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acetate for some hours so as to form acetanilide, which is then purified by crystallization. The acetanilide is powdered, suspended in water, and treated with excess of bromine or chlorine (Proc. Roy. Soc. vol. x. p. 589): the product is heated with powdered potash, moistened with spirit. This method gives good results. The product consists chiefly of mono- and tri- deriva


(8) It is not necessary to prepare acetanilide; a solution of dry aniline in glacial acetate answers equally well. Aniline is dissolved in 2-3 vols. of acetate, and chlorine- or brominevapour passed over the surface of the mixture, which must be well agitated. [In the case of bromine-vapour, the operation is performed in a warm closet, and the bromine is volatilized slowly from a retort, which must be heated by a small flame placed a considerable distance below. It is very easy thus to manage so that, while vapour comes over freely, no drops of bromine are delivered from the tube of the retort. This tube should be bent vertically downwards, and nearly touch the surface of the aniline mixture in the flask where the operation is conducted.] Considerable heat is evolved at first. As the reaction proceeds, the mixture becomes thicker, and partially solidifies; and at this point the operator will arrest it if he requires a minimum of tri- derivative, but continue until total solidification ensues if he wishes the triderivative to be a maximum. The whole may, if desired, be again submitted to further action by gently heating with more glacial acetate, which causes solution to occur. The cooled mass is heated to 100° under water, and afterwards cooled therewith. The supernatant liquid is filtered off and precipitated with alkali: this precipitate contains mono- and di- derivatives. The insoluble portion is mixed with powdered potash, moistened with spirit, and then heated in order to destroy any traces of anilide that may have been formed. The three derivatives are separated from the dark mass as already stated. The distinguishing feature of this mode of reaction is, that it is completely under the control of the experimenter. The ratio C3 H9 ON : Br2 furnishes chiefly dibromaniline. Doubtless this process applies to other amines.

(y) The direct action of chlorine &c. on aniline itself is not attended with satisfactory results; in presence also of water or aqueous hydric salt there is an enormous amount of by-product. Aniline purified by distillation with mercuric iodide yields exceedingly little moniodaniline.

(8) Aniline may be mixed with plumbic oxide, and iodine &c. added*. I have only succeeded in preparing traces of iodaniline in this way. A considerable amount of crude product is obtained, * This is Stenhouse's method of iodating orcin.

but it is difficult to purify. The only substance I was able to separate, in two large operations, was volatile in a current of steam, white, and crystalline; it was soluble in aqueous hydric chloride, and precipitated therefrom by ammonia, but not by platinic chloride after repeated crystallization from spirit. When melted, it gave no definite fusion-point.

Properties. Having contrived a very delicate apparatus for the determination of fusion-point, I have been enabled to make some interesting comparisons among these derivatives; but the actual numbers (though otherwise completely corrected) have not yet been converted into degrees of the air-thermometer. All the determinations are made upon substances repeatedly purified by fractional methods; and in no case is the probable error of the fusion-point greater than 0°.01. The result of fifty-five observations with monochloraniline from acetanilide was 69°69; 0°.03 higher than that of forty-eight observations with the derivative of the direct acetic process. Dichloraniline could not be obtained in sufficient quantity for systematic examination by either of the methods (B) or (y).

Trichloraniline was very easily made by the direct acetic process, and purified by distillation in a current of steam. The anilide process yields little, if any. For the organic analysis of this substance I am indebted to the kind offices of my friend Mr. Valentin.

0.3392 grm. substance gave 0.7186 grm. argentic chloride. 0.2311 grm. of the same substance gave 0.3103 grm. carbonic dioxide.

0.2758 grm. of the same substance furnished 0.3690 grm. carbonic dioxide and 0·0600 grm. water.

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These numbers agree very well with theory. The fusionpoint, as determined by ninety-six observations with two mercurial thermometers, was 77°05; and it occurs so sharply, that the probable error of the result is only 0.0014. Lesimple (Ann. Chem. und Pharm. vol. cxxxvii. pp. 126 & 127) describes a trichloraniline which he obtained by reducing nitrotrichlorobenzol. He states that it has a very unpleasant and persistent smell, and that it melts at 96°.5. On these two points my derivative differs from his it has rather a faint odour, but not very unpleasant, and melts 19° lower. In all the other reactions mentioned by Lesimple the two bodies exhibit a complete agreement.

Monobromaniline prepared from acetanilide melted at 61°.80

(69 obs., two thermometers); the direct process gave 61°.85 (28 obs., one thermometer). Dibromaniline was prepared as stated above (B): the direct acetic process yielded me little, if any, with the same ratio of reagents. The fusion-point was 78°.82 (100 obs., two thermometers). Tribromaniline from acetanilide melted at 116°-22 (30 obs., one thermometer); that which was made by the direct acetic process melted at 116°.28 (42 obs., two thermometers).

From purified aniline only a very minute amount of moniodaniline was obtained by three trials of a direct action in the ratio


2C6 H7N: I2. In presence of plumbic oxide (C6 H7 N: 12: 2 the yield was rather greater; but the fusion-point of the portion volatile in steam gradually rose on repeated crystallization to 86° and beyond, with no certain indication of a settlement. This product appeared to contain traces of ordinary moniodaniline; but after the final crystallization it yielded no platinic salt insoluble in alcohol and ether. The residue in the retort, nonvolatile in steam in presence of potash, contained aminic bodies soluble in dilute aqueous hydric chloride. These are perhaps the missing poly-iodanilines.

