c UNIVERSnTgrCALIFDRNIA COLLEGE of MINING DEPARTMENTAL LIBRARY BEQUEST OF r \ SAM UELBENEDICrCHRlSTV PROFESSOR OF MINING AND METALLURGY 1885-1914 ALUMINIUM. ALUMINIUM: ITS HISTORY, OCCURRENCE, PROPERTIES, METALLURGY AND APPLICATIONS, INCLUDING ITS ALLOYS. JOSEPH W. RICHARDS, M.A., A.C., INSTRUCTOR IN METALLURGY AT THE LEHIGH UNIVERSITY. SECOND EDITION, REVISED AND GREATLY ENLARGED. ILLUSTRATED BY TWENTY-EIGHT ENGRAVINGS AND TWO DIAGRAMS, PHILADELPHIA: HENRY CAREY BAIRD & CO., INDUSTRIAL PUBLISHERS, BOOKSELLERS, AND IMPORTERS, 810 WALNUT STREET. 1890. MIM1N<* FT. COPYRIGHT BY JOSEPH W. RICHARDS, 1890. PRINTED AT THE COLLINS PRINTING HOUSE, 705 Jayne Street, PHILADELPHIA, U. 8. A. PREFACE TO T1IE SECOND EDITION. IF it was true that no apology was necessary in presenting a work on Aluminium in English, as stated in the preface to the first edition of this book, it is equally true that still less apology is necessary in offering an improvement on that work. The present volume is designed to be an improvement on the former one in the following respects : Mistakes have been corrected wherever detected by the author or pointed out by his friends ; in some instances the order of treatment of different parts has been revised, so as to bring them into strict, logical sequence ; the more strictly historical processes are described in greater detail, in order to preserve a complete record of the rise of the aluminium industry ; chapters have been added treating on the properties and the preparation of aluminium compounds, on the theoretical aspect of the reduction of aluminium com- pounds, and on the analysis of commercial aluminium and its common alloys ; the original chapters have been in several cases sub-divided, and every part treated more by itself and in greater detail than before; finally, additions have been made throughout, recording and describing the progress achieved in the last three years, with a completeness which it is hoped is up to the stand- ard of the rest of the book. vi PREFACE TO THE SECOND EDITION. The method of treatment in the present edition will be found to be more critical, for wherever a reasonable doubt might be expressed as to the correctness of certain claims, or a rational explanation advanced for certain phenomena, the author has not hesitated to put his best thought on the question and to state his conclusions unreservedly. The friendly criticisms of the scientific press and their sug- gestions have been kept in view in preparing this new edition. The spelling "aluminium" has been retained, because no sufficient reasons have been advanced for changing it to " aluminum ;" and even if each way was equally old and as well-sanctioned by usage and analogy as the other, the author's choice would be the longer spelling, as being more euphonious and agreeable to the ear. It has been the author's endeavor to make this volume as complete as possible, as accurate as possible, to write it in a manner which will be entertaining to the general reader, and to furnish a treatise which will be of practical value to the practical metallurgist as well as of scientific merit where it touches on matters of theory. J. W. K. BETHLEHEM, PA., March 12, 1890. PREFACE TO THE FIRST EDITION. No apology is necessary in presenting a work on aluminium in English. In 1858 Tissier Bros, published in France a small book on the subject. H. St. Claire Deville, the originator of the aluminium industry, published a treatise, also in French, in 1859. Deville's book is still the standard on the subject. Until December, 1885, we have an intermission, and then a work by Dr. Mierzinski, forming one of Hartleben's Chemisch-Technische Bibliothek, which is a fair presentation of the industry up to about 1883, this being a German contribution. Probably be- cause the English speaking people have taken comparatively little hand in this subject we find no systematic treatise on aluminium in our language. The present work aims to present the subject in its entirety to the English reader. Tissier, Deville, Mierzinski, and the German, French, and English scientific periodicals have been freely consulted and extracted from, full credit being given in each case to the author or journal. As this art has of late advanced so rapidly it has been a special aim to give everything that has been printed up to the time of publication. The different parts of the work are arranged in what seemed their logical order, corresponding closely to that followed by Vlll PREFACE TO THE FIRST EDITION. Deville. The Appendix contains an account of laboratory experiments, etc., several of which, it is trusted, may be of value. In conclusion, the author wishes to thank the faculty of his " Alma Mater," Lehigh University, for their permission to use his Thesis on Aluminium as the basis of this treatise ; also, to acknowledge his indebtedness to Dr. Wm. H. Greene, of Philadelphia, for assistance rendered in the preparation of the work for the press. J. W. R. PHILADELPHIA, November 25, 1886. ABBREVIATIONS USED IN MAKING REFERENCES. Deville De 1' Aluminium. H. St. Claire Deville. Paris, 1859. Fremy Encyclopedic Chimique. Fremy. Paris, 1883. Kerl and Stohman .... Enclyclopadisches Handbuch der Techni- schen Chemie. 4th Ed. Mierzinski Die Fabrikation des Aluminiums. Dr. Mier- zinski. Vienna, 1885. Tissier Recherche de 1' Aluminium. C. & H. Tis- sier. Paris, 1858. Watts Watts' s Dictionary of Chemistry, vol. i. Ann. de Chim. et de Phys. . Annales de Chimie et de Physique. Ann. der Chem. und Pharm. 1 Liebig's Annalen der Chemie und Phar- Liebig's Ann. j macie. Bull, de la Soc. Chim. . . Bulletin de la Soci6t6 Chimique de Paris. Chem. News The Chemical News. Chem. Zeit. ...*... Chemiker Zeitung (Cothen). Compt. Rend Comptes Rendus de les Seances de 1' Acade- mic. Paris. Dingl. Joul Dingier' s Polytechnisches Journal. E. and M. J The Engineering and Mining Journal. Jahresb. der Chem. . . . Jahresbericht ueber die Fortschritte der Chemie. Jrnl. Chem. Soc Journal of the Chemical Society. Jrnl. der Pharm Journal der Pharmacie. Jrnl. fur pr. Chem. . . . Erdmann's Journal ftir praktische Chemie. Mon. Scientif. Le Moniteur Scientifique. Dr. Quesnes- ville. Phil. Mag The London and Edinburgh Philosophical Magazine. Phil. Trans Transactions of the Royal Philosophical Society. Pogg. Ann PoggendorfPs Annalen. ABBREVIATIONS USED IN MAKING REFERENCES. Poly. Centr. Blatt. Proc. Ac. Nat. Sci. Quarterly Journal . Rpt. Brit. A. A. S. . Sci. Am. (Suppl.). Wagner's Jahresb. . . Zeit. fur anal. Chem. Polytechnisches Central-Blatt. Proceedings of the Academy of Natural Science (Philadelphia). Quarterly Journal of the Society of Arts. Report of the British Association for the Advancement of Science. Scientific American (Supplement). Wagner's Jahresbericht der Chemischen Technologic. Zeitschrift fur Analytische Chemie. CONTENTS. CHAPTER I. HISTORY OF ALUMINIUM. PAGE Lavoisier's suggestion of the existence of metallic bases of the earths and alkalies ; Researches in the preparation of aluminium by Davy, Oerstedt, and Wohler ; Isolation of aluminium by Wohler . . 17 Isolation of almost pure aluminium by H. St. Claire Deville, in 1854; Method of Deville's researches . . . . . . .18 Deville's paper on "Aluminium and its Chemical Combinations;" M. Thenard's recommendation ; Pecuniary assistance given Deville by the French Academy ; M. Chenot's claim to priority of invention ; Deville's experiments at the Ecole Normale ; Reduction of alumin- ium chloride by the battery 19 Deville and Debray's experiments in the manufacture of sodium ; Manufacture of metallic sodium at Rousseau Bros.' chemical works at Glaciere, and enormous reduction in its price ; Deville's descrip- tion of his electrolytic methods 20 Experiments in the manufacture of aluminium at the expense of Napoleon III. ; Experiments of Chas. and Alex. Tissier on the production of sodium ; Deville's experiments at Javel . . .21 Aluminium at the Paris Exhibition, 1855 ; First article made of alu- minium ; Dispute between the Tissiers and Deville about a sodium furnace . . . . . . . . . . .22 Foundation of aluminium works by M. Chanu at Rouen ; History of the works at Rouen as described by the Tissiers ; The process finally used at Amfreville ......... 23 Manufacture of aluminium on a large scale at Glaciere, Nanterre, and Salindres ; Tissier Bros.' book on aluminium in 1858 ... 24 Deville's book, 1850 ; His explanation of the uses of the new metal ; Dr. Percy's and H. Rose's experiments 25 Alfred Monnier's production of sodium and aluminium at Camden, N. J. ; W. J. Taylor claiming the possible cost of aluminium at $1 per pound ; First aluminium works in England, 1859 ... 26 Xll CONTENTS. PAGE Bell Bros.' aluminium works at Newcastle-on-Tyne, 1860 ; Price of alu- minium manufactured by them ; Aluminium industry in Germany ; Dr. Clemens Winckler's retrospect of the development of the alu- minium industry, 1879 ......... 27 Prices of aluminium and aluminium bronze in France, 1878 ; Webster's aluminium works in England, 1882; Mr. Walter Weldon on the prospects of the aluminium industry, 1883 28 Improvements in the manufacture outlined by Mr. Weldon . . 29 Reduction in the cost of aluminium in 1882, by Mr. Webster's inven- tions ; Organization of the " Aluminium Crown Metal Company" at Hollywood, near Birmingham ; Mr. H. Y. Castner's new sodium process, 1886 30 Mr. Castner's patent the first granted on that subject in the United States ; Combination of the Castner and Webster processes, in Eng- land; Works at Oldbury near Birmingham, 1888 .... 31 Revolutions in the aluminium industry since 1884 ; Revival of the old methods of electrolysis discovered by Deville and Bunsen ; Gratzel's process patented in Germany, 1883 . \. . . . .32 Mr. Saarburger's process ; Process patented by Dr. E. Kleiner, of Zurich, 1886 ; Electrolytic method of Mr. Chas. M. Hall, of Ober- lin, O., patented in the United States, April, 1889 ; Price of alu- minium made by the process ........ 33 Difference in electrolytic processes ; SirW. Siemens' electric furnace ; Mr. Ludwig Grabau's experiments in the reduction of alumina, 1882 ; Dr. Mierzinski remarks on the use of the electric furnace . 