BARKER AND PORTER THE EFFECT OF ASYMMETRY. 1303 CXL1.-The Efect of Asymmetry. A Study in Crystal Structure. By THOMAS VIPOND BARKER and MARY WINEARLS PORTER. COMPARATIVE stludies of more or less closely rellatled olrganio mm-pounds abound in the literature of oryst(a1lography ; in fact( the attempt to trace sol-Galled " morphotropio resemblanaes " may be regarded as one of the distinotive features of crystallographio investigation during the last fifty years. Whilst such investiga-tions have added elxtelnsively ta the! general stmk of knowledgel, they cannot unfortunately be said t o have led to the formula 1304 BABEER AND PORTER THE EFFEOT OF ASYMMETRY4 tion of any general laws correlating chemical compmition and q s t a l l i n e form. A t least one of the caum of this general fdlure has been reoently rewaled as the result of the invwtigation of urystal struoture by means of X-rays.It is now clear that the Bravais space-lattice do not always represent completely the atruc-ture of a crystal for something like 70 per cent. of the structures already elucidated by X-ray methods consist of several inter-penetrating space-lattices that is of “point system~ ” i n the sense of Sohncke Fedcrrov and Schonflies. Crystal structure is thereby proved to be a subject of great complexity and much further investigation is evidently needed before general laws oan be f ormulatd. The object of the present research was to ascertain whether a definite similarit<y may exist between the orystalline forms of two closely related organio substanw one of which differs from the other in p-sing an asymmetric atom.The kind of similarity sought was of that definite degree which exists between isomorphous substances rat,her than that vaguely implied by a “morphotropio resembl an 08. ” I n selecting materials for examination i t was necessary to find a series of compounds in which the replacement of one radicle by another is not incompatible with an isomorphous relationship (at least so long as the molecule remains symmetrical) before proceed-ing to inquire whether a further replacement of radiclea by which the molecule becomes asymmstric is compatible with the survival of isomorphism. Now experience shows that in series involving the replacement of organio radiclea isomorphism is only ta be found where the molecule is relatively large in proportion t o the ohange of composition and i t therefore seamed probable that com-pounds of the type R,NHgI (that is “double oompunds” of a quaternary ammonium iodide with mercuric iodide in the ratio 1 l) in which R may represent either identical or different organic radioles should be suitable for the end in view.Such compounds, having a pale to deep lemon-yellow colour am known to crystallise well from acetone solutions. A commencement was therefore made with a series of compounds in which R is wholly represented by alkyl groups (compare table I) but no definite cam3 of isomorphism were encountered. This is a fact of some significance as illus-trating the highly sensitive character of the relationship between form and composition in spite of the high molwular weight the replaoement of even a single methyl by an ethyl radicle brings about a fundamental change of crystalline form and structure.The investigation of a still more complex group then became ncmtissary. The phenylalkylanimonium ocunpuunds of the general No 1 2 3 4 5 6 7 Substance. Me,NHgI, MeEt.,NHgI, Et,NHgI, PrEt,NHgI, MePr,NHgI, EtPr,NHgI, Pr,NHgI, TABLE I. The AIkylamrndum Group of Crnpyun&.* Crystallographic cons tan ts. I e \ Axial System. a b c . angles. Rhombic 0-5777 1 0.5199 -Anorthic 1.1202 1 0.5578 a= 102' p= 93'56' y = 108' Monoclinic 1.4826 1 0.8192 p=107'55' Y9 1-1350 1 0.7359 p= 97'11' Y Y 1.0749 1 0.6542 j3= 93'22' Rhombic 0*6:90 1 0.5106 -Monoclinic 1.4965 1 0.7328 p=113'16' The corresponding trimethylethyl and trimethylpropyl compounds were also prepared, In addition to the 1 1-compound tetraethylammonium A description of in a form suitable for measurement.substance with mercuric iodide in the molecular proportions 2 3. part (p. 1314) 1306 BARKER AND PORTER THE EFFECT OF ASYMMETRY. formula R,PhNHgI, furnished clear cases of isomolrphism. I n the annexed table the first member is noh isomorphous wit$ the s u m d i n g compounds. The nextl threel compounds howeveir are dearly isomorphoas and moreover exhibit the following peculiarity. Although the compound Me,EtPhNHg13 (No. 9) differs frolm the compound MeEhPhNHgI (No. 11) by an amount expressible by CH, it is much more olosely isomorphous with it than is tlhe compound M+PrPhNHgI (No.lo) in spite of the fact thatl the last two compounds are isomerides. The