128 ELECTROLYSIS. 



thickness, to separate in bright pellicles. In order to prevent 

 this escape the solution must be concentrated and the power of 

 the battery carefully proportioned to the work to be done. For 

 the first attack a powerful battery, such as three Bunsens in 

 series, is required ; but as soon as a general coating has been 

 obtained economy and quality of work claim a great reduction in 

 the electromotive force of the current. A single Smee cell, for in- 

 stance, proportioned to the intensity required may be sufficient." 



Mr. Sprague adds the following reflection, which we re- 

 produce without comment, although it refers to nickel-plating 

 by means of batteries : " The surface of the deposited nickel, 

 if it is good, presents a peculiar appearance ; it is not bright a 

 bright deposit has a tendency to scaling but its colour is of a 

 dark yellow. After the object has been taken out of the bath 

 and rinsed, it is brought to a bright state by means of the 

 usual polishing processes." 



TREATMENT WHEN TAKEN OUT OF THE BATH. After being 

 taken out of the bath the pieces must be immersed in cold 

 water in order to rid them of any trace of sulphate, then in hot 

 water for raising their temperature, and after in hot sawdust. 

 If amongst the pieces there are hinges or any other apparatus 

 subject to friction, a drop of oil should be poured on the working 

 parts when the temperature of the pieces is comparatively high 

 on coming out of the sawdust. 



If the coating appears a little yellowish after the drying, 

 and it is desirable to give it a beautiful white appearance, it 

 must be polished with chalk powder or English red. 



The drying in a stove is recommended for all hollow or 

 cast objects, and particularly when they are of iron, cast iron, 

 or steel. By placing pieces of this description in a bath of 

 boiling oil they often become rust-proof. 



The nickel-plated pieces can receive a beautiful polish, but, 

 as we have already remarked, the metal is so hard that it is 

 difficult to obtain the polish by the ordinary means in use. 

 The final cleaning must be done on the lathe with brushes 

 revolving very rapidly. An ordinary circular pig-hair brush 

 sprinkled with soft chalk is first used, and a vigorous scrubbing 

 given ; then felt disks and finely pulverised chalk or hard red 



