SOLUTIONS, ETC.] 



UNDULATORY FORCES. ELECTRO-METALLURGY. 



21y 



pure silver iu about 20 or 25 grains of the strongest 

 nitric acid, and then dilute it to the required volume with 

 distilled water. And C, the gold solution : to make 

 twenty ounces of which, dissolve about 5 or C grains of 

 pure gold in about 20 or 25 grains of a hot mixture of 

 one measure of nitric acid, and about two or three 

 measures of hydrochloric acid ; when dissolved, dilute 

 the solution with 20 ounces of distilled water. 



The same patentee includes in his patent a phosphorus 

 moulding composition, by the use of which tho immer- 

 sion in the phosphorus solution is dispensed with, the 

 moulds themselves containing the required amount of 

 phosphorus. To make about one pound of this compo- 

 sition, melt together half a pound each of wax and 

 deers' fat ; then dissolve about 19 or 20 grains of phos- 

 phorus in about 300 grains of bisulphide of carbon ; 

 keep the wax mixture barely melted, and add the phos- 

 phorus solution slowly to it, and with brisk stirring of 

 the fat, pouring it in at the bottom of the melted 

 mixture by a vessel with a long spout, to prevent its 

 inflaming. It is highly dangerous to have split portions 

 of the phosphorus composition where it can come in 

 contact with wood, paper, rags, <fcc., as, after a lapse of 

 some time (even hours), they will often burst into flame. 



88. Selection of Depositing Processes. For very small 

 articles, of which there are a great number, such as 

 buttons, hooks-and-eyes, pins, <fcc., and which require 

 only a very thin deposit, the simple immersion or wash 

 process will answer very well, being both easy of execu- 

 tion and cheap. For the multiplication of numerous 

 small articles in copper, such as medallions, <tc., the 

 single cell process is veiy advantageous ; it is quicker 

 than the battery process ; and considering the time occu- 

 pied, and the other elements of expense, it is to be 

 preferred to that method. But for all ordinary deposits, 

 plating, die., the battery process is by far the best, 

 because coatings of any thickness, in all ordinary metals, 

 may be obtained by it, and the solutions do not, as in 

 othur processes, require renewal. 



89. Methods of Making Depositing Solutions. The 

 operator will next consider about making depositing 

 liquids. This may be done by two methods ; the one 

 called the chemical, and the other the battery process. 