similarity of angles between the first two mentioned compounds is indeed com-parable with the olose isomorphism melt with in the sulphates of potassium rubidium wsium and ammonium. The isomorphism of the t h e cornpounds numbered 9-11 was confirmed by a met!hod which has been espeaially developed by olne of us (T. 1906, 89 1120). Crystal fragmelnts of any one of the1 three substances continue to grow when p l a d in a saturateld solution of either of t h O others and thus satisfy one of the mostl rigid testa for isomorphism. Proweding with the table it is seen that there is a marked change of form in passing from Nor.11 to No. 12 differ-ing in composition by CH, but t,hatl the two compounds Et,PhNHgI (No. 12) and Et,PrPhNHgI (No. 13) also differing by CH, am olosely isomorphoius-a colnolusion whiclh was confirmed by the formation oC regular growths when a crystal of one is immersed in a satnrated solution of thel other. The choice olf the final materials was of course dictlated by practical oonsidma tions . Asymmetry of mole oular configuration is most easily proldud by the inclusion of a beinzyl radide and the phenylbenzylalkylammonium group of compounds represented by the general formula R,(CH,Ph)PhNHgI, in which asymmetry is involved by the seleotion of different R-groups was Berefore elxamined. The results of the crystallographia examination are summarised in table 111.A glance a t the values of tlha axial ratios is sufficlielnt to show that the fir& substance has no relally close1 relationship to the second and third oompounds ; morelover the largel discrepanay in the axial ratio b c of the fourth substance sholws that it aIw stands alone. The relationships of the second and third com-pounds (No. 15 and No 16 of the1 table) deserve further notice. The axial ratios and angle /3 differ by rejlativeily small amounts, thus indicating the possibility that the two substances are isomorphous. A comparison of the f orm-development points tthe same way. I n the1 methylethyl derivative we have b{010} al{lOO}, m{llO) a{001} p{O11} and r{ZOl} with the forms b m d a developed as small facets whilst! in the diethyl derivative we hav TABLE 11.The Phenylullcylammoniwn G ~ o u p of Compowds Crystallographic constants. , K O Substance. System. a b c . B. 8 Me,PhNHgT Monoclinic 2.2400 1 0.6783 104'54' 10 Me,PrPhNHgI 0.7775 1 0-6711 96'34' 9 Me,EtPhNHgI 9 9 0.7391 1 0.6783 94" 9 9 11 MeEt,PhNHgJ 9 9 0.7319 1 0.6976 93'24' 9 ) 12 E t,PhNHg13 1.1250 1 1.3490 101 '2 13 Et,PrPhNHgI 1.1185 1 1.3440 100'57' * Phenyltriethylammonium iodide also forms a second type of compound with A description of this substance is included in the experimental 9 Y 2 1. TABLE 111. The Ph eny I b enz y lalk y lunanz on iu m G r ozi p of Crystallographic constants . v-N O . Substance. System. a b c . P. 14 Me,( CH,Ph)PWHgI Monoclinic 0.7386 1 0.5105 92"26' 16 MeEt(CH,Ph)PhNHgT 99 0.9878 1 0.5797 106' 16 Et,(CH,Ph)PhNHgI 77 1.0301 1 0.6354 108' 17 MePr(CH,Ph)PhNHgT 1.1060 1 0-7766 102'55' Y I308 BARKER AND PORTER THE EFFECT OF ASYMMETRY.the1 same1 forms but without b(010) and a(100). Since in the former compound thew two forms were but slightly developed, their absence in the latter has no particular signifioanm merely indioating that om compound tmds to preseint a rioher form-development than the other. The mincidenm of all the remaining farms and more especially tlhei occurrence in common od the form (ZOl) point to1 an idelntical space-lattice and prove the substancea to h isomorphous in so far as purely geometrical characters can do so. This conclusion is strengthened by the olbservation that a brokeln fragment of the diet~hyl oompolund when plaid in a saturated solution of the methylethyl derivative immedia;tely begins t o grow and eventually becomes a prfeot arystal.The wle remaining question relata to1 the speoial chemical nature of phenylbenzylme~thylelthylamolnium merouri-iodide whether the crystals a,re dextrol- and lzvo-enmtionmrphs or are rsmmio or pseudo-rammia. As no trace1 of optical inhomogeneity was ever observed in crystals selleated from various crops and a,s tlhe measure ments gavel no indioatiolns of tihe wide variations of angle charaoter-istia of pseudo-racemic crystlals it follows that the wystals axel eitlhelr truly raceania or on the otheir hand a conglomerate of the two erzantiomolrphs. I n ordelr to decide this queBtion thrw of the1 largest orystlals weighing approximately 2 1.5 and 1 gram respmtively were powdered and as rapidly as possible dissolved separakelly in about 20 C.C.of amtone and the1 solutions immdia,tely exmind in the polarimekr. I n no o m was an appreoiable rotation observed ; the crystals theref