12 Pemberton Terrace,

St. John's Park, N.

III. Carbon and Hydrocarbon in the Modern Spectroscope. By PIAZZI SMYTH, Astronomer Royal for Scotland*. [With Two Plates.]


N the November Number of the Philosophical Magazine appears a paper "On the Spectrum of Carbon," by an author whose name is well known and widely respected both in spectroscopic inquiries in general, and carbonaceous spectra in particular, viz. W. Marshall Watts, D.Sc. Yet there would seem to be a something somewhere wanting in the said paper if it is to represent the state of knowledge in 1874 rather than 1854, and to lead towards the discovery of truth as it is in


The author sets out by suggesting what he considers an improved method for astronomers in observing the rather puzzling spectra of comets, viz. "to work by eye-estimations of the distance of the bands from the known bands of some equally faint spectrum, made to occupy the lower portion of the field of view, provided," says he, "a faint spectrum can be found possessing a sufficient number of well-defined bands in the region of the spectrum

* Communicated by the Author.

to be mapped." This, as italicized by him, is very clear; and he finds such a reference in what he calls the carbon-spectrum, but which others before him, whom he does not mention, have called the spectrum of carbohydrogen, of acetylene, of marshgas, and of general blue base of flame.

Impressed next with the importance of the places of the bands of that spectrum being known to great accuracy, Dr. Watts proceeds to give his own recent, and doubtless very good, measures of the wave-lengths of certain fine lines therein, and concludes with stating what substance the whole collection is the spectrum of, and what it is not, both in chemistry and physics.

The principle involved.

Now to the principle of spectroscopic observation announced in the first part of the paper I certainly cannot object, seeing that it is, step by step, the very method and the very referencespectrum which I have been employing for four years past, and am still using in this royal observatory, and have often published upon, hoping to promote its general adoption. My first attempt indeed was not very successful; for having sent a paper on the subject to the Royal Astronomical Society on May 30, 1871, with the request that it might be read at the next meeting and printed in the following 'Monthly Notices,' that learned body (which is a very excellent body except in so far as it deals in the accursed thing for all free countries, of secret committees) chose to keep my paper back for six months without rendering any reason why.

However, I having met, during those months, with Professor Swan of St. Andrews, who first accurately measured that spectrum's lines, so far back too as in 1856-and I having held forth to him on the delightful and universal reference for faint astronomical spectra which I had found in that chemical spectrum which he had previously made so peculiarly his own, both by a priority without any question, and an accuracy which Professor Kirchhoff has since then pronounced to be classical, he was induced to go to Section A of the British Association, then meeting in Edinburgh, and gave them a good and sound paper on the subject, besides furnishing me with his own special reductions of some of his angles of the refractive indices of the lines into wave-lengths, agreeably with Angström's normal solar spectrum.

Afterwards, too, I not only printed the so-long-stopped paper in the thirteenth volume of the Astronomical Observations of the Royal Observatory, Edinburgh (together with Professor Swan's wave-lengths as above), but in the beginning of 1872 practised the method still further on the zodiacal light at Palermo, and on

truth to assert that the number of known bodies may soon be doubled.

§ 38. Geological.-The behaviour of mixtures of salts will again offer a new chapter for study; and I suppose we may expect that much light will be thus thrown upon some of the most obscure geological questions. For though we have been considering above cryohydrates (that is, compounds of water solidifying below the freezing-point of water), there can be no discontinuity separating the medium water with its peculiar temperature of solidification from other media of very different melting-points. We know already, indeed, very many instances in which the mixture of two bodies has a lower melting-point than either of its constituents. What must happen, then, if a mass of molten rock, such as a silicate, is saturated at a high temperature with another silicate? When the mixture cools, the second may separate out in the solid form, perhaps as quartz, perhaps as felspar, or what not. Anon, at a certain lower temperature, solidification takes place between the medium and the dissolved rock in definite proportion-definite, though perhaps not necessarily in chemical ratio, but presenting that mineralogical ratio which is so striking, and which has not hitherto been satisfactorily explained.

§ 39. Constant temperatures.-Perhaps one of the most interesting aspects of the experimental results is the establishment of fixed temperatures below zero. With the exception of the melting-points of a few organic bodies such as benzol, and the boiling-points of a few liquids such as liquid ammonia, sulphurous acid, and carbonic acid, and the rather ill-defined temperatures to be got by various freezing-mixtures, there are no means in the hands of physicists for obtaining and maintaining with certainty and ease a fixed temperature below 0° C. Now, if we surround a body with one of the solid cryohydrates described above, the body is kept at a corresponding temperature as long as any of the cryohydrate remains solid, and this with as much certainty as the temperature 0° C. can be maintained by melting ice. We thus command temperatures between -23° and 0° C. with the greatest precision.

§ 40. Invitation to others.-I need scarcely point out that the field of inquiry which has been here opened is far too large to be satisfactorily examined by one worker. It is notably at the commencement that the collaboration of many workers is most beneficial, so that fundamental errors may be quickly corrected. On this ground I respectfully invite my fellowlabourers to this branch of inquiry.

I have received through a considerable part of this inquiry much valuable assistance from my friend Mr. F. H. Marshall.

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