortiunH Huon followed, tu explain wliicli tlie m-IiuoI- uiaNter of Manclu'ster s4et uji Ids Atonuc theory, one hundred years ftf;o — an extraordinary theory, based on exti-aorilinarv factn. Orijjinally invented to explain tin' law of inulti]>le pro|X)rtionM. th' Aton.ic theory sihmi Iwcaine the fundamental dot'trine of 111 try. The hi>;hest aim of chemistry was to heconie the "inv. !<• ;c8 of the atoin.s." In the cylinder we .saw the htilihlin;; lii|uid, the risin^r thermometer, the chanu'e of color We are invited to believe that what was "really" there was: a whirl of atoni.s and molecules, attractinj; and rejiellinj; one another, rusliinj; post one another, collidin<;. uniting; to;;ether. A littk universe in the cylinder ; an astronomical system on the small scale. You have read, no doubt — perha|is in some Commentary on 'le BiHjk of Joshua — of the tremendous i|uantity of heat that would Ix! generated if this earth should suddeidy stand still; or, worse, should colliile with some other planet. The heat of condjustion of dozens of earths "f coal would be nothinj; to it. When the ammonia planet c(, dos with the acid planet in the ivstrniiomical 8y.stem in the cylinder, a similar quantity of In at mu.st obviously lie fjeneratdd : it is only be .use tho.se planets are as small as the others are larjje, that we have escaped with cur lives ! Thomson, of Sweden, and Berthelot, of Paris, were the first tu call attention to this consec|Uence of the " mec'ianies of the atom.s." " Every genuine chemical reaction must be aeconipauieil by evolu- tion of beat " — using words liorrowed fr(>m the science of mechanics, Berthelot baptizcil this jirir.ciple the ' Ijiw of Maximum Work." Nov, Thomsen was a Northern chemist ; but Berthelot lives in Paris, were it is execrably hot in the summer time, and every time he put a bottle of cliampagne on ice he must have been reminded that there are reactions which are icconipanied by a very consicl- erable — and a very grateful and comforting — iihsi>ri>tion of heat. Lest it should escape his notice, this fact was peatedly pointed out to him by others, some of whom were perhaps a little too much inclined to jeer at his law of maximum work. But Berthe- lot hud a reply. He silenced all criticism by distinguishing m'\m mi b«tw««'n " chemical " iiiid " physiciil " n-iictioim. Sucli mictioim itn the chiiiijje of ic- into wiittr, of water into nI.iiiii, iiii.l of Malt iiikI water iiiU) hriiiu, .lo not coine into tlie province of the law of lom- binaticm in multiple pro|M)rtiont*, an.l tlu-y are in ll.it ..pinwition to the law of niaxiniinii work ; so Berthelot reml theiii out of the party, and .linieil their ri^'hl to he ciille.l chemical. When we speak of this celehratea chemist " silencing all opismi- tion " to his law of maximum work, these wonln may U- tak.n, I am Horry to say, in a very literal sense. Iksi.les Iwiiu},' a chemist, this remarkahic man was a politician, and has occupied the |K)si- ti'.n not oidy of liead of the I)e])artment of Kducation, hut of Minister of Koreipi Affairs of the French Kepuhlic. His word was law '•. all that concormil apjxjintmonts in chemistry in the I di- versity of France, and more than one hrench chemist has found that opiKjsitioii to the scientific views of the pow«;rful Minister meant exile from Paris. For them, the law of maximum work read " Maxinmm Work and Minimum Fay " in a .listant part of the provinces, far from the boulevards of Paris where we have pictured the Heail Chemist of France keepin;: himself eoinfortahle durinjj the hot wc athe- hy the help of a heat-absorhint,'— and therefore non-cheiii' laclion. Uniler somewhat similar circumstances Galileo ii canted, consol- in" himself with the reHeetion that his words would not utfect the motion of the earth But these men were teachers; a sin-,de jier- funetory recantation would not serve in their case ; they were called ujMin to temli wli it they iH-lii'ved to be false. If they had consented the motion of the worlil woulil have been perceptibly retarded. Leavin<{ the chemi>ts and returniu}; to chemistry, Berthelot's views met with fair success. Kverywhere we find the majority a'Tced that to boil water is not a " chcmic.d " process, neither is it to dissolve sui;ar in one s tea. Ice and water, water nv.<\ steam, are "the same thing," and in the l)rine both salt and water are present " unchanged." Can one not if the water ' and Ingle the salt ? The physicists, too, were satisfied. The reactions ejected fro-' the " otlici>d tabernacle " of chemistry founl ..t the nhywcist ju.Mt iiH previous to Ijivc.isier tlie l..ilam-e was iiii.l the Hij;,. ,/x W.IH ivs clmracteriHtic of a work on physics as II, <> is of one „n ch.n.istry. How much the times luiv.. ehan-e.l can U, s-en (rom this lftntern-sli,le.» I'hi. c-haM-e came al->ut in n very natural manuer. Some levolhca.le,! manufacturers in place ot settnij; their chomists at w,.rk ai.«-overinK ue comiK,UM.ls, wh h m.