COPPERING. 163 



This result is obtained by mixing in the above-described copper 

 bath a similar bath of tin, zinc, or aluminium, in quantities 

 inversely proportional to the electric conductivity of the two 

 baths, and operating with soluble anodes of bronze, brass, or 

 aluminium bronze. The same results may be obtained by 

 using for a certain time a copper bath with a soluble anode of 

 bronze, brass, aluminium bronze ; or better, tin, zinc, or alumi- 

 nium, taking great care to regulate the tension of the current 

 proportionally to the surface to be coated. This is an essential 

 condition to the success of the operation, for a weak current 

 only affects the copper, whereas a strong current preferably 

 affects the other metals." 



The Societe du Val d'Osne, who are working Gauduin's 

 processes, use a small Gramme machine, No. 2, which requires 

 less than one horse-power for working the immense baths in- 

 stalled in the Boulevard Voltaire, in Paris. It was there that 

 the first experiments on a large scale took place of the excellent 

 chemist whose recent death we chronicle with regret. 



M. Gauduin at first employed soda for the formation of his 

 double salt. The oxalates of copper being only slightly soluble, 

 the effect of the presence of soda was to dissolve a greater 

 quantity of copper, rendering therefore the bath a better con- 

 ductor. But, notwithstanding all his exertions, he never 

 succeeded in constituting a bath rich enough to work in a cold 

 state. 



Heat was indispensable, and caused considerable expenditure 

 in material and fuel. 



A few years later the composition of the bath was altered. 

 Ammonia was substituted for soda, and being an active dissolvent 

 of copper this was the means of obtaining baths very rich in 

 copper. A great economy was thus realised, and from that time 

 the operation has been conducted with the greatest care and in 

 a very regular manner. 



Before being put into the bath, the piece is cleansed by 

 means of potash, and thoroughly scoured by means of sulphuric 

 acid. After being washed in water it is put in the copper bath. 



The anodes being of copper keep the richness of the bath 

 at an almost constant point, and it is sufficient to only add from 



M 2 



