ELECTRO-METALLURGY 223 



previous solution, and it is to be freed from copper and other foreign matters in the 

 same manner. The solution is then to be evaporated to dryness ; it should be made 

 as nearly anhydrous as possible. The salt is then placed in a retort and heated to 

 a bright red heat. The salt sublimes and is collected in a suitable receiver, the earthy 

 matter being left behind. The salt thus purified is dissolved in water, and to the 

 solution is added an equivalent quantity of pure chloride of ammonium. The solution 

 is then ready for use : it may have a specific gravity of 1050 to 1100.' 



Of these two solutions the inventor much prefers the double sulphate, as it gives a 

 softer metal, which can bo polished, or otherwise worked more readily than that 

 obtained from the double chloride solution. The double sulphate solution has this 

 important advantage over any other solution, that it gives a deposit with a smooth 

 surface, which can be polished with comparatively little labour. When the process is 

 properly conducted, the deposit can be made much thicker than is ordinarily required 

 for plating other metals before it acquires a rough or matted surface. With a metal 

 so hard as nickel this is a matter of great importance. 



The Specification of the Patent and the Disclaimer and Memorandum of Alteration 

 of The Plating Company (Limited) to Brookes' patent give still further directions for 

 securing the purity of the nickel solution. These are points, however, to which those 

 only who are likely to carry out the electro-deposition of nickel on a large scale need 

 attend, and to such the papers referred to are always available. 



Having prepared the solutions and anodes, nickel may bo readily deposited ; but, in 

 order to carry on the deposition continuously, it is necessary to observe certain pre- 

 cautions. 



First. The use of a battery of too high an intensity must be avoided ; an intensity 

 of two Smee's cells is sufficient. A high intensity decomposes the solution and liberates 

 free ammonia, thus rendering the solution alkaline, and impairing its value. When- 

 ever the smell of free ammonia arises from the decomposing cell, the operator may be 

 sure that the solution is being injured. It is important that the depositing shall not 

 be forced by the use of too strong a current. 



Second. It is important that great precaution should be used to prevent the intro- 

 duction into the solution of even minute quantities of potash, soda, or nitric acid. 

 When an article to be coated is cleaned in acid or alkaline water, or is introduced into 

 it for any purpose, the greatest care must be taken to remove all traces of these sub- 

 stances before the article is introduced to the nickel solution, as the introduction of 

 the most minute quantities of acids or alkalis will surely be injurious. 



Third. The anode of the depositing cell a nickel plate of the utmost purity- -of 

 copper, or alloyed with a little iron to secure the precipitate, should present a surface 

 to the action of the solution somewhat larger than the surface upon which the deposit 

 is being made, particularly in the double sulphate solution. The reason is that 

 nickel dissolves so slowly that if the exposed surface is not larger than the surface on 

 which the deposit is made, the solution will not keep saturated. On the other hand, 

 if the anode is very much larger than the positive pole, it tends to give a deposit of 

 black powder. 



_ Fourth. With ^ solutions and anodes thus prepared and used, the deposition of 

 nickel can be carried on continuously, and almost as surely and certainly as the depo- 

 sition of copper from the common sulphate solution, though the limits of the battery- 

 power which may be used are narrower. The metal deposited is compact and 

 tenacious. It may be deposited of nearly uniform thickness over any surface, however 

 large. The deposited metal is capable of being annealed by a heat below a low red 

 heat ; it then becomes flexible, malleable, and ductile, either to furnish effectual pro- 

 tection to the metal on which it is deposited, or to bo removed and used separately 

 from the surface on which it may be deposited. Thus electro-type plates of nickel may 

 -bo produced, either as copies of irregular surfaces which it is desired to reproduce, or 

 as plain sheets of nickel, which, after being annealed, may be rolled, hammered, or 

 spun into a variety of forms or articles. 



Far more extensive use has been made of these properties in America than in this 

 country. There His used for carriage and harness fittings, for guns and pistols, for 

 various scientific instruments, and for numerous domestic utensils and articles of 

 furniture from fenders to flat-irons. For brass and iron fittings on board ship, 

 and for lever handles of engines of all kinds it is especially adapted, and for the 

 metals mentioned in all places where they are liable to oxidation or corrosion. 

 The process is, wo believe, carried on in London on an extensive scale, but one 

 establishment, or even half-a-dozen, cannot supply the needs of the public when 

 the value of the process becomes better known, even if they can keep pace with the 

 present demand. Without doubt many improvements upon the process introduced 

 by Prof. Boettger in 1843 will be introduced as soon as the utility of nickel-plating 

 becomes known. 



