106 ELECTROLYSIS. 



The various formulae which we have given are principally 

 based on the use of a double salt of nickel and ammonia indi- 

 cated by Adams ; it is true that Messrs. Becquerel and Euolz 

 had, long before 1869, made mention of ammoniacal baths, but 

 the great success of the Adams process is due to the use of 

 neutral baths. 



Mr. Adams attributed the good deposition of nickel to the 

 absence of potash or soda, whereas in reality excellent deposi- 

 tions can be obtained in ammoniacal baths containing salts of 

 potash or of soda. 



" The deposit of nickel," said M. Bouilhet at the Congress 

 of Electricians, "is beautiful and durable only when it is 

 effected in a neutral, or almost neutral, bath. As soon as the 

 ammonia is in a state of liberty in an ammoniacal bath, the 

 deposit becomes greyish and brittle. If its liberation is pre- 

 vented the deposit remains homogeneous and glittering. The 

 presence of soda or potash produces the same effect ; but they 

 are without any influence upon the deposit when they are in 

 the state of neutral salts." 



When nickel-plating articles of jewellery or philosophical 

 instruments, various compositions of baths should be tried, the 

 one giving the most satisfactory results being adopted. An 

 alkaline nickel bath always gives more or less deep-shaded 

 deposits, whereas a very little excess of acid develops a fine 

 white colour. Instead of the citric acid indicated in the 

 formula No. 5, many large establishments use hydrochloric 

 acid chemically pure, owing to its much lower cost ; the result 

 is much the same, but we think it preferable to use citric acid, 

 which is more easy of manipulation than hydrochloric acid. 



For ironmongery and pieces of machinery, we advise follow- 

 ing M. Perille's indications, which have for many years insured 

 the success of products plated by that firm, viz. : in an 

 enamelled vessel dissolve 80 grammes of double sulphate of 

 nickel and ammonium for each litre of water, mixing it with 

 the water when the latter has reached the state of ebullition. 

 Pour the solution in the vat, filtering it at the same time, and 

 taking care to let it thoroughly cool if the vat is lined with 

 guttapercha. 



