which attention has yet been drawn-of a solution, namely, the physical properties of which are proportional means of those of the constituents.

Although it would appear that the variations in specific rotatory power of a substance dissolved in various chemically inert solvents are due mainly to changes in the association factor of the solute, this does not preclude the solvent from exerting a specific action upon the rotation constants quite apart from its influence upon the association factor. It would seem, however, that such a specific action is not exerted upon an active substance by the mixture of the two antipodes; this is evident from the fact that the specific rotatory powers of lævotetrahydroquinaldine and of levopinene respectively are the same in the solvent free state as in solutions in which the externally compensated substance is used as solvent.

The change of specific rotatory power of a practically monomolecular substance like lævopinene, such as is observed when the solvent and concentration are altered, may be due to a specific action of the solvent apart from its effect upon the association factor of the solute; there is, indeed, evidence supporting the view that combination between the solute and solvent sometimes occurs in similar cases. The above table gives the specific rotatory powers in various organic solvents of a sample of lævopinene having [a]-36.97° at 21.2° when solvent free. The numbers obtained in the dilute solutions (c = 2) are probably con

siderably affected by experimental error. The table shows that the specific rotatory power of levopinene varies in different solvents, but to a minute extent compared with the variation in specific rotatory power of lævotetrahydroquinaldine in different solvents. A series of determinations of the specific rotatory power of lavopinene dissolved in a carefully purified sample of externally compensated pinene was also made, and the results, given in the last table, contrast very strongly with those obtained with solvents other than inactive pinene.

The results obtained with the pinenes point to the same conclusion as do those with tetrahydroquinaldine, namely, that the two optical antipodes, when mixed together, are wholly without mutual influence, and that consequently there is no question of the two substances combining to form a racemic compound.

Our thanks are due to the Government Grant Committee of the Royal Society and to the Research Fund Committee of the Chemical Society for grants defraying the cost of apparatus and materials used in the above work.

GOLDSMITHS' INSTITUTE,
NEW CROSS.

CXIII.-The Characterisation of "Racemic" Liquids.

By FREDERIC STANLEY KIPPING and WILLIAM JACKSON POPE. In a paper published early this year (this vol., p. 36), we proved that Ladenburg's general method for distinguishing between a racemic substance and a mixture of enantiomorphously related compounds (Ber., 1894, 27, 3065) is fallacious and cannot afford the criterion desired. Shortly afterwards, in a reply communicated to this Society (this vol., p. 466), Ladenburg, after admitting the justice of our criticisms, gave what he described as a "different form" to his previous statement of the method in question, but, as was pointed out by one of us at the time (Proc., 1899, 15, 73), the alteration in form was so profound that the new statement had no principle in common with the original one. This new method, which was also described in a German version of the paper (Ber., 1899, 32, 864)-where it appeared as a spontaneous effort on the part of its author-consists in determining the solubility of the externally compensated substance with, and without, the addition of a small proportion of one of its optically active components; if the solubilities are different, then the substance is racemic, whilst, if they are the same, it is a mere mixture of the two enantiomorphs.

This method, so far as it is applied to crystalline substances, is, except

in isolated cases, perfectly valid, and is merely the logical outcome of Kenrick's work (Ber., 1897, 30, 1749) and our own (loc. cit.). Recently, however, Ladenburg has attempted to apply it to externally compensated liquids with the object of ascertaining whether they are racemic or mere mixtures (Ber., 1899, 32, 1822); and in some of these experiments, instead of determining the solubility of the externally compensated substance alone and in admixture with a small proportion of one of its optically active components, he adopts the better and more convenient plan of examining polarimetrically the solutions obtained in the two cases. He takes, for example, an optically inactive mixture of d- and l-limonene, shakes it with dilute alcohol insufficient to dissolve the whole, then adds a little d-limonene, and shakes again; on subsequently examining the alcoholic solution, he finds that it is optically inactive, and so he concludes that d- and l-limonene do not form a racemic liquid at the ordinary temperature.

Now the results obtained by such an application of the method afford no evidence whatever of the non-racemic nature or otherwise of the externally compensated liquid, and consequently the conclusions which Ladenburg draws from them have not the slightest value. The method is valid with crystalline substances, because in the case of a non-racemic mixture of optical antipodes two solid phases in contact with the solution are being dealt with; whilst, in the case of a racemic substance, to which a small proportion of one active isomeride has been added, there is the question only of one solid phase (a racemic one), and this is in contact with a solution saturated with respect to it and partially saturated with respect to the active component. A liquid mixture of d- and l-isomerides, whether they form a racemic liquid or not, only constitutes one phase in the system, and never two, as in the case of a crystalline non-racemic mixture. The error into which Ladenburg has fallen is the more surprising, since Bakhuis Roozeboom has recently contributed a very clear discussion of the subject from the standpoint of the theory of equilibrium (Ber., 1899, 32, 537; Zeit. physikal. Chem., 1899, 28, 494).