34 Cowles' Electric Smelting and Aluminium Company, Lockport, N. Y. ; Works in England and the United States sprung from the Cowles process ; The principle made use of in the Cowles process . . 35 Difference in the products obtained by the various electrolytic methods ; The Heroult process ' . . . .36 Manufacture of aluminium by the Heroult process in Switzerland, France, and the United States ; Comparison of the Cowles and Heroult processes . . . . . . . . . .37 The Alliance Aluminium Company of London, England, and the patents and methods used by it ; Prof. Netto's method of producing sodium ; Cost of aluminium produced by the Alliance Company ; The " Alkali Reduction Syndicate, Limited" .... 38 Ludwig Grabau's improvements in producing aluminium ; " The Amer- ican Aluminium Company" of Milwaukee, Wis. ; Prof. A. J. Rogers's process ; Inaccurate statements inspired by a company hailing from Kentucky 39 Production of iron castings containing aluminium ; Col. Win. Frish- muth's works in Philadelphia . . . . . . .40 CONTENTS. Xlll PAGE Col. Frishmuth's patents and methods; Quality of the metal pro- duced by Col. Frishmuth . . . . . . . .41 Census report on Col. Frishmuth's annual production ; Aluminium casting for the Washington Monument, made by Col. Frishmuth; "The Aluminium Company of America;" The United States Aluminium Company of East St. Louis ; Aluminium exhibits at the Paris Exposition, 1889 . . .' 42 Detailed account of the exhibits ; Great advances in the aluminium industry shown by the exhibit ....... 43 Statistical; Prices of aluminium from 1856 to 1889; Prices of 10 per cent, aluminium bronze from 1878 to 1888 ; Annual outputs of aluminium from 1854 to 1887 ....... 44 Estimate of aluminium produced up to 1886 ; Amount produced since 1886 ; Aluminium imported into the United States from 1870 to 1888 45 CHAPTER II. OCCURRENC^ OF ALUMINIUM IN NATURE. Wide distribution of aluminium ; Combinations of aluminium with oxygen, the alkalies, fluorine, etc. ; Non-occurrence of aluminium in animals and plants ; Appearance of most of the aluminium com- pounds ; Formulas of some aluminium compounds classed as precious stones ............ 46 Formulas of frequently occurring compounds of aluminium ; Minerals most used for producing aluminium ; Beauxite ; Analyses of beauxite 47 Index to analyses of beauxite . . . . . . . .48 Deposit of beauxite in Floyd County, Georgia, with analyses . . 49 Cryolite ; Where found, description, general uses, and analyses ; Im- portation of cryolite by the Pennsylvania Salt Company of Phila- delphia, 1887 50 Deposit of cryolite in the United States ; Minerals associated with it ; Corundum; Discovery of it in the United States, in 1869, by Mr. W. P. Thompson ; Production of corundum in the United States in 1887 ' . 51 Native sulphate of alumina ; Discovery, description, and analysis of "native alum" from the Gila River, Sorocco County, New Mexico 52 CHAPTER III. PHYSICAL PROPERTIES OF ALUMINIUM. What must be understood by the properties of aluminium ; The most frequent impurities of commercial aluminium 53 The r61e of silicon in aluminium ; Table of analyses of commercial aluminium ......... .54 XIV CONTENTS. PAGE Notes on the analyses; Combined and free silicon in aluminium; Analyses of aluminium reduced from cryolite by sodium . . 55 Analysis of aluminium by Prof. Rammelsberg ; Gases in aluminium ; Color 56 Appearance of Grabau's and ordinary commercial aluminium ; Influ- ence of iron and copper on the color of aluminium ; Removal of dis- coloration caused by damp air ; Explanation of the greater promi- nence of the blue tint after the metal has been worked ... 57 Fracture ; Peculiarities in the fracture of the purest varieties of alu- minium ; Increase in the fibrousness of the metal by working ; Hardness ; Its increase by the presence of impurities ... 58 Testing aluminium with the knife ; Specific gravity ; Of commercial aluminium ; Comparison of analyses and specific gravities . . 59 Contraction in the volume of aluminium by alloying ; Increase in the density of aluminium by being worked ; Comparison of the specific gravity of aluminium with that of other metals 60 Comparative value of equal volumes of aluminium and silver ; Fusi- bility ; Determination of the melting point by Pictet, Heeren, Van der Weyde, and Prof. Carnelley . . . . . . .61 Volatilization ; Deville on this subject ; In electric furnace processes ; Odor; Taste 62 Magnetism ; Deville, MM. Poggendorff and Reiss ; Sonorousness ; Results obtained by Deville and M. Lissajous in making bells and tuning forks ; Results obtained by Mr. Faraday ; Verification of Mr. Faraday's observations . 63 Crystalline form; As observed by Deville; Elasticity; Deville, M. Wertheim and Mallet on this subject ...... 64 Tenacity ; Results obtained by W. H. Barlow ; Comparative mechani- cal value of aluminium and steel ; Results as to the strength of aluminium wire obtained by Kamarsch . . . . . .65 Malleability; Aluminium leaf first made by M. Degousse, of Paris, and C. Falk & Co., of Vienna; Thickness of commercial leaf . . 66 Forging, hammering, and shaping of aluminium ; Ductility ; Manufac- ture of aluminium wire ; Expansion by heat ; Fizeau's coefficients of linear expansion of aluminium by heat . . . . .67 Specific heat ; Deville, M. Regnault, Kopp, Mallet, and Nacarri on this subject ; Determination of the latent heat of fusion by Mr. J. W. Richards ; Electric conductivity ; Results obtained by Deville and Buff, M. Margottet, Prof. Mattheisen, and Benoit . . 68 Comparison of the various results ; Thermal conductivity ; Deville, Faraday, and Calvert and Johnson on this subject .... 70 CONTENTS. XV CHAPTER IV. CHEMICAL PROPERTIES OF ALUMINIUM. PAGE Remark ; Action of air ; Deville, Wohler, and M. Peligot on this sub- ject- 71 "Dead" appearance of aluminium objects; Burning of aluminium; Wohler' s observations 72 Action of water ; Decomposition of aluminium leaf by water ; Action of hydrogen sulphide and sulphur .73 Resistance of aluminium to the vapor of sulphur ; Absorption of hy- drogen sulphide by molten aluminium ; Sulphuric acid . . .74 Nitric acid ; Hydrochloric acid . . . . . .75 Organic acids, vinegar, etc. . . . . . . . .76 Tin more attacked by organic acids than aluminium ; Chief cause of the tarnishing of polished aluminium articles ; Ammonia ; Caustic alka- lies 77 Solutions of metallic salts ......... 78 Precipitation of other metals by aluminium . . . .79 Reduction of metallic chlorides by aluminium ; Action of aluminium on alkaline chlorides ; action of aluminium salts on aluminium ; Sod- ium chloride; Salt as a flux for aluminium; Fluorspar; As a flux for the metal 80 Cryolite ; Its action on aluminium ; Silicates and borates ; Their action on aluminium ; Nitre ; Deville on this subject .... 81 Purification by nitre ; Alkaline sulphates and carbonates ; Metallic oxides ; Tissier Brothers' experiments 82 Beke"toff's experiment; Miscellaneous agents 83 General observations on the properties of aluminium, Deville . . 84 CHAPTER Y. PROPERTIES AND PREPARATION OP ALUMINIUM COMPOUNDS. General considerations ; Structure of aluminium compounds ; Chemical position of aluminous salts ........ 85 Neutral and basic salts of aluminium ; Aluminium oxyhydrate ; General methods of formation and properties ; Solubility of aluminium salts 86 Reaction of neutral solutions of aluminium salts ; Aluminium oxide ; Composition and description of alumina ...... 87 Aluminium hydrates ; Diaspore, Beauxite, and Gibbsite ; Artificial hydrates ; Formula and description of the insoluble modification . 88 Aluminates ; Potassium aluminate ; Sodium aluminate ; Barium alumi- nate 89 Calcium aluminate, zinc aluminate, copper aluminate, magnesium alumi- nate ; Aluminium chloride 90 XVI CONTENTS. PAGE Properties of aluminium chloride ; Aluminium-sodium chloride ; Its properties ........... 91 Aluminium-phosphorus chloride ; Aluminium-sulphur chloride ; Alu- minium-selenium chloride ; Aluminium-ammonium chloride . . 92 Aluminium-chlor-sulphydride ; Aluminium-chlor-phosphydride ; Alu- minium bromide 93 Aluminium iodide; Aluminium fluoride; Its first production by De- ville ; Volatilization of aluminium fluoride ..... 94 Aluminium fluorhydrate ; Aluminium-hydrogen fluoride ; Aluminium- sodium fluoride . . . ' . . . . . . .95 Aluminium sulphide ; Aluminium selenide ; Aluminium borides . 96 Borides obtained by Hampe 97 Aluminium nitride ; Aluminium sulphate; Anhydrous; Hjdrated . 98 Halotrichite ; Basic aluminium sulphate ...... 99 Alums ; Definition of alums ; Potash alum ; Calcined alum . .100 Alunite; Ammonia alum; Soda alum ; Aluminium-metallic sulphates 101 Aluminium selenites ; Aluminium nitrate ; Aluminium phosphates . 102 Wavellite ; Kalait ; Turquois ; Aluminium carbonate ; Aluminium borate ; Formation of crystals of corundum ; Aluminium silicates . 103 Disthene ; Andalusite ; Fibrolite; Kaolin; Orthoclase ; Common clays 104 CHAPTER VI. PREPARATION OP ALUMINIUM COMPOUNDS FOR REDUCTION. Preparation of alumina from alums and aluminium sulphate ; Its com- position ........... 105 Various methods of preparing alumina; Deville's method used at Javel 106 Tilghman's method of preparing alumina . . . . . .107 Mr. Webster's process for making pure alumina ..... 108 Preparation of alumina from beauxite ; Occurrence of beauxite in France ; Deville's process as used at Salindres, illustrated and de- scribed 109 Composition of alumina prepared by Deville's process; Behnke's method; Proposed treatment of beauxite, etc., by R. Lieber ; H. Muller's method of extracting alumina from silicates . . .113 Action of common salt on beauxite ; Treatment of beauxite proposed by R. Wagner; Lowig's experiments with solution of sodium alumi- nate; Dr. K. J. Bayer's improvement in the process of extracting alumina from beauxite 114 Preparation of alumina from cryolite ; By the dry way ; Julius Thom- son's method illustrated and described . . . . . .115 Formula according to which the decomposition takes place in Thomson's process . . . . . . . . . . . ,116 CONTENTS. XV11 PAGE " Levisseur methodique" . . . . . . . . .117 Preparation of the carbon dioxide for precipitating the hydrated alumina ; Precipitation with carbonic acid gas ; Composition of the precipitate; Separation of the sodium carbonate . . . .118 Utilization of aluminous fluoride slags 5 Deville's process used at Nan- terre ; Analysis of the residue . . . . . . .119 Decomposition of cryolite in the wet way ; Deville's method used at Javel 120 Modification of Deville's method by Sauerwein ; Tissier's and Hahn's methods; Reactions involved in Hahn's process; Decomposition of cryolite in the establishment of Weber, at Copenhagen . . .121 Schuch's method ; The preparation of aluminium chloride and alumin- ium-sodium chloride; Wohler's method of preparing aluminium chloride 122 Deville's processes for the production and purification of aluminium chloride ; Manufacture on a small scale illustrated and described . 