According to the synthesis discovered by Limpricht, two principal products are obtained on heating chloride of benzyl, CH(CH,Cl), with water in sealed tubes to 180°,-anthracen and dibenzyl. Two molecules of benzylchloride attach themselves to each other, losing two molecules of hydrochloric acid and two atoms of hydrogen.

The latter act upon two other molecules of benzylchloride, and occasion the formation of dibenzyl, which may here be left out of consideration. The formation of anthracen corresponds to the following equation :

2CH(CH,C1)=C11H10+2HCl + 2H.

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The simplest inference from this reaction would be the assumption that anthracen might be regarded as diphenylacetylen (CH)C=C(C,H,), the chlorine and hydrogen atoms of the lateral catena being eliminated during its formation from benzylchloride. But even before the publication of the most recent researches of Limpricht and Schwanert, Graebe and Liebermann pronounced this view inaccurate, in consequence of the derivation of alizarin from anthracen. As the tinctorial body just named yields on oxidation phthalic acid, it cannot be regarded as a derivative of diphenylacetylen, since these derivatives must yield on oxidation, benzoic acid or substituted benzoic acids. In the meantime, Limpricht and Schwanert obtained tolen, which from its formation and properties must indubitably be regarded as diphenylacetylen, which proves the correctness of the assumption, that the constitution of anthracen must be different. Graebe and Liebermann were led by the similarity of anthracen and naphthalin to their view as to the collocation of the atoms in anthracen, as figured above, with which the formation of this hydrocarbon from benzylchloride can be easily harmonised.

If we assume that, firstly, a molecule of hydrochloric acid is removed from each of the lateral chains, which in conse

quence attach themselves to each other by two bonds, and that, secondly, the two benzol rings, corresponding to the formation of diphenyl, unite by the loss of two atoms of hydrogen, we arrive at the following structure of anthracen:

The bonds set free by the removal of the atoms in parenthesis attach themselves, as is easily seen, to each other, so as to form three benzol rings.

The same synthesis, taken in connexion with the circumstance that alizarin yields on oxidation phthalic acid, leads naturally to the following formula, if it is assumed that each methyl group is united by one bond with the benzol-ring of the other benzylchloride, the two lateral chains being simultaneously connected with each other.

Graebe, and along with him probably all chemists, depending on Van Dorp's synthesis, and on the behaviour of anthracen with soda-lime, have adopted this latter structural formula, as belonging to anthracen. It shows that anthraquinon is not a true quinon, but a double keton. The first formula is recognised as appropriate to phenanthren. The formula for anthracen might be most simply written, thus:

We may here go so far as, depending on the formation of phthalic acid, to resolve the formula more in such a direction that in one at least of the benzol nuclei, the lateral chains have the position 1, 2; the formation of alizarin from phthalic acid and pyrocatechin makes this very probable.

The synthesis of anthracen from styrol and benzol, as discovered by Berthelot, may indeed be more readily explained according to the first formula, but the second formula also throws sufficient light on the progress of the reaction. For this reaction benzol and styrol, when passed through a red-hot tube, would lose four atoms of hydrogen, yielding :

But if we bracket those atoms of hydrogen which are evolved, and suppose that the atoms of carbon are connected by the bonds thus set at liberty, we perceive that a compound may be formed from benzol and styrol, which possesses the first constitution of anthracen.

The remaining syntheses observed by Berthelot can all be reduced to the two cases just described; the formation of anthracen from toluol when passed through ignited tubes corresponds to that from benzylchloride—

The synthesis from styrol and benzol can be regarded as

parallel to that from ethylen and benzol, since in this styrol appears as a main product, from which probably the anthracen is afterwards formed.

In its physical properties anthracen much resembles benzol and naphthalin, and forms with these hydrocarbons a series whose members are distinguished by the increment of CH2. Between the boiling points of the bodies there is an approximately equal distance. Anthracen boils about at the same temperature as mercury. If we therefore take its boiling-point as 360°, we find the following scale of diffe

The two higher members are strikingly similar as regards their external properties and crystalline character. They form monoclinar crystals closely resembling each other. In their melting-points and solubilities, benzol, naphthalin, and anthracen evince the character of an ascending series. The former rise with the increasing amount of carbon, and the compound becomes less soluble.

The behaviour of the three hydrocarbons with chemical agents is also very similar. None of them yields on oxidation an acid with the same proportion of carbon. They all evince great permanence as regards the chemical arrangement of the atoms of carbon which are not readily torn asunder. But whilst in benzol and naphthalin chinons appear as the characteristic products of oxidation, anthracen under similar circumstances produces a double keton, for as such we must regard anthraquinon, on account of its formation from the benzoate of lime.

As in benzol and naphthalin, all the hydrogen-atoms of anthracen have a distinct aromatic character; the com