20 IV.-The Magnetic Rotation of Hydyogen Chloride in dz$erent Solvents: and also of Sodium Chloride, Lithium Chloride, and of Chlorine. By W. H. PERKIN, Ph.D., F.R.S. FOUR years ago I gave an account of observations on the magnetic rota- tions of solutions of the hydrogen compounds of the halogens (Trans., 1889, 55, 702, &c.), showing that in aqueous solution the rotations of these compounds yaried with the concentration, and that t-he numbers obtained were smaller when very little water was used than when much was present. It was of interest, therefore, t o examine these compounds in the absence of water, but as it was not possible to work with the liquefied gases, for want of suitable apparatus, a neutral solvent had to be found, which was not easily acted on by these substances.Many liquids were tried, but generally they were either not sufliciently good solvents, or they were acted on by these powerful agents. At last, a trial with isoamyl oxide, or ether, showed that it not only dissolved an appreciable quantity of hydrogen chloride, bnt was scarcely acted on by it, even after many days, and a solution of the gas in this solvent was consequently employed. It could not be used, however, with hydrogen bromide and iodide, as it is attacked by them too readily. The rotation for hydrogen chloride given by this solution was much lower than that yielded by any of even its strongest aqueous solutions, approximating to the value estimated from compounds of the fatty series, and only a little more than half that given by dilute aqueous solutions.Dr. H. Jahn (Ann. Phys. Chem., 43,280), however, has questioned the correctness of my results, and has suggested that when isoamyl oxide is saturated with hydrogen chloride, a change occurs involving the formation of isoamyl chloride and alcohol, and, therefore, that the product I examined was a mixture of these compounds, and not a solution of hydrogen chloride as I had stated. In a recent inaugural dissertation by Dr. Schonrock, describing experiments undertaken at the suggestion of Dr. Jahn, this point is again referred to, and elaborate calculations are made to see whether Dr. Jahn’s hypothesis can be reconciled with my results. Dr. Schonrock considers that, if I had made certain errors in my measure- ments decting the second decimal place of the specific rotations I gave, my results would not be inconsistent with Jahn’s hypo- thesis, remarking that “in the face of these results i t must be admitted that the assumption of the decomposition of amyl ether by hydrogen chloride is in no way opposed to Perkin’s observations.”Tl€E MAGNETIC ROTATION OF HYDROGFX CHLORIDE.21 An account is then given of what is called a special investigation on this subject, of which I need say but little, except that measurements are described made with a solution of hydrogen chloride said to contain 1.0841 per cent. of hydrogen chloride, 1.2193 of amyl chloride, and 1.0079 of amyl alcohol ; from which Schonrock actually ventures to calculate the molecular rotation of hydrogen chloride, and finrllly remarks, " Hydrogen chloride, therefore, turns the plane of polarisa- tion to an equal extent, both in water and in amyl ether" (Zeit.physikal. Chenz., 11, 773-776). The influence of experimental errors on the measurements of dilute solutions cannot have been brought under the notice of Dr. Schonrock, because if he had considered the subject he certainly would not have measured either this or the other very dilute solutions to which he refers in his dissertation. In a paper on the magnetic rotation of sulphnric and nitric acids, &c., I have drawn attention to this subject (Trans., 1893, 63, 58). I have lately made further experiments with solutions of hydrogen chloride in isoamyl oxide. If, in the saturation of this liquid, the hydro- gen chloride be free from air, and the passage of the gas be discon- tinued when it commences to bnbble through unabsorbed, the amount taken up can be pretty closely found by weighings made before and after the experiment. The accurate determination of the free acid is, however, of the simplest character, consisting in merely fransfer- ring a weighed quantity of the solution to a stoppered bottle con- taining water, and titrating with caustic soda solution, In the following table, the results obtained by direct weighings and by titrating solutions made at different temperatures are compared.The results given by the weighings are slightly lower than the othem, but this is only what might be expected, and is caused by loss of the solvent by evaporation. Temperature at which absorption occurred. by weighings.by titration. Per cent. of HC1 Per cent. of HC1 0" 18-61 18-70 5 16.78 17.04 9 16.28 16-26 13 15-05 15.40 15 14.59 14.91 25 11.27 11.58 These results show that very little, if any, action takes place; otherwise the titrations would give lower results than the weighings, but other evidence on this point will be found further on. In the