The principles of the paper are applied to the determination of the pressure of earth against walls, and the power of earth to sustain buildings. The weight of the building which a horizontal bed of earth will sustain, exceeds the weight of the earth displaced by the foundation, in a ratio which is a function of the angle of repose.

V. "On the Geometrical Isomorphism of Crystals." By HENRY JAMES BROOKE, Esq., F.R.S., Hon. M.C.P.S. &c. Received June 11, 1856.

(Abstract.)

The author commences by remarking that all the crystals at present known have been divided into the six following groups or systems: the cubic, pyramidal, rhombohedral, prismatic, oblique, anorthic.

He then states that he has constructed tables which accompany this paper of the minerals comprised in each of these systems, except the cubic, in a manner new, as he believes, to crystallography; and that the unexpected facts exhibited by the tables present that science under a new aspect.

The author explains briefly the language and notation he employs in discussing the results of the new tables.

It appears that the crystals in each system, except the cubic, are distinguished from each other by what are termed their elementary angles, that is by angles between particular faces of what may be termed elementary forms.

It is next observed that there is not in crystals any natural character which indicates an elementary or primary form, and it is shown that cleavage which Hauy regarded as such an indication, is only a physical character depending upon the degree of force with which the crystalline particles cohere at the surfaces of particular faces.

The question of high indices is also considered with reference to their influence on the choice of an elementary or primary form, and a general explanation is given of the nature of such indices.

The author then states that the most important of the facts presented by these tables, are the horizontal ranges of nearly equal

angles, as shown in each system, and the general disagreement in the symbols hitherto assigned to the faces which make with some other face those nearly agreeing angles.

With regard to these facts he observes that no difference of opinion can arise, unless the sources from which they have been derived are incorrect; but that differences of opinion may be entertained relative to the interpretation of them.

The interpretation to which the author inclines is, that the near agreement in angle between two corresponding faces is not simply accidental, but that it is the effect of some natural relation not hitherto noticed, among all the crystals in each respective system; and hence, that where the angles between particular faces nearly agree, there ought to be a corresponding agreement in the forms of their symbols.

With this view of the subject in his mind, it occurred to the author that there might be a similar agreement among the whole of the elementary angles in each system, and an examination of the crystals in the pyramidal and rhombohedral systems to ascertain how far this conjecture might be well-founded, has shown that a geometrical isomorphism does exist throughout each of these systems, and that similar relations may therefore be imagined to exist in the other systems.

The author has also suggested that the oblique and anorthic systems are only hemihedral and tetartohedral varieties of prismatic crystals.

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VI. "On some Compounds of Ethylene." By H. L. Buff. Communicated by A. W. HOFMANN, Ph.D., F.R.S. ceived June 10, 1856.

Among the hydrocarbons which are capable of replacing hydrogen, the radicals of the general formula C2 H(n+1), i. e. the homologues of ethyl, are best examined. There is another class of hydrocarbons which may be represented by the general formula C, H(n-1). The only well-known term of this series is the radical allyl, C, H,, to which the attention of chemists has been especially called of late by

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the researches of Messrs. Hofmann and Cahours on allylic alcohol. These researches have established the most perfect parallelism between the two classes of radicals and their derivatives. Both the radicals C2 H(n+1) and C2 H(n−1) are monatomic, i.e. molecules capable of replacing 1 equiv. of hydrogen.

These two classes stand in the closest relation to each other, and it is by no means improbable that one class may pass over into the other, for instance, that the radical propyl C, II,, or a propyl-compound, may be converted into allyl or an allyl-compound.

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There exist a third series of hydrocarbons, which, again, both by composition and origin, are closely allied to the former two. They are represented by the general formula C, H; and methylene, C, H, ethylene, CH, and propylene, CH, are well-known terms belonging to this series. These hydrocarbons are also radicals; they differ, however, in their nature essentially from those of the former groups, inasmuch as they are biatomic molecules, i. e. molecules capable of replacing 2 equivs. of hydrogen.

There exist parallel with these three series of radicals which form alcohols, three other groups of radicals, which in acids play exactly the same part that in the alcohols is assigned to the hydrocarbons. These acid-forming radicals contain, in addition to carbon and hydrogen, oxygen and other elements belonging to the oxygen group. They are closely connected with the radicals of the alcohols, and this close connexion is particularly well established between the first series of alcohol-forming radicals and the corresponding series of acidforming radicals.

