538 



NATURE 



[October 2, 1890 



made to the experimental preparation of sodium by 

 electrolysis of fused salt. 



The eighth chapter, 13 pages, considers "The 

 Reduction of Aluminium Compounds from the Stand- 

 point of Thermal Chemistry." After a short introduction, 

 a list is given showing the heat developed in the oxidation 

 of various metals. At the head stand magnesium and 

 aluminium, and the author predicts the possibility of 

 reducing alumina by magnesium under certain unknown 

 conditions ; and it is interesting here to note that 

 C. Winkler, only a few months ago, in the course of a 

 series of logical researches, has found that alumina, 

 heated with magnesium, gives (according to the propor- 

 tions) either finely-divided aluminium or a hitherto 

 unknown oxide, viz. AlO, a perfectly black substance ; 

 and this was the substance for which Deville was search- 

 ing in 1854, when for the first time he accidentally ob- 

 tained pure aluminium in globules, an accident which 

 led to his well-known labours in connection with this 

 metal. The chapter concludes with an account of the 

 thermal aspects of the formation and reduction of the 

 chloride and sulphide of aluminium. 



The next two chapters, ix. and x., of 26 and 

 24 pages, are headed, "The Reduction of Aluminium 

 Compounds by Potassium or Sodium," although potas- 

 sium has probably not been used for the preparation 

 of aluminium since the experiments of Wohler, in 1845. 

 The first chapter is devoted to the double sodium chloride 

 as source of the metal, and contains very full accounts 

 of the process as practiced by Deville, and of the various 

 improvements made up to the time of Paul Morin in 

 1882. Describing the patented process of Frishmuth, the 

 author says : " In what the originality of the process con- 

 sists ... we cannot see, and we simply acquiesce blindly 

 to the mysterious penetration of our Patent Office Board " ; 

 and the remark might fitly be applied to other patents 

 than this particular one, and to other Patent Office Boards 

 than that of the United States. The second chapter de- 

 scribes the reduction of the fluorine compounds. From 

 the experiments and experience of H. Rose, Percy, Dick, 

 Deville, Tissier Brothers, all fully described, the conclusion 

 is drawn that the best use of cryolite is as a flux when 

 reducing aluminium sodium chloride ; but as a contrast 

 to this is the account of the Alliance Aluminium Com- 

 pany's processes, by which 'j'] per cent, of the metal con- 

 tained in the cryolite was extracted. The account of 

 Grabau's processes, the reduction of aluminium fluoride 

 by sodium, is very interesting, and especially so as he has 

 been the first to produce on a commercial scale aluminium 

 with less than half of i per cent, of impurities. 



Chapter xi., of 70 pages, is one of the most import- 

 ant chapters in the book. It is an account of the 

 " Reduction of Aluminium Compounds by the use of 

 Electricity," and is introduced by an all too brief review 

 of "the principles of electro-metallurgy as they apply 

 to the decomposition of aluminium compounds." The 

 method of calculating, from the heats of formation, the 

 electromotive forces required to decompose aluminium 

 chloride and alumina having been described, the number 

 of volts thus found are explained to be 



"the absolute minimum of intensity which would pro- 

 duce decomposition, and the actual intensity practically 

 required would be greater than this, varying with the 



NO. 1092, VOL. 42] 



distance of the poles apart and the temperature of the 

 bath as far as it affects the conducting power of the 

 electrolyte. From this it would immediately follow that, 

 if the substance to be decomposed is an absolute non- 

 conductor of electricity, no intensity of current will be 

 able to decompose it. If, on the other hand, the substance 

 is a conductor, and the poles are within reasonable dis- 

 tance, a current of a certain intensity will always produce 

 decomposition." 



We are sure that such an explanation of phenomena 

 that can only be successfully treated mathematically will' 

 not greatly enlighten the uninitiated, and hope that in the 

 next edition the author will find it possible to give a more 

 exact and fuller account of electric phenomena in so far 

 as they apply to the subject in hand ; as, for instance,, 

 an account of Ohm's law applied to electrolytes, of the 

 chemical and thermal effects of electric currents upon 

 electrolytes, of the chemical, electrical, and thermal effects 

 of secondary reactions to which the products of the electro- 

 lysis may give rise, &c., and also even a brief description 

 of the instruments and machines used to measure and 

 generate the powerful currents used in the manufacture 

 of aluminium. With the expression of this hope we 

 will pass over many inaccurate and dubious expressions 

 relating to electrical terms and descriptions. 



Exceedingly curious is the account of some twenty 

 patented processes for depositing aluminium or its alloys 

 from aqueous solutions, and the following remarks of 

 the author summarize the results obtained by all these 

 enthusiastic labourers in Nature's unwilling fields :— 



"We have inventors affirming in the strongest manner 

 the successful working of their methods, while other ex- 

 perimenters have followed these recipes and tried almost 

 every conceivable arrangement, yet report negative re- 

 sults. ... No good authority testifies to the success of 

 any process so far advanced, neither have I seen any so- 

 called aluminium plating (from aqueous solution) which 

 really was aluminium." 



" The Electric Decomposition of Fused Aluminium 

 Compounds " is treated, with the exception of a few cases, 

 chronologically ; in reviewing the chapter v/e shall, how- 

 ever, group them according to the electrolyte used, and 

 we cannot but . think that this very important chapter 

 could have been presented more concisely in such a 

 way. 



First, then, there are accounts of the electrolysis of 

 fused aluminium sodium chloride by Deville, Bunsen, Le 

 Chatellier, Berthaut, and Gratzel, whose process was 

 actually tried on a large scale, but abandoned. The pro- 

 cesses of Omholt and Faure are amusing, inasmuch as the 

 one melts aluminium chloride in a reverberatory furnace ! 

 and the other electrolyzes a bath of the same substance 

 at 300° ! 



The remaining processes may be classified as follows : 

 (i) electrolysis of cryolite without addition of alumina, 

 but with or without addition of salt, &c. ; (2) the same as 

 No. I, except that alumina is also added ; (3) electrolysis 

 of alumina dissolved in cryolite salt, &c. ; (4) electrolysis 

 of fused alumina ; (5) electrically heating mixtures of 

 alumina and carbon to such a temperature that they 

 react upon each other chemically ; (6) methods using 

 crude clay, beauxite, or kaolin as the source of alumina, 

 and not worthy of further consideration. To the first 

 class belong the processes of Gaudin, Grabau, Feldman, 