123 Manufacture on a large scale illustrated and described. . . .124 Purification of aluminium chloride . . . . . . .126 Apparatus for the purification of aluminium chloride used at Salindres, illustrated and described . . . . . . . .127 Cost of aluminium-sodium chloride by Deville's process as made by Wurtz in 1872 ; Plant of the Aluminium Co., L't'd, for the manu- facture of aluminium-sodium chloride . . . . . .129 Chlorine plant of the Aluminium Co., L't'd 130 Amount of double chloride required for the production of 1 Ib. of alu- minium ; Necessity of preventing iron from contaminating the salt . 131 Castner's process for purifying the double chloride ; On what the suc- cess of the manufacture of the double chloride depends; Quantities of materials required for the production of 100 Ibs. of double chloride . . . ... 132 H. A. Gadsden's method of obtaining aluminium chloride ; Count A. de Montgelas's process ; Prof. Chas. F. Mabery's process . . 133 Mr. Paul Curie's plan of making aluminium chloride; H. W. War- ren's process; Camille A. Faure's process ..... 134 The aim of Mr. Faure's process; Estimated cost of the chloride by Mr. Faure's process 135 M. Dullo's method of producing aluminium chloride .... 136 The preparation of aluminium fluoride and aluminium-sodium fluoride (cryolite) ; Berzelius's plan of preparing artificial cryolite ; Deville's statements 137 Pieper's process of preparing artificial cryolite; Bruner's method of producing aluminium fluoride ........ 138 Deville's and Hautefeuille's method of making aluminium fluoride; Lud wig Grabau's process; Reactions outlining this process . . 139 B XV111 CONTENTS. PAGE Method of obtaining aluminium fluoride in practice ; The preparation of aluminium sulphide ; M. Fremy's researches on this subject . . 140 Keichel's experiments on the preparation of aluminium sulphide . 142 J. W. Richards's experiments on the production and reduction of aluminium sulphide; M. Comenge's plan; Messrs. Reillon, Mon- tague, and Bourgerel's patent . . . . . . .143 Petitjean's plan of making aluminium sulphide . . . . .144 CHAPTER VII. THE MANUFACTURE OF SODIUM. The manufacture of sodium a separate metallurgical subject . .144 Davy to Deville (1808-1855); Sodium first isolated by Davy, 1808; Gay-Lussac, Thenard, Curaudau, and Brunner's researches; Donny and Mareska's condenser, illustrated and described . . .145 Deville's improvements at Javel, 1855; His attempts to reduce the cost of producing sodium ; Properties of sodium .... 146 Deville's method of producing sodium ; Composition of mixtures used . 147 Properties a mixture should show ; The r61e of the various ingredients of a mixture ........... 148 Mixture used at La Glacifcre and Nanterre ; Use of these mixtures ; Cost at which sodium was obtained . . . . . .149 Apparatus for reducing, condensing, and heating ; Manufacture in mer- cury bottles ; The most suitable furnace, illustrated and described . 150 The condenser, illustrated and described 151 The most rational form of condenser, illustrated and described ; Mode of conducting the operation . . . ... . . .152 How to prevent the ignition of the sodium ; Use of cast-iron bottles ; Continuous manufacture in cylinders . . . . . .154 Advantage of a strong preliminary calcination of the materials ; Man- ner of using cold, uncalcined mixture 155 Furnace, illustrated and described . . . . . . .156 Mode of conducting the manufacture of sodium in cylinders . .157 Tissier Bros.' method of procedure (1856) ; Details from Tissier's "Recherche de 1' Aluminium ;" Mixtures used . . . 158 Furnace for calcining the mixtures, illustrated and described ; Further treatment of the calcined mixtures 159 Mode of protecting the retorts ; Manner of reducing the sodium . 160 Tissier's method of cleaning the sodium ; Deville's improvements at La Glaciere (1857) ; Results obtained by Deville . . . .161 Reasons for unsuccessful attempts ; Cast-iron vessels . . . .162 Causes of an unfavorable result with cast-iron vessels ; Improvements used at Nanterre (1859) 163 CONTENTS. XIX PAGE Construction of the iron tubes used ; Cost of sodium by Deville's pro- cess (1872) . . . 164 Minor improvements (1859-1888) ; R. Wagner's and J. B. Thompson and W. White's methods 165 H. S. Blackmore's process of obtaining sodium; O. M. Thowless's method; G. A. Jarvis's patent; Castner's process (1886); First public announcement of this process . . . . . .166 Description of Castner's process . . . . . . .167 Claims made by Mr. Castner in his patent 168 Erection of a large sodium furnace in England by Mr. Castner . .169 Mr. J. MacTear's description of the furnace ; Preparation of the com- pounds used . . . . . . . . . . .170 Mode of conducting the operation ; Crucible and furnace, illustrated and described ; Analysis of the gas disengaged . . . .171 Analyses of the residues . . . . . . .. .172 Weight and further treatment of the residues ; Yield obtained ; Aver- age time of distillation ; Capacity of furnace ; Estimated cost of the sodium produced . . . . . . . . . .173 Life of the crucibles ; Reasons for the cheap production of sodium by Mr. Castner's process . . . 174 Details of the latest plant of the Aluminium Co., L't'd, by Mr. Wm. Anderson and Sir Henry Roscoe ; Yield of sodium in twenty-four hours ; Shape of the condenser . . . . . . .175 Melting and preservation of the sodium ; Temperature of the furnace . 176 Average duration of each crucible; Dr. Kosman's explanation of the reactions taking place in Castner's process 177 Netto's process (1887) ; Reaction taking place in this process . . 178 The retort used in Netto's process, illustrated and described ; Mode of operating . . . . . . . . . . .179 Reduction of sodium compounds by electricity ; Economical value of these processes ; P. Jablochoff's apparatus for decomposing sodium or potassium chlorides, illustrated and described ; Prof. A. J. Rogers' s attempts to reduce sodium compounds electrolytically . . . 180 Computation of the amount of coal required to produce a given amount of sodium by electrolysis 181 Results of experiments by Prof. Rogers 182 CHAPTER VIII. THE REDUCTION OF ALUMINIUM COMPOUNDS FROM THE STANDPOINT OF THERMAL CHEMISTRY. The proper way to use the accumulated thermal data in predicting the possibility of any reaction almost unknown . . . . .183 Illustration of the principal barriers in the way 184 XX CONTENTS. PAGE Influence of the relative masses of the reacting bodies ; Heat gene- rated by the combination of aluminium with the different elements . 185 Theoretical aspect of the reduction of aluminium ; Table showing the heat given out by other elements or compounds which unite energeti- cally with oxygen 186 Impossibility of sodium or potassium reducing alumina; Probable im- possibility of some reactions .. . . . . . .187 Calculations which have been made to show that carbon will reduce alumina at a temperature 10,000 C 188 Sources of error in the calculation ; Lowest calculated value for the temperature of reduction of alumina ...... 189 Table of the heat developed by the combination of some of the ele- ments with chlorine, bromine, or iodine 190 Reflections on the table ; Probable substitutes for sodium in reducing aluminium chloride . . . . . . . . .191 Heat of combination of fluorides ; Discussion of the thermal relations of aluminium sulphide 192 Affinity of the metals for sulphur ; Reactions of use in the aluminium industry ; Deficit of heat, which has to be made up in the conversion of alumina into aluminum chloride 193 Hydrated chloride of no value for reduction by sodium . . .194 The reaction made use of for obtaining aluminium sulphide ; Compu- tation of the thermal value of the reaction taking place in the con- version of alumina into aluminium sulphide 195 CHAPTER IX. REDUCTION OF ALUMINIUM COMPOUNDS BY MEANS OF POTASSIUM OR SODIUM. (Reduction of Chlorine Compounds.) Oerstedt's experiments (1824) 196 Oerstedt's original paper; Wohler's experiments (1827); Wb'hler's review of Oerstedt's article 197 Wohler's method of producing aluminium . . . . . .198 Wohler's experiments (1845) . . 199 Accuracy of Wb'hler's results ; Deville's experiments (1854) . . 200 Deville's method for obtaining aluminium chemically pure in the labor- atory 201 Deville's methods (1855) ; Mode of reducing the aluminium chloride by sodium ; Perfectly pure aluminium ; Pure materials . . . 202 Influence of flux or slag ; Influence of the vessel ; Reduction by solid sodium ; Apparatus, illustrated and described .... 203 CONTENTS. XXI PAGE Process by which were made the ingots of aluminium sent to the Paris Exhibition (1855); Nature of this aluminium; M. Mulct's "hard aluminium" ........... 205 Reduction by sodium vapor ; The operation as conducted by Deville ; Deville's process (1859) ; Process used at that time at Nanterre . 206 Production of the works at Nanterre ; Rationale of the process used . 207 Substitution of cyrolite for fluorspar ; Reduction on the bed of a rever- beratory furnace 210 Dimensions of the furnace ; Proportions of the mixture used ; Recov- ery of alumina from the slag 211 Treatment of the slag ; Contents of the slag ; Reason why aluminium absorbs a large quantity of silicon . . . . . . .212 The Deville process (1882) ; Aluminium as made at Salindres by A. R. Pechiney & Co., successors to H. Merle & Co 213 Successive operations of the process, and chemical reactions involved ; Advances made, since 1859, in the reduction of the double chloride by sodium 214 The reduction furnace, illustrated and described . . . .215 Expense of the process . . . . . . . . .216 Niewerth's process (1883) 217 Gadsden's patent (1883) ; Frishmuth's process (1884) ; Claims made by Col. Frishmuth in his patent . . . . . . .218 H. von Grousillier's improvement (1885) ; The Deville-Castner pro- cess as operated by the Aluminium Co., L't'd ; Principle of this pro- cess 219 Description of the works at Oldbury, near Birmingham, England ; Mode of conducting the reduction 220 Reaction taking place in the process ; Yield of the charge ; Purity of the metal 221 CHAPTER X. REDUCTION OF ALUMINIUM COMPOUNDS BY MEANS OF POTASSIUM OR SODIUM (continued). (Reduction of Fluorine Compounds.