Cooley's Cyclopaedia of Practical Receipts Volume I Part 197

=EL'DER.= _Syn._ SAMBUCUS (Ph. L. & E.), L. A large shrub or small tree belonging to the natural order _Caprifoliacae_. It is indigenous in Europe, and has long been valued for its medicinal properties. "The recent flowers of the _Sambucus nigra_" (Ph. L.) or common elder are regarded as diaph.o.r.etic and pectoral, and a distilled water (ELDER-FLOWER WATER; AQUA SAMBUCI) is made of them. The inner bark of the same tree is purgative and emetic, and is used in dropsy; the leaves are purgative; the juice of the fresh berries is made into wine (ELDER WINE), and is largely used to make FACt.i.tIOUS PORT WINE, and to adulterate the real wine. See WATERS (Distilled).

=ELECAMPANE'.= _Syn._ INULA (Ph. L.), L. "The root of _Inula Helenium_"

(Ph. L.). A plant of the nat. order _Compositae_. Tonic, diaph.o.r.etic, and expectorant.--_Dose_, 20 gr. to 1 dr., or more, either in the form of powder or decoction; in catarrh, dyspepsia, &c. It is now seldom used.

=ELECTRANODYN.= For the cure of neuralgia, headache, migrain, faceache, and apoplectic attacks. As a necklace for children for toothache, as a preventive of quinsy, &c. A tissue paper converted into a nitrogenous material (pyroxylin or _duppelpapier_) by immersion in a mixture of sulphuric and nitric acid, and containing besides an insignificant proportion of wax and resin. (Hager.)

=ELEC'TRIC.= _Syn._ ELECTRICAL. Exhibiting the effects of ELECTRICITY when 'excited' by friction; pertaining to, derived from, or produced by electricity.

=Electric.= _Syn._ INSULATOR, NON-CONDUCTOR. A substance which may under ordinary circ.u.mstances be readily made to evince electrical properties by friction. Electrics do not transmit, or conduct, electricity; whilst, on the other hand, ANELECTRICS are good transmitters or conductors of electrical action. The most perfect electrics are sh.e.l.l-lac, sulphur, amber, jet, resinous bodies, gums, gun-cotton, gla.s.s, silk, diamond, agate, and tourmaline; dry fur, hair, wood, feathers, and paper; turpentine and various oils; dry atmospheric air and other gases, steam of high elasticity, and ice at 0 Fahr. The most perfect anelectrics or conductors are the metals, charcoal, and saline fluids.

=Electric Eel.= The _Gynotus electricus_, a fish having the power or giving violent electric 'shocks'; which power it exerts for killing or stunning its prey. It is an inhabitant of the fresh-water lakes and rivers of the warmer regions of America, Africa, and Asia.

=Electrical Machine.= An instrument for the excitation and collection of electricity. The term is only applied to contrivances in which friction is the immediate cause of the electrical disturbance; those which act through chemical force, magnetism, or heat, being known by various distinctive names, as 'voltaic battery,' 'electro-magnetic machine,' 'induction-coil,'

'thermo-electric pile,' &c.

The electrical machines in common use are composed of a hollow gla.s.s cylinder, or circular plate of gla.s.s, turning on an axis, and rubbing against two or more leather rubbers covered with silk, the electricity being collected by sharp points fixed in a metal rod standing on a gla.s.s pillar. A description of these instruments, however, would be out of place in the present work, which does not aim at giving information that may be easily obtained from other sources.

Cylinder machines are seldom made of greater size than 13 inches by 9, and are about as powerful as an 18-inch plate machine. The latter are commonly made up to 3 and 4 feet diameter, and will, with a suitable condenser, give 15 inch sparks in air.

=ELECTRI"CITY= (-tris'-it-e). The name given primarily to one of the great forces of nature, and secondarily to that department of physical science which embraces all that is known respecting this particular force.

Many theories respecting the nature of electricity have been advanced for the purpose of explaining electrical phenomena. The theory of Dr Franklin supposed the existence of a single h.o.m.ogeneous, imponderable fluid, of extreme tenuity and elasticity, in a state of equable distribution throughout the material world. This fluid is a.s.sumed to be repulsive of its own particles, but attractive of all other matter. When distributed in bodies, in quant.i.ties proportionate to their capacities or attraction for it, such bodies are said to be in their 'natural state.' When we increase or diminish the natural quant.i.ty of electricity in any substance, excitation is the result, and the substance, if 'overcharged,' is said to be electrified 'positively,' or if 'undercharged,' 'negatively.' These theories, and all others based upon the a.s.sumption that electricity is a form of matter, have been found to be inadequate for the elucidation of electrical phenomena.

