GLADSTONE ON THE REFRACTION EQUNALENTS ETC. 147 XVIIL-On the Refraction -Equivalents of the Aromatic Hydro-carbons and tlteii. Derivatives. By J. H. GLADSTONE, Ph.D. F.R.S. IN Professor Landol t’s important paper on Refraction Equivalents,* he shows that assuming 5 as the value of carbon 1.3 as that of hydrogen and 3 as that of oxygen we may reckon the refisaction of a large number of organic com-pounds with a close approximation to the truth. But in the table attached to an earlier paper,t there are several refraction equivalents given which are not conformable to these theoretical values. They are the equivalents of phenylic acid oil of bitter almonds salicylous acid salicylate of methyl benzoate of methyl and befizoate of ethyl. In the previous papers of Mr.Dale and myself‘,$ there had been given the specific refractive energies of a great vaiiety of organic compounds and most of these were found to be in accord- ance with Landolt’s numbers; but the following stand out cxceptioiially-phenylic and cresylic acids oil of cassia benzol toluol xylol cumol cymol carvol and eugenic acid. f Ueber den Einfluss der atomistischen Zuaammensetzung C- H- and O-haltiger fltjssiger Verbindungen auf die Fortpflanzung des Lichtes (Yogg. Ann. cxxiii 595). .F Ibid. cxxii 545. $ Phil. Tram. 1858 p. 887; and 1863,p. 317. 148 GLADSTONE ON THE REFRACTION EQUIVALENTS have since been led to assign 4.1or thereabouts as the value of nitrogen and 9.9 as that of chlorine; and these throw into the list of exceptions-pyridine picoline lutidine collidine chino- line lepidine aniline amyl-aniline nitrobenzol diiiitrobenzol chlorobenzol and trichlorobenzol.While investigating the essential oils I also found salicylate of' methyl anethol and myristicol to have remarkably high refractive indices ; and similar results have since been obtained from naphthalin benzoic acid benzoate of potassium sulpho- phenylate of potassium chloride of benzoyl sulphide of phenyl chlorhydraiiil) and thymol. The last three substances were kindly placed at my disposal by Dr. 8t e:nhous e. A glance at the names of these exceptional substances will show that they consist of the aromatic hydrocarbons with the bodies derived from or related to them ; two groups of nitro- genized bases; naphthalin; and some oxidised essential oils.In the followiiig table they are divided into these several groups:- Substance. Formula. Refraction :quivalent CalcuIated refraction tquivalent. Difference. Benzol. ................... !roluol .................... Xylol.. .................... Cumol .................... Cymol.. ................... Chlorobenzol ............... 43 *7 51 -4 59.2 66 -6 73 -9 52 *I 37 *8 45 *4 53 *o 60 *6 68 *2 46 -4 5 69 6 .O 6 *2 6 *O 5 *7 5-7 Trichlorobenzol ............. 69 *7 63.6 6 *1 Nitrobenzol ................ 56 -0 47 *6 a -4 Dinitrobenzol.. ............. 65 -2 57 '4 7.8 Aniline.. .................. Amyl-aniline .............. Sulphide of phenyl .......... Sulphophenylate of potassium. Chlorhydranil.. .............Ditto (Gladstone) ......... Cresylic acid.. .............. Benzoic acid.. .............. Phenylic acid (Landolt) .... 51 *1 91 -1 103.1 6'7 -6 85 -6 47 -7 47 *3 55 .3 56 *6 43 '2 81.2 89 '0 61 '6 78 .O 40 -7 40 *7 48 *3 48.6 7'9 9 -9 2(7 *O)6 -0 7.6 7.0 6 *6 7.0 8 $0 Benzoate of methyl.. ........ Benzoate of e thy1 (D e 1 f fs). ... Ditto (Landolt). ........... Benzoate of potassium.. ...... Hydride of benzoyl. .......... Chloride of benzoyl.. ........ Salicylous acid.. ............ Salicylate of methyl(L andol t) Ditto (Gladstone). ......... Ditto (Delffs) ............. Hydride of cinnamyl.. ....... 63.9 71 -3 71 6 62 .6 54 *6 62 -2 58 *9 68 .2 67 -3 6'7*2 75 -3 56.2 63 '8 63.8 55 .4 45 -7 54.3 48 *6 59 *1 59 .1 59 *1 58.3 7-7 7'5 7.8 7'2 8.9 7 -9 10.3 9 -i 8 -2 8 -1 17*o OF THE AROMATIU RYDROCARBONS ETC.' 4-5 45 Lutidine.. ................. C7H9N....... 56 .1 50 -8 5.3 Collidine.. ................. CdHl,N...... 65 *O 58 *4 6*6 Chinoline .................. Lepidine.. ................. C,H,N. ...... CloHgN.. .... 