ore presumably repreenti a tlrrue rawmate. This conclusioln was suppolrtd by &ah-figures on the crysbal fa,oes for they were in accordanw with holohedral symmetry. The main result1 olf this investigation is to prove that racelmia cryst a,ls olf phelnylbelnzyhet hylethylammolnium merauri-iodide are isomorphous with the corresponding diethyl derivative although the raaemio crystals contain two kinds of asymmetrio rnoledes, whilst in the diethyl derivative all the moleaulee are newssarily idelntioally similar and symmetrioal.E x P E R I M E N TAL. Preparation of CompoyuncEs. The general method of preparing tqhe compounds was as follows. The proper mohxular proportions ojf the tertiary mine alkyl iodide and mercuric iodide1 were warmed tlogetsher with acetone until the whole was dissolved and the solution allowed to remain olvernight. Crystals were usually obtained the following day A STUDY IN CRYSTAL STRUCTURE. 1300 adthough two1 o r three rmrystallisations weire somethes nelcasary before really good crystals were formed. Some of the1 ccmpoands prepamred werel found to be unsuitable for orysta#llographia inve& gation ; t,he t,rimethyletjhyl and tri-metbylprolpyl compounds for example cryst,aJlise in needles. On the olther hand in some1 cases morel t h n one oompoand is foamed ; thus tetrad,hylamoniu.m io.dide unit,es with melrcurio iodide in the prolportions 1 1 and 2 3.Wit'h regard tlol the phenyldkyl group it wa,s observed thattj increla5sei of molelcular weight lowereid the crystxadlisability of the coimpoands ; somelt,imes five or six rmryst~allisations we98 nec,essa.ry bef orel suffioielntlly goold crystlals welre obtaineld. The phenyldimethylpropyl a.nd phelnyldimethyl-elt3hyl compounds have1 at stmng telnde!ncy tlol folrm needle's but after repateld remysta'llisatiolns t.hey finally yieilded some meiasurable crystlals. I n one a<nd the same so;lutJo8n phelnylt'riethyla~olnium ioldidtr folrrms with melrouria ioidide two1 CompoIunds which on analysis proved t o be1 the 2 1- and 1 I-compounds respeotively ; t'hese were1 separated by hand.I n tlhe phenylbenzylalkyl group, thel chemical cormbinastion olf t,hel va,rious components was relativelly slow; seve1ra.l afAempta t.o prepare1 phenylbenzylet.hylpropy1-ammo'nium me,rauri-ioldidel welre! madel but a pure product could no't he isolated. Mrthod of Analysis. The method employed for the quantitative estimation of the1 mercury was that dewribsd by Marsh and Lye (Analyst 1917, 42 84). The prolaem is a modificatioa of the method of estimating mercury by combustion with quicklime. Calcium olxalate is placed a t the close& elnd of the tube! and after this a few grams of dry caloium sulphate and quicklime; next comes about 1 gram of the substance grolund up with abolut the same weight of potassium cyanidel and a few grams of calcium salphatlet aad quicklimel.* After this 5 olr 6 grams of a mixture1 of oalcium sulphata and quiaklime are packed in and the remainder of the tube is filled with quicklime.The1 vapolriseld melrcury is collected in EL small flask of water. No calcium sulphatef was meld with the teltra-meithyl phenyl limethylpropyl and phenyldiethylpropyl com-pounds. It may be noted that more satisfactory results were obtained with a t u b longer than that remmmendeld by Marsh and Lye(; the length of the tube beifore drawing olutl should be about1 50 am. * In the case of the phenylbenzylalkylammonium group about a gram of black copper oxide was mixed with the substance and the potassium cyanide waa placed nearer the drawn-out end of the tube 1310 BARKER AND PORTER THE EFFECT OF ASYMMETRY.Method of CrystaUograpFyic Esanthaitimt. A Fedojrov tlwoLcirclel goiiiometer was exclusivelly employeld in the measurement of the crystals. Apart from its other advantages a two(-circle instrument> is especially useful for the measurement of laboratory products the crystals of which are frer quently od microscopic dimensions since it nelceesitates only one adjustment of the crystal. The raults were plotted on a Fedorov stereographic netl and the crystal systelm if not immediately olbvious was deduced from zonal angles graphically determined by tlhe help of the1 three-polint compass and stelreographic netl and latelr ooafirmed by an elxamination of the optioal propelrties. The crystlallographia indices were deftermined graphiodly in every case by the help 04 the1 gnomonic projeotion.I n order to1 avoid powible errors the axial ratios havs belen calculateld in two1 independent ways for evelry compound. First by the melthod in common use, depending on the1 sollutioln of spherical triangles and secondly by Goldschmidt’s melthod (Zeitsch. I f r y s t . Mirt. 1893 21 