} Rose's experiments (1855) 222 Experiments of Percy and Dick (1855) . . . . . .230 Tissier Bros.' method (1857) . .234 Advantages claimed by Tissier Bros.' for the use of the cryolite ; Diffi- culties met with in this process ....... 235 Wohler's modifications (1856) ; Gerhard's furnace (1858) . . . 236 Thompson and White's patent (1887) ; Hampe's experiment (1888) ; Netto's process (1887) 237 XX11 CONTENTS. Operations of the Alliance Aluminium Co., of London, England; Production of sodium by Capt. Cunningham's process . . . 238 Dr. Netto's process 239 Construction and operation of Dr. Netto's experimental apparatus at Krupp's works at Essen 240 Cost of aluminium to the Alliance Aluminium Company ; Ludwig Grabau's process for the reduction of aluminium fluoride by sodium 241 The reaction taking place in the process . . . . . . 242 The furnace used in Grabau's process, illustrated and described . .244 Summary of the advantages claimed by M. Grabau for his process . 245 Purity of M. Grabau's product 246 CHAPTER XI. REDUCTION OF ALUMINIUM COMPOUNDS BY THE USE OF ELECTRICITY. Principles of electro-metallurgy applying to the decomposition of alu- minium compounds 246 Calculation of the theoretical intensity of current necessary to over- come the affinities of any aluminium compound . . . .247 Utilization of such calculations ........ 248 Deposition of aluminium from aqueous solutions . . . 249 Mr. George Gore's experiments; Messrs. Thomas and Tilly's process; M. Corbelli's mode of depositing aluminium ..... 250 J. B. Thompson on depositing aluminium on iron, steel, etc. ; Pro- cedure for depositing aluminium on copper, brass, or German silver recommended by George Gore 251 J. A. Jeancon's process for depositing aluminium ; Methods of M A. Bertrand, Jas. S. Haurd, and John Braun ; Dr. Fred. Fischer on Braun's proposition . . . . . . . . . 252 Apparatus patented by Moses G. Farmer ; Methods of M. L. Senet, Col. Frishmuth, Baron Overbeck, and H. Niewerth, and Herman Rienbold 253 Summary of Count R. de Montegelas's patents for the electrolysis of aqueous solutions of aluminium ....... 254 Methods of procedure patented by A. Walker; H. C. Bull's proposi- tion for manufacturing aluminium alloys ..... 255 Methods patented by C. A. Burghardt and W. J. Twining, of Man- chester, England ; Various other patents taken out in England . 256 Various authorities who consider that aluminium cannot be deposited by electricity in the wet way ; Letter on this subject from Dr. Justin D. Lisle, of Springfield, 257 The electric decomposition of fused aluminium compounds ; The different ways of operating ; Davy's experiments (1810) . . 258 CONTENTS. XX111 PAGE Duvivier's experiment (1854) ; Bunsen's and Deville's methods (1854) ; Deville's description of the process ...... 259 The apparatus used by Deville, illustrated and described . . . 260 Arrangement adopted by Bunsen ; Plating aluminium on copper ; Capt. Caron and Deville's experiments . . . . . .262 Le Chatellier's method (1861) ; Monckton's patent (1862); Gaudin's process (1869) 263 Kagenbusch's process (1872) ; Berthaut's proposition (1879) ; Griitzel's process (1883) ; The apparatus used, illustrated and described . 264 Works erected near Bremen for carrying out GratzePs process ; The uselessness of Gratzel's patent claims maintained by Prof. Fischer . 266 Abandonment of the Gratzel process by the works at Hemelingen ; Kleiner's process (1886) 267 Plants for working Kleiner's process put up in England; Acquirement of the patents by the Aluminium Syndicate, Limited, of London ; The rationale of the process 268 Purity of the metal produced by Kleiner's process; Lossier's method 271 Omholt's furnace 272 Henderson's process (1887) ; Bernard Bros.' process (1887) . . 273 Details of the apparatus and bath used in Bernard Bros.' process . 274 Power required . . . . . . . . . .276 Quality of metal ; Reactions in the process 277 Messrs. Bernard's exhibit at the Paris Exposition; Feldman's method (1887) 278 Warren's experiments (1887) . . . . . . .279 Bognski's patent ; Grabau's apparatus ; Rogers's patent (1887) . 280 The principle made use of in Rogers's process ; Experiments with a small experimental plant, 1888 281 Dr. Hampe on the electrolysis of cryolite ; Dr. O. Schmidt's experi- ence 283 Dr. Hampe' s reply to several communications 284 Winkler's patent . 287 Faure's proposition; Hall's process (1889); Formation of the Pitts- burgh Reduction Company ; Claims made by Mr. Hall in his patents 288 Description of the plant erected in Pittsburgh ..... 290 Features of Mr. Hall's process 291 Quality of the metal produced ; Efficiency of the process . . . 292 Probable cost of aluminium by Hall's process; Cowles Bros.' process . 293 Prof. Chas. F. Mabery's and Dr. T. Sterry Hunt's descriptions of Cowles Bros.' process ......... 294 Shapes of furnaces used by the Cowles Bros.' ; Retort patented by Chas. S. Bradley and Francis B. Crocker, of New York . . 296 Furnace devised by Mr. A. H. Cowles ; W. P. Thompson's complete description of the Cowles process 297 XXIV CONTENTS. PAGE Illustrative description of the furnace ; Mode of operating the furnace . 298 The Cowles Syndicate Company of England, and its plant at Milton . 303 Standard grades of bronze produced by the Cowles Company ; Pro- ducts of the Cowles. furnace; Analyses of 10 per cent, bronze; Analysis of ferro- aluminium ........ 304 Analysis of slag formed when producing bronze ..... 305 Reactions in Cowles' process ; Views of Prof. Mabery, Dr. Hunt and Dr. Kosman 306 Dr. Hampe's conclusions ; Useful effect of the current . . . 307 Mr. H. T. Dagger's paper on the Cowles process in England; Menge's patent; Farmer's patent ........ 308 The Heroult process (1887) ; Specification of the English patent . 309 Description of the plant erected by the Societ6 Metallurgique Suisse for working the Heroult process .310 The furnace or crucible, illustrated and described . . . .311 The mode of operation . . . . .. . . .312 Percentage of useful effect derived from the current ; Proof that the process is not essentially electrolytic . . . . . .314 Rapid extension of the Heroult process ; Location of plants in Europe and in the United States 315 CHAPTER XII. REDUCTION OF ALUMINIUM COMPOUNDS BY OTHER MEANS THAN SODIUM OR ELECTRICITY. Reduction by carbon without the presence of other metals ; Article on this subject by M. Chapelle 316 Statement of G. W. Reinar ; Claims of an aluminium company in Kentucky 317 O. M. Thowless' proposition ; Messrs. Pearson, Liddon, and Pratt's patent; Reduction by carbon and carbon dioxide; J. Morris' claims 318 Reduction by hydrogen ; Process of F. W. Gerhard . . . .319 Reduction by carburetted hydrogen ; Process of Mr. A. L. Fleury, of Boston; Statement by Petitjean 320 Reduction by cyanogen ; Knowles' patent ; Corbelli's method . . 321 Deville's comments ; Experiments of Lowthian Bell ; Reduction by double reaction ; M. Comenge's mode of producing aluminium sul- phide ; The reactions involved ; Mr. Niewerth's process . . 322 Construction of a furnace used in Niewerth's process; Mode of opera- ting the furnace 323 Messrs. Pearson, Turner, and Andrews' claim ; Reduction in presence of, or by, copper; Messrs. Calvert and Johnson's experiments . 324 Mr. Evrard's method of making aluminium bronze ; Benzon's patent 325 CONTENTS. XXV PAGE G. A. Faurie's method of obtaining aluminium bronze ; Bolley's and List's examination of Benson's process; Experiment by J. W. Richards and Dr. Lisle 326 Dr. W. Hampe's test of this subject and his conclusions; M. Co- menge's claim ; Reichel's statement ...... 327 Andrew Mann's patent; L. Q. Brin's process of producing aluminium bronze ; Reduction by, or in presence of, iron ; M. Comenge's claim ; F. Lauterborn's and Reichel's statements . . . . .328 Niewerth's process ; W. P. Thompson's patent . . . . 329 Calvert and Johnson's experiments on the reduction of aluminium with iron 330 Mr. Chenot's experiments . . . . . . . . .331 Faraday and Stodart's investigation on the preparation of iron-alumin- ium alloys ; Bombay " wootz" steel 332 Reduction of aluminium in small quantities in the blast furnace ; Alu- minium in pig-iron; Schafhautl's, Lohage's, Corbin's, and Blair's statements 333 G. H. Billings' experiment on reducing alumina in contact with iron ; E. Cleaver's patent specification 334 Mode of producing ferro- aluminium in Sweden; Brin Bros.' method; Similar claim made by an aluminium company in Kentucky . . 335 W. A. Baldwin's patents, owned by the Aluminium Process Company, of Washington, D. C. ; Aluminium-ferro-silicon manufactured by the Williams Aluminium Company, of New York City . . . 336 Reduction by, or in the presence of, zinc ; Observations by M. Bek6toff' and M. Dullo ; M. N. Basset's patent 337 Mr. Wedding's remarks on Basset's process ; Experiment by J. W r . Richards on the reduction of cryolite by zinc ; Mr. Fred J. Sey- mour's patent .......... 339 Description of the plant of the American Aluminium Company of De- troit, working Dr. Smith's patents . . . . . . . 340 Patent of F. Lauterborn; J. Clark's patents 341 Practicability of the distillation of zinc from an aluminium-zinc alloy ; Reduction by lead ; Invention of Mr. A. E. Wilde .... 342 Reduction by manganese ; Claims of Walter Weldon ; Experiment of Dr. Greene, of Philadelphia; Reduction by magnesium ; R. Gratzel's patent; Roussin's statement 343 Patent of Count R. de Montgelas, of Philadelphia ; Reduction by anti- mony ; F. Lauterborn's process 344 Reduction by tin ; Statements by J. S. Howard and F. M. Hill in their patent specifications ; Experiment by J. W. Richards ; Reduction by phosphorus ; L. Grabau's patent 345 Reduction by silicon ; General claims made by M. Wanner . . 