1S53.] 



ON ELECTROTYPING OPERATIONS. 



■227 



be attributed to the rn'al daimants for the invention of electro- 

 metailurgy ; f)r neitlier the Enghsh nor Russian philosopher 

 revealed what had not been known before. 



Yet to Jaeobi and Spencer is due the merit of having called 

 public attention to the subject; for in doing this, they have con- 

 ferred benefits on the world greater, perhaps, than by making an 

 original di.'-;co\ery. 



After the publications of Jacobi and of Spencer had called the 

 attention of tlie scientific woild to the new art, the principles 

 involved in it became the study of several eminent philosophers, 

 who disclosed the methods to be foliowe<.l for obtaining reguline 

 metal. After this, several departments of electro-metallurgy 

 rapidly advanced. Electro-plating, and the multiplication of 

 pages of letter-press woi-k, as pages of type, and wood-cuts, (elec- 

 tro-stereotyping,) were soon extensively practised; hut the copy- 

 ing of the delicate touches of the copper-plate engraver (the 

 electrotj'pe proper) was beset with difficulties. On account of 

 the great value of the engraved plate, together with the risk of 

 its being destro3-ed in the attempt to copy it, and the uncertainty 

 as to whether the duplicate would have good metallic properties, 

 even if the operator should have the good fortune to obtain one, 

 this department of the art (the first and most beautiful of 

 Spencer's suggestions) was allowed to rest as an experiment or be 

 confined to articles of small size and value. 



Adhesion of Deposit to Matrix. — Electro-metallurgy requires 

 that the depositea metal should have all its cohesive properties. 

 If such a deposit of copper is made on a clean plate of copjjer, 

 it is obvious that the deposited metal will cohere with the plate 

 on which it is made, and an elaborately engraved plate would 

 thus be converted into a mere mass of metal. The electrotype 

 art, therefoi'e, cannot exist befoi'e means are provided for preventing 

 this destructive adhesion. 



Various plans for overcoming this difficulty have been proposed 

 All these, howevei', have a cornraon feature, which is to prevent 

 the dejiosit and matrix from touching by means of an intervening 

 film of heterogeneous matter. 



Mr. Smee proposes to use that coating of air wdiich adheres so 

 firmly to polished metals (so strikingly exhibited "when the 

 attempt is made to wet a polished knife-blade). To obtain the 

 air coating, he directs that, after every attachment has been made 

 to the plate, it be placed in a cool and moist celler for a few days 

 before introducing it into the electrotype vat. 



Smoke, black lead, oils, and powders, and wax, have also been 

 proposed for covering the face of the plate. 



The method used in the British ordnance survey is perhaps 

 the best of all these. This is conducted as follows: The plate 

 is first well oiled, and the oil well wiped away widi soft bread. 

 The plate is then heated to above the temperature of melting 

 wax, and a cake of white wax pressed against the eilge. The 

 oil having removed the air from the plate, the wax will flash over 

 it in an extremely thin sheet or film. AH excess of wax is then 

 to be wiped away with a fine linen cloth, free from lint. The 

 plate must be left to cool before introducing it into the vat. 



To smear the face of the finely engraved plate is in opposition 

 to the fundamental idea of the electrotype, which is that of atomic 

 c;isting. In the process of Mr. Smee, air bubbles will be retained 

 in the fine lines of the graving, thus mutilating the copy; more- 

 over, the face of the new plate is waved from the agitation of the 

 stratum of air when receiving the firet portion of copper. 



In the waxing process it is almost impossible to free every 

 line from excess of wax. Even days of tedious application do 

 not insure perfection. In addition to the coareene*? of these va- 



rious methods, they are extremely uncertain as to whether they 

 efl'ect the purpose for which they are applied. 



It was always observed that if the deposited metal was not de- 

 ficient in mechanical properties, it stuck very hard to the origi- 

 nal, and the plates had to be subjected to violent jarring, heating 

 and beating, to separate them. But if the deposited metal was 

 of very fine quahty, then most likely the deposit was inseparably 

 united to it. From these circumstances attending the adhesion 

 of the deposit, it occurred to me that, when the cohesi^'e force 

 was but feebly developed in the deposited metal, then the force 

 of cohesion or homogeneous attraction could not exteud the dis- 

 tance presented by the thickness of the film of heterogeneous 

 matter between the plates; but that when these forces were well 

 developed, the spheres of homogeneous attraction of each plate 

 would extend through the wax or air film. 



It may be proper here to remark that the above views of ad- 

 hesion have been applied to another department of electro-metal- 

 lurgy with the most gratifying success. In electro-plating the 

 difficulty of obtaining a firm adhesion of the film of precious 

 metal is entirely obviated by making such arrangements as in- 

 sure a rapid deposition of highly ductile metal at the moment the 

 article to be plated is immersed in the electrolyte. 



In considering the sticking of the plates, after homogeneous 

 attraction or cohesion, heterogeneous attraction or adhesion de- 

 mands attention ; for two similar bodies may be separated by a 

 film of heterogeneous matter, w liich binds them more firmly to- 

 gether than their particles are held together by cohesion, as we 

 see in the use of cements. 



This force is very powerful between some bodies, while be- 

 tween others it is very slight. Aii- adheres very strongly to 

 metals, as before referred to ; hence a film of air may unite two 

 copper plates, even though they are separated beyond the distance 

 at which cohesise attraction takes place. 



Wax is a common ingredient in cements; its adhesive proper- 

 ties have become proverbial; its use is evidently improper. 

 Therefore a substance having a strong adhesive attraction for the 

 plates must not be on the face, and the cohesive force of the sur- 

 face particles must be suspended by other methods than making 

 the deposited metal deficient in mechanical properties. 



It was hoped that a substance could be found that would act 

 uniformly and gently on the surface of the engraved plate, and 

 wdiich in destroying the homogeneous attraction of the surface 

 particles, would, by chemical union with them, form an insolu- 

 ble and friable compound, having but a slight adhesion to the 

 plate. I was led to select iodine for the experiment on account 

 of its sparing solubihtj' in water, its high equivalent number, and 

 innoxious qualities. A copper plate was well cleaned, exposed 

 to the vapor of iodine, and electrotyped ; the deposit separated 

 from it readily. This w;is rejieated some hundred times with 

 invariable success. 



It was found in cleaning large plates fir the application of the 

 iodine \'apor, that while one part of the plate was being cleaned, 

 another part would tarnish, and hence a uniform action of the 

 iodine could not be obtained. This led to silvering the plates 

 before iodizing, which facilitated the cleaning and exhibited the 

 action of the halogen. A silvered plate was washed with an 

 alcoholic solution of iodine and electrotyped; the electrotvpe 

 separated from the matrix yet more readily than before, the iodid 

 of silver ser\ing better to pi-event adhesion than the iodid of 

 copper. 



"But it was soon observed that a ]'late prepared on a dull day 

 did not separate so readily as one prepared under a bright sky, 

 and on experimenting it was found that a plate iodized and ex- 



