Wells's principles and applications of chemistry; . the extremity of the negative wire The general name of electro-metallurgy includes all the various processes and resultswhich different inventors and manufacturers have designated as galvano-plastic, electro-plastic, galvano-type, electro-typing, and electro-plating and gilding. QtTESTiONS.—What suhstance is always negative? What one always positive? Defineelectro-metallurgy. Upon what is the process hased ? How is the thickness of the de-posit regulated ? Describe the arrangement for conducting the electrotype process. ELECTRICITY, 153 and a
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Wells's principles and applications of chemistry; . the extremity of the negative wire The general name of electro-metallurgy includes all the various processes and resultswhich different inventors and manufacturers have designated as galvano-plastic, electro-plastic, galvano-type, electro-typing, and electro-plating and gilding. QtTESTiONS.—What suhstance is always negative? What one always positive? Defineelectro-metallurgy. Upon what is the process hased ? How is the thickness of the de-posit regulated ? Describe the arrangement for conducting the electrotype process. ELECTRICITY, 153 and a plate of metallic copper to the end of the positive wire. When bothof these are immersed m the liquid, the action commences—the sulphate ofcopper is decomposed—the copper being deposited on the medal attachedto the negative pole, and the oxygen, before combined with it, on the copperplate attached to the positive pole, forming oxyd of copper. As the with-drawal of the metal from the solution goes on, the oxyd of copper thus formed Fia. 13.. unites with the sulphuric acid which is liberated in the solution, and formssulphate of copper. This dissolving in the hquid, maintains it at a constantstrength. The sole object of attaching a plate of metallic copper to the positive poleis to thus preserve the strength of the solution of sulphate of copper. If thepositive pole had terminated with a plate of platinum or gold, the actionwould have commenced equally well, but the oxygen liberated from the cop-per, through its want of affinity to either the platinum or the gold, wouldhave escaped as gas, and the solution gradually becoming weaker from thewithdrawal of its elements, the electro-plating action would cease. When theoperator judges that the deposit on the medal is sufficiently thiclc, he removesit from the trough, and detaches the coating. The deposit is prevented fromadhering to the medal by rubbing its surface in the first instance with oil, orblack-lead, and if it is desi