THIOSINNAMINE-SINNAMINE-SINAPOLINE.

647

Thiosinnamine corresponds to the urea of the allyl series, in which I atom of sulphur is present instead of 1 of oxygen. Allyl sulphocyanide also unites with other bases, such as ethylia, aniline, and naphthalidine, and forms with them compounds analogous to thiosinnamine.

If thiosinnamine be triturated with mercuric oxide, water and mercuric sulphide are formed, and a new basic substance free from sulphur, termed sinnamine, is obtained :

Thiosinnamine.

Sinnamine.

¤ ̧H.N2S + Hg→ = HgS + H2O + ¤ ̧H ̧Ñ2.

Oxide of lead produces a similar decomposition.

Sinnamine has been regarded as a compound ammonia, in which one atom of hydrogen has been displaced by allyl, and a second atom by cyanogen; as for example:

Sinnamine is soluble in water, and may be obtained in prismatic crystals. It is a powerful base, and expels ammonia from its salts. It occasions precipitates in solutions of lead, of iron, and of copper. The oxalate is the only salt of sinnamine which crystallizes readily; solutions of the salts of sinnamine which contain an excess of acid impart a yellow colour to a slip of deal.

(1477) Sinapoline (E,H,,N,O).-This base is usually formed by digesting essence of mustard upon hydrated oxide of lead :—

2 €,H,NS + 3 (Pb0,H20) = ¤,H12N,0 + 2 PbS + Pb¤¤ ̧ + 2 H2O;

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but it may also be produced by the action of water upon allylcyanic ether, which will be immediately described. Sinapoline is a feeble base which crystallizes from its solution in water in brilliant greasy flakes: it fuses below 212°. Its aqueous Its aqueous solution occasions a precipitate in solutions of corrosive sublimate and of platinic chloride.

(1478) Hofmann and Cahours have also obtained a variety of compound allylic ethers. These bodies have an ethereal odour which recals that of mustard. The most interesting of them are Allyl-cyanic ether or cyanate of

the oxalate and the cyanate.

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allyl (ЄH¿‚ENÐ; Sp. gr. of vapour 3'045; Boiling pt. 180° (82° C.), is prepared by acting upon cyanate of silver with allyl iodide; the heat generated by the reaction is sufficient to cause the distillation of the ether, whilst iodide of silver remains in the retort. A colourless liquid is thus obtained, the vapour of which possesses

648

ALLYL-CYANIC ETHER-ALLYLIA-RESINS.

an intensely penetrating odour, and produces a copious flow of tears. When this ether is gently warmed with a solution of ammonia it is dissolved, and the solution on evaporation deposits magnificent crystals of allylic urea :—

Corresponding crystalline compounds may be obtained if methylia, ethylia, amylia, or aniline be substituted for ammonia. When allyl-cyanic ether is treated with water, carbonic anhydride is eliminated, and the ether is slowly converted into sinapoline (Є,H,,N,→), which by its production in this manner, is shown (1164) to be diallyl-urea :

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(1479) Allylia (Є,H,N).—A concentrated solution of potash decomposes allyl-cyanic ether; sinapoline is formed, and if the liquid be distilled, allylia, a basic substance which boils between 356° and 374° (190° C.), passes over, mixed with methylia and tritylia. Allylia is the volatile alkali of the allylic series; it corresponds to ethylia in the ethylic series:

The following table gives a synoptic view of the principal compounds in the allylic series :

(1480) These substances are produced by certain families of plants in considerable abundance, and they also are very numerous. They have a considerable commercial value, and are extensively employed in the preparation of the different kinds of varnish. They are generally obtained by making incisions into the wood of

trees which produce them, when they exude in the form of a viscid liquid, consisting of the resin in solution in the essential oil of the plant. In the majority of cases they are formed by the oxidation of the essential oils contained in the trees; hence it is not surprising that in many instances they have the composition of oxides of the hydrocarbon CH, or of a hydrocarbon derived from this, having lost a certain number of atoms of hydrogen in exchange for half that number of atoms of oxygen.

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As a class, the resins are insoluble in water, but they are soluble in alcohol, especially when heated with it; many of them may be obtained from this solution in crystals by evaporation. A considerable number of them possess acid characters, in which case their alcoholic solutions redden litmus. The acid resins combine with the alkalies, and remain soluble in alkaline leys; these solutions, when agitated, produce a lather like that furnished by soap, but they are not precipitated like ordinary soap on the addition of chloride of sodium. Like the essential oils, the natural resins are usually mixtures of two or more resins, which often admit of separation by their unequal solubility in different menstrua.*

The resins are transparent or translucent brittle solids; they are insulators of electricity, and become negatively electric by friction; they fuse at a moderate temperature, are very inflammable, and burn with a white smoky flame. If heated in closed vessels they undergo decomposition, and yield various forms of hydrocarbon.

Common rosin is thus found to furnish the following products among others which have been less perfectly investigated :

* Mr. Hunt has recently contrived a method of distilling common resin in a current of superheated steam, by which means he has been enabled to separate and purify these different resinous acids on a very large scale for the manufacture of soap.