346 XXVI CONTENTS. CHAPTER XIII. WORKING IN ALUMINIUM. PAGE Melting aluminium ; Deville's instructions . . . . .347 Biederman's directions ; Crucibles for melting aluminium . . . 348 Protection of the hearth of a reverberatory furnace used for melting alu- minium ; Casting aluminium ; Deville's instructions . . . 349 Peculiarity of molten aluminium ; Manner of obtaining sharp castings ; Dr. C. C. Carroll's method of casting in closed moulds . . . 350 Purification of aluminium; Freeing from slag ; Deville on this subject 351 Freeing from impurities; Deville's instructions 352 Removal of zinc from aluminium by distillation; Cupellation of alu- minium with lead ; G. Buchner's treatment of commercial aluminium to eliminate silicon ; Experiments to test this point . . . 353 Prof. Mallet's process of obtaining pure, from commercial aluminium . 354 Annealing; Hardening; Rolling ....... 355 Thin leaf of aluminium first made, in 1859, by M. Degousse ; Drawing ; Ductility of aluminium; Manner of drawing aluminium tubes ; Stamp- ing and spinning 356 Grinding, polishing, and burnishing ; Biederman's remarks on polishing ; Mr. J. Richards' experiments in buffing ; Engraving . . . 357 Mat ; Soldering of aluminium ; Deville's views ; Hulot's process ; Mou- rey's solders ; Mourey's improved solders ; Directions for preparing them 359 Operation of soldering 360 Solders and flux recommended by Col. Frishmuth and by Schlosser . 361 M. Bourbouze's method of soldering aluminium; O. M. Thowless's patent solder and method of applying it ...... 362 J. S. Sellon's method; Coating metals with aluminium; The different methods of procedure 363 Electrolytic deposition of aluminium, Veneering with aluminium ; De- ville's account of M. Sevrard's success, in 1854 ; Dr. Clemens Winck- ler on this subject .......... 364 Dr. G. Gehring's method of aluminizing ; Analogous results obtained by Brin Bros. 365 Plating on aluminium ; Gilding and silvering ; Coppering of aluminium ; Gilding aluminium without the use of a battery ; Veneering of alu- minium with other metals . . . . . . . .366 Morin's description of veneering with silver ; Uses of aluminium ; The place assigned to aluminium by Deville ; Aluminium as a substitute for silver ; Future wide applications of aluminium . . . .367 The first article of aluminium ; Napoleon III. interested in aluminium ; Military uses of aluminium 368 CONTENTS. XXV11 PAGE Superiority of aluminium for culinary articles and other purposes . 369 Aluminium for coinage ; Its use in surgery 370 For mountings of opera-glasses, etc. ; Sextant made for Capt. Gordon by Loiseau, of Paris . . . . . . .371 Aluminium for aerial vessels, torpedo boats, etc 372 Aluminium for dental plates, etc 373 Dr. Fowler's patent ; Use of aluminium for battery purposes . . 374 For balances and weights ; Aluminium beams for balances made by Sartorius, of Gbttingen ; Various uses of aluminium . . .375 CHAPTER XIY. ALLOYS OP ALUMINIUM. The practical manufacture of aluminium alloys . . . . .376 Group of useful alloys; Reason why the color of aluminium is not radically altered by the foreign metal 377 Explanation of the hardening and strengthening effect on aluminium by the addition of a small quantity of copper or silver . . .378 Effect of aluminium on metals alloyed with a small quantity of it ; Alu- minium and nickel ; Tissier's remarks on this subject . . .379 Michel's method ; Aluminium-nickel-copper alloys ; Formulas . . 380 Formulas of alloys resembling silver; Prof. Kirkaldy's tests of Mr. James Webster's compositions ; Formulas of these alloys . . 381 " Lechesne" and its composition ....... 383 Cowles Bros.' " Aluminium- Silver" and " Hercules Metal" . . 384 Aluminium and silver ; Beneficial effects of silver on alumininm . . 385 Dr. Carroll's alloy for dental plates ; Tiers Argent ; Hirzel's alloys . 386 Aluminium and gold ; Prof. W. Chandler Roberts- Austin on the influ- ence of aluminium on gold; " Nurnberg gold"; Aluminium and platinum . . . . . . . . . . .387 Aluminium and tin ; Alloy for the interior parts of optical instruments 388 Influence of aluminium on tin; Tissier Bros.' statement; Curious pro- perty of an alloy prepared by Mr. Joseph Richards . . .389 Aluminium and zinc ; Effect of zinc in small proportion on aluminium ; Deville on the presence of zinc in aluminium ..... 390 Aluminium-zinc-copper alloys; " Aluminium brasses;" Mode of pro- ducing them and their properties ; Julius Bauer's patent . .391 Alloy patented by M. G. Farmer, of Salem, Mass. ; Series of tests made in 1886, at the works of Cowles Bros 392 Tests by the Aluminium und Magnesium Fabrik, of Bremen ; Test of aluminium brasses by Prof. Tetmayer, of Zurich ; aluminium and cadmium . 393 Aluminium and mercury ; Experiments by Deville, Wollaston and Richards; Investigations by Caillet and Joule . . . .394 XXV111 CONTENTS. PAGE Gmelin's statement; Results obtained by J. B. Bailie and C. Fery . 395 Properties of aluminium amalgam . . . . . . .396 Aluminium and lead 397 Aluminium and antimony ; Aluminium and bismuth ; Aluminium and silicon 398 Effect of silicon on aluminium ; Aluminium and magnesium . . 400 Aluminium and chromium ; Aluminium and manganese . . . 401 Aluminium and titanium ; Aluminium and tungsten .... 402 Aluminium and molybdenum ; Aluminium and gallium ; Aluminium and calcium . . . . ... . . . . . 403 Aluminium and sodium ; Aluminium and boron ; Aluminium and arsenic. . . . . . . . . . . 404 Aluminium and selenium ; Aluminium and tellurium ; Aluminium and phosphorus ; Aluminium and carbon ...... 405 CHAPTER XV. ALUMINIUM-COPPER ALLOYS. Arrangement of these alloys in two groups ..... 406 Alloys of the first class; Effect of copper on aluminium; Properties and color of alloys with over 30 per cent, of copper . . . 407 Alloys of the second class ; Efficiency of aluminium in improving the qualities of copper ; "Aluminium-bronze;" Dr. Percy, the first to draw attention to these alloys . . . . . . . 408 Former mode of making aluminium-bronze; Prices in 1864, quoted by Morin; Prices in 1879; Reduction in price in 1885, by Cowles Bros 409 Present prices ; The low figure at which aluminium-bronze is claimed to be produced by the Heroult process ; Composition and nature of the bronzes; Formulas 410 Morin' s argument to prove that these alloys are true chemical combina- tions 411 Argument why aluminium forms valuable bronzes . . . .412 Weak point in the argument . . . . . . . .413 Reasons why bronze made by diluting bronze with copper will be prac- tically as good as the one made directly from the metals . . .414 Preparing the bronzes ; Impurities in copper which effect the quality of the bronze ; Quality of the aluminium ; Directions for preparing the bronzes by the "Magnesium und Aluminium Fabrik" of Heme- lingen . . . . . . . . . . . .415 Remelting of the bronze ; Operation of diluting a high per cent, bronze to a lower one . . . . . . . . . .416 Fusibility; Casting; Best crucible, for this purpose . . . .417 CONTENTS. XXIX PAGE Moulds for casting; Thomas D. West on "Casting aluminium and other strong metals" . . . . . . . . .418 Shrinkage of aluminium bronze ; Color . . . . . .421 Specific gravity ; Table of specific gravities ; Hardness ; Influence of working on the metal ; Determinations made on Cowles Bros.' bronzes at the Washington Navy Yard . . . . . .422 Transverse strength ; Compressive strength ; Results obtained by Mr. Anderson in the Royal Gun Foundry at Woolwich ; Tests made on Cowles' bronze at the Watertown Arsenal 423 Tensile strength ; Results obtained by Lechatelier, 1858; Determina- tions by Deville ; Experiments made in 1861 424 Results obtained by Anderson at the Woolwich Arsenal ; Official tests of the Cowles' bronzes at the Watertown Arsenal and at the Wash- ington Navy Yard . . . . . . . . .425 Diagram showing tenacity of bronzes; Test of Cowles' bronzes of " A3" grade by Prof. Un win 426 Test of Cowles' B and C grades by Mr. Edw. D. Self, at the Stevens Institute, Hoboken, N. J. ; Tests of bronzes made at Neuhausen by the Heroult process ; Results obtained by Prof. Tetmayer . . 427 Diagram showing the variation of tensile strength and elongation of aluminium bronzes ; Tests of the effect of temperature on the strength of aluminium bronzes ; Annealing and hardening . .428 Working ; Proper temperature for working the bronzes ; Effect of cold working 429 Rolling, drawing, and forging the bronzes ; Spinning, stamping, press- ing, working with the file, etc. ....... 430 Anti-friction qualities ; Morin's opinion; Cowles Bros.' recommenda- tion; Mr. Joseph Richards' s experiment 431 Conductivity for heat and electricity ; Resistance to corrosion . . 432 Non-oxidability of aluminium bronze when heated in the air . . 433 Effect of the weather on aluminium bronze ; Uses of the aluminium bronzes ............ 434 The merits of aluminium bronze as a metal for casting heavy guns, urged by Mr. A. H. Cowles 435 Aluminium bronze as material for propeller blades .... 436 Brazing; Solder for brazing; Soldering; Deville on this subject; Directions by Schlosser for preparing solder ; Formulas of solders recommended by the Cowles Co. . . . . . . .437 Silicon-aluminium bronze; Phosphor-aluminium bronze; Patents of Thos. Shaw, of Newark, N. J. 438 XXX CONTENTS. CHAPTER XYI. ALUMINIUM-IRON ALLOYS. PAGE Useful alloys of this class . . . . . . . . .438 Influence of iron in small quantities on the properties of aluminium . 439 Ferro-aluminium ; Composition of the Cowles Company's ferro-alu- minium ; Method of making ferro-aluminium ; Properties of these alloys 440 Different grades of ferro- aluminium ; Absorption of aluminium by iron and steel in the process of their manufacture . . . . .441 Effect of aluminium on steel ; Faraday's experiments . . . 442 Experiments at Faustman & Ostberg's Mitis Foundry at Carlsvick, Sweden, 1885 443 Results obtained by the addition of aluminium to steel; Explanation of its effect 444 Effect of aluminium on the welding of steel ; Poor results obtained by adding ferro-aluminium to high-carbon steels 445 Summary of Mr. Spencer's experience ...... 446 Steel-aluminium ; Best time to add the aluminium ; Effect of alu- minium on wrought-iron ; Discovery by Mr. Wittenstroem, of Stockholm, 1 and Mr. L. Nobel, of St. Petersburg . . . .447 "Mitis" castings 448 Details of the production of mitis castings ; Raw material . . . 