At the present day, however, two kinds of electric forces are recognised, and distinguished as negative and positive, but they are both a.s.sumed to be a.n.a.logous in principle, and very generally a.s.sumed to be simply due to different a.n.a.logous motions of matter. For a full exposition, however, the reader must refer to some of the especial works on the subject.

=ELECTRICITY, Iron reduced by.= Gelatin capsules of the size of a 2-grain pill, filled with powdered blacksmith scales (black oxide of iron).

(Hager.)

=ELECTRO-CHEM'ISTRY.= That branch of chemistry which treats of the agency of electricity in effecting chemical changes.

=ELECTRO-ETCH'ING.= See ETCHING.

=ELECTROL'YSIS.= (-trol'-e-sis). Electro-chemical decomposition. The voltaic current has the power of loosening and separating the const.i.tuents of certain compound bodies when these are interposed in the circuit. The substances which are thus susceptible of decomposition are termed electrolytes. They are all binary compounds, containing single equivalents of their components, which are held together by very powerful affinities.

The amount of electrical power required to effect decomposition varies greatly with different electrolytes: solution of iodide of pota.s.sium, melted chloride of lead, hydrochloric acid, water mixed with a little sulphuric acid, and pure water, demand very different degrees of decomposing force, the resistance increasing from the first-mentioned substance to the last, which latter it has been denied can be decomposed.

One of the indispensable conditions of electrolysis is fluidity. When a liquid is electrolysed its components are discharged solely at the limiting surfaces, where, according to the usual figurative mode of speech, the current enters and leaves the liquid, all the intermediate portions appearing quiescent. The terms 'anode' and 'cathode' have been proposed respectively for the surfaces which are supposed to receive and let out the current of positive electricity. The anode is therefore directly against or opposite the positive pole of the battery, or, according to the improved nomenclature, the positive electrode; and the cathode against the negative pole, or electrode. The bodies which are set free by the action of the current are termed ions; those which go to the anode and appear at the positive electrode being distinguished by the term anions, and those which go to the cathode and appear at the negative electrode by the term cathions. This nomenclature has, however, been but partially adopted, and is making but slow way, if any, many preferring the old terms of electro-positive for anions, and electro-negative for cathions.

The relative decomposing effects produced by the same current in different electrolytes are exactly expressed by the chemical equivalents of the electrolytes. Thus, if a current be made to traverse acidulated water, iodide of pota.s.sium, and chloride of lead, these three electrolytes will suffer decomposition at the same time, but by no means to the same extent; for the current which decomposes but 9 parts of water will separate into their elements 166 parts of iodide of pota.s.sium and 139 parts of chloride of lead. The electrolysis of metallic salts is now carried out on a large scale in the beautiful arts, which we notice under the general head of ELECTROTYPE.

=ELECTROMOTIVE ESSENCE= (Romershausen). An embrocation for restoring the suspended functions of the skin by stimulating the flow of vital electricity and the functions of the nerves. A solution of oils of turpentine and rosemary in the ninth dilution of alcohol previously coloured red with some vegetable dye. (Reithner.)

=ELECTRO-PLA"TING and GILDING.= See ELECTROTYPE.

=ELECTROPH'ORUS.= A simple instrument for exciting electricity, generally used in the chemical laboratory for charging small Leyden jars when gases have to be exploded by the electric spark. To construct it, a plate of tinned iron is made into a circle of about 12 inches diameter; a raised border is then turned up for about half an inch, and the extreme edge is turned outwards over a wire to avoid a sharp border. A mixture of equal parts by weight of sh.e.l.l-lac, Venice turpentine, and resin, is made by gently heating them together with stirring until well fused and thoroughly incorporated. This composition is poured into the plate, to quite fill it, and kept melted until all bubbles have disappeared. Another portion of the instrument, serving the same purpose as the conductor of an electric machine, is a circle of wood, rather smaller than the resinous plate, rounded at the edge, and neatly covered with tin-foil. An insulating handle, formed of a piece of stout gla.s.s rod, is cemented into the centre of this wooden disc. Before using the instrument it must be carefully dried and slightly warmed. The resinous surface is excited by beating it obliquely with a folded piece of warm flannel. When this has been done for about a minute, the warm dry cover of the instrument is to be placed upon the resinous plate, and touched with the finger. If the cover is then raised a few inches, and the knuckle approached, a powerful spark of positive electricity will pa.s.s; and if the cover be again replaced, touched, and raised, a second spark will pa.s.s. This may be repeated many times without again exciting the resinous plate. By receiving the sparks with the k.n.o.bs of a Leyden jar, a charge strong enough to give a powerful shock, or explode a gaseous mixture, may be rapidly obtained. Other forms have been given to the instrument, but the essential part of every one is a plate of some resinous substance.

