DNDULATORY FORCES. ELECTRO-METALLURGY [BLACKLEADIKO, nc. 



Encircle iU edge by a strip of itout paper, and pour 

 the mixture upon it* surface quite hot, and of tho con- 

 sistency of treacle, to the depth of half an inch or more, 

 according to the site of the modal and the depth of its 

 hollow part*, brushing its surface beneath lot liquid 

 with a brush having fine and long hairs, to remove 

 air-bubble*. Allow the mixture to remain until it is 

 quite firm, which will be from two to twenty-four hours, 

 according to its bulk ; take off the paper, and remove 

 tlio mould very gently, carefully stretching and drawing 

 it at the same time in the direction of tho overhanging 

 parti!, to prevent injury. Should tho object to be copied 

 be a hollow metallic bust, proceed as follows : Partly 

 fill it with sand, to make it heavy and thus prevent its 

 rising in the liqnid, and cover its opening by sticking a 

 | piece of millboard strongly over it ; then place tho bust 

 in the centre of a cylindrical and tapering vessel, a few 

 inches deeper and Wider than itself, and pour the melted 

 composition in steadily, until it is a few inches above 

 the top of tho head, tapping the bust, and inclining the 

 outer vessel, to facilitate tho escape of air-bubbles. 

 When the composition is quite firm, which it will be in 

 about twenty hours, it may easily be removed from the 

 vessel by shaking, the vessel having been previously well 

 oilod ; tho mould may then be removed from the bust by 

 previously marking on its lower end the position of the 

 face, passing a knife carefully up the back of the bust 

 nearly to the crown of tho head, and opening tho elastic 

 mould with the hands, whilst a second person lifts out 

 the bust. If tho original bust bo composed of plaster, it 

 must bo previously saturated with oil, to prevent the 

 melted composition adhering to it. 



181. Rendering Mouldi Conduct'Me. To render the 

 surfaces of non-metallic moulds conductible, there are 

 two methods in use : first, to cover them with a thin 

 film of blacldead by brushing; and, second, to coat 

 them with a minute film of gold or silver by ohomical 

 means. The first of these methods is generally used fur 

 moulds composed of gutta-percha, wax, resinous com- 

 position; or plaster saturated with oil, whore tho parts 

 are not much under-cut; and the second for elastic 

 moulds, because the blacldead cannot be readily applied 

 to all their recesses. 



182. BlackUofling. To apply blacklead to a small 

 round or oval medallion formed of gutta-percha and 

 marine glue, first insert tho sharp end of a piece of 

 copper wire, size No. 16 or 18, and about fifteen or 

 twenty inches long, into the edge of the mould near its 

 face ; then pass a piece of fine copper wire, size No. 28 

 or 30, once tightly round the edge of tho mould, close to 

 its face, securing its ends to the other wire. Fix a strip 

 of paper about one inch wide, by means of sailing-wax, 

 tightly round the edge, to prevent the blacklead passing 

 anywhere except upon tho face of the mould. Apply 

 the blitckload by a soft camel's-hair brush with a large 

 and thick body of short hairs, broatliing upon tho face 

 of tho mould occasionally to facilitate tho adhesion of 

 tho material. When tho modal i.s perfectly black and 

 bright, blow off tho superfluous blacklead, and remove 

 tho paper ; it is then ready for receiving a deposit, tho 

 whole operation occupying about ten or fifteen minutes 

 with a small object the first time of preparing it, but 

 less in subsequent operations. If the mould bo very 

 large, and especially if it have deep hollows in its sur- 

 face, it will require, after being blackleaded, to have 

 several short and fine copper "guiding-wires" carefully 

 attached to tho main wire, and their free ends slightly 

 inserted in tho face of tho mould, in tho most hollow and 

 distant parts, or to lie in contact with them, in order to 

 cause the deposit to commence and spread there as well 

 as round tho edge. If this precaution bo not taken, 

 the deposit will bo much thinner over those parta than 

 upon the nearer and more prominent places, and some- 

 time* will not spread over them at all. 