449 Analyses of mitis metal by Mr. Edward Riley ; Method of treatment 450 Devices used in connection with the process ; Nobel's furnace for burn- ing naphtha or crude petroleum ; Moulding material . . .451 Properties of mitis castings ; Experiments at the Bethlehem Iron Works; Rationale of the process ; Mr. Ostberg's explanation . 452 Failure of Mr. R. W. Davenport and Mr. A. A. Blair to find any alu- minium in mitis castings ; Admission of Mr. Ostberg ; Explanation by R. W. Davenport ; Reasons for the non-tenability of this ex- planation ........... 453 Explanation of the increased fluidity of the iron 454 Causes of blow-holes in wrought-iron castings 455 Causes of the comparative freedom of mitis castings from blow-holes ; Mr. Howe's suggestion ......... 457 Summary of arguments presented ; Influence of aluminium in puddling iron 458 Influence of aluminium on cast-iron 459 Method of adding ferro aluminium 460 Investigation of this subject by Mr. W. J. Keep with the co-opera- tion of Prof. C. F. Mabery and L. D. Vorce . . . .461 Solidity of castings ; Does the aluminium remain in the iron ? Tests to determine this question .462 CONTENTS. XXXI PAGE Transverse strength ; Table giving the percentage increase in strength by the addition of aluminium . 463 Elasticity ; Percentage increase in deflection ; Tests to distinguish the effect due to the silicon added ....... 464 Effect on the grain ; Activity of aluminium in changing combined into graphitic carbon 465 Fluidity of the iron ; Shrinkage ; Table showing the reduction in the shrinkage ........... 466 Hardness ; Practical benefit to poor iron gained by adding ferro- alu- minium '........... 467 Practical results ; The rationale of the action of aluminium on cast- iron 468 CHAPTER XYIL ANALYSIS OF ALUMINIUM AND ALUMINIUM ALLOYS. Elements commercial aluminium may contain ; Method of attack generally preferred 469 Qualitative tests ; Specific gravity as a test . . . . .470 Test proposed by Fr. Schulze ; Determination of silicon ; Deville's methods ........... 471 Observation by Prof. Rammelsberg . . . . . . .472 Determination of iron (and aluminium) ; Deville's method . .473 H. Rose's method ...... ... 474 Determination of lead ; Determination of copper ; Determination of zinc ............ 476 Determination of tin ; Determination of silver ; Determination of sodium 477 Determination of chlorine ; Determination of carbon ; Determination of fluorine ; Procedure recommended by Deville ; Analysis of ferro- aluminiums 478 Mr. H. N. Yates's experience ; Chancel's separation . . .479 Mr. R. T. Thompson's method 480 Method giving the author satisfactory results ; Method recommended by A. A. Blair 481 Electrolytic method 482 Method of procedure given by Dr. Classen ; Electrolytic method of Prof. Edgar T. Smith 483 Analysis of aluminium bronze ........ 484 General remarks .......... 486 INDEX .- . ... 489 ERRATA. Page 54, analysis 7 : Instead of " silicon 0.80, iron 4.40, read " silicon 4.40, iron 0.80." Page 61, ninth line from foot : Instead of Picktet, read Pictet. TEMPERATURES. Unless otherwise stated, all temperatures are given in Centigrade degrees. ALUMINIUM. CHAPTER I. HISTORY OF ALUMINIUM. ABOUT 1760, Morveau called the substance obtained by cal- cining alum-alumina. When, afterwards, Lavoisier first sug- gested the existence of metallic bases of the earths and alkalies, and alumina was suspected of being the oxide of a metal, the metal was called aluminium. This, long before it was isolated. The first researches in the preparation of aluminium date back to 1807. Davy tried, but in vain, to decompose alumina by an electric current, or to reduce it by vapor of potassium. Oer- stedt, in 1824, believed he had isolated aluminium. He decom- posed anhydrous aluminium chloride by potassium amalgam, and obtained, along with some potassium chloride, an amalgam which when decomposed by heat furnished him a metal resembling tin. It is probable that he employed either some moist aluminium chloride or potassium amalgam which contained caustic potash, for it is only when wetted with a solution of caustic potash that aluminium alloys with mercury ; for when Wohler, later, wished to prepare aluminium by this method, he found it impossible to obtain an aluminium amalgam when he employed materials pure and dry. Nevertheless, the method of Oerstedt marks an epoch in the history of aluminium, for, in 1827, Wohler isolated it by decomposing aluminium chloride by potassium. The metal first isolated by Wohler was a gray powder, taking under the polisher the brilliancy of tin. It was very easily changed, because of its extreme division, and also because it was mixed 2 18 ALUMINIUM. with the potassium or aluminium chloride used in excess. At that time no further use was made of these facts. Later, in 1845, 011 making vapor of aluminium chloride pass over potassium placed in platinum boats, Wohler obtained the metal in small, malleable globules of metallic appearance, from which he was able to deter- mine the principal properties of aluminium. But the metal thus obtained was scarcely as fusible as cast iron, without doubt because of the platinum with which it had alloyed during its preparation. In addition to this, it decomposed water at 100, from which we suppose that it was still impregnated with potas- sium or aluminium chloride. It is to H. St. Claire Deville that the honor belongs of having, in 1854, isolated aluminium in a state of almost perfect purity, determining its true properties. Thus, while aluminium had been isolated in 1827, for eighteen years its properties en masse were unknown, and it was only at the end of twenty-seven years after its discovery that the true properties of the pure metal were established by Deville. The second birth of aluminium, the time at which it stepped from the rank of a curiosity into the number of the useful metals, dates from the labors of Deville in 1854. If Wohler was the dis- coverer of aluminium, Deville was the founder of the aluminium industry. In commencing researches on aluminium, Deville, while he applied the method of Wohler, was ignorant of the latter' s results of 1845. Besides, he was not seeking to produce aluminium that he might turn its valuable properties to practical account, but that it might serve for the production of aluminium prot- oxide (A1O), which he believed could exist as well as ferrous oxide (FeO). The aluminium he wished to prepare would, he thought, by its further reaction on aluminium chloride, form alu- minium proto-chloride (A1C1 2 ) from which he might derive the protoxide and the other proto-salts. But on passing vapor of alu- minium chloride over the metallic powder formed by reduction by potassium, this proto-chloride was not thus produced ; he obtained, inclosed in a mass of aluminium-potassium chloride (APC1 6 .2KC1), fine globules of a brilliant substance, ductile, malle- able, and very light, capable of being melted in a muffle without oxidizing, attacked by nitric acid with difficulty, but dissolved HISTORY OF ALUMINIUM. 19 easily by hydrochloric acid or caustic potash with evolution of hydrogen. Deville troubled himself no more about the proto-salts of aluminium, but, recognizing the importance of his discovery, turned his attention to preparing the metal. He was at this time Professor of Chemistry in the Ecole Normale, Paris, his salary was but 3000 francs, his estate was small, and he was practically without the means of doing anything further. On Monday, February 6, 1854, Deville read at the seance of the Academy a short paper entitled " Aluminium and its Chemi- cal Combinations," in w r hich he explained the results of this experiment as showing the true properties of aluminium and also furnishing a method of purifying it, and declared his intention oi commencing immediate search for a process which could be eco- nomically applied on a commercial scale. M. Thenard, at the close of the communication, remarked that such experiments ought to be actively pursued, and that, since they were costly, he believed the Academy would hasten the accomplishment of the work by placing at Deville's disposal the necessary funds. As the outcome of this, the Academy appointed Deville one of a committee to experiment on producing aluminium, and 2000 francs were placed at his disposal for the work. It was on the occasion of the reading of this paper that M. Chenot addressed a note to the Academy on the preparation of aluminium and other earthy and alkaline metals, in which he claimed, in some regards, priority for his inventions. (See fur- ther under " Reduction by Carbon.") This note was reserved to be examined by a commission appointed to take notice of all communications relative to the production of aluminium. With the funds thus placed at Deville's disposal he experi- mented at the ficole Normale for several months. As potassium is very dangerous to handle, cost then 900 francs a kilo, and gives comparatively but a small return of aluminium, Deville, in view of the successful work of Bunsen on the electric decomposition of magnesium chloride, tried first the reduction of aluminium chloride by the battery. On March 20, 1854, Deville an- nounced to the Academy in a letter to Dumas that he had pro- duced aluminium without alkaline help, and sent a leaf of the 20 ALUMINIUM. metal thus obtained. At that time Thenard, Boussingault, Pelouze, Peligot, and later, de-la-Rive, Regnault and other well- known scientists shared the honor of assisting in the laboratory experiments. Deville sent, in the following May, a mass of five or six grammes weight to Liebig, making no secret of the fact that it was reduced by the battery ; while Balard, at the Sorbonne, and Fremy, at the Ecole Polytechnique, publicly re- peated his experiments and explained them in all their details. Although these experiments succeeded quite well, yet, because of the large consumption of zinc in the battery used the process could evidently not be applied industrially, and Deville felt obliged to return to the use of the alkaline metals. Towards the middle of 1854, Deville turned to sodium, with- out a knowledge of