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Ne* rork 14609 (716) 482 - 0300 - Phone (716) 288- 5989 - fox USA ' i tiHh T- i r i N i - -i M M i iiii m i Kinni ai i i w i i i ii ■!—■<[■> CHEMICAL LAWS: A SUPPLEMENT ' ro GOODWIN'S TEXT BOOK OF CHEMISTRY r-i I TO [{ONTO: THE COPP. CLAKK CO., LFMITED, PUINTEHS, COLBORNE .STREET. 1893. .•f.'li I' k I [Mi i^fi ,.:„„.n..l iu.-nlir.u' to A.'t ..f tl.e IMrliamei.t of C'anu.la. i.> Uu- year one thousand .•i;:l.t lnn..l.L..l aiul niiutv-tliri-e, l.y Tiik (V.it, Ci-akk CoMTANY (LiMiTKii), Ti)roiito, Ontario, of Asiricultnre. the Ulliif of the MiTiistir PKEFACE. In the following pagt-s tho princijKil cheinicHl laws are developed independently of theories. DoiihtleHs the iiiental bias con.se«|uent upon the hal)itual use of theory will appear here and there. In the writer's teaching exi)erience he has found that when chemical laws are presented in the usual way ah)ng with cheniical theories, there conunonly results a wrong idea of their relations. The principal object ..f this short treatise is to emphasise the truth that chemical laws are generalisations from facts, and can he considered a)iart from theory. \V. L. (JOODWIN. Queen's Univeusity. Kingston, Out., March 21)th. 18!)3. rf*» K.I ■:% CONTENTS. 1. ClIKMUAI, C'llANtiK. 2. 'I'm. Law ok CnMUiMN'i Wkkmiis. :\. TnK Law <>k (Jah Dknmiv. 4. riiK Law <'K Stkcikk' Hkat. '). TllK l.AW OK ISOMOIIMIISM. <), 'I'liK rKiiioiHf Law. 7. Uevkksai. ok Chkmmai. ('han<;k.s. 5. llAom.Ts Law. <» Van t'Hoki's Law. CMKMKAI- LAWS. 1. A Chemical species iiu-iiKles nil portions of tlie KHine kind of Iiouio^^mmicoiis sulmtunw. Pnn^ .suit, sugar, watcu-, ;;;oI(l, iron, and oxvi^'cn aro exain|tlt's of elu'niioal species. When a suhstunci! crystallises, the crystals ur« the iwiividua/s of the species. Clieinical species are cither eletnents or compounds. When substances nndergo such a change that they di.sappear and become other species of substance, a 'He.nical cliauffe, or chetnical action, hius taken plac«'. Cheudcal changes are of several kinds : — (1) CoMlUNATlON. — Two or more substances (chenucal species) combine to form one. (2) Simple dkcom position. — One substance (s|)ecies) gives rise to two or more different substances (species). (3) DouHLK I) Kf'OM POSITION or Mktatmksis. — Two sul)- stancea exchange one or more of their (elements, so as to foi-m two new substances. (4) liKPLAcKMKNT or Slmwtitutiov.— On,! species re- places one or more constituents of another. This replace- ment may lie accomj)anied by the union of another por- tion of the replacing species with the replaced, as when chlorine replaces hydrogen in hydiocarbons. It not only takes the place of the hydrogen, but also forms a com- pound, hy«''••>' in|«'.^ition), a suh.st.i.hv .lim'.rnt in its pro- luM-tieH .l//(-»(r>,.;//m |Miiiic)ii i)f \^\ to -j.'M (or ;{ x 7 7) to form nuli)liH tt'ioxi '.((. If lOO I Ih),hi'ii us tlic coiiiliiii- ins,' nmnl>«r tor Imi 1, tlji-n 77 l»..c.)in«s tlnil of oxyi^nii, and \')-\ tint, of Hiilpliiir. Hut Ifa.l forms other com pomitls with oxy;,'fH. in oii«" of which, lf(uiperoxliie,t\umi are l')-4 partH of oxygen for every 100 of lead. This Inid.s to a douhf as to whidi number should he chosen for tho cornhining number of oxv''en ; and the dillicnltv in- creases as elements are examined which combine with other elements in a lar;,'e numlter of dit!(M-ent proportions. It is now th(! universal practice to refer the combining numbeis of the elements to / part hi/ m-ight of hijilrv ini ; and oxygen must be Hrst «^xamined. But hydrogen forn»s two comj)oun«ls with oxygen. imUr (1:6), n\n\ hi/ frinj^.n fM'.ro.cili' (1:10). Hliall H or I »i be fukeu as tin; combin- ing miml)er for oxygeti f The s.iiuo dithculty appears when compounds are studied. For example, hydrogen combines witli acetylene in two proportions forming ethi/leio; (I of hydrogen to 13 of acetylene) and ethane (I of hydrogen to Oj, of acetylene); there is thus a choice betweiiu I ."J and G^. Up to tht^ middle of this cen- tury, this ditHctdty existed and le.i to great confu.si(Hi, hh different ciiemists used ditferent combining numbers and » employed tiie same symbols* to represent them ; so that the composition of the same compound was re(»resented by different formulas. Tliu.s, Ag,,(J, AgO, and AgO.