5'2 



NA TURE 



[April I, 1886 



was to enable the workman to compensate for deficiency 

 of knowledge of scientific laws by means of "rule-of- 

 thumb" experience and by remembrance of a multitude 

 of empirical instructions. In order therefore to enable 

 the artisan reader to make the best use of the book, we 

 would recommend him to previously learn sufficient of 

 the principles of chemistry and of voltaic and electrolytic 

 action, and then master the very numerous practical 

 details of this book. 



Repetitions of small matters are frequent in the book ; 

 in more than twenty instances the same statement has 

 been made in modified forms, from two to four times. 

 These repetitions are most frequent in the chapters on 

 deposition of nickel. 



In consequence of the considerable redundancies, the 

 large amount of extraneous matter, the excess of details 

 of manipulation, and the repetitions, a large quantity of 

 matter might have been omitted, and the contents of the 

 book would have been rendered more in accordance with 

 the title. According to the present contents, a more 

 appropriate title would have been " Manipulations in 

 Electro-deposition," &c. 



The writer of the book makes the following statement 

 on p. 213; speaking of "cheap jewellery" he says: 

 " The author has found it a very convenient plan to use 

 a copper anode for gilding work of this description, and 

 by making small additions of chloride of gold when the 

 bath exhibited signs of weakness, he has been able to 

 gild a very large number of articles of a very fine colour, 

 with an infinitesimal amount of the precious metal. In 

 his experience, although the prices were very low, the 

 result was exceedingly profitable. Against the employ- 

 ment of a copper anode it has been argued that the solu- 

 tion must of necessity become highly impregnated with 

 copper, to which we may reply that we did not find such 

 to be the case in practice." The circumstance he men- 

 tions — that the solution " did not become highly impreg- 

 nated with copper" is easily and correctly explained : the 

 solution did become charged with copper, but not 

 " highly," because the copper was deposited as fast as it 

 was dissolved in alloy with gold upon the articles, and 

 thus produced the "very fine colour," and conduced to 

 the " exceedingly profitable " character of the result. A 

 complete proof of this is afforded by the author on p. 197 

 of his book, in his instructions for depositing alloys of 

 gold. 



On p. 214 he very truly remarks ; " The introduction of 

 the electro-gilding art greatly favoured such unscrupulous 

 persons as desired to prey upon the public by selling as 

 gold, electro-gilt articles which had not a fraction of the 

 precious metal in their composition." As an example of 

 this he mentions " mystery-gold," and states that " the 

 chief aim of the manufacturers" of articles made of that 

 composition "is to defraud pawnbrokers." 



In Chapters XXIX., XXX., and XXXI., on "Electro- 

 metallurgy," the author has copied and collected together, 

 from Fontaine and Berly's books on " Electrolysis," and 

 various periodicals, &c., nearly all the information yet 

 published respecting the electrolytic refining of crude 

 copper, lead, zinc, itc, on the commercial scale, and the 

 economic extraction of metals from minerals by the aid 

 of electrolysis. Six pages of those chapters are devoted 

 to a description, with drawings, of Cowle's electric furnace. 



But this furnace is not "electrolytic": it is one in which 

 an intense heat is obtained by means of the electric arc on 

 a large scale in an inclosed fire-resisting chamber, in 

 which carbon at an enormous temperature reduces 

 aluminium and silicon from their oxides, and those re- 

 duced elements form alloys with copper previously mixed 

 with the carbon. Much of the information contained in 

 these chapters is useful, but a large portion of it relates 

 to new processes, and partly unsuccessful experiments 

 on a large scale ; and as some of those processes are 

 imperfect and in a state of development, the statements 

 made respecting them should be received with caution. 



In consequence of the serious deficiency of information 

 respecting the chemical, voltaic, and electrolytic principles 

 of the subject, we do not consider that the author has 

 succeeded in his aim "to treat the more scientific portion 

 of the work in such a manner that those who are not 

 deeply versed in science may readily comprehend the 

 chemical and electrical principles of electrolysis." But 

 notwithstanding the fundamental and minor defects which 

 we have pointed out, as the details of workshop informa- 

 tion and manipulation contained in the book are so 

 copious and complete, we think he has substantially 

 attained his " desire to furnish a comprehensive treatise 

 embodying all the practical processes and improvements 

 in the art of electro-deposition" ; and, irrespective of its 

 shortcomings, the book will prove of great value to many 

 electro-depositors, jewellers, and various other workers in 

 metal. 



OUR BOOK SHELF 

 ^^W'cathcrology" and the Use of Weather Charts. By 

 Campbell M. Hepworth, R.N.R. (London : Laurie, 

 1 886.) 



Meteorologists must wish success to this endeavour 

 of Capt. Hepworth's to popularise their technical phraseo- 

 logy, and to explain how the public can utilise the weather- 

 charts which appear daily in the Times and Lloyd's List, 

 in combination with local observations of wind, sky, and 

 weather. The author has considerable sea experience in 

 the North and South Atlantic, and he imparts the results 

 of it freely, but his language is still rather too scientific 

 for an ordinary reader. 



Without being hypercritical, we must take exception to 

 two statements. The definition of a "gradient" is de- 

 fective, for no mention is made of the unit of barometrical 

 difference (o'oi inch), which is emplojed, while the 

 modern unit of distance is 15 miles, not 5o. 



Again we must protest against fathering on Admiral 

 FitzRoy (p. 5) the form of siphon barometer which is sold 

 for a guinea, and sometimes is called after him, some- 

 times dubbed the " Polytechnic barometer." There is no 

 authority to connect the Admiral with it, as either invent- 

 ing or even approving of it. RoBB:Rr H. Scott 



LETTERS TO THE EDI I OR 



\^7 he Editor does not hold himself responsibli for opinions expressed 

 bv his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripti. 

 No notice is taken of anonymous comvninications, 

 \^The Editor urgently requests correspondents to keep their lettet s 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containinginteresting and novel facts.l 

 Residual Magnetism in Diamagnetic Substances 

 In the account which Prof. Li dge gives of his very interest- 

 ing experiments (Nature, March 25, p. 484) he describes an 