case of the solutions given above, the saturation was not carried out so far as to be quite complete, but the results show that isoamyl oxide behaves like an ordinary solvent, the amount of hydrogen chloride absorbed increasing as the temperature is reduced.22 PERKIN: THE MAGNETIC ROTATION It is scarcely necessary to say that in preparing a solution of hydro- gen chloride in isoamyl oxide, it is better to do so at a temperature several degrees above that at which t'he solution is to be wed, so that it may not give off gas and change in composition, during the observa- tions.Of course, such soln tions require very careful manipulation whilst being examined; it would never do, for example, to pour them from one vessel to another. I have again determined the magnetic rotation of hydrogen chloride in isoamyl oxide. The solution was prepared at 13", and contained 1441 per cent. of dissolved gas = HCi + 1.372C,oH2,0. Density : d 4"/4", 0.8366 and d 9"/9", 0.8323. Magnetic rotation : t. Sp. rotation. Xol. rotation. 9.3" 1.0398 17.584 Less C1,H,O (11.168 x 1.372) = 15.323 Mol. rotation of HC1 = 2.261 These numbers correspond very closely with those previously ob- tained, namely, 2.211 and 2.265.A solution containing 14-8 per cent. of hydrogen chloride, after it had been made three days, was freed from hydrogen chloride by washing first with water, and subsequently with dilute alkali, and the amyl oxide was then quantitatively examined for isoamyl chloride ; for this purpose rather large quantities mere used-6 and 7 grams-and to decompose any chloride it might contain, the liquid was heated in a sealed tube with alcohol and sodium ethylate at 120-130" (the chloride is decomposed at 100" by this reagent). After the alcohol and isoamyl oxide had been removed, the saline solution was neutralised with nitric acid, and titrated with decinormal solution of silver nitrate. Two determinations were made, and gave 0.0071 and 0.0058 per cent., so that the extent to which action took place between isoamjl oxide and hydrogen chloride during three days' contact is so small that it can be ignored, so far as the magnetic rotation is concerned.I have found that chemical action does very slowly take place if a solution of hjdrogen chloride in this solvent is kept in a warm place, an aqueous layer containing hydrogen chloride separating after the lapse of several months. The above solution containing 14.41 per cent. of hydrogen chloride, examined three weeks after its preparation, mas found to contain 14-29 per cent. of hydrogen chloride. It had been kept at a temperature of from about 6" to 12". I may here mention that I have made a few quantitatire experi- ments with hydrogen bromide and isoamyl oxide. A solution wasOF HTDROQEN CHLORIDE IN DIFFEREXT SOLVENTS.23 prepared which wa,s found by direct weighing to contain 36.5 per cent. of the gas; at the end of ten hours, however, this gave, on titration, only 32.1 per cent. of hydrogen bromide. A second solution, containing 45-7 per cent. of bromide, at the end of 12 hours, contained only 39.3, and,after 36 hours, 31.1 per cent., showing that interaction takes place too rapidly in this case to allow of this solvent being used for measurements of the magnetic rotation of hydrogen bromide as previously mentioned. While experimenting on the preparation of chlorides from alcohols and hydrogen chloride, I had occasion to notice how small an amount of chemical change appears to take place unless a, dehydrating agent be also present, or the temperature be considerably raised, and it occurred t o me that it might be useful to make a few experiments in connection with this subject, to ascertain whether the formation of chlorides really took place at ordinary temperatures ; and if so, at what rate.For this purpose, isoamyl alcohol, kept at about loo, w a ~ slowly saturated with hydrogen chloride ; weighings being made before and after the saturation. The titrations of this solution agreed closely with the numbers given by the weighings, being slightly higher, as in the case of the isoamyl oxide solutions. After keeping for a week and' again titrating, practically the same numbers were obtained, so that it is evident scarcely any chemical action had taken place, the product being simply a solution of hydrogen chloride in isoamyl alcohol.Experiments were then made with ethylic alcohol with the following r eault s. Ethyl alcohol taken ............. Weight of solution .............. Percentage of hydrogen chloride Hydrogen chloride absorbed.. .... according to weighings. ........ Percentage found by t,itrat,ion .... Two days after preparation ....... Five days 3, Seven days ....... ....... 99 19-566 grams 12.142 ,, 31.708 ,, 38.29 per cent. 35-45 ,, 38.46 ,, 38.27 ,, 38-08 ,, From these results, it is evident that with this alcohol also chemical change takes place with remarkable slowness, and it was, therefore, thought worth while to examine the magnetic rotation of hydrogen chloride both in isoamyl alcohol and in ethyl alcohol. Two different solutions in isoamyl alcohol were examined ; they gave the following results.SoZution 1.