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the battery, the quantity of zinc dissolved to do any amount of work, is the same, or even less, than attends the use of the other apparatus, because the local action in a battery of this construction is less than in the single-cell apparatus; and lastly, the quality of the precipitated metal can be regulated with the utmost nicety; and I have no hesitation in stating, that the battery process is the only one that ever can be employed by the manufacturer with advantage.

The platinized silver battery is peculiarly suitable for the operator, for when it is in action it communicates to him the degree of work that it is doing; in fact, it completely talks to its possessor. If the current is very feeble, a faint whisper is heard; if a little stronger, the battery murmurs; if a moderate current is passing, it hisses; but if a violent one, it roars. At this present moment I have nineteen batteries at work in the same room where I am writing, and they are each telling me the work they are performing. This very instant the fall of a heavy ledger in a neighbouring office has jarred two wires into contact, and the roar of that one battery has immediately informed me of the fact, notwithstanding the action of the eighteen others; I have separated the wires, and the universal singing communicates to me that all are now working satisfactorily. Any local action on the zinc in the same way is immediately notified by its different and peculiar voice, and I have been surprised how quickly the experimentor catches the characteristic peculiarity of each noise, which is learnt more readily than the sound of different bells in a strange house.

With regard to the constancy of this battery, I may be expected to say a few words, for although theoretically it is not absolutely constant, yet practically, for the purposes of the electro-metallurgist, its constancy remains for two or three days, or in other words until the battery is nearly exhausted; and then, to replenish the solution of zinc with a fresh supply of dilute acid will not occupy more than half a minute. In recording my own experience of its practical, though not of

its absolute constancy, I can at the same time conjoin the testimony of some of the most extensive manufacturers in this country. Whilst, upon the practical use of the battery I may state, that the platinum never wears off the silver, and that the platinized silver never undergoes the slightest change, or is affected by the slightest local action.

The perfect modes of gilding and plating, &c., must rest alone upon the authority of this work, for although De la Rive has given a process for gilding, it appears, not only from my own observation, but also from the statements of others, doubtful, whether his mode is really voltaic; and certainly the evolution of hydrogen from the object to be gilt, does not at all agree with the laws regulating the precipitation of the metals which I have detailed; in fact, it is diametrically opposite to them. The process given in this work was discovered in August, before I had seen De la Rive's paper. By my process the gold can be obtained of any thickness, an inch or more, if the operator please. The processes for platinating, palladiating, &c., entirely rest upon the authority of this work, for hitherto the reduction of these metals, in any other state than that of the black powder, has been always considered impossible. The electro-metallurgist will be enabled, by the processes which he will find here fully described, to execute reliefs and intaglios in gold, or in fact, in nearly every other metal; facts altogether new in science. The working of all metals except copper, is also due to the discovery of the laws regulating the precipitation of the metals.

Every author has given directions for making moulds on plaster casts in metal; but it is singular, that by no process hitherto known, can a perfect reverse of plaster be obtained. In investigating the cause of this, I soon discovered that the extreme porosity of the plaster was the block over which they had all stumbled, and the difficulty was overcome by rendering the plaster non-absorbent. In this work, the reader will

find, that the copying of reliefs in plaster, is brought to the utmost possible perfection, and by very simple means.

The extended use of white-wax, bees-wax, rosin, &c., for the electro-metallurgist, I trust will be found acceptable. Their manipulation I have given as the result of my own experience, and therefore, doubtless, those who make a trade of working these substances, will find the account not so full as might have been expected, or wished; yet I believe practice alone is required to make the operator perfect in these arts.

The application of electro-metallurgy to the copying of leaves, fruit, &c., is for the first time described in this work. The new mode of etching here detailed, I confidently trust will be also found a valuable adjunct to the knowledge of the engraver. The principle which regulates the adhesion and non-adhesion of the plates will enable the operator to conduct his operations with certainty, a circumstance of no small importance to the engraver; ignorance on this score having already produced untoward results.

In this history, a sketch only has been given of the leading discoveries; but undoubtedly the person who carries out a new science is also deserving of considerable praise, for frequently he has to incur great expense without any immediate prospect of a return for his capital. Many persons are now entering into the electrotype with great spirit, but none at all equal to the manner in which Mr. Palmer has undertaken it.

The laws which I have given in this work, and the universality of their application, will doubtless influence importantly the attainment of the grand object of using the galvanic fluid commonly among our manufacturers; and having thus, as I believe, raised the isolated facts called the electrotype, into a vast and comprehensive science, a new name is required which may be suitable to its importance, and capable of embracing its application. The term which I have ventured to apply to it, is ELECTRO-METALLURGY, OR THE ART OF WORKING IN METALS BY THE GALVANIC

FLUID, and the value of the new nomenclature is evident, when we consider that it takes in every mode by which it is possible to work the metals, either by dissolving, or precipitating them, by the agency of the voltaic current.

As a surgeon, I feel bound to pass my opinion upon the effect which an extensive application of electro-metallurgy would have on the health of the workman, and in one word I may state, that I believe the mode of working in metals by the galvanic fluid is more wholesome, and would be attended with far less deleterious properties than the methods now practised. The use of the salts of gold, silver, and platinum, is liable to discolour the fingers, but the other salts have no particular effect. However, in passing the above decided opinion, strengthened as it is by watching the effects of the experiments on myself, and also from paying attention to the health of some who have reduced electrotype copper by the hundred weight, I feel but little doubt that if the electro-metallurgist was several times in a day to leave his work with fingers covered with metallic solutions, and take his meals without any ablution, and repeat this for a long time, that the quantity of metal which he would thus draw insensibly into his system, might be attended with inconvenience. Several of the processes here detailed, as those of gilding, &c., are likely most materially to benefit the health of the workman as they supersede the use of pernicious mercurial fumes.

The books which the electro-metallurgist may consult for a more extensive knowledge than is contained in the present treatise, are Daniell's Elements of Chemical Philosophy, and Dr. Bird's Treatise on the same subject. He may farther consult the original papers of Faraday, Daniell, and others, in the Philosophical Transactions of the Royal Society, and he ought by all means, for a description of the metallic salts, to make use of that complete Encyclopedia of Chemistry, by Professor Brande, which has been erroneously named a manual.

It has often been mentioned to me, and considered strange that the societies, whose business it is to superintend and cherish the rising arts and infant sciences, should not contain any single paper on the new science of electro-metallurgy, and that the student is compelled to obtain his knowledge from other sources. For the electrotype, he may possess Spencer's treatise on that subject, although the mode of proceeding detailed by him is very different from those which the laws I have developed, require me to recommend. Jacobi has written a treatise, in German, on Galvano Plastics, De la Rive's paper on gilding, is translated in the Polytechnic Journal, where it can be easily procured, and there are besides various original papers in the Literary Gazette, Atheneum, and Philosophical Magazine, upon the electrotype. The value of these excellent periodicals in making public new discoveries and fostering talent which would otherwise be frequently crushed by the overwhelming weight of interested opinion, is here evident, and to their spirited editors this country is daily owing increase of knowledge, power, and wealth.

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