210) based on the gnomonic projection. The crystal drawings were made directly from the! gnomonic projection by the1 method delvised by Goldsohmidt (Zeitsch. Kryst. Min. 1891 19 352). Attention is especially called to1 this point because1 the method does not appear to have come1 into! gelneral use although elxperience proves it to bO superior to all the other melthods olf drawing crystals.In the descriptions of the crystals the convelntional rules have been adopted [in the molnoclinic system f o r instance\ the indices (010) have beeln uniformly assigned to1 the planel of symmetry]; but in addition the (( correct setting ” of the crystal according to Feidorolv’s melthobds and his (‘ complex-symbol,” have been woirked out in ewelry case and the “transformation elquations,” by which the1 indices corresponding with Fedorov’s theoretical ideas may be obtained from the conventional indices are also given. The dewriptions consequently contain everything necelssary for an absolute idelntification of any of the1 compounds on any future occasion by the melthod now genelrally known as ‘( crystallo-ohemicd analysis,” a descriptive1 outline of which has already been given elsewheas ( A m .Reports 1913 10 245; 1914 11 248; 1917 (14 227). An explanation of the1 meaning olf thel terms ( ( transfolrmatioa equations ” and ‘I complex-symbol1 ” may well1 be appended here as not having been previously given. The1 oonnexian between the indices representing any face of a crystal when refelrred to twol different sets of axes is most con-venienttly expressed by means of “ transformation equations,” by which one set of indices can be immetdiately delduced from th A STUDY IN CRYSTAL STRVCTURE. 1311 other. Thus ;In the1 case1 of the1 anolrthic melthyltlriethylammolnium mercuri-iodide (p. 1313) the new indices (pyr) of any face referred to the axes chosen by Fedorov on structural grounds can be obtained from its indices ( h k l ) when referreld to the conventional axes by the equations p = - l h + O k + 21 y = l h + Ok + 21, r=lh+22k+01.Thel numerioal colefficients of hkl in these equa-tiolns are 102 102 and 120 respectively and the1 equatiolns oan be abbrelviated to “ trans. T02/102/ 120 ”-a form which is adopted in this papes. The1 Fedorov “ complex-symbol ” is an expression which indicates simultaneously both the1 type of structlural arrangementl and the characteristic angles of the crystal (if necessary after a suitable homogeneous defolrmation or shear). The initial term of the symbol is the number 6 4 or 3 according as the crystal is helld to1 approximate most closely t o a hexagonal tetragolnal o r trigonal (rhombohedral) folrm respectively. When necemary this number is immeldiately follloweld by a letter h 01 or d respectively indicating in Feidolrov’s phraseology that the arrangelment is ( ( helxahedral ” (that is thatl of a simple space-lattice) ( I octa-hedral ” (that of a centred lattice) or “ dodecahedra1 ” (that of a facel-centred lattice).Thus 4h signified that the type of the struc-tural arrangement is that of a simple tetragonal spacerlattice!, whilstl 3d indicates the face-centred trigonal lattice as being the structural typei. All remaining terms of the complex-symbol are numerical const ants representing degree& of arc which serve to characterise each crystal species. As described below one of these numerical telrms expressing in genetral the vadue of the angle (after a shejar) beltween the correct basal plane and primary pyramid is especially important in Feldorov’s classification so by way of cant-rast he1 elncloses in brackets all other terms as are necessary to1 express the1 angular delviatiolns of the1 lattice from an ideal hexagonal tetragonal o r trigonal folrm.Thus in the symbol “ (6)37$(+3),” the1 first term means thatl the crystal approaches ideal heixagonal symmekry the selcond that the principal angle is 37i0 and the1 third thatl the prism angle has the value 6 O o + 3 O instead of the value 60° proper to1 an ideal hexagonal lattice. The abselnce of any furthes term indicates that the system is ortho-rhombic. On the1 other hand in the symbol1 ‘‘ ( 3 h ; + 2)58(0) ” we have a new kind of numerical term namely + 2 immeldiately following thel structural term 3h.This means that the1 angle between two1 of the1 structural planes is not 90° but 9O0+2O in other words thatq the1 crystal is monoclinic with a value P=92O. The last term (‘(O),” refers as beforei t o the1 prism angle and means that the deviation (from the ideal value olf 60°) is neare I312 BARKER AND PORTER THE EFFECT OF ASYMMETRY. Oo than +O. The1 anglea in the cornplelx-symbolls are olnly given to the nearest half degrele since this