-This contained 28.03 per cent. of dissolved gas = HCl + 1-065C5H,,O.24 PERKIN: THE MAGNETIC ROTATION Density : d 4"/4", 0.9356; d 8"/8", 0.9326. Magnetic rotation, average of 40 readings : t. Sp. rotation. MoI. rotation. 7-5" 1-2403 9.617 6-329 3.288 Less C,H,,O (5.943 x 1.065) = Mol. rotation of HCl = Solution 2.-This contained 25.45 per cent. of dissolved gas = Density d 4"/4", 0-9281 ; d 9"/9", 0.9244 Magnetic rotation, average of 32 readings : - HC1 + 1'215C5H12O. t. Sp. rotation. Mol. rotation. 8%" 1.2189 10.505 7.320 Less Ca,,O (5.943 x 1.215) = Mol. rotation of HC1 = 3.285 The average of these closely concordant results is 3.286. The solution containing 25.45 per cent.of hydrogen chloride when first prepared, after being kept for three weeks at a temperature of frcm about 6" to 12O, contained 25.32 per cent. Only one solution of hydrogen chloride in ethyl alcohol has been examined ; it gave the following results. This contained 40.04 per cent. of the dissolved gas = HC1 + Density : d 4"/4", 09897 ; d S"/S", 0.9863. Magnetic rotations, average of 64 readings : 1.1 88 C,H,O. t. Sp. rotation. Mol. rotation. 7.75" 1.2991 6.668 3.305 Less C2H60 (2.780 x 1.188) = 3.365 This number is slightly higher than that obtained with the isoamyl alcohol solution, but only by 0.083, and this may be parti- ally due t o the presence of the trace of water which is usually found in alcohol even when carefully dried (the density was 0.7967 a t 15"/15"), aqueous hydrogen chloride having a high rotation.Solutions of hydrogen chloride in both liquids were examined to see whether they contained any appreciable amount of chlorides. The isoamyl alcohol solution was treated in the same manner as the isoamyl oxide solution, the hydrogen chloride being removed, and the remaining alcohol heated in a sealed tube at 120-130" with alcohol and sodium ethylate, &c. Two determinations mere made, and gave 0.0062 and 0.0058 per cent. of chlorine, so that practicallyOP HYDROGEN CHLORIDE IN DIFFERENT SOLVENTS. 25 in these solutions, which were three days old, no change capable of influencing the rotation had taken place. The examination of the ethyl alcohol solution for ethylic chloride was not so simple as the foregoing.The following method was adopted : 34 grams of a freshly-prepared solution containing 32.37 per cent. of hydrogen chloride was taken and diluted with its own bulk of water; the product was nearly nentralised with sodium hydrate, and then rendered alkaline with sodium carbonate ; after this it was distilled in an apparatus provided with a fractionating column until about 30 C.C. had passed over. All these operations were performed in an apparatus provided with one exit only, and this was guarded with a potash bulb containing alcohol to absorb any ethyl chloride that might otherwise escape. The distillate and alcohol from the bulbs were mixed and heated with sodium hydrate in sealed tube at 100" for about two hours (ethyl chloride is quickly decomposed under these conditions).The chlorine found in the saline solution by this process amounted to only 0.00054 per cent. ; therefore, ethyl alcohol can be saturated with hydrogen chloride without any appreciable chemical change taking place, and from the results previously given it is seen that combination afterwards proceeds but very slowly with the lapse of time. The isoamyl oxide used in the foregoing experiments was obtained from Kahlbanm; it had scarcely any permanentl rotation, but when saturated with hydrogen chloride it produced a slight rotation t o the left. The permanent rotation of the isoamyl alcohol, on the other hand, was reduced to about one-third by satmating with hydrogen chloride, which is much more than ca2 be accounted for by the increase in volume due to the gas absorbed.The magnetic rotation of hydrogen chloride dissolved in these alcohols lies between that of its rotation in isoamyl oxide and in water, thus : Diff. Rotation of aqueous solution (20 p. c.) . Rotation in alcohols (average). . . . . . . . Rotation in isoamyl oxide (average) . . 4.412) 1.086 3.326 2*245} 1.081 That the alcoholic solution should give lower results than the aqueous is only what might be expected from analogy, as I have found that diethylamine hydrochloride and ammonium iodide (Trans., 1889, 55, 714, 720, 744) and other compounds behave in the same manner when dissolved in this liquid. Sodizcm Chloride.