Quite a number of the salts of silver have been used in forming solutions for silver plating by means of the electric current, all of which have proved more or less successful, but the solution that has the best stood the test of time and experience, is the commonly called cyanide solution, and which may be formed either by chemical means, or by means of an electric cur¬rent. The former method, we think, is to be preferred, especially when the operation is to be conducted by those having but little experience in such matters. To prepare the solution by this method, make a solution of nitrate of silver in the proportion of about one pint of water to each half ounce of nitrate of silver; also have prepared a solution of cyanide of potassium in the proportion of about two ounces of cyanide of potassium to one quart of water, which should be added to the solution of nitrate of silver as long as any precipitate is formed (which is the cyanide of silver.) Should too much be added some of this precipitate will be redis solved and wasted. This will be indicated by a clear and slightly discolored tint being imparted to the liquid, where the cyanide of potassium solution passes. Should this be the case, add a weak solution of nitrate of silver in small quantities at a time, and at the same time stirring the liquid gently as long as it produces a light cloudy appearance. This amount of care is necessary in order that all of the silver may be utilized, as when too much or too little of the cyanide solution is added, some of the silver remains held in the solution. In the former case, in the shape of the double cyanide of silver and potassium, and when too little is added the silver remains in the clear portion of the solution in the form of nitrate of silver, but when just the proper amount is added, all of the silver is precipitated in the form of the simple cyanide of silver. After the exact neutral paint has been attained, allow the liquid to set¬tle, and pour off the clear liquid, carefully preserving the precipitate which should be well washed by adding a quantity of water, stirring oo
it up thoroughly, and after it has settled pour off the clear liquid, repeating the operation several times until all traces of acid have been removed. The wash waters, as well as the clear liquid first poured off should be preserved and tested in order to recover any traces of silver they may contain. Next add to the wet precipitate a strong solution of cyanide of po¬tassium until barely the whole of it is dissolved, leaving a clear and light amber colored liquid. The cyanide solution should be added in small quantities at a time, and the solution thoroughly stirred upon each addition, then allow it to settle. Should any of the precipitate then remain undissolved, add a little more of the cyanide solution, stir briskly, and allow it to settle, re-peating the operation until barely the whole is dissolved, and finally having observed how s much of the cyanide of potassium solution was required to merely dissolve the precipitate, add about one third teTone half as much more of it, in order to form what is called "free cyanide," and then add enough water to dilute the whole to the proportion of about two ounces of nitrate of silver per gallon or more of the solution. The solution is then ready for immediate use.
There are also quite a number of methods other than this oi making the cyanide solution, but all of them necessitate the introduction of various impurities that are often highly detrimental ; for instance, suppose we add a solution of cyanide of potassium to a solution of oxide of silver as long as it will dissolve, and then add the usual amount of free cyanide part of the cyanide of potassium will be converted into caustic potash, or if chloride of silver be used instead of the oxide, part of the cyanide of potassium will be converted into chloride of potash, or if the nitrate of silver be used, it will produce almost an equal amount of the nitrate of potash as an impurity in the solution. Nor is this process an economical one by any means, as it requires exactly the same amount of cyanide of potassium to convert it into the plating solution as where the solution is made by the method we have first given, and besides it has the very great disadvantage of introducing impurities very detrimental to the satisfactory working of the solution.
The strength of silver plating solutions may vary greatly without materially affecting their operation, some platers doing excellent work
with solutions containing half an ounce of silver per gallon, and others using solutions containing several ounces of silver, and almost as many pounds of cyanide of potassium. A good working solution should contain from one to three ounces of silver per gallon, converted into cyanide, and from thirty to fifty per cent, of free cyanide. A good solution should not have a corroding effect on the base metals because it is those metals we wish to plate, and if the solution should have a corroding effect upon them, it will infallibly cause the deposit to strip and scale off. The cyanide silver plating solution may be made by the battery process, with but very little trouble, and some electro platers prefer this method to any other, but while it possesses the advantage of simplicity, it also has the disadvantage of forming a small quantity of potash in the solution. This, however, may be remedied by the addition of a small quantity of the strongest prussic acid, which converts the caustic potash into cyanide. To make the solution by this process, make a moderately strong solution of cyanide of potas¬sium and suspend in it a large anode and a small cathode of silver and then pass a strong
current of electricity through it until a clean sheet of copper substituted for a short time for the small silver cathode, receives a good deposit of silver, or until the solution contains about one ounce of silver per gallon which may be determined by weighing both the anode and the cathode before placing them in the solution and then weighing them from time to time, until the proper amount of silver is known to have been dissolved, the solution is then ready for use.
The silver deposited by these solutions has a frosted appearance, and must be burnished in order to make them bright, or they may be placed in a specially prepared solution in order to deposit a coating of bright silver upon them.