^ were all u.sed to indicate a compound compo.sed of silver and oxygen in the proportion of 108 to 8. h is evident that this ditticulty could not have been surmounted bv mere study of the proportions in which substances react. I . * SyinholM are lettt^rs (•hnsi'i! to represent the comhininjr vi'p;ghr« nf the e!e- nients. FDtmulax of coiiiikjuiuIs are ol)taine(i tiy coinl)ininjf these syiutwU no a.s to represeiu correctly the composition of couipoumls. TllK LAW OF t^AS |)I;NSITV, .}. The Law of Gas Density*.— It is clear, too, that if soiiH! systematic way nin Ik; fomi-l lor choosing the coinbiniiij,' wei<,'lits of conipnunds, the problem will at the same time; he solved for elements. Kor, let th(n-e he taken as the comhining weight of any element the sinal/est weight of it found in tlie comhining weight of any of its con.pounds. Now, it has been foun.l that a very simple law connects the physical an.l clieniical properties of gaseous substances. The following table will make clear the nature of this law : — Sjieiitic Wi'ij.'lils. (Air-1.) ! 11. Hvdrochlorio Acid (Ka**) WjittT (ill tlie Ki^stMiuH state).. .\iiimiiiiia ( 'ailHin nioxidt' ( 'ailxiii .Mdiioxiclf Mfthiiiif Kthaiic Kthvltne .\cci\lciif riij ii-ltT •M-r> IH 17 44 •28 Ki »» 28 S6 III. Combining VVeij;htf!. >) or lb f)ii, lHori; •22 or 44 14 or 28 8 or 1(( 1!") or 30 M or 28 13 or 2(> In order to l.iing out the relation between these num- V)ers. calculate the specitic weights to the same scale as tiie coml)ining weights. Tliis can be done by taking 30-5 as the; specilic weight of hydrocliloric acid and multiply- ing all the other numbers in the column by ,%^g4. This, of"coui-se, preserves the ratio between the speciHc weights, but refers them to 3G-r) of hydrochloric a(;i.i instead of 1 of air. These nund)ers have been placed in column II. of the table. Small fractious are neglected. It is at once evident that, if the right choice is made, the sjyeafic ' "• ,;,,. I>,;,.it!> is use.l xs a «i-..eral wvm for the s,HTirtc weight of a substance In the ^'aseoiis state. It is convenieiit. if not Muite eorreet. and THE LAW OF -eferred to hydrogen. The combining weight of hydrochloric acid is thus 36-5. As specitic weights of gases and vapours are generally referred to air as unity, it will be convenient to derive anecpiation for calculating the combininir weight (C) of any compound gas or vapo"" from its specific weight ((/as tlensiti/) S'. Accoiding ,,j the convention — C : C : : S : S' : and for hydrochloric acid gas C Substituting these values — 3(;-r), and S == 1-2G5. n tj 36-5 : C 1-2 Of) and When the specific weights are referred to hydrogen as unit, a very simple relation a|»pears between S|iecific weights and conjbining weights. The specitic weight of air referred to hydrogen as standardis iiA'.ib nearly. Dividing the former value for C by this number, ■> i I jj) THE LAW «»K ining weights ot the dements in the compound, these combuung weights huvin- all the accuracy which can b(^ attained by exact wei.ddu.'sof liquids and solids in analytical operations. A few examples will make clear the manner in which the method of <,as d.asit,, is applied to the selection of combining numb.n-s for the elements. A vast amount of labour has been expended in determining accurately the composition of water. For I part by weight of hy.lrogen water has 7-98 parts of oxygen. It remains to .li.scover what multiple of the latter numb.-r is to be taken as the combining weight of oxygen. In the following table tlun-e are given, neglecting small fractions, the specihc weights (air= 1) a), combining weights (IL). percentage of oxv-ren (111.), and the .piantities of oxygen in the combining weights (IV.), of a number of gaseous or .rasiHable oxvg.'n com. rounds. The numbers m the last column are calculated as follows : — Specitic weight of gaseous water, 0-6L>:i, multiplied by 26'87 gives its combining weight — 0-G-23x2887 = l7-!)8b01,say 18. TUB t,AW OK <1AS DENSH V. 11 Analysis (if watt'i- shows tluit 88-iS'J /^ of this (or 1 oDS, say 1(5) is oxviicn :- — - ~ -- - ■ — CoMPOiNns. (. 11. in. I\. WilttT C'arlxiii iimnoxidt' Ciirlxin ilioxidf N'itroy^i'ti inotio.xifle . NiirfiKcii (lioxiile Nitroircn tctroxide Sulpliiir (lioxiiie ('•f.23 ll-'.N17 1 ■.