April I, 1 886 J 



NATURE 



511 



nor does the table of " atomic-weights " necessarily indi" 

 cate them ; and either the above numbers given by the 

 author for iron and lead are double the correct amounts, 

 or that for silver is only half the proper c[uantity. This 

 is an example of the misleading effect we have already 

 referred to, of the table of atomic-weights, when unac- 

 companied by valencies or by one of combining-propor- 

 tions, and used by a person unacquainted with the differ- 

 ence between atomic-weights and chemical-equivalents. 

 The nearest approach to information respecting chemical- 

 equivalents is indicated on p. 480, in instructions for 

 testing the strength of potassic cyanide, but this is appli- 

 cable only to the particular substances employed in the 

 case. .Any electro-depositor therefore who, relying upon 

 the information contained in this book, wished to cal- 

 culate the cost of depositing various metals, or to make 

 e.xperiments or improvements in his processes, outside 

 the mere empirical or " rule-of-thumb " circle of know- 

 ledge, and involving chemical principles, would not be 

 enabled to do so ; in novel cases of difficulty in electro- 

 deposition also, this deficiency of knowledge of chemical 

 principles might prove a great disadvantage to him. 



On p. So the writer says : — " It is necessary, in the 

 present advanced state of electrical science, that both the 

 student and practical operator should be acquainted with 

 the principles and laws which govern the development of 

 electricity ; " and in the preface he speaks of " the che- 

 mical and electrical principles of electrolysis," " the 

 knowledge of which is essential to those who would 

 practise the art of electro-deposition w-ith economy and 

 success." But notwithstanding these statements, the 

 important matters we have mentioned are omitted, and 

 the student and practical operator are referred (pp. 80-90) 

 " for a more intimate acquaintance with the principles of 

 voltaic and dynamic electricity " to other books. 



We observe that in Chapters V. and VI., on the theory 

 of the subject, nothing is said about the thermal prin- 

 ciples of electrolysis, or of the absorption and evolution 

 of heat by chemical changes at the surfaces of the plates 

 in voltaic and electrolytic cells. In the chapters on 

 electro-deposition and electro-metallurgy of copper, the 

 chemical analyses made by the Duke of Leuchtenberg 

 (P- 395) ciiid others, showing the composition of the in- 

 soluble matter of the anodes, are not given. The special 

 defect of thermo-electric piles, viz. that they are only 

 durable if kept at unvarying temperatures, is also not 

 mentioned. And nothing is said of the presence of 

 sulphur in electro-deposited " bright " silver. These, 

 however, are much less important omissions. 



The errors in the book are not many ; we have observed 

 the following : — " Nine parts of water consist of one part, 

 by -dieight, of hydrogen, and eight parts, by weight, of 

 oxygen ; or by volume, i part hydrogen and 16 parts 

 oxygen " (p. 74) ; the error is obvious. Roseleur says, 

 " that solutions of cyanides, even without the aid of the 

 electric current, rapidly dissolve in the cold, or at a 

 moderate temperature, all the metals, except platinum" 

 (p. 174) ; this statement of Roseleurs is not quite correct, 

 iron is nearly as little dissolved as platinum, in a cold 

 solution of pure potassic cyanide. 



The author says that for containing cyanide of silver 

 plating solution, " wooden tubs may be employed for 

 small operations, but since that material absorbs the 



silver solution, such vessels should be well soaked in hot 

 water before pouring in the solution" (p. 241). We may 

 remark that such soaking does not prevent the wood 

 becoming saturated with the silvering liquid. 



On p. 270 it is stated that a solution of sulphide of 

 potassium "dissolves" silver. This is not correct; it 

 converts the surface of the silver into sulphide without 

 dissolving either. On p. 365 the author speaks of 

 " Chevalier Bunsen's methods " of electrolysis. We may 

 state that the " Chevalier," and Bunsen the chemist, 

 whose methods are referred to, are two different persons. 

 In various parts of Chapter XXX., on the electrolytic 

 refining of copper, the author, speaking of where this 

 process is in use, says : — " Besides Messrs. Elkington's 

 works at Pembrey, South Wales," "by the Elliott Metal 

 Refining Company at Selly Oak, near Birmingham, where 

 Wilde's machines are employed." And under the head- 

 ing of " Electrolytic Refining at Birmingham," he says : — 

 " The Elliott Metal Refining Company, of Selly Oak, 

 near Birmingham, employ five large Wilde machines, 

 which refine about ten tons of copper per week ; " and he 

 then gives a variety of particulars respecting the arrange- 

 ments employed, the " thickness of deposit " of copper 

 per week at the " Selly Oak Works, Birmingham ; " the 

 " cost of electrolytic copper refining " at those and other 

 works, based partly upon the cost of fuel " in Birmingham 

 and Swansea," &c. (pp. 416, 420, 423, 424, 425). All this 

 is founded upon a mistake ; there is not, nor ever has 

 been, any " electrolytic refining of copper," nor any plant 

 for such a purpose, at " Selly Oak " or at " Birmingham," 

 or anywhere near those places. This error appears to 

 have been first published by M. Fontaine in his book on 

 " Electrolyse," then copied by Berly in his English trans- 

 lation of that book, and again copied by Watt. The 

 explanation and facts are : the Elliott Metal Company; 

 of Selly Oak, near Birmingham, possess and carry on the 

 Electrolytic Refining Works at Pembrej-, near Swansea, 

 formerly possessed by Messrs. Elkington. 



The redundancies in the book are considerable ; the 

 following are examples : — Description of several voltaic 

 batteries which are rarely used for electro-deposition, viz. 

 Callan's, Walker's, Leclanche's, the bichromate, and 

 Marie Davy's (pp. II, 13, 15, i6) ; an account of Mr. 

 Charles Watt's magneto-electric machine (p. 25) ; de- 

 scription and engraving of Mr. C. Watt's thermo-electric 

 battery (pp. 42-45) ; the source, mode of collecting, and 

 purifying gutta-percha (pp. 94, 95) ; gilding metals with 

 gold leaf (p. 195) ; processes and compositions for colour- 

 ing ordinary gold articles by chemical means (pp. 19S- 

 201) ; mercurial gilding, gilding bronzes with amalgam, 

 ormolu (pp. 202-208). 



A considerable portion of the book also is occupied by 

 information which, although very useful to jewellers and 

 other workers in metal, does not strictly belong to the 

 subject of" Electro-deposition ; '' we allude to the follow- 

 ing : — Driving-belts (pp. 487-493) ; gas-engines (p. 492) ; 

 speed indicator (p. 497) ; characteristics of metals (pp. 

 49S, 499) ; alloys (pp. 500-504) ; soldering metals (pp. 

 504-507) ; table of high temperatures (p. 515) ; tables of 

 different wire-gauges (p. 517). 



In various parts of the book, whilst there is an excess 

 of details of manipulation, there are very few references 

 to general principles, as if the main object of the author 