 The chemical process consists in mixing the various 

 ingredients by the usual means, and in suitable propor- 

 tii uis to form the liquids : for instance 1st, the ordinary 

 sulphate of copper solution is prepared by dissolving 

 a certain proportion of commercial sulphate of copper in 

 water, and adding to it a definite quantity of sulphuric 

 acid to afford free acid; and, 2nd, to form tho ordinary 

 cyanide of silver and potassium plating liquid, silver is 



.Ived in dilute nitric acid ; the solution of nitrate of 

 silver formed is precipitated by addition of a solution of 

 cyanide of potassium ; tho white precipitate of cyanide 

 of silver is washed, and then added, as much of it as will 

 dissolve, to a solution of cyanide of potassium; after 

 that, an additional portion of cyanide of potassium is 

 added to afford free cyanide. The battery process con- 

 gists in taking some water, and dissolving in it a certain 

 proportion of acid or salt, as the case may be ; then 

 placing a large anode of the given metal at the lower 

 part of the liquid, and a small bright cathode at the 

 upper part, and, if necessary, applying heat. Con- 

 nection is to be made with a suitable battery until tho 

 required quantity of metal is dissolved, which is indi- 

 cated by the cathode receiving a good deposit : in 

 making gold solutions the cathode is generally placed iu 

 a small porous cell tilled with tho same liquid, and 

 immersed nearly to its edge in the outer liquid ; and by 

 transferring tho cathode occasionally to the gold solu- 

 tion, and observing if it receive a good deposit, we may 

 know that sufficient metal is dissolved ; the liquid of the 

 cell may then be added to the outer solution. If it be 

 wished to make sulphate of copper solution by this 

 method (which we should uot advise, however, tho salt 

 being so cheap), take the same quantity of water as we 

 prescribed for the chemical method, and add to it as 

 much acid as was contained in the salt of copper with 

 the free acid as before, and then pass a current from a 



battery of one or two pairs by a large anode and small 

 cathode, until sufficient metal is dissolved; or if it be 

 desired to make some cyanide of silver and potassium 

 solution by this method, which is sometimes done, tako 

 the same proportions of water, cyanide of potassium, 

 and free cyanide as in the chemical process, and pass the 

 electric current by a large silver anode, until the same 

 proportion of silver is dissolved as required by the 

 chemical method. 



90. Selection of Depositing Liquids. The following 

 rules should be observed in selecting a suitable depositing 

 liquid for the battery process. 



1st. It should act strongly upon the anode, and hold 

 abundance of metal in solution. 



2nd. It should possess good electrical conducting 

 power. 



3rd. It should yield its metal freely, and in a reguline 

 state. 



4th. It should not act chemically to any great extent 

 upon the base metals, because it is those that wo gene- 

 rally wish to coat, and chemical action upon them would 

 endanger the adhesion of the deposited metal. 



5th. It should not decompose by contact with the 

 atmosphere, nor should light influence it in such a way 

 as to injure it for depositing purposes. 



Cth. It is better if it do not evolve gas at the surface 

 of the receiving article whilst depositing, because that 

 generally indicates a waste of battery power, attended by 

 oxidation of the liquid. 



91. Testing a Dejiositing Liquid. To test a depositing 

 liquid, pass a current of electricity through it, from about 

 two pairs of Sinee's batteries, with a suitable clean anode 

 of proper size, and a clean piece of iron, brass, or copper, 

 of about the same size, to receive a deposit, observing 

 how much gas is evolved in the battery ; if the deposit 

 appear quickly, and of a bright and proper colour; 

 and if it adhere to the oietal, the cathode evolving 

 ga from its surface, and the anode dissolving freely, 

 cleanly, and without escape of gas, work it at intervals, 

 keeping it exposed to light and air ; observe if it con- 

 tinue to work well, or whether, on the contrary, it 

 shows a decrease of conductibility, deposits a sediment, 

 or if the anode become covered with an insoluble crust 

 (this last may arise either from deficiency of free acid, 

 or from impurities in the metal). If but little gas be 

 evolved in the battery, the liquid in the cell is a bad 

 conductor, and will neither dissolve nor deposit the 

 metal freely at that temperature, or it is deficient in 

 free acid or free salt. If the deposited metal be of a 

 bad colour, either the battery is too strong, tho receiving 

 article too small, or the liquid is incapable of yielding 

 good metal. If the immersed metal or article be coated 

 by simple immersion without the aid of the battery, it 

 shows that, to adapt the liquid to articles made of that 

 particular metal or alloy, they must receive some pre- 

 vious preparation, in order to make the deposit adhere. 

 If it deposit a sediment, or alter in conductibility by 

 exposure to air and light, the probability is that those 

 influences alter either its chemical composition, or the 

 arrangement of its particles. If it evolve gas at the 

 receiving surface during deposition, it shows either that 

 there is too much battery power, too little metal in 

 solution, too much free acid, or that it is a wasteful 

 liquid, in which one part only of the current is employed 

 in depositing metal, whilst another part of it is em- 

 ployed in evolving gas and oxidating the liquid. 



92. Testing Solutions for Depositing Alloys. With so- 

 lutions in which alloys are to be deposited, tho most 

 important condition is, that neither of tho motals to bo 

 deposited should be electro-positive to each other in 

 that liquid. This is best tested by taking a wire of 

 each metal, connecting them with a galvanometer, and 

 simultaneously immersing their free ends in tho liquid ; 

 if either be electro-positive, the needles of the instru- 

 ment will be deflected, and the direction of the deflec- 

 tion will indicate which is positive, wliile the amount of 

 deflection will indicate the amount of their electric 

 difference in that liquid. It may also be tested by 

 immersing a wire of each metal (uot in mutual contact) 



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