■.li4 1 •r.-_'7 1(141 1 TiS 2-23 2-77 IS ■IS 44 44 30 4C) 64 80 . .^7•l4 f.3'3 , 71 Wi 6(1 ; It; itj 32 16 16 32 32 Sulphur tiii)xi(li' 48 The smallest quantity of o.Kygen found in the couil)ining woii^'lit of any of the oxygen compoiunls is thus sfM'ii to Ix' in. Tn all the lar^^e nunihei' of oxygen coin|>()unils siiliniitt('(l to this test no smaller ({'lantity has lieeii found. Therefore, 1() is the approximate comltining weight of oxygfU. The aecurate oouil>iiiing weight is 7''J8x2 = The numl)eis determined hv the method of una density and cormctfjl hij a reference to the composition of coni- pomulsas deter 1)1 ineil hi/ ana/ijsis, di'peml for their accura(;y on the analytical int;thods employed. The greatest perfec- tion in tlu^se has been reached by J. S. 8tas, and the fol- lowing <;xami)le of his work is added (without explanation) to show the degree of accuracy attained. This is marked by the close agreement of the numljers in the third column : — I'oTAH.Sir.M Chm>I!1i>k takkn. 7-4oOk' linOg 7-4')<»g 7 4.")0g 7 4oOg •J (>!»4")g 22 •;{.■)(%/ SlLVKR TO l>W(iMriiSK IT. l(»-78(i7 1()-7SI0 l(J-7H(M>4 IO-780!> iO-781i 3()308«; .S'2:H1>8 ("OMBIMNO Wkioiit ok Silvkr. 107!>3!){> 107 <.)4(>4 1U7.".».S1)8 1()7-!>.TJ4 iOV 938G 107 i>3()l 107-9398 m 12 THK LAW f)F .SPECIFIC HEAT. 4 The Law of Specific Heat. Tlu' -nethoa of .as .Jonsitv l.as been applir.! partioularly to the non- motals, a.s they ge..M-ally form nuu.y K'=tsiliaMo non.ponM.ls. Alanv of th. metals have not so far yi.-l.UHl comm.ou.hIs .asiliahle at t.Mnperatures wl.ioh permit a aetennuuvtiou of .MH .lensitv. But another n.etho.l of .leter.nm.ng eo.nbinin^' wJi^^.ts is at hand svhich can he nsed with particula,- facility in the case of metals. The following table indicates the nature of tliis law :— ?]I,KMRNT. I'hosjihorua /iiic Arsfiiii". . . . . Tin Aiititnony Mermiry — I-oiul COMHININO Wt. (by itan density). 7.5 lis •200 207 Sl'KllKR' IlKAT. (l-2()'20 0-0«.'.t) 0-0830 o-o:ni> o(i:u4 COMBIN'INO WT. ' SrKClKIC llBAT. ti-2 ((•3 61 0-4 The snecitic heats are for th.' solid elements. A glance .,t this table shows that the larger the combining weight the smaller the specific heat of the elements ; an.l, further, th.. proauct of the combining weight and the specihc heat i. approximately the same for all the elements inclu.lea in this table. The same has bee,> found to hohl true for „,arlv all the ehunents the specific h.-ats of which have ,H...n"aetermine then, be found (apjn-oxiinately) by dividing 3 by its specific heat. The metals of the alkalis and alkaline earths do not yiehi easily gasifiable compounds ; but they have been obtained pur(! and their specitic JKjats deter- n)ined ; and theii- condtining weights have been settled upon by the method just indicated. Analysis of magne- sium sulphate bus shown that the equioahnt weiijJit of mag- nesium, i.e. the weigh*, of magnesium combined with eight parts of oxygen, is l'JU>. Its specific heat is 0"24r). Its approximate cond>ining weight is theietbre „YiT< ~ '-^'^• From this it is plain that its accuiate con)bining weight is 12-19 X 2 -: 24 •;]?<. Again, tlie analyses of Stas (s.-e p. 11) have tixed the ('(piivalent of silver as I0794. Its specific heat is O-O^fi. Its approximate combining weight is therefore o!'o|g= 112; which is near enougli to 107-91 to justify us in clioosing this numlier as the accurate com- binint: wei<'ht. Jt has been found, too, that tlie specific heats of solid compounds multiplied by their combining weights usually give numbers which are approximately inultiples of G-3*. For example, the specilic heat of lead sulphiih^ (PbS) is 0"053. Its condtining weight (reckoned as equal to that of lead added to that of sulphur) is 239. The ju-oduct of these is about 12 6 = 2 x 6-3. Again, for red leatl (Pb^O^'. the nuujbers are 00(5 1 G and G21 (i.e. 3 x 207 + 4 x 1G\. 621 X 00616 = 42196 = 7 X 60 nearlv. \'.