those properties which render it so pref- erable to potassium, but solely because of its smaller equivalent (23 to that of potassium 39) and the greater cheapness of soda salts. He studied the manufacture of sodium, with the aid of M. Debray, in his laboratory at the Ecole Normale, and their experiments were repeated at Rousseau Bros/ chemical works at Glaciere, when they were so successful that Rousseau Bros, very soon put metallic sodium on the market at a much reduced price. It is said that while metallic sodium was a chemical curiosity in 1855, costing something like 2000 francs a kilo, its cost in 1859 is put down at 10 francs. Deville carried this process to such perfection that for twenty-five years it remained almost pre- cisely at the status in which he left it in 1859. In order to still further cheapen aluminium, Deville busied himself with the economic production of alumina, which gave later a lively im- pulse to the cryolite and bauxite industries. On August 14, 1854, Deville read a paper before the Aca- demy describing his electrolytic methods at length (s^e under " Reduction by Electricity"), showing several small bars of the metal and also stating some of the results already achieved by the use of sodium but not going into details, since he believed that numerous analyses were necessary to confirm these results which he was unable to have made with the funds at his disposal. He also stated that the desire to show, in connection with his assertions, interesting masses of the metal, alone prevented the HISTORY OF ALUMINIUM. 21 earlier publication of the methods used. Several days before this, Bunsen published in Poggendorff s Annalen a process for obtaining aluminium by the battery, which resembled Deville's method, but of which the latter was ignorant when he read his paper. Thus it is evident that the isolation of aluminium by elec- trolysis was the simultaneous invention of Deville and Bunsen. After reading this paper, Deville caused a medal of aluminium to be struck, which he presented to the Emperor Napoleon III. The latter, looking forward to applying such a light metal to the armor and helmets of the French Cuirassiers, immediately authorized experiments to be continued at his own expense on a large scale. This anticipation ultimately proved impracticable, but the ambition in which it was bred was caused for once to minister to the lasting benefit of mankind. Deville, however, about this time accepted, in addition to his duties as professor at the Ecole Normale, a lectureship at the Sorbonne (where he after- wards obtained a full professorship), and it was not until March of the next year that the experiments at the cost of the Emperor were begun. It was about August, 1854, that two young chemists, Chas. and Alex. Tissier, at the suggestion of Deville, persuaded M. De Sussex, director of a chemical works at Javel, to let them ex- periment in his laboratory (of which they had charge) on the production of sodium. Towards the commencement of 1855, Deville took up the in- dustrial question, the Emperor putting at his disposition all the funds necessary for the enterprise, and in March the investigator Avent to work and installed himself at the chemical works at Javel in a large shed which the director, M. De Sussex, kindly put at his service. The investigations were carried on here for nearly four months, ending June 29th, and the process elaborated was an application on a large scale of the experiments he had made at the expense of the Academy, which he described in his paper of August 14, 1854, and by which he had been able to obtain a few pencils of metal. In this work such success attended his efforts that on June 18, Deville presented to the Academy through M. Dumas large bars of pure aluminium, sodium and masses of aluminium 22 ALUMINIUM. chloride. The members- and large audience were loud in their admiration and surprise at the beauty of the metal. Dumas stated that the experiments at Javel had put beyond a doubt the possibility of extracting aluminium on a large scale by prac- tical processes. Deville's paper was then read, describing all his processes in detail, and concluding with the following words : " After four months of work on a large scale, undertaken with- out responsibility on my part, and, in consequence, with the tran- quillity and repose of mind which are so often wanting to the investigator ; without the preoccupation of expense, borne by his Majesty the Emperor, whose generosity had left me entire liberty of action; encouraged each day by distinguished men of science, I hope to have placed the aluminium industry on a firm basis." It was the metal made at this time at Javel which was ex- hibited at the Paris Exposition in 1855. In the Palais de Fln- dustrie, among the display from the porcelain works at Sevres, were ingots and some manufactured objects. The first article made of aluminium was, in compliment to the Emperor, a baby- rattle for the infant Prince Imperial, for which purpose it must have served well because of the sonorousness of the metal. After terminating these experiments, Deville continued work- ing at the ficole Normale, the Emperor defraying his expenses, until April, 1856. The memoir published in the " Ann. de Chim. et de Phys.," April, 1856, contains, besides the results obtained at Javel, the improvements devised in the meantime. It appears that when Deville first went to Javel, he had for assistants the Tissier Brothers, who were charged by M. de Sus- sex to give him all the aid they could. Since the previous autumn the Tissiers had been experimenting on sodium furnaces, and now, in concert with Deville, they drew up plans for furnaces, and aided in devising other apparatus. Under these circum- stances the furnace for the continuous manufacture of sodium in cylinders was devised, which the Tissiers claim Deville strongly advised them to make their property by patenting, asking only from them the use of it for his experiments. So, immediately after the experiments were ended, in July, the Tissiers patented the furnace in question, and, leaving Paris, took charge of M. Chanu's works at Rouen. On the other hand, Deville always HISTORY OF ALUMINIUM. 23 reproached them for acting in bad faith. He says that after having assisted for about two months in setting up his apparatus, being forced to leave the works because of misunderstandings between them and M. de Sussex, they were admitted to his laboratory at the Ecole Nor male, and initiated by him into the knowledge of all those processes which they made use of after- wards, then suddenly left, taking drawings of furnaces, details of processes, etc., which they not only made free use of, but even patented. However, whichever party was in the right (and those who comprehend the character of Deville can hardly doubt which was), the fact stands that in July, 1855, M. Chanu, an honorable manufacturer of Rouen, founded a works in which Deville's processes were to be applied, and intrusted the direction of it to the Tissier Brothers. The history of the works at Rouen is thus described by the Tissiers in their book on aluminium, of which we shall speak a little further on : "In July, 1855, Messrs. Maletra, Chanu, and Davey, of Rouen, formed a company to produce aluminium, and we were intrusted with the organization and special charge of the in- dustry. The commencement was beset with difficulties, not only in producing but in using the metal. It then sold at $200 per kilo, the price being an insurmountable obstacle to its employ- ment in the arts. The small capital at our disposal was not enough to start the industry, to pay general expenses, and the losses occasioned by the many experiments necessary. On Feb- ruary 28, 1856, the society was dissolved. In April of the same year, Mr. William Martin, struck by the results already obtained and sanguine of greater success, united with us. From that time daily improvements confirmed M. Martin's hopes, and in 1857 the works at Amfreville-la-mi-Voie, near Rouen, sold the metal at $60 per kilo ($2 per oz.). The laboratory of this works was devoted to researches on everything concerning the production and application of aluminium. M. Martin has our sincere grati- tude for the kindness with which he so willingly encouraged and contributed to the progress of the manufacture of this wonderful metal." The process ultimately used at Amfreville was the reduction of 24 ALUMINIUM. cryolite by sodium, but the enterprise was not a permanent suc- cess, and after running for a few years it was abandoned and the works closed. Returning to Deville, we find that after leaving Javel one of the first subjects he investigated was the use of cryolite for pro- ducing aluminium. The researches made with the aid of MM. Morin and Debray were published in the memoir of April, 1856, and became the basis of the process carried out by the Tissiers at Rouen. Besides this, Deville perfected many of the details of a practicable aluminium plant, with the result that in the spring of 1856 he united with Messrs. Debray, Morin, and Rosseau Bros, (the latter manufacturers of chemicals at Glaciere, in whose works aluminium had been made since the middle of 1855) and put up new apparatus in the works at Glaciere, the company fur- thering the work entirely at their own cost. This enterprise lasted for more than a year, during which a number of processes were tried and continued improvements made, so that towards August of the same year aluminium was put on the market in Paris at 300 francs a kilo, being one-third what it cost a year previous. Finally, in April, 1857, the little works at Glaciere, a suburb of Paris, in the midst of gardens and houses, and turning into the air fumes charged with chlorine and salts, was obliged by reason of general complaints to stop making aluminium. The plant was moved to Nanterre, where it remained for some years, under the direction of M. Paul Morin, being on a scale four times as large as the actual demand. Afterwards part of the plant was moved to the works of H. Merle & Co.", at Salindres, and later on the whole plant, where the manufacture is now car- ried on by the firm of Pechiney & Co. The works at Nanterre were really the only "aluminium works" built by Deville, the others were plants installed at general chemical works, but these at Nanterre were built by the united efforts of Deville, his brothers and parents, and a few personal friends. Among those who aided Deville, especially in the problems which the new industry presented, he speaks warmly of Messrs. d'Eichtal, Lechatelier, and Jacquemont. In 1858 the Tissiers wrote and published a small work entitled HISTORY OF ALUMINIUM. 