This brightening solution is prepared by tak¬ing one pint of the ordinary silver plating solu¬tion, containing about two pounds of cyanide of potassium per gallon, and add to it two ounces of bisulphide of carbon, two of strong liquor ammonia and one of ether, and shake well. Let it stand at least twenty-four hours, shaking it occasionally, and then add the clear liquid to the ordinary silver plating solution, with gentle stirring in the proportion of one ounce to every ten gallons. This would make less than a small tea spoon full per gallon. This brightening mixture should be added in the above propor¬tions about every other day, but great care must be observed that too much is not used, as more solutions have been ruined by the excess of the brightening solution, than by all other causes put together. It is best to add but very little at first, and if from the Working of the solution, you conclude it needs more, then add a very little more taking care to use only the very least possible amount necessary to produce the desired effect. If too much is added, it will cause the articles to have a dull and dark appearance, and perhaps to have dark streaks or spots on them. As often as a quantity of the brightening liquid is used, add a similar amount of the ordinary plating solution, or the same amount of a solution of cyanide of potassium, containing two pounds of cyanide of potassium per gallon. Another brightening solution is prepared by taking one quart of ordinary silver plating liquid containing about a half pound of cyanide of potassium, and adding to it two ounces of bisulphide of carbon, shaking well, and then set aside for a day or two, and adding to the ordinary plating solution in the same proportion as the first liquid we mention, always replacing the amount used by a similar amount of the ordinary silver plating solution, and shaking well. The "bright" solution is only used to finish articles in they having previously received a deposit in the ordinary plat¬ing solution, and then transferred immediately to the "bright" solution. Now having de¬scribed the different methods of making the solutions, we will give the reader a few practical hints as to their management.
Copper, brass, and German silver become coated with silver much easier than any other metal, and for this reason all articles of other metals should, if possible, first receive a deposit of copper before attempting to plate them with silver. This, however, is not absolutely necessary, when plating by means of the electric cur¬rent. All articles must of course be made perfectly clean before attempting to plate them and when the cleaning operation has been con-cluded, great care must be taken to prevent them coming in contact with anything that would tarnish them in the least, handling them only with metallic hooks or tongs and never with the naked hand.
Articles of iron and steel are first immersed in a hot and strong potash solution, then dipped for a short time only in a liquid prepared as follows • Take one pint of water, add to it slowly two ounces of sulphuric acid that has had a small piece of zinc dissolved in it and then add one ounce of nitric acid ; This should give the articles a clean bright appearance.
They may then be plated with copper in a cyanide solution as previously described or they may be placed in the ordinary silver plating solution, using a strong battery of considerable "quantity" at first, or until they have acquired a thin deposit, when the battery should be reduced to the ordinary strength, until the deposit is sufficiently heavy.
All articles should be suspended in the solution by means of a wire or hook of the same or similar metal, small articles may be strung on a wire of the same metal as the contact of different metals in the solution is apt to leave a stain.
Articles of copper, brass and German silver, after being thoroughly cleaned by means of the potash and acid solutions, should be immersed in the following solution and then well rinsed in clean water just previous to placing them in the silver solution : Dissolve one ounce of mercury in a mixture composed of nitric acid one part and water three parts, add no more mercury than the acid will dissolve, dilute it with as much more water and add a strong solution of cyanide of potassium as long as it forms a precipitate but no longer. Collect the precipitate and wash it two or three times with clear water, then add to it with occasional stirring a strong solution of cyanide of potassium until it is all dissolved, then add a little more of the cyanide solution and enough water to make the whole measure a gallon. This solution will cover the articles with a thin coating of mercury and will generally insure a firm adherent deposit.
The articles should not remain in the murcuric solution any longer than is necessary to make them look white, and should be well rinsed in water after taking them out, in order to remove all excess of it.
The solution will last a long time, but it final¬ly becomes weak and impure from continued use, and blackens the articles immersed in it. It is then better to make a new solution than to try to revive the old one, almost any salt of mercury may be dissolved in a solution of cyanide of potassium to be used as a "quick-ing" solution. For instance, dissolve a quantity of red precipitate in an excess of a solution of cyanide of potassium ; that is, add the red precipitate as long as the cyanide solution will dissolve it; then add a small quantity of the cyanide solution.
The mercuric solution may be prepared in a number of ways, but the result is practically the same, viz. : The forming of a solution of the double cyanide of mercury and potassium.
The brightening solution works slower and requires a stronger battery than the ordinary solution; it generally requiring from ten to twenty minutes for the articles to become wholly bright. The deposit is also much harder.
When the articles are once placed in the solution they must not be moved or disturbed until the operation is completed, and where a number of articles are being brightened at the same time none of them must be taken out or disturbed in any way until all of them have be¬come bright.
When the articles have become sufficiently bright disconnect them from the battery and
remove them from the solution and place them immediately in boiling water and allow them to remain there a few minutes, then take them out and dry them.
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