\ "The approxiuiation is not very close for many coni|)ouii'ls of j^aseous •lements like oxygen and hydrof^en. 14 THE LAW OF ISOMOUrHIH.M Frc.u these examples it seems that the ehji.ieuts carry with them into tlieir compouiuls their caiMcity for heat, [t can also he .h^.hice.l tliat the specitic heat ot sohd oxyen is such that when multiplie.! hy its comhimug wei-ht the product is not far removed from G. But in the'case of many solid oxygen comi.ounds the numW nuist he co.isiderably less. To solid compounds of those elements which in the free state come uny surfaces which are arranged with u.ore or less svuMuetry around certain (imaginary) axial lines. In actual c-vstals, however, it is nu,re a summetry of direc- tion than" of position, as the conditions of growth usually pn.vent e.iuallv rapi.l growth on the ditf.-rent faces. Thus one face becomes further remove Cobalt suli)hate Co SO^'THjO NickL-1 sulphate Ni S()/7Hg() These formulas ditf.'r only in tli.' symbols for the metals, iin.l in each formula the symbol for the metal is single. The resemblance wouM be imperfect if that for green vitriol were Fe,SO,-7H,() (Fe being '28 instead of 50). Tt is reasonable to suppose that, if another sulphate is found isoniorphous with these, the coa.bining weights sliould be so chosen as to give a forniula similar to those of green vitriol, white vitriol, etc. Manganous sulphate is iso- morphous with green vitri.)l. By analysis of the sulphat^>, the enpoHn,fH in the propurfion nf fj,,- ron,f>nn»;/ ,n'i;;/,fs „f the dementi Tlif tollowiii'' ,ii«; tliH CO elements 111 moil i,'i()M|)s of is(jmor{>liou.s I. — Fhioi-iiip. ehloiiiu., hroniine, iodine; inan^'une.se Ipei-chlomtes and pernian-aiiates arc isoinoiphous). Tr. — I.itliiuni, .sodinni potassium, nihidium. cwsium, iMMimoniiim]; silver an.. .:i,.„.. . .J.J. and double cyanides) \ I ^ ili 18 TlIK rKUloKK' LAW. i TIm- law of iHomorpliisiii lias Imm-ii of aHsistaiico in «leci«l- iii^' tful caH<'S, wli.-iv tlM! m(!tli(»ls of .<,'as ilensity iiJl of s|KK;ilic h.'ats liav.- .itli.T 1.(mm. .litVuMilt of applicH- tion or have yit-Mfd ootiHicliii;,' ivsnlts. In such Ciisos, thos(! multiples of the ('(luivalcnt w.;ighis have l.wt) taken whit-li -ivc. similar formulas for isomorphous comiKJunds of the elfinents. (). The Periodic Law (Newlands, 1804; Men- (l('l.'-<'fi; 18<"»"; I- M<'>'«'i-, 1870). — From tlM^u-emling sections it can l.e se«ni that the properties of the elements are closely connectf'd wilh those numbers which express the proportions in which they enter into combination ; and the faither investigation is carried, the clowr is this eonne.Mion f.mnd to he. Th.; r«dation between the combining wei«,'hts and tlu^ other properties of the ele- ments has its most -eneral expression iu the IWiodic Law. When the elements are ai ranj,'ed in tlie order of their eombininj,' wei;,dits beginning with /ifhinin (hydro- gen is omitted because it does not fall naturally into any groupof elements) and following with b.-yllium, boron, carbon, nitrogen, oxygen, and tluoi-ine, the 8th element, soJinin, is like the 1st, the 'Jtli like the secoiul, and so on to the loth, potassium, which is again like the 1st. This suggests the idea that all the elements may in the same way be found to fall into families or grou[)S of like ele- ments when arranged in this way. The following table shows this to be the case, allowan^'e being made for un- discovereil elements, and for certain deviations from the simjde series of seven elements, aftei- the first two series are completed : — o mm oi u CL. u 33 H O S g o o mm H < O mm o S o u as H s H U g O § H •< U o I THK I'KUKMiIC I,AW. ss« .^ .0 :- 335 a: Six IS II 2 I X. in II 'I S3 ^ _ if o II :SI ^ O 3f 1; N 1- II 'J r. N i| ^ _ o ,1 i !l ?^ 3 II 2 a z; II ^ M ?? ^ 11 u: a; r1 I- X as ]f> II "l* H - Ti (5 ;i S m SHIHaS ») TIIK I'KlUoltK I, AW .1 'I: TIm- ivUitloiis to .-Ihll ..tll.T of the clcllKMltK UH aiTiuigwl in U s1hM«- WW l.' •'': '•"•' -'"' '" ^••''■''«'"' ^^„, .. a 1-.. Na, K, '■'«, HI., A-, Cs, An 1 \ Ah the trM»-.l series .« I.ia.ie U|. ol ll),, is |.raetieally insolul.h- in water , 1 ,,arl in •)r».UO MM) + -'n(M S.Mlinin ehlori.h- (Na Cl ) is not .h-eoin|M.se,l hy water. In fa.-t u.aunesiun. is decidedly less powerfid in its h.usic .-haracter than sodium, hut it shows no acidic properties. ^Afumixum is a metal in lustn. and other propertie.s. It does not, however, deeomposo water at any tempera- t,ure. Its only hydroxide, A1(()H):„ is insoluhle in water. The hydroxide forms soluhle compounds both with stiong Hchls'and with stron- h.