-ht or miKht not prove serviceal.le to them .. . m .liscovere I t...m instead to tin.l the K-st n.etho-ls of making; pr.KUlC. t reaiy known, for which there was ahva.ly a m ■ Ket -.n-l thus a new prohlem aros,. in chemistry; to Ix.. soU •: ....ly l-y siu.ly.uj,' the inrtuences that modify the nMure and v' '♦'f'^s ol the pr... ducts of chemical reactions, an.lt r.vtes at wh, h -hey tak.. plac- ; -for time is money in a elMiuic. . tory as well as etsewher.. This was the very pr..l.le.ii that Ke^nault an.l (Mausius ha.l solv.-,l for the channe of water iiit.j steam. One of the m.M famous of the early experinuMiters in the n.'W .lirection was a ch.'n.ist who stu.lie.l the l.ehavior of a ^real many substances at very hii;hten.p.fature; his favrrite pu'Ce -.t appar- atus was a whit..-h.,t plaliiunn tube. This n.an went by the appro- priate name of Deville. His most important .liscov.ry was that many .snUtances, water for instance, which are rea.lily forn.e.l Irom their el. nients at ordinary temperatures, are dec..mp..s.Ml nito their ele.a.M.ts agai.. at a white heat. That, in fact, the n-action 211 f20 =H () i^ a " reversibl. •" reacti. m the same sense that the reaction " water = stean. " is revers.ble ; the <,ue substance turns into the other, or the other into the .m.v .l.-pen-hn;; on th.- temperature. .... i This discovery was a sta-;«erer to the law ot .nax.mum work. When water is forme.l from its elements heat is jr.ven out : when it is .lecomposed heat is absorlx.d. If b..th pl,...u.me,m w.n- to be regarded as " chemical " reactions the law ha.l to U- repeale.l. I shall not "o into .letails as to the .letermine.l attempts that were ina.le t.ruph..ld the majesty of this particular law. the last struggles of the phloKintonists a hundre.l years a-., w.;re not M'h„to«rapl. ..f .. iwge of vat, UaiV •• Matlu-ntafs, he thenm-." ri—h^li* ^-;:JJ^c^; 6 more in^niuus iukI ]>eniisteiit. But t)iu iiuw facts bnjiight to light in the course of the argument have gradually made it clear to every one that the reactions studied by Deville are not isolated, exceptional cases ; but that, under suitable circumstances many of the best known " genuine chemical " reactions are as capable of taking place in either direction as are the physical reactions : Wm r = ice; water = steam; water + salt = brine. The factors that determine the direction of the reaction — tem- perature, pressure, concentration — are the same that affect the physical reactions just enumerated ; and lastly, while the theory of Clausius has proved copable of predicting the direction and the yield of particular reactions under given circumstances, the Atomic theory cannot even " explain " the formulas and equations by which this result is accomplished. This seems to me a very striking cir- cumstance ; everyone who has used a "4cey" knows how easy it is in general to solve a problem when the answer is supplied. And so, with heavy hearts, perhaps, and some of them later than others, the chemi.sts took to buying Clausius' works and then books on the calculus, as a preliminary to understanding him ; a bitter dose for those among them who had all their lives " thrown physics to the dogs," and whose higher mathematics were limited to the expression D — x. But, needs must ! and now they are writing books on the same lines themselves. You remember the lantern slide ? Naturally enough an " anti-atom " party has arisen. " The mechanics of the atoms raised a barrier where none .should exist," they say, " A la Itniterne with the mechanics of the atoms!" Of course, it is possible to go too far in this direction also, and perhaps the Germans need to be reminded of their own proverbs : " When emptying the bath don't throw out the baby," and " The scum is at the top, and the dregs at the bottom, but the Ijeer is in the middle." The past hi.story of the science however encourages us to hope that if there is any baby at all, or any Ijeer, the chemists will succeed in finding them. I have endeavored to give a short account of the history of the distinction between chemical and physical reactions. There was thought to be a ditfercnce of kind, it is now known to be one of degree onlv. 7 At the doso of the paper an experiment* was shown, illustra- ting the reversibility of the reaction, 2SbCl, + 3H,S = Sb,S, + 6HCl. An antimony solution was prepared by dissolvin}; 2 <{rammes of tarUr-emetic in 20 cc. of hydrochloric iicitl sp. gr. 1.148, and dilut- ing with 80 cc. of water. (a) Paased a little H.jS into 5 cc. antimony solution - — > (6) Added 15 cc. hydrochloric acid (sp. gr. 1.148) - - < — (c) Added .') cc. antimony solution — > (d) Heated over a Bunson burner < — («) Cooled again in a dish of water -> (/) Added 10 cc. liydrochloric acid < ~ {g) Saturated with H.jS under 4 atmospheres pressure — > (A) Reduced the pressure to .50 mm. (by a filter pump) < — NoiB.— Tlie arrows indicati! the diruotiiin of the reaction ; — > meaning pre- cipitation of Sb,S„ and < formation of antimony chloride from the sulphide and hydrochloric acid. • W. LaHh Miller and F. U. Kcnrick, Lecture Experiments, Reverailile Chemica Reactions. Jour. Aimr. Chum. Sor. xxii. W\ (IIMK)).