SILVER SOLUTIONS. ] UNDULATORY FORCES. ELECTRO-METALLURGY. 



223 



But all the brassing solutions are, in a greater or less 

 degree, imperfect. 



Deposition of German Silver. The same patentees 

 also deposit German silver by the following process : 

 Dissolve 1 pound of cyanide of potassium and 1 pound 

 of carbonate of ammonia in 1 gallon of water ; heat the 

 solution to 150 Fah. ; immerse a large anode of German 

 silver in the liquid, and a small cathode of any suitabli 

 metal ; connect the two with a powerful battery, anc 

 pass the current of electricity until considerable meta 

 is dissolved and a bright cathode receives a deposit o: 

 good colour : the solution is then ready for use. 



129. Mercury Solutions. The ordinary compounds ol 

 mercury are the binoxide (red precipitate), bisulphide 

 (vermilion), bichloride (corrosive sublimate), nitrate, anc 

 bicyanide. The nitrate is formed by dissolving mercury 

 in nitric acid diluted with three times its bulk of water, 

 the mixture being cold, and no more metal added than 

 the acid will dissolve. The solution, when diluted with 

 water, may be used for depositing by the battery pro- 

 cess a layer of mercury at the bottom of the liquid 

 being used as the anode, and connected with the bat- 

 tery by a platina wire passing through a tube of glass 

 or gutta-percha. The bicyanide is made by taking 8 

 parts of Prussian blue and 16 parts of peroxide of mer- 

 cury, both in the state of fine powder, in 30 parts of 

 water, boiling the mixture for about a quarter of an 

 hour, filtering the liquid, and evaporating, and crystal- 

 lising the solution; the resulting salt is the bicyanide ; 

 and to form it into a solution fit for depositing, it must 

 be dissolved in a solution of cyanide of potassium : the 

 solution may be used with a mercury anode and batten-, 

 as already described. 



130. Silver Salta. The most common salts, <tc. , of silver 

 are the oxide, chloride, nitrate, and cyanide. Oxide of 

 silver is prepared by adding a solution of caustic potash 

 to a solution of nitrate of silver, as long as a precipitate 

 can be produced, which is oxide of silver. Chloride of 

 silver is made by adding either hydrochloric acid or a 

 solution of common salt to a solution of nitrate of silver, 

 until a precipitate ceases to be formed : the white pre- 

 cipitate of chloride of silver should be washed, dried, 

 and preserved out of the influence of light. Nitrate of 

 silver is easily formed by adding grain silver, in small 

 quantities at a time, to a warm mixture of one measure 

 of distilled water and four measures of the strongest 

 nitric acid : if the liquid bo too hot, or too much silver 

 bo added at a time, the action will be very strong, and 

 loss of materials may be occasioned ; in such a case add 

 a small quantity of cold distilled water. When the 

 liquid ceases to dissolve more metal, it should be evapo- 

 rated and crystallised, or else kept protected from the 

 li^lit until required to be used : nearly all the com- 

 pounds of silver are formed by means of this salt. 

 Acetate of silver is made either by adding a solution of 

 acetate of potash or acetate of soda, to a solution of 

 nitrate of silver, as long as a precipitate occurs, or by 

 digesting the oxide or the carbonate of silver in hot and 

 strong acetic acid ; it is freely dissolved by a solution of 

 cyanide of potassium. Cyanide of silver is generally 

 .xred by adding a solution of cyanide of potassium 

 to one of nitrate of silver as long as a precipitate occurs ; 

 the white precipitate, which is cyanide of silver, is in- 

 soluble in water, and is not perceptibly soluble in com- 

 mercial hydrocyanic acid ; it dissolves very freely in a 

 solution of cyanide of ammonium, potassium, or sodium, 

 in hyposulphite of soda ; it is also said to be soluble 

 in solutions of ammonia, carbonate of ammonia, sal- 

 ammoniac, nitrate of ammonia, and ferro-cyanide of 

 potassium. 



