104 ELECTROLYSIS. 



contains in suspension the dust and other impurities from the 

 roof; and the clean rain water should be kept in glass or 

 earthenware vessels, or even in pine-wood troughs (oak troughs 

 are not suitable). 



The proportions of salts contained in a bath must be 

 rigorously observed, if it is proposed to carry out any observa- 

 tion on the advantages of any given formula. A weak bath 

 becomes rapidly exhausted, whereas a too concentrated bath 

 gives rise to irregular crystallisations and deep colorations. 



Above all, the salts added to a solution in order to render 

 it more active, must not decompose the salts of nickel, they 

 must contain no foreign substances, and, as much as possible, be 

 neutral. 



There are a great number of formulae for the composition of 

 a nickel bath, a few of which are given in the following table, 

 together with their mode of preparation, and the name of the 

 persons who recommend them. Mr. Adams was the first to point 

 out the use of the double chloride of nickel and ammonium, or of 

 the double sulphate of nickel and ammonium. His patents bear 

 date 1869, and in them he claims the two following preparations, 

 which are now the most extensively used in every country : 



1. Chloride. Dissolve 135 grammes of pure nickel in hydro- 

 chloric acid, taking care not to have an excess of acid, and heat 

 gently. When the dissolution is effected, add 2-25 litres of 

 cold water ; pour gradually some ammonia until the solution 

 becomes neutral to the test paper. 



On the other part, dissolve 70 grammes of sal-ammoniac in 

 water, and mix it with the previous solution. Add cold water 

 so as to make 10 litres. 



2. Sulphate. Dissolve 135 grammes of pure nickel in a 

 mixture of sulphuric acid diluted in twice its weight of water, 

 and heat until completely dissolved. Add some water, and 

 neutralise the liquor with ammonia. Dissolve 70 grammes of 

 carbonate of ammonia, and pour the sulphuric acid with care 

 until the solution becomes neutral. Mix the sulphate of 

 ammonia with the sulphate of nickel, and add cold water to 

 make 10 litres. In both cases filter the liquors, or decant them 

 after settling. 