is the limit of accuraay of the graphioal methods employeld . The Fedorov cornplex-symbol derive6 its immense importance from two facts first unlike axial ratios i t is an unambiguous constant f o r each crystal-species and secondly such symbolls can be reladily dasifield in ordelreld form. I n his " Diotionary of the Crystal-Kingdom," the publiclation of which by the Petrograd Aaademy of Scielnce has been delayed by ciroumstanws beyond its control the late Profasor Fedorolv has classified all the1 existing data.All clrystals bellonging to the same1 type (say 4h or 3d and SQ on) are1 first broaght together and then arranged in olrder accolrding to1 tlhe value1 of the1 principal angle melntioned abmel. Any well-delvelopd crystalline1 substance which has once beein melasureld and placeid in the1 dictionary in the place relquird by itis complejx-symbol can be identified on any future olcmsioln for it is only neicessary to1 measure the1 crystal to1 be identifield deduce itk; complex-symbol from the form-development, and refer to the dictionary for a statement olf the ohemical composition.A naly tical and Crystal I ograp hic De'tails . Folllowing is ay detailed summary of the! reaults sb chemioal analysis and Crystallographic measurement of the various substances prepared. Although measured angles only are1 reproduced in this paper (the angles which served as a basis folr calculation being markeld with an asterisk) i t may be1 rnentioneld thah the1 correot-neas of the various indices was checked by the logarithmic cojm-putation of the angular values demanded by the! law of simples, rational indices and thatl these computed angles were in evesy case1 satisfactorily do= to1 the1 meamred angles. The1 omission of these computed angles results in a grelatl saving of space and does nok seem to1 us to1 involve1 tlhel loss of anything essential t o the future usefulness of the crystallographic descriptions.Tetramethy2ammonium Mercziriiodide MqNHgI,.-M. p. above 200° (Found Hg=30.43. Calc. Hg= 30.53 pelr cent.). Ortho-rhombic a;:h:c=0*5777:1:0*5199. Fosrms b{010} al{lOO), m{110} m{120} e{001} e{101} ~ { l l l } C(121). Two distinct habits were observeld on crystals from acetonel. The more usual habit is sholwn in Fig. 1. The seciond habit is bipyramidal and tabular pasallell to h(010). Following are the1 mean angular values olbtained from five crystals : b(OIO',. a{1OO). m{11O). n{12O}. eilO1). p{lll). t(121). Azimuth (+) ...... 0" 0' 90' 4' "59'59' 40'50' 89'53' 59'59' 40"54' Polar distance (p) 89'59' 89'59' 90" 0' 90" 2' "41'59' 46" 3' 53"57 A STUDY IN CRYSTAL STRUCTURE.1313 Clela;vages a { loo} fair; c{OOl) imprfeati Optic axid plane, a{ 100) ; acute bisectrix pelrpeindicrulax t'ol (001) ; wide axial angle; biredringenml strolng ; dispersion p>w. Trans. lOO/OOl/OlO. Complex-symbol (4d)69( + 3). Met hybtket hylamrnonium Mercuri-iodide MeEt3NHgI,.-M. p . 104O (Found Hg = 28.67. C,H,,NI,HgI requires Hg = 28.73 per cent.). Anolrtlhic ai:b :e=1*1202:1:0-5578; c~=102~55/ ,8= 93O56/ ~ = 1 0 8 ~ 2 5 / . Forms b{010} a{100} m{110} ,{liO>, k(iZo} 1{2i0) g { o i i } t { o i l ) r{ioi}. FIG. 1. FIG. 2. The' commo8n habit is FIG. 3. Tetramethylammonium Meth,yltriethylammonium Tetraethylammonium rnercuri-iodide. mercuri-iodide. mercuri -iodide. slender prismatic as shown in Fig. 2. angular values obtained from nine1 crystals : b(010j.a{1001. millo). n{iio). k{lZO). Azimuth (q) ......... 0" 0' *70" 5' *32"18' 130'40' 154'17' Polar distance ( p ) ... 90" 0' 90" 0' 90' 0' 90" 0' 90" 0' Following are the mean z(2io). q{ol I). t{oii]. r{iolj. Azimuth ( q ) ......... 104" 5' *4"29 *190 168"32' 3 28 23041' 1'43' Polar distance ( p ) ... 90" 0' *41"21 Clea#vagea m(110) and n(liO} good. Trans. 102/102/120. Complex-symbol (4d; *21)62(0 ; 0 1 ) . Tetra e t h yla;mnz o n izi nc M ercuri-iodide E t,NHg I,. -M . p . 1 1 Oo (Found Hg= 27.95. Calc;. Hg=28*13 per cent.). Monoclinic, a:b:a=1*4826:1:0.8192; P=107O55/. Porms. al{lOO} m{110}, c(OOl} T { 901 o{T11}. The common habit is stout' prismatic as shocwn in Fig. 3. Follolwing ase the mean angular values obtained from five crystals: a(100).m(1lOt. C ~ O O ~ ] . r(701). 0{111). Azimuth ( q ) . . . . . . . . . 90" 0' *35"20' 89"46' 269"58' *342"34' Polar distance ( p ) ... 90" 0' 90" 0' 17"54' 39'56' *40"39' Optics All the prism faces give1 oblique extinction. 1314 BARKER AND PORTER THE EFFECT OF ASYMMETRY. Cleavages a { 100 1 pelrfect,; c { 001 } imperfectl. Opt'io axial plane b(010). An optic axis emerges nearly pelrpendicular to c(OO1). Trans. O l l / O l i /101. Complex-symbol (4d; - 144)55( - 64). Tetraethylammornim Memiiri-iodide 2Et4NI,3HgI,.