UNDULATOKY FORCES. ELECTRO-METALLURGY. [SILVKB sou 



hundred parti of hyposulphite of tod* and chloride, or 

 any other salt of silvor, fifteen part*, Compound* of 

 thU description are aUo used for silvering clock-faces, 

 t li'-nnomotor and barometer plates, and many other arti- 

 cles of copper and brass. 



133. Silvering by Immening. Mr. Joseph Steele took 

 out a patent, dated August 9th, I860, for silvering arti- 

 cles, by immersing them in a silver solution in contact 

 with a piece of rinc of proper size. The process is as 

 follow* : Dissolve four ounces of pure silver in twenty 

 ounces of nitric acid ; also dissolve, separately, one-and- 

 a-half pounds of common salt in one-and-a-half gallons of 

 water ; mix the two solutions together, allow the mixture 

 to remain till clear, pour away the clear liquid, and wash 

 the precipitate, which is chloride of silver ; next fuse to- 

 gether twenty-four ounces of ferro-cyanide of potassium, 

 and twelve ounces of carbonate of potash ; and when the 

 mass is cold, add it, together with the chloride of silver, 

 to one gallon and a-half of water ; boil the mixture, and 

 filter it ; it is then ready for use. 



134. Silrtring Solution for Battery Process. Many 

 solutions have been proposed and tried for depositing 

 silver by the battery process, but none have stood the 

 test of time and experience like the one composed of 

 double cyanide of silver and potassium dissolved in 

 water, and a little free cyanide of potassium added. It 

 may be mode of various strengths, from half an ounce of 

 silver to the gallon of water, to two, four, six, or more 

 ounces ; and from an ounce of cyanide of potassium to 

 several pounds per gallon, and still bo effective in work- 

 ing. The formula of M. do Iluolz is as follows : Dissolve 

 one part of cyanide of silver and ten parts of cyanide of 

 potassium in one hundred parts of water, and dilute the 

 resulting liquid with water to the required strength. 



136. Silver Plating Solution. The following is the 

 most practical method of making a large quantity of the 

 ordinary cyanide of silver plating liquid : Take four 

 parts of grain silver, add it, in small portions at a time, 

 to a warm mixture of about five ports by weight of strong 

 commercial nitric acid (the acid varies greatly in strength), 

 and one part of water, contained either in a glass or 

 stoneware vessel. Gas will be evolved from the surfaces 

 of the pieces of silver, and brown fumes of nitrous acid 

 will arise from the mixture, which should be conveyed 

 out of the apartment by means of the chimney. The 

 action should be maintained moderate and uniform, and 

 if it should become too strong, a little cold water should 

 1 added, and the mixture kept more cool ; when the 

 whole of the metal is dissolved, apply a greater heat, 

 and evaporate the solution nearly to dryness, which will 

 drive off any excess of acid tliat may be present ; the 

 resulting salt, nitrate of silver, may then be dissolved in 

 a large quantity of water, in the proportion of half a 

 gallon (more or less) to each ounce of the silver used ; at 

 the same time a solution should be mode of from 3 to If; 

 parts (according to its quality) of cyanide of potassium, 

 in 30 or 40 parts of water, which is to be added gradually 

 to the solution of nitrate of silver as long as it produces 

 a precipitate ; if too much be added, it will cause some 

 of the precipitate to redissolve and be wasted ; it will 

 also make the liquid appear clear where it posses : in 

 such a case the liquid should be stirred, then allowed to 

 settle clear, and a small quantity of nitrate of silver, dis- 

 solved in diftilUil water, should be added as long as it 

 produces a white cloud. By conducting the operation in 

 a glass vessel, adding the liquid towards the latter period 

 in small quantities at a time, and at intervals of a few 

 minutes each, with gentle stirring immediately upon euch 

 addition, carefully observing when it ceases to produce a 

 precipitate, the point of neutralisation may bo very accu- 

 rately determined. The liquid must now be allowed to 

 remain undisturbed until quite clear, the clear portion 

 poured steadily away from the precipitate of cyanide of 

 silver, and the precipitate washed five or six times in a 

 large quantity of water, by simply adding the water 

 briskly to it, allowing it to settle, and then pouring off 

 the clear portion. Next dissolve from 3 to 3} parts 

 (.according to its quality) of cyanide of potassium in 20 

 parte of water, adding it, in portions at a time, to the 



wet cyanide of silvor, with free stirring, until the \\ In <!. 

 is dissolved ; then add about 3 parta more of cyanide of 

 potassium to form free cyanide, and sufficient water to 

 reduce the whole to the proportion of aliout one ounce of 

 silver to the gallon : finally, when all the free cyanide is 

 dissolved, filter the solution through a piece of unglazed 

 calico. On the small scale, distilled water is used in the 

 various parts of the process, except the washing ; but, 

 on the large scale, clean rain-water or spring-water is used 

 in all the operations. 