We have shown, then, by the foregoing argument, that Ladenburg's method of dealing with liquid externally compensated substances is in disagreement with the very principles from which its author professes to deduce it, namely, the principles of equilibrium. Since, however, the examination of optically active and externally compensated substances in as many directions as possible is urgently desirable at the present time, in order to make certain that the laws of equilibrium have been properly applied, we have made a fresh investigation of some substances of this kind, with results which are quite in accordance with our theoretical argument.

Pseudoracemic and Dextro-Camphorsulphonic Chlorides.

We have previously shown that the sulphonic chloride obtained from the product of the sulphonation of d-camphor with anhydrosulphuric acid, consists of a mixture of the d- and l-isomerides, the former being present in the larger proportion. For many reasons, discussed in earlier papers (Trans., 1893, 63, 548; 1895, 67, 354; 1897, 71, 989), we have also concluded that the externally compensated substance is not truly racemic, but that the antipodes crystallise together, forming a pseudoracemic substance.

We defined a pseudoracemic substance as one in which the enantiomorphously related components are twinned together, and we may therefore take this opportunity of pointing out that the term seems to be understood in a different sense by Roozeboom (Zeit. physikal. Chem., 1899, 28, 494), who attributes to pseudoracemic substances the properties of isomorphous mixtures or solid solutions. As we alone, so far, have worked with pseudoracemic substances, and have observed no marked analogy between isomorphism and pseudoracemism, we cannot share Roozeboom's views as to the nature of such substances; possibly, however, the pinonic acids, recently examined by Fock (Zeit. Kryst. Min., 1899, 31, 479), afford a case of pseudoracemism in the sense in which Roozeboom understands it.

However, according to our views of pseudoracemism, a substance such as crystalline externally compensated camphorsulphonic chloride should behave towards solvents in a manner geometrically similar to that of a non-racemic mixture of optical antipodes, and consequently, on extracting with a solvent a sample of this substance containing a small proportion of one or other isomeride, an optically inactive solution should be obtained; this we find to be the case.

A considerable quantity of crude camphorsulphonic chloride was purified by recrystallisation from ethylic acetate, and a sample was ultimately obtained having the specific rotatory power [a] + 12° in chloroform solution; since d-camphorsulphonic chloride has the specific rotatory power [a] + 128°, the sample contained about 45 per cent. of l- and about 55 per cent. of the d-sulphonic chloride.

Portions of 5 grams of this mixture, when agitated for 5-7 hours at constant temperature with 30 cc. of various mixtures of light petroleum (b. p. 40-60°) and chloroform, yielded solutions devoid of optical activity when examined in 200 mm. tubes in a polarimeter reading to 0·01°. Our previous conclusion is thus confirmed; crystalline externally compensated camphorsulphonic chloride is not a racemic substance, but is pseudoracemic in the sense of our definition,

But, since externally compensated camphorsulphonic chloride is not racemic in the solid state, there is no reason for expecting that it would be racemic in the pure liquid state at the same temperature, and the probability that it would exist as a racemic substance in dilute solution is even more remote, because, so far as they have been investigated, compounds proved to be racemic in a crystalline condition are known to be wholly resolved into their components in solution.

In order, however, to study the behaviour of mixtures of d- and l-camphorsulphonic chloride in a dissolved condition, the following experiments were made: portions of 3 grams of the same sample as before were completely dissolved in mixtures of chloroform (10 c.c.) and light petroleum (20 c.c.); a mixture of alcohol (30 c.c.) and water (7 c.c.) was then added to the solution, and the whole shaken during 3-4 hours at the ordinary temperature. The liquid, which at the end, as at the commencement of the experiment, was free from crystals, separated when left at rest into two layers; the lower one (about 32 c.c.), we may call the alcoholic, the upper one, the petroleum, solution of camphorsulphonic chloride. Both these solutions were found to be optically active when examined in a 200 mm. tube, the alcoholic solution showing a rotatory power of about a +0.6°, the petroleum about a +0.9°. A repetition of these experiments with 2 grams of the same sample of sulphonic chloride afforded similar results. Now, if Ladenburg's application of the method referred to above to liquids were valid, we should have to conclude that dissolved, externally compensated camphorsulphonic chloride is a racemic substance—a conclusion which, as indicated above, is scarcely within the bounds of possibility; there are, moreover, other arguments which lead equally to the conclusion that the sulphonic chloride in the state of solution does not show the behaviour of a racemic compound, so far as the disputed method is concerned. In the first place, the result of shaking together the two solutions of unequal quantities of the two optically active sulphonic chlorides is quite different from that obtained on shaking a solid mixture of a racemic substance and one of its optically active components with a solvent; in the former case, both solutions (the extract and the extracted) remain optically active, whereas in the latter the optical activity is wholly confined to the liquid extract; even granting the existence of a racemic sulphonic chloride in solution, it seems to us that, according to Ladenburg's views, one of the solutions should become optically inactive. In the second place, or rather, putting this same argument differently-if pseudoracemic camphorsulphonic chloride become racemic when it is dissolved in a mixture of chloroform and petroleum, it could not possibly yield an optically inactive solution when a mixture of unequal quantities