-M. p. 1 5 4 O (Found Hg=31.94. Calc. Hg=31*98 per cent.). Tetra-gcmal c:a=0.8186:1. Forms n{100} m{110} e{101} d{20l}, ~ { l l l } ~ ( 2 2 1 ) . The common habit of the crystlals is shown in Fig. 4. Following are1 the mean angular value8 obtained from four cryst,a,ls : FIG.4. FIG. 5. FIG. 6. Tetraethylammonium mercuri-iodide. Triethylpropylammonium mercuri-iodide. I I 1 I I ml rn I I I I I Methyltriprop yl-. ammonzum mcrcurm-iodide. a{1001. mfllO}. e j l O l i . d{201}. p(ll1). sI22l). Azimuth (q) ............ 0' 0' 45" 0' 0' 3' 0" 3' 45" 3' 45" 2' Polar distance ( p ) ...... 90" 0' 90" 8' 39'13' *58'35' 49' 9' 66'35' Cleia,vagel a{ loo} goo,d. Donble redraction very strong ; posit ive . Com plex-sym bol (4 h) 4 9 O 9 I . Triethyl-a-propylmmonium Mercwi-iodide Etq3PraNHg13.-M. p. 85O (Found Hg= 27.33. C,H,,NI,HgI requires Hg = 27.58 per oent.). Monoclinic a b c = 1.1350 1 0.7359 /3=97O11'. Forms n'{100} m{110} c{OOl} e{101} r{iOl} ~ { l l l } .Two habite were) observeld one ot which is shown in Fig. 5. The second habit sholws the pyramid p{111) and n { l O O } is much narrower. Following are the metan angular valueis obtained from six crystals : a{100}. m(110). c@01]. e(1011. T { i O i ) . ~ ( 1 1 1 ) . Azimuth ($) ... ..... ,. .. 90" 0' *41"36' 89'58' 89'59' 270" 4' 46"39' Polar distance ( p ) ...... 90" 0' 90" 0' 7' 5' *37'51' 27'58' *46"59 A STUDY IN CRYSTAIJ STRIJCTURE 1315 Cleavage n ~ { 11O} perfect. Optic axial planel b(010). An optio axis is visible! through a{100} on the! extreme edge of the field. Trans. ~lO/TTO/OO2. Complelx-symbol (3h ; + 2)58(0). Me t h y 1 t ri-a-p-oljyl LC nz m o n i 1 ( m Me r c 11 1.i- iodide Me P r a,N H g I .-&I. p. 1 2 3 O (Found Hg = 26.55. Cl,,H,,NI,Hg12 requirw Hg = 27.06 per cent.).Monoclinic a b c = 1.0749 1 0.6542 ; P= 93'22'. Forms nz{llO} p{Oll} r{TOl} p{111} o{T11}. Two1 disttbnct habits were olbserveld one of which is shown by Fig. 6. The second habit is stout prismatic with large pyramidal faoes. Following are1 the) mean angular values obtained from five crystals : r n { l l O j . q(o11). r(iO1;. p{Ili). o { i i i j . Azimuth (q) ......... *42"59' 4'59' 269'53' *45"37' 319'50' Polar distance ( p ) ... 90" 1' 33'24' 28'56' *43" 5' 40'26' Cleavages q { 01 1 } fair ; 712. { 1 l o } imperfect. Optic axial plane, b(010) and an optio axis is visiblel tlhrough a(100) on the1 ledge of the1 field. Trans. TlO/T~O/OO2. Complex-symbod (40; + 3$)50( - 2). FIG. 7. FIG. 8. Ethyltriprop yEamrnoi&m rnercuri -iodide.n FIG. 9. I I m m . I I ,", Tetraprop y~ammoniurn Phenyltrimethyl -mercuri-iodide. arnmonwm mercuri-iodide. Ethyltri-a-popylammonium rVercuri-iodide EtPrn3NHg13.-M. p. 135O (Found Hg=26.43. C,,H~NI,Hgf requires Hg= 26.56 per cent..). Ortborhombio a b c = 0.6890 1 0.5106. Forms b { 0 1 0 } m{110} p(O11). The common habit' is sholwn in Fig. 7. A second habit was observed much shortemd along the vertical axis. Following are the mean angular values obtained from six orystads : bt010). rnfl10). q{Ol I}. Azimuth (q) ......... 0" 0' *55'26' 0" 0' Polar distance ( p ) ... 89"58' 90" 0' *27" 3 1316 BARKER AND PORTER THE EFFECT OF ASYMMETRY. Cleta,vage,s g { 01 I } perfect ; c { 001 } imperfect. Optic axial Trans.100/011 /OO% planel a(100) and tbel c-axis is the negative acute bisectrix. Complex-symbol (6)37+( + 3). T e trara-popylanzmo niu m M erc wi-iodide Pra,NHgI,.-M. p. 178O (Found Hg = 25-75. C,,H,,NI,HgI requires Hg= 26.07 per cent,.). P = 113'16'. Forms b{010} a{100} m{110} n{120} c{OOl} r{2Ol}, ~ { l l l } . Folllowing are the1 mean angular vaJues obtained from five crystals : Molnoclinic, The habit is prismatic as shown in Fig. 8. a b c = 1.4965 1 0-7328; b{010}. a(100',. m(110). 74120). c(OO1). Azimuth ( q ) ......... 0" 0' 90" 0' *36' 2' 20' 1' 89"58' Polar distance ( p ) ... 90" 0' 90" 2' 90' 2' 90" 0' *23"16' rpo1;. p{l11). Polar distance (p) ... 32"19' *50'26' Azimuth (+) ......... 270" 0' 52'45' Clelavages m { 110 1 and r{ 201 f good.OptJa axial plane, b(010). An optic a,xis emerges nearly peIrpendicular to ~(301) and the1 acute! negative bisecbrix nearly ooincyidefi with the c-axis. Dispe,rsion moderatel p>v. Trans. O T l / O l l l ~ O ~ . Ph emy l t rim e t h yla,mnz mizc nz Complelx-symbol (3d; - 14)50( + 18). Mercur i-iodid e P hM%NHgI .-M. p. 135O' (Found Hg=27.80. C,H,,NI,Hg12 requires Hg= 27.89 per cent .). Monoolinia al b c = 1.2400 1 0.6783 ; P = 104O'54'. Folrms a{100} m{110} 721{210} q{Oll} e{101}, r{FOl} ~ { l l l } ~ ( I l l } . The habit is prismatic as shown in Fig. 9. Following asel thel mean angular values as obtained from five crystals : a(100;. m(110). 42101. q(0llj. eflOl}. Azimuth ( q ) ......... 