-.ses ; but it does not cou.bine with weak acids or weak bases. Aluminum has there- -.•o,,. a dual character, possessing both basic and acid pio- perties, but neither in a very marked degree. This dual character is n.anifested in an ordinary teat for aluminum ii» salt solutions. It to a solution of aluur,nun.. chloride i u g«'latin(i down : — Here the is hIiowu. is added, then fount aluminum in its aci not metal acid. lu i>eliind tin elcii:('iit of eletuent in d«vid(!dly hypopliosp being well sixth m«'ni even uiort; with oxyg( of which, powerful ol phorus, or saline com' a feeblo aci gen sulphi( compounds perties ; an respect its It) chlorine, found at it! f-A^X^i"! Tin; i'*rKi(»i»H' law. 21 chloii.l,. (Alt'l;,). solution ().• .Mulinm l.y.ln.xi.l.- i.s a.l.|.Ml, a «.>latiiio.iH |.n-ci|»itaU" oJahm.imim liy' Iroxi.le in tl.iown l>I<' LAW. :,ci(l> (H('K>, IKMO,. HCIO;;, H(:!l(),), witli l.y.lrog.-n and (.xy.cii, i.ut it conibiiics witl. l.y.ho-cn JiK.no to form a puurrful a.i.l. vi/: l.y.ln.cl.luric aoi.l (I lCl).-Tlns scries lM.^rins will, so.liun;, an ••l..n..>i.t of strongly i.nsic cl.arac- t<-r, aial, i.as.Miig tlirougl. .■Ic.n.'ntH of deer, asing basic and (,t inereasing aei.lic cliaraeters, einls with elilorine, a ,K)werf,.l aci.l.furniii.g element. In the -JihI seri.'S the i-an..; l.iogression from hasic to aei.lic character can be tra.-.'.l ; aiul. iii.lee.l, with .■.•rtain mo.litications, ir. all the MM-ies. The mo.lifications can be seen in th.; 1th an.l .-)lh seri.'s. The 1th seri.'s begins with potassium, a n.Hal nf tin. alkali family. The .sevnth elem.mt from this is „nnni,nn-,,'. a basir .-l.-ment, as seen m the mangan- <,us salts, MnSO,, MiiCO,. MnCl,, •■tc. Imt als.) aeiilic in ,1,,. n,«niin„nt>'s an.l ,.riua,>,iaw,trx. Then follows a trio „f very similar .h'lnents, iron, cnhaU, an.l xi'-keL which, liaving no lik.-n.'ss to so.limn or (.otassinm, are j-ut in an H.hlitional group- VIII. Tin- next eh-m.-nt, ,v.;>/,er. has a few points (.f likeness to th<' alkali metals and begins the .")th s.-ri.'s, I.ut nostr.>ngly a.'idie elem.-nt is reached befoiv ,irs,'>n,\ schn'mm, an.l hrowlun, at the .'U.l ot this seii.'s ; an.l at the beginning of the alt, and nickel) copi).'!-, un.l it is onlv at tlic l)ei,MniiiiiL,' of the (ith scii.'s lliat \v»> find nil.idiiiiu, the next alkali iM"t li. Simiiailv foi- anv I'lrinrut after the 3rd series; anoilicr- clriiii-iir with str.mi; likeness to ji is not found nutil the ir)th is reaehed. although the 8th i.s alwHvs sutliciently like it to jiistifv its liejuir placed in the same gronp. Thns th(! elennMils anaiii^'ed in the oi(h>r of their ooml)inint,' weii^hts form two s/wit periodft and four lomj j)erioils, witli thorium and ui-anium as a fragment of a seventh*. — The i,'radation in propeities in passing' along the sei-ies appears in properties other than the acidic and basic. The /////^x of compounds varv in a regular manner. In the following tal.le are the formnlas of the h\(jhist liasic oi- aci.'•; (;...,o, As,0, Sf,0„ lUt.o SrJ». V„(> Ti,,o, NI..O, .Mo„0,, II, •»;l Ajf./) Cd.^O.^ ln„(». ZrJ., 8b.O- Ttvo,, . . C8,() IJu.o, l,a.,0, 1 Yl..,<.t,, 1M),,0, Ta.O.J Hi.,0, W.,o. <>S«0^ AikO l\'». ■ ... TLo, Til J), i i NoTK. - -/i is a gen i-ral s_viiil)o to iiulicat i thu i\1lM of coinpouii 1. 'Theelonients of jrintip Mil. ;in.' coiiimonly spoken of as tnnisiil.ni /■/.■.?.,.,./» tieiitu^e Uiio foiin ii imiv iaiwifn the end of one serie.s ami the l.evrinnintr of another. ^ tCopperhasa hi^'lier basic oxide. Ciio. J A hiudier arid oxide fo^ j.s know n. n 24 THE I'KIUOItIC LAW. In all tlin he eonsitoxiile, CI J );. is not known, but the corresponding iicid. ])crchloric acid, 1Iining ca|iacities for hydrogen the elements are somewhat diHerent, but they show in this case also that their properties are of a periodic character. As comparatively few of the ele- ments form distinct compounds with hydrogen, the demonstration cannot be made so complete as with the , oxides. Compounds of tlu' metals of tlu; first three groups with univalent radicles aro inserted in the table, where livdrogen compounds are not known. The radicle CH., is e(piivalent to one part of hydrogen, as can be seen in the fonnula ClflU. • The coiubiniii),' capacity of oxytfen is two, as shown liy tlif formula for water, H^O. \ (■()MmMN<; VOIJMKS (»F SOMI) Kf.KMKNTS. 