66 -7 80 *6 58 -2 65.8 8.6 14 *8 Naphthdin ................ CloHS........ 75 *o 60 *4 14-6 Anethol.. .................. C10H120.. .... 81 *4 68 -5 12-9 Carvol .................... UIOH140...... 76 9 7 *1 6 *8 Thymol ................... Myriaticol ................. Eugenic acid.. .............. CIOH,IO...... C10H140...... C10H1202.. ... 80 *2 76 .8 81 *1 71.1 71 -1 71 *4 9.1 5.7 9 -7 The refraction equivalents in the fourth column are calculated from the numbers given in my paper now being printed by the Royal Society viz.C = 5.0; H = 1.3; 0 = 2.9; C1 = 9.9; S = 16.0; SO = 17.0; N = 4.1; NO = 11.1. It will be seen that in every case they are amaller than the experimental numbers. The first group contains every derivative of the aromatic hydrocarbons of which the refiaction equivalent has been satis- factorily determined as far as I am aware. It will be at once seen that the hydrocarbons themselves and their chloiine sub-stitution-products are about 6.0 above what theory requires while the compounds from creosote are a little higher still. The azotised products and those containing C, are nearly if not quite 8.0 above the calculated values ; and that peculiar com-pound hydride of cinnamyl which constitutes the bulk of oil of casgia is well known to be among the most refractive and dispersive of bodies.To what can this increased refraction be attributed? It is evidently connected with the nucleus of the whole group and my first theory was that the hydrogen in benzol and its con-geners or derivatives had a higher refraction equivalent than in the generality of organic bodies; in fact that instead of 1.3 it ought to be taken at 3.5 as in hydrochloric hydrobromic and hydriodic acids or at an intermediate figure as in nitric or sulphuiic acids. Dinitrobenzol and even trichlorobenzol it is VOL. XXIII. N 150 GLADSTONE ON THE REFRAOTION EQUIFALENTS true still exhibited the increased refraction but the hydrogeii remaining unchanged was sufficient to account for an increase of 8.8 or 6.6.It became very interesting therefore to examine some member of the same group in which less than 3 atoms of hydrogen had escaped substitution. Chlorhydranil C6C1,0,H2 appeared peculiarly well adapted to the purpose especially as its 2 atoms of hydrogen are considered not to belong to the nucleus; and on examination of its solution in ether it was found to give a refraction equivalent of 7.6 that is about the usual amount above the calculated value. I am now disposed rather to regard the nucleus phenyl C6H, as an entity having an exceptionally great influence on the rays of light and to seek an analogy in that augmentation of refractive power which certain elements (for instance iron and phosphorus) undergo when they alter their atomicity ; arid this entity is not destroyed by the replacement of its hydrogen by chlorine nitric oxide oxygen or sulphur.As long indeed as this nucleus retains its integrity of constitution its special optical property continues; but when it is subjected to such chemical change as to break it up the resulting products have only the ordinary effect on light. Thus chloropicrin C(NO,)Cl, though prepared from trinitrophenylic acid C6H,(N0,),0,has only the refraction equivalent 45.2 the calculated value being 45.8. Thymol has claims even on chemical grounds to be considered a higher homologue of phenylic acid and its optical character lends much support to tliis view. It might therefore be placed in the first group. Of the other groups of substances having an exceptionally high refraction equivalent I may have something to say on a fiiture occasion.The great dispersive power of all these bodies likewise claims a