90" 0' "39'51' 59" 6' 21'28' 90' 0' Polar distance (p) ...90" 1' 90" 0' 90" 0' 36" G' *39'46' T ( ~ o I } . p f i i i ) . o(Ti1). Azimuth ($) ......... 269'59' 50"54' 336" 4' Polar distance ( p ) ... 55" 7' *47' 2' 36'34' Clelavagei a{ loo} good. Optic axial plane b(010). Through Tram. llO/Tl0/002. Complex-symbol (401; + 15)48&( - 5). P h en. y 1 dim e t h y t e t h y la mm omium M e r c u ?% - iodide P h Me E tN Hg I,. -M. p. 95O (Folund Hg =27-21. C,,H,GNI,Hg12 requires Hg= 27-36 per cent.). Monoclinio a( b c = 0.7391 1 :0'6783 ; P = 94O6'. The common habit is that of unmeasura(b1e radiating needles. A few measurable1 crystals were obtained of the type shown in Fig. 10. a(100) an optic axis is visible on thel edge of the fiedd. A STUDY 13' CRYSTAL STRUCTURE. 1317 Forms m{110} q{Oll} e { l O l } r(TOl} ~ ( 0 0 1 ) .Following are the1 mean angular values obtained from seven crystals (no1 trust-wolrthy results welrel obtainable from thel face1 c which was always curved) : m(110). q ( 0 l l J . e(101;. r { i o i ) . Azimuth ( q ) ......... *53'36' *6' 2' 89'59' 270' 0' Polar distance ( p ) ... 90" 1' *34'18' 44'43' 40'22' Cleavage1 c { 001 } perfect). Optic axial planel b(010). An The1 optic axis is visible1 through c{OOl} on the1 edge od the field. dispelrsion of t3hel opticl axes is strong. Trans. lOl/TOT/OlO. Complefx-symbol (46; 4)53( - 24). P~en~yldimethyl-a-yurolr?/lumm~~~~~na Merczwi-iodide, -PhM%PraNHgI,. -M. p. 880 (Found Hg = 26.54. C11H,8NI,IEgI requires Hg = 26-84 per cent.). Molnoclinic a b c = 0.7775 1 0.6711 ; P= 96O34'.Forms m{110) q{O11} e{101} y(TOl}. Thei common FIG. 10. . FIG. 11. FIG. 12. Phenyldimethylethyl- Phenyldimethylpropyl- Phe?aylTethyldiethy!-anmwnzum mercwz- ammonium mercuri - arnmonwm mercum-iodide. iodide. iodide. form is t h a t of radiating neadlee. A feiw measurablel crystals welrei obtaineld of the habit shown in Fig. 11 with p r i m faces much curved. Follotwing are the mean angular values obtained from setvein Crryshls : m(110). q{Oll). e.1101). T p o i ) . Azimuth ( q ) ......... "53'19' "9'44' 89'52' 269"57' Polar distance (p) ... 90' 0' "34'14' 44"44' 36'58' Cle,a,vage c { 001 } perfect. Optic axial plane perpendicular t o The acute1 negative bisectrix is nearly perpendicular to Dispersion strong p>v. b(010). c { 001 }. -Trans. 101/lOT/OlO.Complex-symbol (4d; 64)52&( - 4). Ph.enyZmetTLy2diethyk~mnaoiii~m Mercwi-iodide PhMeEt2NHgI,. -M. p. 9 6 O (Found Hg- 26.63. Cl~H18NI,HgI~ requires Hg 1315 BARKER AND PORTER THE EFFECT O P ASYMMETRY. 26.84 per cent?.). Monoclinio a b c = 0.7319 1 0.6976 ; P =a 93O24'. Forms b{010} m{110) r2.{120} c{OOl} p{O11) a(101)-r(101). The common habit is shown by Fig. 12. Following are' the mean angular values obtained from five crystals: Azimuth (q) ......... 0" 0' *53"51' 34'18' 89'54' *4"52' bfOlOl. m{llO). n1120). cj001;. q{Oll]. Polar distance ( p ) ... 90" 0' 90" 0' 90" 0' 3'25' "34'57' eC1OI). r(ioi;. Azimuth ($) ...... 90" 2' 269' 57' Polar distance ( p ) 45"19 41O42' Cleavages c { 001 } perfect; m { 110 f impelrfect. plane b(O10). The double retfraction is negakive with sbrong dispelrsioln p<v.Optic axia' 1 An optio axis is inclined at abolut 20" to c{OOlj ' -_ Trans. l O l / l O l / O l O . Complex-symbol (4d; 3)55( + 2 ) . Ph erhy I t rie t h y lam m om ium M e 4-c u ?.i-iodidle Ph E hN Hg I,. -&I. p , C,2H,,NI,Hg12 requires Hg = 26-35 per 9 8 O (Folund Hg = 25-94. FIG. 13. Phenyl triethyl-ammonzum mercuri-iodide (1 1). Fm. 14. Fra. 15. Phenyltriethyl- Phen yld iethylpropyl-ammonzum mercuri- ammonium mercurz-iodide (2 1). iodide. a Ir c = 1.1250 1 1.3490; /3 = 101O20'. Forms a{100} m{110) r(T02} y(O11} p{lll}. The common habit is shown by Fig. 13. Following are the mean angular values obtained from five crystals : a{100;. m{110). rf102). q{OlI). p(ll1;.Azimuth (+) ......... 90" 0' *42'12' 269'58' 8" 5' *46"33' Polar distance ( p ) ... 90" 0' 90" 1' 22'48' 53"39' *62"59' Clea,vagei a{ 1001 perfect. Optic axial plane is b(010). Inclineid dispersioln strong. Trans. OOl/~OO/OlO. Complex-symbol ( 4 h ; 9&)46( - 5+). Plt e n yl t r ie t by la mm omium ill e ~ C Z L ri-iodide 2 Ph E t ,NI Hg I .-&I. p. 144O (Found Hg = 19.21. (CI2H,,NI),HgI2 require A STUDY IN CRYSTAL STRUCTURE. 1311) Hg=18.80 per miit.). Orthmhmbic a b c=0*8G42 1 1.1605. Forms at{lOO} m{llO) c{OOl) s{104) ~(111). The habit is shown by Fig. 14. Following are the1 mean angular value? obtaineld from five crystals : Azimuth (+) ......... 