i::l. M. Tirandelev, a French experimentalist, makes 

 the following remarks upon the preparation of cyanide 

 of silver: "To obtain a beautiful and easy deposit of 

 silver, we choose, among all the salts of silver, the 

 M,' the best results ; but as the dealers sell 

 tliU af n hi^h price, both amateurs and manufacturers 

 reject it. Others, for the sake of economy in procuring 

 it, purchase hydrocyanic acid ; but this, also, is of too 

 high a price ; and independently of our being obliged to 



use it immediately, it is both dangerous and difficult to 

 preserve, as the air and light decompose it. If we take 

 commercial hydrocyanic acid wliich has been prepared 

 fifteen days, and pour it into a solution of nitrate of 

 silver, consisting of one part of the nitrate to six parts 

 of water, cyanide of silver will be formed ; but it is more 

 or less yellow, and much ammonia and hydrocyanic gases 

 are evolved. On the other hand, if we make a solution 

 of cyanide of potassium, filter it, and dissolve cyanide of 

 silver in it, this solution, which was clear and colourless, 

 immediately becomes troubled and black, and betrays 

 an odour of ammonia and hydrocyanic acid. The odour 

 will continue as long as the solution exists, and a deposit 

 of carbon will be found in the vessel containing it. This 

 sediment arises from the decomposition of one part of the 

 cyanide of potassium, caused by the presence of the 

 cyanide of silver. Having occasion to use considerable 

 quantities of the cyanide of silver, I dissolve pure silver 

 in pure nitric acid ; evaporate just to dryness ; dissolve 

 the nitrate of silver thus obtained in distilled water, and 

 pass hydrocyanic gas (prussic acid) through it, from a 

 mixture of pounded ferro-cyanide of potassium and sul- 

 phuric acid, diluted with twice its weight of water con- 

 tinuing this as long as a precipitate will form. Wash the 

 cyanide of silver, and preserve it below water, away from 

 the light Thus precipitated, the salt dissolves w'ithout 

 resiiluum or colour, and gives splendid results." 



With regard to this process, we may remark, that six 

 parts of sulphuric acid should be mixed with from thirty 

 to forty parts of water, and the mixture allowed to cool ; 

 then put it into a glass vessel (Fig. 80), together with ten 



Fig. 88. 



parts of coarsely-powdered ferro-cyanide of potassium; 

 lieat must be applied until gas is evolved from the mix- 

 ture, and continued as long as any is given off, or as long 

 as a precipitate is produced in the silver solution, the 

 jas being passed into the liquid by a suitable tube. (See 

 Fig. 86). This process may yield a purer product than 

 when the nitrate solution is precipitated by cyanide of 

 potassium ; but it cannot be very economical, because 

 only half of the cyanogen of the ferro-cyanido passes over 

 as hydrocyanic acid ; the remainder is left behind, and 

 is contained in the yellowish-white residuum in tho gas- 

 jenerating vessel. 



132. Silver Solutions. Silver has been deposited by 

 .he ordinary dipping or wash process, by tho single cell, 

 ind by the battery process. The following are recipes 

 'or solutions, taken from various sources, adapted for 

 silvering articles by the simple immersion or wash pro- 

 loss, chiefly applicable to small articles, such as pins, 

 >uttons, buckles, coffin-nails, hooks-and-eyes, etc. , where 

 only a very thin coating of silver is required. Tho solu- 

 ions in the proportions indicated, are used by adding a 

 small quantity of water, sufficient to form the ingredients 

 nto a pasty liquid of the consistence of cream, stirring 

 .he articles thoroughly about in it, or nibbing them over 

 with it until they have acquired the desired degree of 

 whiteness : 1st, take equal parts of chloride of silver anil 

 litartrate of potash; 2nd, take chloride of silver one 

 >art, alum two parts, common salt eight parts, and tartar 

 right parts; 3rd, take chloride of silver ono part, piv- 

 >ared chalk one part, common salt oue-and-a-quai ter 

 nirts, and pearLush three parts; 4th, a "novargeut" 

 wlution for resiivering old plated goods, consists of one 