Methyl, C, H,-2H+20=Formyl, C, HO,

Ethyl, C, H-2H+20=Acetyl, C, H, O,

Propyl, CH,-2H+20=Propionyl, C, H, O.

Formic, acetic and propionic acids are formed by the imperfect oxidation of methyl-, ethyl- and propyl-alcohol, and we may consider them to be simple substitution-products of these alcohols.

By means of the electric current we are able to produce ethyl, methyl and hydrogen from propionic, acetic and formic acids, and these acids we may reproduce again by the action of hydrate of potassa on the cyanogen compounds of hydrogen, methyl and ethyl.

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Both series of radicals are chained together by these reactions, and we may view acetyl and propionyl as formyl, the hydrogen of which is replaced by methyl and ethyl.

There is no doubt that the same relation exists between the hydrocarbons of the other series of radicals and the radicals of the corresponding acids, between allyl, C. II, and the radical of acrylic acid, acryl C, II, O, and between methylene, C, H, ethylene, C, HI,, propylene, &c., and the radicals of the bibasic acids, which are homologues of succinic acid, C. H ̧ O ̧.

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The biatomic radicals are in general far less studied than the monatomic radicals; still they occur in many compounds, and are met with in different departments of chemistry.

In addition to the terms already mentioned, we find them in the phenyl, benzyl, naphthyl and other series.

In the hope of adding some facts to the history of the polyatomic radicals, I have made some experiments with chloride of ethylene, C4 H, Cl2.

This compound, as well as the bromide of ethylene, refused to act in many instances; in others it underwent the same change which is induced by the action on it of a solution of potassa in alcohol, splitting into the compound C, H, Cl and hydrochloric acid.

On boiling chloride or bromide of ethylene with an alcoholic solution of sulphocyanide of potassium, a very definite reaction takes place. The change being completed, the alcohol is separated by distillation, and the residue treated with a small quantity of cold water in order to remove chloride or bromide of potassium, which is produced, and the excess of sulphocyanide of potassium. The more or less coloured residue is then dissolved in boiling alcohol, and the solution, after digestion for some time with animal charcoal and a few drops of hydrochloric acid, filtered whilst hot. This solution deposits on cooling fine white, very brilliant and large rhombic plates of a hard and brittle substance*.

* Whilst M. Buff was engaged with these researches, M. Sonnenschein has communicated some experiments made in the same direction, which have likewise

and its formation may be represented by the equation

C, H, Cl2+2K Cy S2=2K Cl+C ̧ H ̧ Cy2 S ̧.

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Sulphocyanide of ethylene fuses at 90° C. and solidifies at 83°. It is but slightly soluble in cold water, more so in boiling water, from which it crystallizes in groups of needles. It is decomposed at a higher temperature, and evolves a highly pungent vapour, the odour of which very much resembles that of burnt onions. On boiling a solution of sulphocyanide of ethylene in water, a very acrid odour is observed, which produces lacrymation and violent sneezing. Sulphocyanide of ethylene has a sharp taste, causing a burning sensation in the throat.

Solution of ammonia decomposes sulphocyanide of ethylene even at the common temperature. A flocculent substance separates, and the solution contains several compounds which I have been unable to separate.

At the temperature of boiling water sulphocyanide of ethylene mixes with aniline in every proportion; no reaction, however, is perceptible. But on boiling the mixture decomposition sets in, and a volatile substance is evolved which restores the colour of reddened litmus paper.

When boiled with solution of hydrate of baryta and oxide of lead or mercury, sulphocyanide of ethylene loses its sulphur; the substance left behind possesses very little power of crystallizing. In the case of oxide of mercury, besides sulphide of mercury and carbonate of barium, a difficultly soluble body containing mercury is formed.

At the temperature of boiling water, sulphocyanide of ethylene dissolves readily in very dilute nitric acid; on cooling of the solution the substance is deposited unchanged. On treating it with stronger nitric acid a decomposition takes place, and a crystalline acid is formed. This acid is best produced by heating sulphocyanide of ethylene on the water-bath with dilute nitric acid as long as red led to the discovery of this substance. Sonnenschein's results, which are published in the Journ. für Prakt. Chem. June 1855, came to our knowledge only after a summary of the results had been sent to the editor of the Annalen der Chem. und Pharm.-A. W. H.