further notice. In answer to a question by Mr. Perkin Dr. Gladstone stated that since the above paper was sent in to the Society he had examined the refraction of anthracene. A solution of it in beiizol gave for the hydrocarbon Cl4Hl0,the value 100-3 instead of 83.0 being an excess over theory of no less than 17.3. OF 1HE AROMATIU HYDROCARBONS ETC. He had also considered more attentively the effect which an excess of carbon in the composition of a substance exerts on its propagation of light. Among the hydrocarbons the paraffins and olefines give normal values but all the essential oils of the C1,H16 type that have been examined more than 30 in number give refi-action equivalents a little above theorj- those of the great turpentine group generally exceed the calculated number 70.8 by amounts varying from 2 to 3 those of the orange group by amounts varying from 3 to 4.The refraction equivalents of the typical hydrocarbons may be thus expressed in a series :-Hydrocarbon. Typical formula. Refraction equivalent. ____-----Paraffins .............. CnH2n +2 Normal Olefines. ............... cnH2n Terpenes .............. CnH,n -4 Aromatic hydrocarbons . . C,H, -6 Naphthalin ............ CnH,n -12 Anthracene ............ CnH2n -18 These higher numbers must be considered only as rough deter- minations but the gradual advance is sufficiently apparent.There is a similar advance in dispersion. Another illustration of the increased influence on light of carbon which is uncombined with two atoms of hydrogen or one of oxygen may be found in a series of oxidized bodiesJ which are obtained from various essential oils and differ from one another only in the quantity of hydrogen. Substance. Formula. I Refraction equivalent. ---I Peppermint camphor .. ' Cl,H2,0 Normal Bihydrate of cajeput .. C,,H,,O 7 Oil of wormwood.. .... 'lOH16' + 1 99 Carvol .............. ClOHl*O + 6 79 Anethol .............. C,OHl2O + 13 99 -.---Carbon alone in the form of diamond has only the normal refraction equivalent 5 0 TABLE OF DATANOT HITHERTO PUBLISHED.& Refractive indices. Specific Temp. Substance. Equivalents of solvent. gravity. centigrade. A. D. H. -L_.--Benzol ....................... ......................... 0-887 11 1 *4953 1 -5052 1 *5393 Ditto.. ....................... ......................... 0*878 10 1.4925 1 -5021 1 .5358 Ditto. ........................ ......................... 0*886 7 1 -4981 1.5071 1 *ti411 Cymol ....................... ......................... 0*872 11 1.4801 1 -4877 1.5130 Nitrobenzol .................. ......................... 1.193 7 1 *5438 1.5565 ...... Ditto,. ....................... ......................... 1 a191 8 1.5426 1*5564 ...... Sulphide of phenyl ............. ......................... 1.126 8 1.6244 1 -6398 1 $942 Sulphophenylateof potassium ....111 -36 of water.. ......... 1.092 11 1 *3587 1 -3638 1 *3767 Chlorhydranil .................. 23.74ofether. ........... 0-802 12 -5 ...... 1.3775 ...... Benzoic acid.. ................. 11 a14 of alcohol.. ........ 0-859 7 1.3913 1.3968 1.4116 Ditto.. ....................... 17.44of alcohol.. ........ 0‘838 8.5 1 *3806 1.3850 1 -3993 Benzoate of potassium .......... 22 -90 of water + 0 .06 K20 1-139 6 1.3917 1’3974 1.4149 Ditto.. ....................... 38.24 of water + 0 *09 KzO 1 *091 6 1 *3705 1 -3751 1 *3904 Chloride of benzoyl.. ........... ......................... 1 -228 10 1.5438 1 -5568 1 *6012 Hydride of cinnamyl.. .......... ......................... 1 *059 11 1,6045 1.6253 ...... Naphthelin .................. 7 -95 of ether.. .......... 0-789 6 1.3950 1.4005 1.4189 Anethol ...................... ......................... 0-9877 .. 1.5430 ...... 1 -6129 Thymol ...................... 18 .39 of alcohol.. ........ 0*832 8 1.3845 1 *3890 1 *4031 Myristicol .................... ......................... 0.9446 .. 1 -4848 ...... 1 -5160