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cooled the sea-water to -2° C. in a beaker, which I enveloped thickly with flannel. I tried in vain to freeze the surface by blowing over it dry air which had passed immediately before through a long pewter worm immersed in a freezing-mixture. But I succeeded in getting a sheet of ice when I hung a freezingmixture contained in a blackened tin pan within about } inch of the surface of the water, the whole being plentifully enveloped in flannel. Perhaps here the actual conditions which obtain when sea-water freezes were reproduced. I found that the pressed ice contained only 0.4052 of solid residue at 100° C.

$ 35. The question suggested itself to me whether, when one part of a solution of a salt is cooled, there may not be an accumulation of salt in the cooler part, although not accompanied by any solid separation. I accordingly cooled a saturated solution of nitre to -1° C. and decanted from the separated nitre. I then warmed the solution in a tall beakerglass to 60° C. and placed the bottom of the beaker in melting ice. In an hour's time a thermometer at the bottom stood at 10° C., at the top at 33°. A specimen from the bottom contained 11:3 per cent. of nitre; one from the top contained 11:7 per cent. of nitre-showing that there was no sensible diffusion of the salt one way or the other.

General Considerations. § 36. Maximum density of Water.-It was shown that brines of various strength, when mixed with water, absorbed heat and expanded. Let us look upon ice as the cryohydrate of water, Water shrinks as it loses heat till it reaches 4° C. At this point ice is formed, which, however, is dissolved in the water. A solution is obtained having a temperature of solidification below 4° C., namely at 0° C. At 0° C. the ice and the water solidify together, producing the compound body or cryohydrate called ice, which is thus a cryohydrate of water. The expansion from 4° to 0°is due to the greater and greater amount of ice which the water holds in solution, and which expansion is greater than the contraction of the water due to the diminished temperature.

§ 37. Variation of media.—There can be no doubt that the discovery of an enormous number of new bodies of definite composition will reward those who labour in this field. Taking water as the medium for solution, there appears to be no doubt that every soluble salt has a definite cryohydrate ; so that in this direction alone the number of new bodies awaiting discovery and description may be estimated at half the number of bodies already known. If we vary the medium, employing, say, alcohols or hydrocarbons as solvents, the number of new compounds will be again indefinitely increased; so that it is fairly within the

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.

II. On Aniline Derivatives.

By EDMUND J. Mills., D.Sc., F.R.S.* THE following results in connexion with aniline derivatives

were obtained during the course of an investigation for which the substances that will be referred to were required.

Separation.—When chloraniline, bromaniline, &c. are prepared by acting on an anilide with chlorine &c., the function has usually a double period; so that mono-, di-, and tri- derivatives are generated in presence of each other. In order to separate these I proceed as follows. The mixed derivatives are immersed in a very large excess of aqueous hydric chloride (1 vol. common fuming chloride to 9 vols. water) and heated to nearly 100°, with frequent stirring, for about an hour in a loosely covered vessel; the whole is then allowed to cool down until the next day. The clear liquid contains only mono- and di- derivatives, the insoluble portion di- and tri- derivatives. The latter is submitted to repeated hydrochloric treatment as before, until the supernatant clear liquid no longer gives any precipitate with ammonia; it then consists of tri- derivative only-contaminated, indeed, with some black tarry products. This derivative can be purified by distillation per se, or from strong aqueous hydric chloride or potash-lime. The clear liquids are united and precipitated with ammonia during twenty-four hours, a large excess of animonia being avoided. The precipitate is then washed, rapidly evaporated with hydric chloride to dryness on the water-bath, redissolved (or at any rate well stirred) in hot water, and left to cool thoroughly: the insoluble portion consists of di- derivative, and must be filtered off. The filtrate is again evaporated to dryness and stirred with hot water &c. Three evaporations to dryvess are necessary, and usually sufficient; and the final solution contains mono- derivative only, which yields but an inappreciably small amount of insoluble residue when so evaporated. The mono- derivative can be purified by distillation from aqueous soda in a current of steam; the di- derivative by distillation per se, or by successive crystallizations from naphtha and spirit.

When aniline is intended to be converted into chlorine, bromine, or iodine derivatives, it should be dried and purified by cohobation for a few hours with about one eighth to one

sixteenth of its weight of mercuric chloride, bromide, or iodide respectively. Subsequent fractional distillation easily furuishes a very pure product. Only aniline so purified is referred to in the following experiments.

Preparation.—(@) Aniline is cohobated with glacial hydric 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- derivatives.

* Communicated by the Author.

(B) 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 bromine. vapour 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, wbich 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 C® HP ON : Bro furnishes chiefly dibromaniline. Doubtless this process applies to other amines.

(w) 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, 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 therefroin by ammonia, but not by platinic chloride after repeated crystallization from spirit. When melted, it gave no definite fusion-point.

* This is Stenhouse's method of iodating orcin.

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 grmi. water.

Found.

Calculated.
Argentic chloride

220.7

219.1 Carbonic dioxide. 134:3, 133.8

131.4 Water

21•7 18:3 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 00:0014. Lesimple (Ann. Chem. und Pharm. vol. cxxxvii. pp. 126 & 127) describes a trichloraniline wbich he obtained by reducing nitrotrichlorobenzol. He states that it has a very unpleasant and persistent smell, and that it melts at 96o.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 61o80

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