VULCANIZED CAOUTCHOUC.

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parts of caoutchouc to one of sulphur. Exposure for some hours to a heat of from 300° to 350° effects the conversion. Ebonite, or vulcanite, is one of the best insulators of electricity that is known, and becomes powerfully negatively electric when excited by friction. Elastic vulcanized caoutchouc appears to consist of a combination of the elastic gum with 2 or 3 per cent. of its weight of sulphur. The excess of sulphur which is usually present is only mechanically distributed through the mass, and may be removed by the use of solvents, such as benzol or sodic sulphite. This excess of sulphur is injurious to the elasticity of the material, and gradually renders it brittle and rotten. Several modes of effecting the combination of sulphur with caoutchouc are ployed. One of the most usual consists in grinding the caoutchouc between heated rollers with the proper proportion of sulphur; the mixture of caoutchouc and sulphur is left endued with the properties of common caoutchouc, and may be easily moulded into the form of the various articles required: it is only on the application of a temperature ranging from 270° to 300° that the peculiar properties of the sulphurized compound are developed. The heat is most advantageously applied by exposing the articles to the direct action of high-pressure steam at 270° or 280°. A still easier method adapted for thin articles consists in immersing the caoutchouc for a few moments in a solution of 1 part of chloride of sulphur (S,Cl) in 60 of carbonic disulphide : by simple exposure of the object thus treated to the air, it assumes the character of vulcanized caoutchouc without the aid of heat. The addition of a certain proportion of carbonate of lead to the compound is found to produce an article better adapted for some purposes, such as the manufacture of overshoes or goloshes, than one in which sulphur only is used; due proportions of sulphur and of the salt of lead are incorporated with the caoutchouc by causing the caoutchouc mixed with the other ingredients to pass repeatedly between polished hollow iron rollers maintained at a temperature of about 170° (77° C.), by the injection of steam into their interior. Vulcanized Indian rubber withstands prolonged digestion in naphtha or turpentine without undergoing solution.

(1490) GUTTA PERCHA.-This substance, which is similar in chemical properties to caoutchouc, was introduced into this country as an article of commerce about the year 1844. Gutta percha is the concrete juice of the Isonandra percha, a tree belonging to the family of the Sapotacea, which grows abundantly in Singapore, Borneo, and other islands of the Eastern archipelago. The

name percha is that given by the Malays to the tree which produces it; it grows to a diameter of five or six feet, and though as timber it is valueless, the fruit yields an oil fit for food. On cutting notches through the bark into the wood, a milky juice exudes, which speedily solidifies. Gutta percha is a tough inelastic substance, which at ordinary temperatures retains any shape which may have been impressed upon it, but below 212° it becomes so soft that it may be moulded like wax, and indeed may be employed for taking casts and impressions, since it will copy the finest lines with fidelity; beautiful mouldings, and a variety of useful and ornamental articles are thus made with great facility. It also possesses the valuable property of welding together when in this soft condition, provided that the surfaces are quite free from any film of moisture. Below 110° it again becomes hard, and is possessed of extraordinary tenacity. It is, when pure, of a pale brown colour, possessing a peculiar odour somewhat resembling that of caoutchouc. When rubbed it becomes negatively electric, and if dry it is an insulator of electricity; and this property has led to its extensive employment in the covering of wires for telegraphic purposes (309). It is also largely used as a waterproofing material, and is employed as a substitute for leather in soling boots and shoes. It furnishes a valuable material for the preparation of tubes for conveying liquids; it is likewise used as a substitute for leather in the construction of bands for driving machinery, and is daily receiving new and useful applications.

Gutta percha is quite insoluble in water; it is not attacked by Stockholm tar, or by linseed oil; but it is dissolved readily by benzol, chloroform, carbonic disulphide, oil of turpentine, and the essential oils in general. If heated moderately it melts; and beyond this point is decomposed, yielding hydrocarbons identical with those from caoutchouc (Williams). Solutions of the alkalies are without action upon gutta percha. Hydrochloric and dilute hydrofluoric acids, as well as the dilute acids in general, have no action upon it; hence it is employed in the preparation of bottles and vessels used for containing these liquids. The principal drawback to this use is the difficulty of preventing it from retaining a certain degree of porosity, which allows the slow transudation of liquids through its mass. Concentrated nitric acid attacks and disintegrates it rapidly, and oil of vitriol produces the same effect more gradually.

Purified commercial gutta percha consists of three distinct portions; the most abundant of these, the pure gutta, constitutes

20 32.

from 75 to 82 per cent. of the mass: it is milk-white and fusible at about 302 (150° C.); it is insoluble in alcohol, but is soluble in ether. This substance is a hydrocarbon of the form ЄH The other two constituents are a white and a yellow resin, both of which are soluble in boiling alcohol; but the white resin (20H322) is nearly insoluble in this liquid when cold; by deposition from a hot alcoholic solution it may be obtained crystallized in pearly plates, disposed in radiated tufts. The yellow resin (20H32) is amorphous. Pure gutta percha, indeed, slowly absorbs oxygen when exposed to the combined influence of light and atmospheric air, and is gradually converted into a brittle resin freely soluble in hot alcohol. It then entirely loses its plastic character, and this is one of its principal defects; but it may be preserved in the dark or under water for an indefinite period without change.

