I I.KCTROPLAT1N: AM' I LKCTROTYPIXO. I 77 



lion, even \\lion the intensity of the current allows of operating 

 quieUl \ . If the bath is too dense owing to an excess of copper, 

 the deposit will form slowly and have a crystalline appearance. 

 If the bath is too poor, the deposit may be quickly effected but 

 the grain will be porous, which will be still worse. Variations 

 of temperature also exert a considerable influence upon the 

 speed of the deposition and the quality of the metal. It is 

 necessary, as far as possible, to maintain in every season the 

 temperature of the bath at 1 6 C. The purity of the anodes, 

 their surface, and their distance from the moulds, equally con- 

 stitute the essential elements of a good result. 



The anodes must be of chemically pure copper, which is 

 now very easy to obtain owing to the progress accomplished by 

 electrolysis in the refining of copper. Impure anodes are 

 extremely annoying as they get covered with certain impurities 

 which are insoluble in the bath. Their surface must be at 

 least equal to those of the moulds to be coppered ; too small 

 an anode weakens the solution, and too large a one enriches it. 

 Their distance from the moulds varies with the dimensions of 

 these moulds and the intensity of the current; it generally 

 varies from 2 to 5 centimetres. 



DURATION OF THE OPERATION. According to Mr. Urquhart 

 a deposition of copper of 3 millimetres' thickness can easily be 

 deposited in two days, and if the work is pushed with all the 

 available power of current a good electro with fine close grain 

 can be obtained in ten or twelve hours. (A single coppering 

 can be effected in one hour at a maximum.) 



According to M. Stoesser the average duration of an electro- 

 typing operation is twenty-four hours. The average thickness 

 of the deposition is '3 millimetre; it corresponds to a layer of 

 25 grammes per square decimetre or a deposition of about 

 1 gramme per hour per square decimetre. The author states 

 that the intensity of the current may be doubled, and a deposi- 

 tion of the same quality be obtained in twelve hours, and in 

 this he is in accordance with Mr. Urquhart, but the duration of 

 the twenty-four hours' operation is convenient for preparing the 

 moulds during daytime, and putting them in the bath in the 

 evening. 



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