183 Preparing the Surface* of Elastic Mould* Elastic 

 moulds are treated in a different manner. First, a stout 

 connecting wire is attached ; then a number of lino copper 

 "guiding-wire*" are twisted round it, and their froo 

 end* slightly inserted in tho face of tho mould, in all tho 



hollow and distant parts; the mould is then either 

 dipped into the phosphorus solution (87), or its surface 

 is covered with that liquid ; and, after it has been drain.'. I 

 clean, it is allowed to remain until perfectly dry ; the 

 silver solution is next applied to it (87), in like nwBMr, 

 for several minutes, until it appears black, with a m.-t.dlir 

 lustre like black china; it is then gently rinsed with 

 distilled water, and tho gold solution applied in the 

 same way (87), which gives it a yellowish aspect ; after 

 another rinsing in distilled water, it is ready for re- 

 ceiving a deposit. 



184. Mi'iMinij by Photphoru* Composition. Some ob- 

 ject* which are not much under-cut, are moulded in tho 

 phosphorus moulding composition (87) ; and, in some 

 oases, whore they are under-cut, as well as busts, they 

 are first copied in tho elastic moulding, and then the 

 elastic mould ia copied in this material, the composition 

 being but barely melted that it may not dissolve the 

 elastic moulding. In either of those cases, instead of 

 immersing the mould in the phosphorus, silver, and 

 gold solutions, it is only immersed in the two latter, in 

 the manner already described, tho phosphorus contained 

 in the mould itself serving to reduce the silver and gold. 



185. Preparing Surfaces of Qlatt for Deposition. 

 Glass surfaces may bo prepared for receiving a dej*>sit 

 by means of tho phosphorus, silver, and gold solutions, 

 but not very satisfactorily. A bettor method, which we 

 have tried, has boon silvering them by Uraytou's patent 

 process, thus : Take one part, by weight, of liquid 

 ammonia, throe parts of alcohol, two parts of nitrate 

 of silver, and throe parts of distilled water; dissolve 

 the silver salt in tho water, add tho liquid ammonia 

 and tho alcohol, shake tho mixture, allow it to remain 

 until quito clear, and pour olf tho clear part into tho 

 glass vessel to bo silvered, which must be perfectly 

 clean : then add to it one quarter of a part of grape- 

 sugar dissolved in weak spirits of wine, mix the liquid, 

 and heat it to about 160 or 160 Fah. for about twenty 

 or thirty minutes, and the glass vessel will become sil- 

 vered. The liquid may then bo removed ; tho vessel 

 gently rinsed with distilled water ; a connection is to be 

 formed by means of a line copper wire with tho film of 

 silver and the battery ; the vessel tilled witli a suitable 

 depositing liquid, an anode immersed, and tho surface 

 deposited upon in the ordinary way. If tho process 

 be successfully performed, the deposit, whether of silver 

 or copper, will spread instantaneously over tho sil- 

 vered surface. The only way by which we have been 

 able to form an adhesive deposit upon glass or por- 

 celain, has been to send the articles to a gla<s and por- 

 celain gilder, and have gold-leaf burnt into their sur- 

 faces, aud then depositing upon them in the usual 

 manner may be successfully effected. 



180. Immersion of Articles in the Fat. Tho operator 

 having prepared tho various articles and moulds, will 

 immerse them in tho depositing solution, having pre- 

 viously introduced the anode and completed all the 

 nectiona, taking care always to connect the article to 

 receive tho deposit with the zinc of tho battery, and tho 

 metal to be dissolved with tho copper or silver plate. 



187. Regulation of Mattery Pouter. In depositing all 

 metals, it is of the greatest importance that the ba, 

 power bo properly regulated ; and this may bo done in a 

 variety of ways, which colloctiv. either in mak- 



ing alterations in the battery, in tho depositing vessel, 

 or in tho vires connecting them. The int* -nxily of tho 

 current is increased by increasing tho number of alter- 

 nations of the battery plates. Resistance to the current 

 is diminished by increasing the conductibility of tho 

 battery liquid or depositing solution, which may bo 

 effected either by tho addition of free acid to tho battery 

 or more salt to the solution; or by increasing tho thick- 

 ness and decreasing tho length of tho connecting u i 

 Tho qiMHitty of tho current is ineivastrd l>y immersing 

 all the battery plates deeper in their liquids ; aUo by 

 of those means which increase the iiiten>iiy. Dou 

 the intensity and the quantity may bo decreased by 

 separating the electrodes in tho dept>siiin > l.htr 



asunder, or by interposing a long and lino iron wire in 