90' 0' *49"10' - 89'58' 49"IO' a{100}. nt(1lOf. ~(0011. ~ ( 1 0 4 ) . p:lllt. Polar distance ( p ) ...90" 0' 90" 0' 0" 0' 18'38' *60"36' Cleavage c { 001 } imperfect. Optic axial plane! b (010) ; the The optic axial angle is acute biselctrix is pespendicular to c{OOl). wide. Trans. OlO/lOO/OOl. Complex-symbol (4d)60&( + 4). Ph en y ldie t h yl- a- proipy lam mom'um Merczcri-iodide, PhEtgPraNHgI,. -M. p. 93O (Found Hg == 26.33. C,,H,NI,BgI requires Hg = 25.87 per cent.). Monoclinic n h c = 1.1185:1:1*3440; /3= ~ { l l l ) . Another habit was observeld t'abular to! a{ 100). Following arel the melan angular values obtained from five crystals: Azimuth (+) ...... 90" 0' *42'19' 90" 4' 8'10' 270'16' "46'31' Polar distance ( p ) 90' 1' 90" 1' 1l0 0' 53'43' 22'45' *62"53' 100057'. F O ~ S ~{Ioo) ?n{iio) c{ooi} q { o i i ) T { i o q , The1 common habit is shown by Fig.15. a{100]. mfiiof. ciooi;. 9:oii;. ~p02:. p;iii;. Clelavagee a{ loo} perfect ; m { 11O} imperfect. Optio axial plane perpendicular to b(010). The1 po'sitive acute bisedris is visible through a{ loo} on the edge of the fielld. Dispersion strong, P C V . Trans. OOl/lOO/OlO. Complex-symbol (4k; 11)50( + 6). Z'h eny llb enzy Zdim e t Ii y lam moniu m iMercuriiodide, Ph( CH,Ph) MekNHg I,. -M. p. 1 4 3 O (Found Hg = 24.74. C,,H,,NI,Hg12 requires Hg = 25-22 per cent).). Monoclinic a b c = 0.7386 1 0.5105, j3=92O26/. Forms b { 0 1 0 } a{lOO} ?n{110} p{O11) r{lOlt, s(121} u{T4l} t ( 3 3 1 ) . The commoii habit4 is shown in Fig. 16. Following are the mean angular values obtained from five orystals : b(O10;. a,'100). m(110;. q(0ll;.T l i o i ) . Azimuth (q) ......... 0' 0' 89'59' "53'34' 4'44' 270" 1' 4121]. ~ ( i 4 i ) . t1321). Polar distance ( p ) ... 90' 0' 90" 0' 90" 0' 27" 7' 32'57' Azimuth (+) ......... *35"43' 342'24' 296"41' Polar distance ( p ) .. 32"31' 65" 1' 66"15' Cleavage uI{ l O O } fair. Optic axial plaue b(010). Trans. oT'o/ioi/ios. CompIels-symbol ( 4 d ; - 7+)69( I 4 1320 BARKER AND PORTER THE EFFECT OB' ASYMMETRY. Phee?tylbenz?/lmeth!/lethylan,Ln2onizcita Merciie?*i-iodide, Ph( CH,Ph) MelEt NHg I,. -M. p. 127' (Found M g - 24.68. Clfj~LoNI,Hg12 reqiiires Hg = 24.78 per cent .). Monoclinic a b c = 0.9878 1 0.3'797, P=106O9/. Forms h ( O l O ) a{100} m{llO] c{O01) y(O11], r{901). Following are the mean angular values obtaineld from seven crystals : b{010;.a;100!. r r ~ ; 1 1 0 f . c{OOl;. qi0lli. ri201;. Azimuth ($) ............ 0" 0' 90" 1' *46"30' 90" 8' 46'37' 269"58' Polar distance (p) ...... 90" 0' 90" 0' 90" 0' 16" 9' 32'57' 42"51' A n optic The! habit is shown in Fig. 17. Cleavage m{ 110} good. Trans. O l O / l O O / O O l . Optdc axial plane1 is b(010). Complex-symbol (4h ; - 16)40(1&). axis is visible through r { 201 } . The dispersion is strong. FIG. 16. FIG. 1 7 Phenytbenzyldimethylamr~,~iu?n PiLenyllberLzylnaethylethyE-mercuri -iodide. ammonium mercuri-iodide. Phenyl b enzyl~ieth~lnnanaoniit tit Merczcri-iodide, Ph(CH,Ph)EhNHgI,. -M. p. 138.5' (Found Hg= 23'71. CI7H2,NI,HgI requires Hg = 24.36 per cwnt .). Monoclinic a h c = 1.0301 1 0.6354, @=108O7/. Forms n t { l l O ) c{001} q{O11} r(ZO1).The crystals are curved and distorted. The com.momn habit is shown in Fig. 18. Following are the mean angular values obtained from seven cryst a'ls : m.(110:. c{O01). q(011). r(z01;. Azimuth (+) ......... *45"36' 90" 0' *27"14' 270" 0' Polar distance ( p ) ... 90" 0" 18"25' 35'33' 43'49' Cleavage6 c{001} imperfect; r { 201 1 perfectl. Optic axial r(2011 plane, h(010) and thelre is an optic axis visible1 through on the edge of t\he field. Trans. O l O / l O O / O O l . Complex-symbol (4h ; - 18)42(&). There is strong dispersion ri STUDY TN CRYSTAL STRUTCTIJRE. 1321 l'h ethyl b enz ylm e t I~yl-a-pro yylam~noiLium Mer curi-iodide, Ph(CH,Ph)E t,NHgI,. -M. p. 134O (Found Hg = 24.34. C,,H,,NI,HgI requires EIg = 24.36 per cent.). Monoclinic a 0 c= 1.1060 1 0.7766, p- 102O5V. Forins u { loo} m{110} c{OOl} r{lOl} s{221}, ~ ( 2 2 1 ) . Following are the mean angular values obtlaineld from seven crystals : The common habit is sholwn by Fig. 19. a{100]. m(110]. Azimuth (9) . . . . . . 90" 0' Polar distance ( p ) 90" 0' *42O5 1' 90" 0' FIG. 18. . - - - - & - - - . - - I - - -I Pheizylbeiazyldiet~yla7nmoniu?n mercuri-iodide. ~ ( o o i f . qioi;. ~{221',. 4221) 89'52' 270" 0' *47" 4' 321'45' 12'36' 26'45' 66'19' 63' 1' FIa. 19. Phenylbsnzy lmetlzylpropyl-ammonium mercuri-iodidc . Cleavage, a { l O O } . The optio axial plane is perpendicular to the plane of symmetry and an optic axis is visible1 t'hrough m{ l l O } . Tra,ns. lOO/Ol0/002. Complelx-symbol (4d; + 13)64%( + 2). Our thanks are due to! the Research Fund Committee of the Chemical Society and to the Scielntific and Industrial Research Department for grants in aid of this work and also to Professor N. L. Bolwman Mr. J. E. Marsh and Professor W. H. Perkin for much help and advice. MINERALOGICAL DEPARTMENT, UNIVERSITY &$USEUM OSI'ORD. [Receiced September 14th 1920.] VOL. CXVII. 3