=ELECTROTYPE.= _Syn._ ELECTRO-MET'ALLURGY, GALVAN'O-PLAS'TIC. The art of working in metals by the aid of electricity. Strictly speaking, the term electrotype is only applicable to one branch of 'electro-metallurgy'--that which relates to the production of copies of engraved plates, medals, coins, and other works--but it is now commonly employed in the sense indicated by our definition. According to this extended signification of the term, the art of electrotype includes ELECTRO-PLATING, and ELECTRO-GILDING.

_General Principles._--If a current from a voltaic battery be pa.s.sed, by means of platinum electrodes, through water to which some sulphuric acid has been added, electrolysis, takes place, hydrogen appearing at the cathode, and oxygen at the anode. If into the acid liquid some crystals of sulphate of copper be now thrown, electrolysis will still go on, but only one of the elements of the water, namely oxygen, will be evolved; for the hydrogen, on being released, will take the place of the copper in the solution, and the copper thus liberated will be deposited on the platinum plate or wire which const.i.tutes the negative electrode. This experiment may be continued until all the copper is extracted from the solution. Let this experiment be repeated with a copper plate for the positive electrode, and it will be found that neither of the gases will be evolved.

The hydrogen, as before, will take the place of the copper in the solution; the oxygen, instead of escaping at the anode, will combine with the copper of the electrode and the sulphuric acid to form sulphate of copper. The chemical forces called into action by the current are so beautifully balanced, that in the last experiment the quant.i.ty of copper supplied by the positive electrode exactly equals the quant.i.ty withdrawn from the solution and deposited upon the negative electrode. The whole art of electrotype consists in applying the metals thus released from their solutions to artistic or useful purposes. To obtain compact and brilliant deposits, many precautions have to be observed. The solutions must be kept saturated, or nearly so; the mould to be copied, or object to be coated, must not be too small, or out of proportion to the size of the zinc plate of the battery; in fine, the power employed must be carefully regulated according to the work to be done. In all arrangements the moulds or objects which receive the deposits act as negative electrodes, and are consequently in connection with the zinc of the battery or generating cell.

_Electrotype Processes._ Although reguline deposits of many metals can be obtained through the agency of voltaic electricity, we shall only treat of those of copper, silver, gold, and platinum. When copper is deposited, the object is generally to produce a substantial copy of a medal, an engraved plate, or other work of art; but when solutions containing the precious metals are electrolysed, the deposits are nearly always used for covering the surface of inferior metals. We shall notice the operations connected with the deposition of copper, and those relating to electro-plating under separate heads.

1. DEPOSITION OF COPPER:

The moulds or models intended to receive the deposited metals may be formed of various materials. For medals and similar small works, moulds of fusible metal, white wax, stearine, stearic acid, and gutta percha, are commonly used. The first are formed by dropping or pressing the medals to be copied upon the melted metal, taking care that the former are quite cold, and that the surface of the metal is bright or free from oxide. To make a mould in gutta percha, the material must be softened in warm water, and then pressed upon the medal by means of a strong screw press. With the other materials the manipulation is very easy. A ribbon of cardboard or thick paper is placed round the medal, so as to form a rim; the material, which has been melted in an earthen vessel, is then poured on, and allowed to remain until quite cold and hard, when it is cautiously removed. For large works, moulds of plaster of Paris are usually employed; these require to be saturated with wax or tallow, by standing them in a shallow vessel containing these substances in a melted state. For copying seals and small coins, impressions in ordinary sealing-wax may be used as electrotype moulds. Non-metallic moulds must be coated with some substance which has the property of conducting electricity before they can be used as negative electrodes. The substance commonly employed is plumbago or black-lead. It must be in the condition of an impalpable powder. It is rubbed briskly over the surface of the mould (wax, stearine, plaster, &c.) by means of a strong fine camel-hair brush, till the whole presents the well-known black-lead polish. The adhesion of the plumbago may be often promoted by breathing slightly on the mould. To cause it to adhere to sealing wax impressions, the wax may be slightly moistened with spirits of wine, or exposed to the vapour of ether. Delicate moulds and objects, which cannot well be black-leaded, may be covered with a conducting film of silver, by first dipping them in bisulphuret of carbon holding about 1/20th part of phosphorus in solution, and then, after a few seconds, immersing them in a weak solution of nitrate of silver, and allowing them to dry in the light. Metallic moulds require no preparation.