-As I have examined sodium chloride in the dry state as rock salt, and also in aqueous solution, this seems to be a suitable occasion to give an account of the results, so that a compari-26 PERKTN: THE MAGNETIC ROTATION son may be made between the hydrogen and sodium compounds of chlorine.The column of rock salt examined was 136 mm. long. Density : d 6"/6" = 2.1675. Magnetic rotation : Although almost perfectly transparent when viewed with the polariscope, the rock salt did not show such distinct changes as transparent fluids do, owing, it is believed, to the presence of an extremely minute quantity of selenite, or some other crystalline sub- stance, but by taking a considerable number of readings errors from want of sharpness were no doubt overcome. It was examined on two occasions, 50 readings being made each time ; the following are the averages : t. Sp. rotation. Mol. rotation.15-0" 2.7168 4.073 16.0 2.7269 4.088 Entire average.. 15.5" 2.7213 4.080 The solution of sodium chloride employed contained 26.174 per cent. ; its composition was therefore NaCl + 9.166Hz0. Density: d 10°/lOo = 1.2028 ; d 20"/20" = 1.1995. Magnetic rotation, average of 32 readings : t. Sp. rotation. Mol. rotation. 15.5" 1.3769 14.234 Less OH, = 9.166 - ~~- Mol. rotation of NaCl = It will be seen from the above results that there is an analogy between the rotation exhibited by sodium chloride and hydrogen d o r i d e in aqueous solution, and when water is absent, inasmuch as in both cases the aqueous solution gives the higher results. In the presence of water, sodium chloride, however, does not increase in rotation t o nearly the same extent as hydrogen chloride does.H. Becqnerel, who also has measured the rotation of rock salt, as well as of chloride of sodium in solution, has found that the latter gives the higher numbers. From the rotation of rock crystal, a .value for sodium is obtained by subtracting from it that of chlorine as found in organic chlorides, namely, 1.733 ; this gives 2.347, a number considerably higher than that estimated from the solutions of the sodium salts of the fatty acids or the inorganic acids containing oxygen. Lithium Chloride.-This salt being very soluble, it is possible to examine it in very concentrated, as well as in dilute, solutions, and the results obtained are interesting, inasmuch as the strong solutions 5.068OF HPDROGEN CHLORIDE IN DIFFERENT SOLVENTS. 27 give lower results than the dilute.Three different solutions were ex- amined, about 64 readings being made wit'h each. I. LiCl + 11. LiCl + 3.213 mols. OH, : d 15"/15", 1.3066 ; d 20"/20", 1.3059. 7.411 mols. OH, : d 15"/15", 1.1575 ; d 25"/25", 1.1568. 111. LiCl + 11.760 mols. OH, : d 15"/15", 1.10649; d 25"/25", 1.10600. Magnetic rotation : t . 8p. rotation. 3101. rotation. I. 19" 1.7294 7.379 Less OH, = 3.213 4.166 Mol. rotation of LiCl = 11. 23.2" 1.41 70 11.970 Less OH, = 7.411 4.559 -- 3101. rotation of LiCl = 111. 17.4" 1.2877 16.440 Less OH, = 11.760 4.680 -_ - 3101. rotation of LiCl = These results therefore show that aqueous solutions of this salt behave in an analogous manner to solutions of hydrogen chloride. These results were referred to in the "Proceedings," 1890-91, p.142. Chlorine.-This is probably the only element of its class that it will be possible to measure in a satisfactory manner by the method at present in use, as both bromine and iodine are so strongly colonred that light will not penetrate through a layer sufficiently thick-to afford trustworthy results, either in the case of the pure substance or of a sufficiently strong solution. H. Becquerel, how- ever, who attempted to measure bromine, using the red light of the lithium flame, obtained a number which gives a high value for this element. I n the case of chlorine, it would have been best to examine it in the liquid condition, but at present I have no convenient ar- rangement for this purpose ; therefore a suitable solvent for the gas had to be found. The best for this purpose is carbon tetrachloride, which at about 13" dissolves snfEcient to form a 10 per cent. s o h - tion. The determination of the amount of chlorine taken up by the solvent was made by introducing a weighed quantity of the solution into a bottle containing potassium iodide, and titrating with sodium thiosulphate. Two solutions were examined. 1. Contained 10.29 per cent. of chlorine; composition = C1, + Density : d 4"/4", 1.6085 ; d 10°/lOo, 1-5973. 4.02CC1,.28 EASTERFIELD AND SELL ON CITRAZINIC ACID. Magnetic rotations, average of 190 readings made on four diil'erent occasions : f. Sp. rotation. Mol. rotation. 7.1" 1.2866 30.760 26.460 C1, = 4.300 Less CCl, (6.582 x 4.02) = 11. Contained 9.88 per cent. of chlorine; composition = C1, + Density : d 4"/4", 1.6093 ; d 9"/9", 1.5998. Magnetic rotation, average of 72 readings : 4.d04C C1,. f . Sp. rotation. Mol. rotation. 8.2" 1.2858 32.058 27.670 Less CCl, (6.582 x 4.20-4) = C1, = 4.388 The average number for the molecular rotation of chlorine from the above is 4.344. If the atomic value be taken as half this, it will be 2.172. This result is higher by 0.439 than the value found for this ele- ment when in combination, as in propylic chloride, in which case it is 1.733. At the same time, it is a much lower value than that calculated from the rotation of a dilute solution of hydrogen chloride (4.154 about).