136. Another Solution. The cyanide of silver plating 

 solution may bo mode by other modifications of the 

 chemical method than the one described : for instance, 

 some eloctrotypists make the solutions by dissolv- 

 ing oxide, carbonate, or even chloride of silver in a 

 solution of cyanide of potassium to saturation, and 

 then adding an amount of free cyanide ; by this process 

 wo are enabled to use caustic potash, carbonate of potash, 

 hydrochloric acid, or common salt, instead of cyonidu 

 of potassium, for precipitating the nitrate of sil 

 nevertheless it still requires two equivalents of cyanide 

 of potassium to bo used as before viz., one to com. 1 1 

 the salt of silver into cyanide, and the other to dissolve 

 the cyanide of silver formed ; because, in all such cases, 

 according to the researches of Messrs. Glassford and 

 Napier,* when any salt of silver is added to a solution 

 of cyanide of potassium, it is first converted into cyanide 

 of silver at the expense 1 of one portion of the cyanide nf 

 potassium ; it then combines with the remaining cyanide 

 to form double cyanide of silver and potassium, which 

 dissolves in the water : therefore, by this modification of 

 the chemical method, no cvanide of potassium is saved, 

 and the carbonate of potash, hydroclUoric acid, <tc., are 

 wasted. This modification has a still greater disad- 

 vantage; it introduces substances into the depositing 

 liquid which ore injurious. We have before said (90) 

 that a good depositing solution should dissolve the anode 

 freely, hold abundance of metal in solution, and not act 

 chemically upon base metals, because it is such metals 

 we generally wish to coat. Now, if instead of cyanide 

 of silver, wo add oxide of 'silver to the cyanide of 

 potassium liquid, it converts part of the cyanide into 

 caustic potash ; if we add carbonate of silver, it converts 

 it into carbonate of potash ; and if chloride of silver, it con- 

 verts it into chloride of potassium ; and each of these sub- 

 stances, especially the last, diminishes the action of the 

 liquid upon the dissolving plate, decreases its solvent 

 power for cyanide of silver, makes its particles less inol >ile, 

 and causes it to act in some degree upon base metals, and 

 thus endangers the adhesion of the deposits upon them. 

 Some electro-platers think the presence of these salts not 

 injurious, but many consider them highly detrimental. 



137. Solution by Battery Process. The same silver 

 solution may be formed by the battery process (89) as 

 well as by the chemical method ; and this process lias its 

 advantages and disadvantages: it is very convenient in 

 making a small quantity of liquid, because it enables 

 the operator to do so quickly, to avoid the trouble of 

 making the nitrate solution, of precipitation, of washing, 

 and of the attendant risk of loss of materials ; but it has 

 the disadvantage of converting a large proportion of tho 

 cyanide of potassium into caustic potash, by taking its 

 cyanogen to form cyanide of silver, and setting the 

 potassium free, which immediately combines with the 

 oxygen of the water, forming caustic potash, which 

 dissolves in the liquid. The hydrogen of the water is 

 evolved at the cathode, and the dissolved potash gradually 

 becomes converted into carbonate of potash by absorption 

 of carbonic acid from the atmosphere. Neither M 

 potash nor carbonate of potash are so injurious in the 

 liquid a* chloride of potassium; still they diminish the 

 action of the liquid upon the dissolving plate, render it 

 a worse conductor, reduce its solvent power for cyanide 

 of silver, and make its particles less mobile. 



138. Solid Deposition of Silver. Mr. Alexander Park cs 

 took out a patent^ March 29th, 1841, for improvements 

 in the solid deposition of silver. He converts an ounce 

 of silver into oxide of silver, by first dissolving it iu 



2'kilolopMcal Uttfazint, 1811. 



