BATTEUIES, ETC.] U^DULATORY FORCES. ELECTRO-METALLURGY. 



215 



batteries, and is now being moulded into large vessels for 

 the use of some of the electro-plate manufacturers : 

 gutta-percha has been also used, but possesses rather 

 less advantage, upon the whole, than the other materials, 

 being opaque and expensive, while the zinc salt of the 

 battery liquid passes rather rapidly over its edges by 

 capillary action. 



73. Porous Cells. When Daniell's or any other battery 

 with two liquids is used, porous vessels are required 

 also, to allow the two liquids to touch each other with- 

 out mixing : they are of three kinds unglazed earthen- 

 ware, wood, and bladder. The first of these is the only 

 kind in use by manufacturers ; they should always be 

 kept in clean water when not in use, to remove the salts 

 of the battery liquids from them, to prevent their 

 cracking, and to preserve them always fit for imme- 

 diate use. 



74. Zinc for Batteries. The best kind of zinc for 

 batteries, and the kind chiefly in use by electro-platers, 

 is the German or Liege zinc, known as " Mosselman's," 

 from the name of a former manufacturer of it. The 

 thickness of the plate should vary with the size of the 

 battery ; the smallest should not be less than one-eighth 

 of an inch thick, on account of its brittleness when 

 amalgamated ; large ones are generally about one quarter 

 or throe-eighths of an inch in thickness. Zinc bolts for 

 Darnell's batteries are generally made by melting to- 

 ur a number of old worn-out pieces of battery plates, 



sting in a suitable mould. 



Amalgamation of Zinc. Zinc plates or bolts are 

 best amalgamated by immersing them, during a quarter 

 of an hour, in a mixture of about one part of sulphuric 

 acid and ten or twenty parts of water ; then pouring 

 mercury upon them, and rubbing it all over them with 

 a hare's foot or piece of old cloth, using a small hard 

 brush for the refractory places ; they are then washed 

 in water, and drained for half-au-hour, and brushed, to 

 r the superfluous mercury. 



70. Copper and Platinised Silver for BatUrie*. Ordi- 

 nary sheet copper answers very well for this purpose, 

 and platinised silver may bo obtained of most philoso- 

 phical instrument-makers, or it may be easily prepared 

 by any one by the following means : Immerse a piece 

 of zinc in dilute sulphuric acid contained in a porous 

 cell ; place the cell in an outer vessel, and fill the outer 

 space with water, to which a few drops of sulphuric acid 

 have been added ; add to this a sufficient quantity of a 

 solution of bichloride of platina to render it of a brown 

 colour ; immerse the piece of silver to be platinised in 

 the outer liquid, and connect it by a wire with the piece 

 of zinc ; gas will soon be evolved from the surface of the 

 silver, when the silver will gradually become black with 

 a deposit of platina ; it may then be removed, dipped 

 several times in water, and afterwards dried, car* being 

 taken not to nib off the platina. The porous cell ru- 

 quires to be immersed a short tune beforehand. The 

 solution of bichloride- of platina may be easily and 

 ;>ly made by adding scraps of the metal foil to a 

 lint mixture of one measure of nitric acid and two-and- 

 a-half measures of hydrochloric acid, as long as gas is 

 evolved from them; the liquid will then be of a deep 

 red colour. 



Silvi;r alone is not nearly so effective for the negative 

 metal of voltaic batteries as platinised silver, because 

 the hydrogen gas evolved adheres very strongly to it, 

 ami gnratly reduces the amount of its surface in contact 

 witli the liquid ; whereas the platina being a very 

 ive metal, and being deposited in the state of 

 a lino powder, causes the hydrogen to be thrown 

 off very rapidly from its surface, and thus increases the 

 action. 



r is still less effective than silver, because the 

 battery liquid acts chemically upon it, and forms a salt 

 of copper, which dissolve* in the liquid and reacts upon 

 the zinc plates, causing them to waste rapidly ; for this 

 reason they cannot, like silver, be safely left in the 

 liquid any great length of time when the battery is not 

 at work. In addition to this, when they are taken out 

 and exposed to the air, they soon become covered with a 



film of oxide, which considerably weakens tho electric 

 current on their reimmersion. 



77. Depositing Vessels, Vats, etc. The depositing ves- 

 sels are made of various materials. For small opera- 

 tions, nothing is so su-table as glass vessels or a stoneware 

 pan ; but for ordinary manufacturing purposes, vats 

 containing from twenty to several thousand gallons are 

 used : they are generally made of wood, lined with sheet 

 lead ; but very large ones, for containing sulphate of 

 copper solution, such as are used for depositing life-sized 

 figures in copper, have iu some instances been built of 

 bricks, coated with cement, and lined with gutta-percha. 

 Vats used to contain cyanide solutions should not bo 

 lined with this substance, because the cyanide of potas- 

 sium acts upon it. The vats used for ordinary silver- 

 plating are about twenty-four or thirty inches deep, from 

 two to three feet wide, and from three to twenty feet 

 long ; their dimensions vary greatly in different manu- 

 factories, and depend upon tho number and size of the 

 articles to bo plated in them. Some electro-depositors 

 use vats formed of sheets of wrought-iron riveted toge- 

 ther ; but there is always a slight salt or sediment found 

 on their sides, which settles at the bottom of the liquid. 



78. Arrangement of Dinsolciny Plates in Vat. In tho 

 vats used for silvering general articles, such as spoons, 

 knives, forks, teapots, plates, etc., the dissolving plates 

 are sometimes fixed all round the sides of the vessel just 

 beneath the surface of the liquid ; in addition to this, 

 vertical wooden frames are fixed at intervals of about 

 two feet, across the vat (Fig. 84), with dissolving plates 



Fig. M. 



upon them, and all the dissolving plates are connected 

 together metallically. The articles to be plated are sus- 

 pended by small copper wires, from brass or copper tubox 

 resting across the vessel upon two other and longer tubes 

 passing along tho upper edges of tho vat Thesi- 

 connected by a large copper wire with tho negative pole 

 of tho battery ; whilst the dissolving plates are connected 

 by another large copper wire with the positive pole : by 

 this arrangement, each row of articles has dissolving 

 plates all round it, which greatly facilitate tho rapidity 

 of deposition. The -wooden cross-frames are movable, so 

 that when large articles are to be plated, one or more of 

 them may bo removed to make more room. 



79. Tho large vessels used for depositing solutions 

 which require to be worked hot, such as the cyanide cop- 

 pering or brassing liquids, are formed either of cast-iron, 

 wrought-iron, or iron coated with enamel ; and tho 

 smaller vessels, such as are used for gilding, are often- 

 times of stoneware or glass ; enamelled iron pans are also 

 used for this purpose. 



80. " Scratch'bruih Lathe." The deposition will re- 

 quire several " scratch-brush " lathes, ono in each depo- 

 siting-room, for scouring and preparing the surfaces of 

 metal articles to receive a deposit. This instrument 

 (Fig. 85) consists simply of an ordinary lathe A, with a 

 wooden chuck B, to tho sides of which are firmly secured 

 four horizontal bundles of fine brass wire ; above it is a 

 vessel 0, containing stale beer, which is allowed to drop 

 constantly, by tho pipe and tap D, upon tho revolving 

 brushes whilst working; tho sides E E aro to prevent 

 splashing, and the tray F, and pipe G, aro to collect and 

 remove the waste liquid. The workman stands opposite 

 tho end of tho machine in using it, working the treadle 

 with his foot, and pressing tho article against tho ends of 