650

COMMON RESIN, OR COLOPHONY-WHITE RESIN.

(1481) Common Rosin, or Colophony.-When ordinary turpentine is distilled with water, it leaves a residue of rosin amounting to from 75 to 90 per cent. of the turpentine employed. There are two principal kinds of rosin in the market, a brown and a white resin. The brown variety is furnished by the Pinus abies; it is an amber-coloured brittle solid, which consists of two distinct but isomeric resinous acids, the sylvic and pinic (HЄ20H292; Laurent). Cold alcohol (sp. gr. o'87) dissolves the pinic acid, which forms the larger proportion of the resin, and leaves it on evaporation as an amorphous mass. It may be purified from adhering traces of a neutral resin by precipitating its solution in cold alcohol by the addition of an alcoholic solution of acetate of copper: the cupric pinate thus precipitated may then be decomposed by any acid. When pinic acid is heated to partial decomposition, the residue in the retort is found to consist of another isomeric resinous acid, the colopholic; it neutralizes bases more perfectly than pinic acid, and is much less soluble in alcohol (Unverdorben).

The other constituent of rosin, sylvic acid, may be obtained from its solution in hot alcohol, in colourless rhombic prisms or plates, fusible at 260° (127° C.). Its ethereal solution expels carbonic acid from the alkaline carbonates. It furnishes with oxide of lead a salt which crystallizes in slender four-sided needles.

White resin or galipot is obtained from Bordeaux turpentine, furnished by the Pinus maritima, and consists almost entirely of an acid resin, the pimaric, which is isomeric with the preceding. This acid may be extracted by removing from the powdered resin the substances which are soluble in a mixture of six parts of cold alcohol and one of ether: the residue, if treated with boiling alcohol, deposits pimaric acid as it cools. When the alcoholic solution of pimaric acid is evaporated, the acid is deposited in masses indistinctly crystallized. If this acid be melted and allowed to cool, it yields a colourless glass as clear as crystal: this melted resin when powdered is dissolved by an equal weight of alcohol, but the solution thus obtained, if left for a few minutes, suddenly begins to deposit elliptical crystals, which require for solution ten times their weight of alcohol, and possess all the properties of pimaric acid before fusion. Pimaric acid is freely soluble in ether. If it be distilled in vessels from which air is excluded, the distillate is found to consist principally of another isomeric resin, termed pyromaric acid, distinguished by forming with lead a salt which crystallizes in delicate needles. Pyromaric acid, according to Gerhardt, is identical with sylvic acid

VARNISHES-GUAIACUM.

651

Ordinary rosin is dissolved completely by alkaline leys: it enters largely into the formation of yellow soap.

If nitric acid be boiled upon ordinary rosin, the compound is oxidized and dissolved, and on evaporating the solution to the consistence of a syrup, it deposits, when left to itself for some weeks, small four-sided prisms with an oblique terminal face. This substance is named terebic acid (HE,H,4). It is sparingly soluble in cold water, but much more soluble in boiling water, as well as in alcohol and ether; it requires a high temperature for its fusion, and is decomposed at about 401° (205° C.).

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(1482) Varnishes.-The resins most extensively employed in the preparation of the different kinds of varnish are those of copal (from the Hymenæa verrucosa ?), mastic (from the Pistachia lentiscus), sandarach (from the Juniperus communis), lac, and occasionally those of elemi and anime. Copal is a hard, nearly colourless, transparent resin, which is dissolved with difficulty in the state in which it is imported; but if powdered and exposed to the air for some weeks, or if fused so as to enable it to absorb oxygen, it is more readily attacked by solvents.

The solvents employed in preparing varnishes are oil of turpentine, wood naphtha, and spirit of wine; the resin before being added to the solvent must be pulverized, and afterwards mixed with sand or broken glass in order to prevent the powder from agglutinating into lumps. When the varnish is spread over the surface of any object which it is intended to protect, the solvent evaporates and leaves a thin transparent coating of resin. The spirituous varnishes dry the most rapidly, but they are apt to crack and scale off. This defect is partially remedied in the turpentine varnishes, which dry more slowly; and it is still more effectually obviated in what are termed oil varnishes, in which a small quantity of some drying oil, such as that of linseed or of poppy, is added to the solution in rectified turpentine: these varnishes require a considerable time for complete hardening, but they are very durable. The common varnish used for oil paintings and maps consists of 24 parts of mastic, 3 of Venice turpentine, and I of camphor; these are mixed with 10 parts of pounded glass, and dissolved in 72 of rectified oil of turpentine.

(1483) GUAIACUM resin is the exudation of the Guaiacum officinale. It is of a dark greenish-brown colour, and is readily pulverized. It has a taste which is at first slight, but afterwards becomes acrid and hot; its odour is feeble, but resembles that of penzoin. Alcohol dissolves the greater part of this resin; ether does not dissolve it so completely, and it is insoluble in the fixed