25 RH HM.. Li(CH,) .He(CH,),, Na(CH„) i RH, BH, KU, ' RH, CII, NH, RH., RH OH, KH AKCH,), SiH, I'H, I SI!, cm Tlio 10 inaxnnnni conil.inin- ciiMcity lor liydio.i^r.Mi (four) is readiod in ti.e middle of tin- .scrips, fro.n ul.ich tlieiv is a decrease to one. 1^l,e point to he noted in these table.s is that each series sliows with more or less completeness the ^awe regular variation in the combining capacity of its elements. Similar taldes can he made for the hydr- oxides, (liloiidfs. l.romide.s, iodides, etc. The periodic re.iinence of like properties is (oimd, loo, in tho.se physical properties whieh .an he exactly iir.'a,'sun;»^ bininfj columes of the xoli,! elements. Most of the .le- ments have been obtaine.l in the .soli.l st.at.". .so that the table of combining volumes i^ pretty comph'te. The rela- tion of th.- combining weights to the cond.ining v.>lumes of the (.soli.l; eh.ments can best be .shown by measuring off from two lines meeting at right angles distances p.n! portional to the combining weight and condnning volum.- of each element, tind connecting the points thus obtained by a continuous line. Thus is obtained the curve of com- bining weights and combining volumes. This is called a perioilic carve, consisting, as it does, of a .series of wav^^s. TIIK I'Kl'.IuDIC LAW. No THE rKHIOKIC LAW. 27 JAke e/emetits occnpi/ lih- jiositionx (ju tin; ascending antl "'^•••■<- '• ween <'orresin>;id 1112 e lenn'iits in tiie short periods. Tliu.s each group siih- divides after the first tw o elements into two families. In group ],, potassium, ruhidinm. and (a'sium form one family; and copper, silver, and gold, the other. The distinction between the families is more or h'ss marked in the .litfeient groups, in groups \. and VII. the family are stronger than the -loup re.senddances ; for, certainly, copper, silver and g(,id are more like each other hoth physically ami ehemi(ally than they ar- like any u\' the alkali metals. Also, there are few i-esetnbl; man mces l)etweeii gane.se and the halogen family. In groups II., III., v., and VI. the group and family resemblances are pietty evenly balanced ; while in IV. tl prexail. le grouj) characteristics No general statement can be made with regard to the fii.st two elements of each group. In group I. they evi- dently both belong to the alkali family. So, fluorine and chlorine of grouj) VII. both belong to.the halogen family. 28 THK I'KRIODIC LAW. Ill the otlitn- j,Moiii)s tlicy .sry strong, so that the (/roup rhdrK-feristics ar«' reduced to a <,'eneral reseml)lam.'e in th«' type of compounds, e.g., MCI, M.,0, ote., wlifH! .M stands for any metal of the group. However, sihcr forms an aiiiin in which it |>lays the part of an alkali metal. The fainilji cU(ir>i<-/''ristici on tlif oilier hand arc wi-U defined. Tiio-^e of tie- alkali amilv are lmv( n al p if)'' ol tie I'Xt l>OOi< 'I'o th statemt'iit given there may add'il the t'oiin ilion of isomorphous alums (p. 'V.^C) of Text l>)ok). of other iloulile liphates. an:i '1,1' .\i)ov(' omr Olts V.llow l'ot;V!,. Awi,- ac/7, HAuO.., is a weak acid, l.nt f.oms crN stalli.^ahle .salts of the alkali metals. The.se with chloraurir acid, IlAtiCI,. and its salts recall similar c(miponnds of horon and aluminum. These compounds of copper and gold are examples of many similar ca.ses in which eh-ments of one group have a distinct reseml)lance to those of another. In fact, it follow.s from tlie gra.lation in properties hoth in the .series and in the groups, (hat each ehMuent nuist hear a re.sem 1.1a nee more or le.ss elo.se to the foui' elements next it in the family and tlie .series to which it belongs. J{ut apait from this iheie are ap),arently irregular likene.sscs, as that of tliallium to the alkali metals, of chronium to aluminum, and of titanium to iron. Indee.I, the periodic law places manganese in the .same group wiUi the halogens with which it'has very few affinities, and .separates it tVon. iron, nickel, and cobalt which it resend,les much more; so that for Diacticjil miipo.t;^^.*. purp (for etc.) this cla.ssitication needs to be cliemicHJ analvsiH considerably modi- 30 THK I'Klt IODIC I,.