IV PREFACE. 



The first section is devoted to the theoretical notions 

 indispensible to experimenters who wish to understand the 

 electrical phenomena which they are daily witnessing ; the 

 second deals with the description of the principal batteries and 

 dynamo machines used in electro-chemistry ; the third section 

 treats of electro-deposition : nickeling, silvering, gilding, copper- 

 ing, &c. ; and the fourth relates to the refining of metals and 

 the treatment of ores. 



Two of the chapters are of an exceptional length, those 

 dealing with nickeling and the refining of copper. The 

 relations which for the last twelve years we have had with a 

 number of specialists, and our own private experience, have 

 enabled us to collect a very precise and detailed series of 

 information upon these subjects. 



The theoretical part can easily be understood by practical 

 men, consisting, as it does, of only very simple formula and 

 elementary calculations, completed by a series of recapitulating 

 tables on conductivity, electro-chemical equivalents, the heat 

 generated by the formation of compound bodies, and the limits 

 of electrolysis. 