(1491) RESIN OF JALAP.-This substance has been made the subject of numerous careful experiments. It may be obtained in a colourless form by treating the chopped roots of jalap with boiling water repeatedly, submitting them to pressure between each operation, and when the expressed liquid is no longer coloured, extracting the resin from the undissolved portion by means of boiling alcohol (sp. gr. o.880). This resin amounts to from 10 to 15 per cent. of the weight of the root operated on. It is a mixture of two definite resins. One of these (pararhodeoretin) is soluble in ether, and is powerfully acid; it has the peculiar odour and acrid taste of jalap. It does not crystallize from its alcoholic or ethereal solutions, but if these be mixed with water, the semi-solid mass which is formed becomes gradually filled with needle-shaped crystals; it may be sublimed. According to the analysis of Johnston it may be represented as (Є20H309).

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The resin which is insoluble in ether (jalapin or rhodeoretin), is remarkable for being susceptible of decomposition into glucose and a resinous acid. Jalapin, according to Spirgatis, is identical with the active principle of scammony. Jalapin is white, and destitute of odour and taste. It is fusible at 300° (149° C.). Alcohol and acetic acid dissolve it readily. It is also easily soluble in alkaline solutions, especially if boiled with them. Mayer terms it convolvulin, and assigns to it the formula (Є31H5016). This resin appears to constitute the purgative principle of the jalap. Oil of vitriol dissolves it slowly, and assumes a beautiful red colour, which gradually passes into brown. On dilution an oily-looking acid body (HЄ16H293) is precipitated, and glucose remains in solution. According to

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THE GLUCOSIDES-PHLORIDZIN.

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Mayer, the fusiform variety of jalap (Convolvulus Orizabensis) contains a resin homologous with rhodeoretin (ЄH5616), which when treated with sulphuric acid is similarly decomposed, glucose remaining in the solution.

§ III. GLUCOSIDES, OR COMPOUNDS WHICH FURNISH GLUCOSE.

(1492) In the course of the present chapter some crystalline compounds have been described which, like amygdalin, salicin, and populin, under certain circumstances, break up into glucose, and into some compound or compounds characteristic of the substance from which it is derived. The simplest condition under which this transformation is effected consists in exposing the compound to the action of water at a high temperature under pressure; salicin and phloridzin may thus be made to furnish glucose. The compounds which yield sugar when broken up by any of these processes are termed glucosides. They may be subdivided into two classes: one of these consists of neutral substances, like amygdalin and salicin; the other consists of acid bodies, such as gallotannic acid. We shall now proceed to notice some of these compounds; viz., phloridzin, quercitrin, datiscin, arbutin, esculin, and saponin, with one or two others.

(1493) PHLORIDZIN (CH24102H2O; Strecker).—This is a substance which occurs in the bark of the apple, pear, cherry, and plum, and probably in that of other fruit trees, and especially, as its name implies, in the root-bark of those trees (from pλotòs, bark, pila, root). In order to extract it, it is sufficient to boil the bark for some time with water, and to allow the liquid to cool. Phloridzin is deposited in silky crystals, which may be purified by redissolving them in water, digesting with animal charcoal, and recrystallizing. It has a slightly bitter flavour, followed by a sweetish taste. It requires upwards of 1000 parts of cold water for solution, but it is largely soluble in boiling water. Alcohol and wood spirit dissolve it freely, but it is nearly insoluble in ether. Its alcoholic solution causes left-handed rotation in a ray of polarized light. When heated to 212° it loses 2 H,O, and at a temperature between 223° and 228° it undergoes fusion, after which, by an additional elevation of temperature, without undergoing any further loss of water, it becomes solid, and does not melt again until the temperature has been raised to 320°. 392° it again begins to give off water, and assume a red colour, forming a resinoid body (H2O), termed rufin; this substance is soluble in alcohol; boiling water also dissolves it, but the solution is entirely colourless.

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An aqueous solution of phloridzin yields a white precipitate with one of basic acetate of lead (3 PbO,CH2,010?). It also forms compounds with baryta and lime, but these substances become brown by exposure to air.

Phloridzin, when boiled with weak acids, is decomposed into grape sugar, and a resinous matter termed phloretin :—

and phloretin, when boiled with potash ley, yields potassic phloretate, and a very sweet crystallizable compound termed phloroglucin by Hlasiwetz:

Phloroglucin is sweeter than common sugar. It crystallizes in efflorescent prisms, which contain 2 H2O. It is very soluble in ether, and crystallizes in anhydrous crystals, fusible at 428° (220° C.), and susceptible of partial sublimation. It reduces an alkaline solution of cupric tartrate, but is not susceptible of fermentation.

Phloridzin, under the combined influence of air and ammonia, yields a red, bitter, uncrystallizable compound termed phlorizein, (Є21H30N213), which is readily soluble in boiling water. When phloridzin is exposed to the vapour of ammonia, it produces a beautiful blue compound with a coppery lustre, which appears to be a compound of phlorizein with ammonia; this substance is very soluble in water, and cannot be obtained in crystals; sulphuretted hydrogen and other deoxidizing agents destroy this blue colour, but it is restored by exposure to the air.

Phloridzin does not yield any essential oil when treated with chromic acid or other oxidizing agents; in this respect it presents an important difference from salicin, which in other points it greatly resembles.

(1494) QUERCITRIN (29H3017)2H2; at 212°; Hlasiwetz.— This substance is the yellow, crystallizable colouring matter contained in the bark of the quercitron, or Quercus tinctoria, and it appears to occur in some other plants. It may be extracted from the bark by means of alcohol, of sp. gr. o'84; the tannic acid is removed by the addition of gelatin, and the liquid on evaporation yields quercitrin, which may be purified by recrystallization from alcohol. It is sparingly soluble in boiling water and in ether, but is readily dissolved by hot acetic acid, as well as by weak solutions of the alkalies, with which it forms a liquid of a