\\V. Ck'.!. I'.iit a careful study of the whole system will show that to a lar^'(! (ixteut tiie properties iu coniinuu which justify the natiiral classiHeation of the eleineuts are the properties upon which the analyst (I(;|UMi<1s for the prac- tical separation of tin; elements into ^'rou[>H and families. Tilt! use of the jM'iiodic; law in settling; douhts with re<'ard to the choie*! of comhinini^ weij,'hts is ol)vious. The equivalent w('i-,dit of hery Ilium was fotmd to he I'f). ]u its chemical pro[»erties it was found to resemhle bonm and aluminuM) , its oxide would thus have the formula I3('.,(), wiili r>e - ;i X tf). liut the chuuent showeil closer relationship to magnesium. In order to he classcul with this element its oxides must hi; He( ) (like M,<,'( ; with Be = l! X 4-."). A determination of the specific heat of the ele- ment (0.1-) favoured the first value; for ^~ = l-'>- 'I'he classification l>y the periodic law .settles the ditli-ulty. An element with (•oml)inini,' wei;,dit 1:)5 would comt? hcLwcM'ii carbon and nitrogen wlun-e there is no pl.ict,' for it. With th(! combining weight U it comes between lithium and boron, an.l h.-n; then; is a vacant j.lace for it. The periodic law has also been used in pnidicting the proper- ties of undiscovered (dements and thtnr comi)ounds. (Jallium. scandium and germanium have been discovered since Mendcleeir published his Periodic Lair of the Element.'^ with its accomi)anying description of the pro- perties of elements which woiild fit in between calcium and titanium, and between zinc and arsenic. The follow- ing paralhd descrii)tion (from-Richter's Inorganic Chem- isti'v) shows the remarkable agreement in the case of germanium between tlie predicted * and the discovered elctnents ; — 'Calk'd ("ika-f>i7u'"H I'V Mi'iulelieff. Kv Comhiiiii Density', Coinhiniii Form of i Sp. gr., 4 Easily ol witli ca Dirty gn •litlicult when ii Will for. wliich I>rohal.I Its .snl|)lii in watt.' t)l(' ill ai Will l,f 8 acids. 7 Re changt' i: temporati under cei ditions ai are (piite peratnre. point in and form: raised, the When bai iu a curre * Discovere< t See p. 2.'). RKVKKSAI. OF ClIKMK \r, CIlAMiKS. 31 il KkaSiijcon, Ks. Coinl)itiiii^' wt. about 72. Density, •")"). Coinltiniiiy v(.I.,t i;{ nt-arly. Form of oxide, KsUj. Sp. gr., 4-7. Easily ohtainod l)y reduction with carhoii or sodiuui. Dirty gray metal, fuses witli (litfieulty, forming tiie oxide when lieated in tiie air. Will f(irm a chloride, KsCl^, which will hoil near 1 00*, l>rol)al)iy lower. Its sulpliide will l.e in.soluhle in Water, Imt iiroltaldy smIu- ble in ammonium sulpliide. Will lie scarcely acted on hy acids. . Forms an oxide, (ieO.^. Sp. gr., 470.S. Easily obtained by reduction with carbon or hydrogen. A gray-white metal, fusing at IKK) ('. and forming the oxide when heated in air. Forms the chloride, (SeCI,. boiling at 80 I'. Tlie .sul|)hi(h- \H moderately Hohiblc in water, more reae ici^'arded as dissociation, sinee tlie oxyi,'en reeniiiliines when the teniperat nie is h)weicd Hut a ivhieai e\ani|>h' of dissociation is seen in the case ot (iiiniKiniii in i-hliirid' , the i^^as ih'nsity of which was found to he oidy half that cahaihited iVom the fornnda NH,('l ; that is. a i:iven weight cccu](ieil twice the cah'tdateil vohiine. Tins sui,'i,'este«l tlie idea that the douhle volume IS i\y\v to the decom|»i)sition of the ammoiMiim chloride into t wo ^ases. Tiiis can lie proved to lie the case l)y a simple experiment. Heat a little ammonium cidoride in a co\erei| platinum (Miicil)le until it is voliitilise>(. He- move tln^ cover and ins(!rt (juickly a strip o\' moistened hlue litmus paper. It is turned red. The ammonium chloride was dissoeiat(Ml into amnioir'a and hydrochloric acid. The lormer, heing the lightei- j,'as, diHused out more rapidly, so that the remainder was acid in i-eaction. By 11 more complicated aj)piiratus the separation l>y diU'usion can he etl'ected in suoli a way as to show the presence of each of tlie leases, PlioHphoriiA pnitachlorvi'-, PCi,, is an exami)le of a volatih? sul)stance whicli dissociates partly hilt nif thecjret Tlie «|H by cxj»( Th(^ spf phosjilio it may 1 pentachi the (ILssc by th«; ji chlorine. stroni(e!