The voltaic apparatus used may now be described. The single-cell arrangement, used for small works, is formed on the principle of Daniell's Constant Battery. It consists of a vessel of gla.s.s, earthenware, or wood, containing a smaller cell of thin biscuit ware, or other porous material; a rod or plate of amalgamated zinc, placed within the porous cell, and a wire connecting the zinc with the mould to be copied; the latter being placed in the outer vessel. The annexed figure represents a convenient form of the single-cell:--

The battery arrangement has many advantages over that described above, and should always be employed when large objects are to be electrotyped, or when a number of small moulds are to be operated upon. In this arrangement the copper solution is electrolysed in a separate vessel, termed the decomposition cell, and the current generated by one or more cells of a Daniell's or Smee's battery. This arrangement is shown in the following engraving:--

[Ill.u.s.tration:

_a._ An oval vessel of salt-glazed earthenware or wood nearly filled with a saturated solution of sulphate of copper.

_b._ A porous diaphragm, containing the cylinder or plate of zinc (_c_), and filled with dilute sulphuric acid.

_d._ A small bar of bra.s.s or copper fastened to the vessel by the binding screws (_e, e_), and supporting the plate of zinc (_c_), by the hook of copper wire (_f_), and the mould (_g_), by the hook (_h_).

_i._ A small shelf or part.i.tion to support crystals of sulphate of copper, to keep up the strength of the solution.]

[Ill.u.s.tration:

_a._ A constant battery cell.

_b._ Decomposition cell, a cubical vessel made of wood or earthenware, and filled with a mixture of 1 part of dilute sulphuric acid (1 acid + 9 water), and 2 parts of saturated solution of sulphate of copper by measure.

_c, c, c._ Moulds suspended to the bra.s.s rod (_f_), and connected with the zinc or positive element of the battery (_a_), by means of the screw (_g_.) _d, d._ Pieces of sheet copper suspended on the bra.s.s rod (_h_), and connected with the zinc end of the battery, by means of the screw (_i_), employed to keep up the strength of the cupreous solution in the decomposition cell.]

To connect the moulds with the zinc or positive element, stout copper wires or strips of thin sheet copper are employed. In the case of a non-metallic mould, the wire must lead directly to the plumbagoed surface, or, what amounts to the same thing, the plumbago must be extended to the point of attachment. The connecting wires, and the backs and edges of metallic moulds, must be covered with sealing-wax varnish, or other non-conducting substance, to prevent them receiving the deposit. Before a mould is placed in the copper solution it is advisable that everything should be arranged, so that the immersion may occasion immediate voltaic action. If the connection between the zinc and the mould is not effected until after the immersion, the solution may act chemically on the surface of the mould, and cause the deposit to appear dark and dirty. When a mould has remained in the solution long enough to receive a complete coating of copper, it may be lifted out with impunity for examination. If everything is going on well, the deposited metal will present a brilliant, light, copper-coloured surface. When sufficiently thick, the deposit is removed with care, washed and placed to dry. Electrotype medals may be polished with wash-leather and the plate brush, or bronzed. Various natural objects such as insects, fruits, &c.; small works of art, such as busts and statuettes; chemical vessels, particularly gla.s.s flasks and retorts; and numerous cla.s.ses of articles, may be rendered less fragile by coating them with copper by the electrotype process.

II. DEPOSITION OF THE PRECIOUS METALS--

The solutions generally employed as electrolytes from which silver and gold are respectively separated, are those of the argento-cyanide and the auro-cyanide of pota.s.sium. These compounds are what chemists call double salts; for instance, cyanide of pota.s.sium is simply a compound of pota.s.sium and cyanogen; but argento-cyanide of pota.s.sium is cyanide of silver united with cyanide of pota.s.sium. When a solution of this double salt is electrolysed silver appears at one electrode and cyanogen at the other, while a proportionate amount of the simple cyanide of pota.s.sium is formed in the solution. But if the positive electrode is of silver, the cyanogen combines with it, and forms cyanide of silver, which unites with the liberated cyanide of pota.s.sium, and so keeps up the strength of the solution.

