COPPERING. 165 



tartrate with a determined quantity of the metal in dissolution. 

 The potassic cyanide maintains the metal in a state of dissolu- 

 tion and freely abandons it under the influence of the current. 

 The neutral ammonic tartrate prevents the formation of pre- 

 cipitates. The bath, if suitably prepared, retains a normal 

 composition without giving off any vapours or disagreable 

 smells. 



Walenn's process is characterised by the following advan- 

 tages : No gas is liberated upon the piece when under treat- 

 ment; the deposition is obtained with a comparatively small 

 quantity of electricity at low tension ; the same liquid is 

 used whatever may be the thickness of the intended deposition ; 

 the duration of the operation is comparatively short ; and 

 lastly, the deposition is of a perfect homogeneity in all its 

 parts. 



This process being new cannot be fully appreciated at 

 present, as the principal merit of a good deposition is to resist 

 the action of time. All we now know is that M. Walenn has 

 been coppering the plungers of the hydraulic presses used by 

 the Thames Dock Company, and that this Company has declared 

 itself perfectly satisfied. 



COPPERING^ OF CAST-IRON EOLLERS FOE CALICO PRINTING. 

 Numerous trials have been made with a view of substituting 

 cast-iron or iron rollers coated with a deposit of galvanic copper 

 for the massive copper rollers previously used. Some had a 

 comparative success in spite of the length of time required for 

 the deposition ; some others have been immediately abandoned 

 owing to the bad quality of the deposited metal ; actually, with 

 the exception of the Wilde and Schlumberger's systems which 

 are in operation in a few factories, there is no other process for 

 coppering rollers which can be recommended. 



WILDE'S PROCESS. Mr. Wilde has, for a long time, made 

 electrolytic deposition his speciality; his machines are in great 

 favour in the North of England, and his competency in matters 

 of electro depositions is universally acknowledged ; his process 

 for coppering has been in regular operation for some years at 

 Manchester ; it therefore deserves to receive the best attention 

 at the hands of the practises 