\ reveisal Chenii condition decompos carbonate goes on u to about * See p. 9. t I'hoKphor pcntachloritl( 3 KKFKCT MK I'llKssi KK, "j;{ partly into the tnd.l.Mi.lo nn-l chlorine when vohuilised hut more un.l more as the ten.perutnre is ,aise,|. ffH theoretical .s| i(ie wri-ht refnred to air is ^""^ 7 •»♦; ♦ Thes,KviHe wei^^hts at .lidcent ten.,«.ra,„;;;'..s foun.l by experiment are ^.iven in the lollowin^' tal,h. :— '**- .V078 '^>«° 41.87 -"0 48.-.I ZiO ^..j,,., -^' ;{!)t>i ^'^ .S-W 2S8 .^.,.- 28!r ''''.'.'.'."" "[m, swr .,.,.. > ().» 'n.o speeiti,. w<.i.ht of a n.ixtu.e of c.jnal vohn.H.t ..f phosphorus triehh.ri.h. an.l .hlo.in,. is :{•.;! ; f,,,,,. which Jtmay be conclu.l.-N. CPiiHOH imlrss tlif pn-ssiin^ of tlin oiul.«»ii dioxide is lower- ed. On tlin otlKT liiiiitl if tlu^ piosHuiv in incrciiHCMl, re- rc.nihiimtion Uikcs pliic' until tln^ pirssun- is M<,'aiu t'qual to :>2()mm. Ill '• luiruinj,' " liiiKstonc it is iiewssiiry to icmovo tlio aulton dioxidr us it is s. t fi«'«. otlMTwiso the -icconipoHition would miso uh hooii as the jdehsure of the i,MS ivH(!li('d a cortiiiu limit. This reinovHl is etlected hy the t'n'e diiiu«,dit of hot j^'as.-s througli the kiln. Anothor important condition intluenoin^' chrinical chan".' is the relative quantities of sul..stanoeK present, i.e. tin; action of matts. When a solution of l.isniuth tri- chloride in water is diluted with water, a white preci- pitate appears, which increases with the (piantity of water lid. led. It is an o.xychloride of Uisinuth formed l.y the action of the water : — liiCl3 + lla() Hi<>Cl + 2HCl. If enou^di hy!(»iM)rtions ol hy«l!oo!tion of watei- vapoiii- is iiicjoased, the i!iixture l»ecomes oapal.le of oxidising ii'on at a !vd heat ; l.nt if the ])io|H)i-tion of hy to dilute solutions. .M» I{\ori,TS I, AW. iiiL( |)oiiits (if iuiucuiis soliitioiis of soiliiiin ('liloi-ifh' coii- tMiiiini;- 1. ."), and 10 giaiiis ot' lln- salt to 100 of water are ifs|M-cli\cly — •r)8, — 2 01, and — t't'lO, — iminlxirs niMi'ly |iii>|iori ion;d to 1. "). ami i 0. Wlim the ctl't'cts of dili'cicnt coniiioiintls an- rohi|(aicd, a it inaikahlc law a)i|tf;iis. Fur Ncrv diliitt; solutions, t/ie jWciiu;/ ixi'nd of luiy so/i'enf Is /(iirercd to the name r.ffenf hi/ wi'ights of thi; (Uxsidvi'il '■(iiiij>(>ait(ls p)'v/)orlion SriWTASCKW. M.th.sl A1r,,h..l, CIliO GIvci'iiiH', <',ll,o SlluMI. ''i jlli:-''! I I'lllMllit. <',.II„0 .hectic- A. id, r.ll,(>._. Oxalic Ai'iil. (',ll,0, KtlUT, <',ll|.,o llvilritcN iiiiic Ai'iil, IICN II. To KlOlKjRAMS (IK W.\rKit. III. |-'HKK/.I.N(I I'liIM. :ii — i-7:r !»-i -l-7r Ml l-siV it! -1 -fi-V (il — liK)' t)ll •2.2!t' 71 - r«i(i' r, -1!)4' liy means of this law the comhinini,' weii,dits of eotu- pounds can !»»• deUu'niined, Thus, analysis of lactic acid leatls to the formula ('1I^,<), as expressing its composition. Jiiit, it has l)cen found that three times the weight (in grams) indi'-ati.! hy tlsis formula di.ssolved in 1000 graiiiH ■ OslwaUl's Lelirtiuch der All(feineiiie Cheinie, Vol. I., p. 415. V\N T HOFK S I, AW. 37 1 of Wilier lowers the t'it'('ziii<^ |ii)int of water to — I It'J . 'J'lie eoiiil(inii)if weiijht of lactic acid is thou iinlicaleil l)v the fni inula <';H,A- *.*• Van t HofTs Law. — When a volatile sul)staiice i-. jiassPil up into the \aciiuin of a haroineter, the \;i|iour whicli escaj)es into the vaniuiu exeits a pressure upon the mercury and pvjshes it down a certain distani.-e. If tlie teiupei'ature is raised, more vapour is formeil and the vai»our is expandetl l»y the heal. l)Oth effects comhiniiii,' to depress the niei'cury still fui"th(ir. When the t«;mperature is raised to the hoiliui^ point of the substance, the mercury sinks to the same level as that in the troui,di, showini; that the [iressui'e inside the tube eipials that of the atmospheic*. For any i^iven temperature, the vapour of a volatile substance exerts in this way a certain pressure, known as its raponr fen^iion and usually meiisiired in millimetres of mercury. For e.vample, the va}»our tension of wat«!r at <>^(J is toG'J ; i.e. if water l)e passed up into a barometer tulx' kept at 0'(J, the vapour troin it will de[>ress the mi'iviiry t-otJDmm. TIk^ vapoui- tension of water at 100'(,' is 7()(). /.''. e(pial to tlm iKjrmal pressure of the atujosphere. The pre.seuce of dissolved substances decreases the vapour tension of the solvent, and accor