As in the deposition of copper, the apparatus used for plating or gilding may be the single cell or the decomposition cell and battery. The necessity of economising solutions of silver and gold has, however, led to certain modifications in the apparatus. The single-cell arrangement consists, as before (see _above_), of an outer vessel of gla.s.s or earthenware, containing a cell of porous biscuit ware; but the object to be silvered or gilded is placed, with the cyanide solution in the latter, while the zinc is placed in the outer vessel, with the dilute sulphuric acid.[273] The zinc is usually employed in the form of a cylinder, completely surrounding the porous cell. In the battery arrangement the decomposition cell may be of porcelain or gla.s.s; the silver or gold employed to keep up the strength of the solution may be in plates, wires, or ingots. For plating small objects, a single cell of a Daniell's battery will afford ample decomposing power; gilding may be better accomplished by using three such cells. The battery arrangement is much more convenient, effective, and economical than the single-cell arrangement.

[Footnote 273: The strength of the acid water acting upon the zinc must be regulated according to the work to be done. If the action between the acid and the zinc be too energetic, the electricity developed will be more than sufficient to release pure metal, and hydrogen will be evolved, which will interfere with the deposition.]

On a large scale, electro-plating is carried out in oblong vats, occasionally holding from 200 to 250 gallons of solution. Silver plates connected with a powerful voltaic or magneto-electric battery, are placed at intervals in the vats; they form the positive electrodes, and correspond in extent of surface with the articles to be coated, and face them on both sides. The articles (tea-pots, cruet-frames, forks, spoons, &c.) act as the negative electrodes, and are suspended by copper wires from bra.s.s rods laid lengthways over the vats, and connected with the battery. The articles plated are usually formed of nickel silver or German silver, which is chosen on account of its silvery whiteness, a quality of great importance when portions of the coating of n.o.ble metal have been worn away by use.

To prepare the articles for plating, they are first boiled in a solution of pota.s.sa, to free them from grease; they are then quickly dipped in red nitrous acid, to remove any oxide that may have formed on the surface, and after this well washed in water, to remove every trace of acid. They are then suspended from copper wires, and dipped into a solution of mercury in cyanide of pota.s.sium, or some other mercurial solution, and afterwards washed in water, as before. The amalgamation of the surface effected by the last operation promotes the adhesion of the film of silver. The articles having been weighed, are now immersed in the silvering solution, and left until a sufficient amount of silver has been deposited on them.

Their condition at any time may be ascertained by weighing a test-object removed from the solution. In some electro-plating establishments the silvering solution is kept constantly stirred by simple mechanical arrangements; in others, continual motion is given to the suspended articles. On being removed from the vats the plated articles are well brushed with brushes of fine bra.s.s wire attached to a lathe, and cleaned with fine Calais sand; they are afterwards polished on revolving brushes with rottenstone, then by hand with soft leather and rouge, and, lastly, with the naked female hand. A lasting polish is given to some articles by burnishing with a burnisher formed of highly polished hardened steel, bloodstone, agate, or flint. The process of electro-gilding on the large scale is nearly the same as that of electro-plating or silvering, but, of course, plates of gold are suspended in the solution instead of silver plates.

Various solutions for silvering, plating, and platinising, have been recommended. We give below those generally employed.

1. Solvent solution. Cyanide of pota.s.sium, 2 oz; distilled water or rain water, 1 pint; dissolve. Other proportions may be employed. Used as a general solvent for salts of silver, gold, and platinum.

2. Silver solution. Oxide of silver?[274] (not dried), 1 oz.; the solvent solution (No. 1), 1 pint. Used for the single-cell apparatus, its strength being maintained as the deposition proceeds by a fresh supply of oxide from time to time.

[Footnote 274: Precipitated from pure solution of nitrate of silver by excess of lime water. It should be well washed, and preserved in bottles with distilled water.]

Cyanide of silver dissolved in solvent solution (No. 1). This is the solution generally employed for plating with a separate decomposition cell.

3. Gold solution. Add to a pint of No. 1 oxide of gold, 1/4 oz. Used in the same manner as the second silver solution.