25 " Recherches sur 1 J Aluminium/' which, in view of what Deville could have written about the subject, was a decided misrepre- sentation of the results which had been thus far accomplished. Deville thought that the industry was yet too young to merit any sort of publication, yet he naively writes in his work "De V Alu- minium/ 7 in 1859, " I will sincerely acknowledge that my writing is a little due to my pride, for I decided to take the pen to speak of my work only to avoid seeing it belittled and disfigured as it has been lately in the book written by the MM. Tissier." Deville published his book in September, 1859, and he con- cludes it with these words : " I have tried to show that aluminium may become a useful metal by studying with care its physical and chemical properties, and showing the actual state of its manufacture. As to the place which it may occupy in our daily life, that will depend on the public's estimation of it and its com- mercial price. The introduction of a new metal into the usages of man's life is an operation of extreme difficulty. At first aluminium was spoken of too highly in some publications, which made it out to be a precious metal ; but later these estimates have depreciated even to the point of considering it attackable by pure water. The cause of this is the desire which many have to see taken out of common field-mud a metal superior to silver itself; the opposite opinion established itself because of very impure specimens of the metal which were put in circulation. It seems now that the intermediate opinion, that which I have always held and which I express in the first lines of my book, is be- coming more public and will stop the illusions and exaggerated beliefs which can only be prejudicial to the adoption of aluminium as a useful metal. Moreover, the industry, established as it now is, can be the cause of loss to no one ; as for myself, I take no account of the large part of my estate which I have devoted, but am only too happy, if my efforts are crowned with definite success, in having made fruitful the work of a man whom I am pleased to call my friend the illustrious Wb'hler." Contemporary with the early labors of Deville, among the numerous chemists and metallurgists investigating this attractive field we find Dr. Percy in England, and H. Rose in Germany, 26 ALUMINIUM. whose experiments on the reduction of cryolite by sodium were quite successful, and are herein described later on. As early as 1856 we find an article in an American magazine* showing that there were already chemists in the United States spending time and money on this subject. The following is the substance of the article alluded to: "Within the last two years Deville has extracted 50 to 60 Ibs. of aluminium. At the pre- sent time, M. Rousseau, the successor of Deville in this manu- facture, produces aluminium which he sells at $100 per pound. No one in the United States has undertaken to make the metal until recently Mons. Alfred Monnier, of Camden, N. J., has, ac- cording to the statement of Prof. James C. Booth in the ' Penn. Inquirer/ been successful in making sodium by a continuous pro- cess, so as to procure it in large bars, and has made aluminium in considerable quantity, specimens of which he has exhibited to the Franklin Institute. Mons. Monnier is desirous of forming a company for the manufacture of aluminium, and is confident that by operating in a large way he can produce it at a much less cost than has heretofore been realized. We would suggest the propriety of giving aid to this manufacturer at the expense of the government, for the introduction of a new metal into the arts is a matter of national importance, and no one can yet realize the various and innumerable uses to which this new metal may be applied. It would be quite proper and constitutional for Con- gress to appropriate a sum of money to be expended under the direction of the Secretary of the Treasury in the improvement of this branch of metallurgy, and in testing the value of the metal for coinage and other public use." In the next volume of the " Mining Magazine"f there is a long article by Mr. W. J. Taylor, containing nothing new in regard to the metallurgy of aluminium, but chiefly concerned in calcu- lating theoretically the cost of the metal from the raw materials and labor required by Deville's processes, and concluding that it is quite possible to make it for $1.00 per pound. In 1859 the first aluminium works in England were started at * Mining Magazine,. 1856, vii. 317. f Mining Magazine, viii. 167 and 228. Proc. Ac. Nat. Soi., Jan. 1857. HISTORY OF ALUMINIUM. 27 Battersea, near London. No details are attainable respecting the size of these works or the length of time they were in operation. They very probably were merged into the enterprise started the next year, I860, at Newcastle-on-Tyne, by the Bell Bros. one of whom was I. Lowthian Bell, so prominent in connection with the metallurgy of iron. In 1862 this company was selling their aluminium at 40 shillings per troy pound, and they continued operations until 1874, when the works w r ere closed. It was probably shortly after 1874 that the large firm of J. F. Wirtz & Co., Berlin, made an attempt to start an aluminium works. The project drooped before it w r as well started, and it is only within the last five years that Germany has possessed a flourishing aluminium industry. The further we get away from an age the better able are we to write the true history of that age. And so, as years pass since the labors of Wohler, Deville, and Tissier, we are now able to see better the whole connected history of the development of this art. Dr. Clemens Winckler gives us a comprehensive retrospect of the field seen from the standpoint of 1879, from which we condense the following.* "The history of the art of working in aluminium is a very short one, so short that the present genera- tion, with which it is contemporary, is in danger of overlooking it altogether. The three international exhibitions which have been held in Paris since aluminium first began to be made on a com- mercial scale form so many memorials of its career, giving as they did at almost equal intervals evidence of the progress made in its application. In 1855 we meet for the first time in the Palais de ^Industrie with a large bar of the wonderful metal, docketed with the extravagant name of the ' silver from clay.' In 1867 we meet with it again worked up in various forms, and get a view of the many difficulties which had to be overcome in producing it on a large scale, purifying and moulding it. We find it present as sheets, wire, foil, or worked-up goods, polished, engraved, and soldered, and see for the first time its most import- ant alloy aluminium bronze. After a lapse of almost another dozen years, we see at the Paris Exhibition of 1878 the maturity * Industrie Blatter, 1879 ; Sci. Am. Suppl., Sept. 6, 1879. 28 ALUMINIUM. of the industry. We have passed out of the epoch in which the metal was worked up in single specimens, showing only the future capabilities of the metal, and we see it accepted as a cur- rent manufacture having a regular supply and demand, and being in some regards commercially complete. The despair which has been indulged in as to the future of the metal is thus seen to have been premature. The manufacture of aluminium and goods made of it has certainly not taken the extension at first hoped for in its behalf; the lowest limit of the cost of manufacture was soon reached, and aluminium remains as a metal won by expensive operations from the cheapest of raw materials. " There are several reasons why the metal is shown so little favor by mathematical instrument makers and others. First of all, there is the price ; then the methods of working it are not everywhere known ; and further, no one knows how to cast it. Molten aluminium attacks the common earthen crucible, reduces silicon from it, and becomes gray and brittle. This inconvenience is overcome by using lime crucibles, or by lining an earthen cru- cible with carbon or strongly burnt cryolite clay. If any one would take up the casting of aluminium and bring it into vogue as a current industrial operation, there is no doubt that the metal would be more freely used in the finer branches of practical mechanics." At the time of Dr. Winckler's writing, the extraction of aluminium in France was carried on by Merle & Co., at Salindres, while the Societe Anonyme de 1' Aluminium, at Nanterre, worked up the metal. Both firms were represented at the Exposition of 1878. The prices quoted then were 130 francs a kilo for alumin- ium, and 18 francs for ten per cent, aluminium bronze. From 1874, when Bell Bros/ works at Newcastle-on-Tyne stopped operations, until 1882, when a new enterprise was started in England by Mr. Webster, the French company were the only producers of aluminium. Regarding the prospects of the aluminium industry at this period, we can very appropriately quote some remarks of the late Mr. Walter Weldon, F.R.S., who was a personal friend of M. Pechiuey (director of the works at Salindres), had given great attention to aluminium, and was considered as a first authority on HISTORY OF ALUMINIUM. 29 the subject. Speaking in March 1883, before the London Section of the Society of Chemical Industry, he stated that the only method then practised for the manufacture of aluminium was Deville's classical one ; that at Salindres, M. Pechiney had im- proved and cheapened it, but that was all the progress made in the industry in twenty-five years. Continuing, Mr. Weldon out- lined the possible lines on which improvements might be made as : 1st. Cheapening the production of aluminium chloride, or of aluminium-sodium chloride. 2nd. Substituting for these chlorides some other cheaper anhy- drous compounds of aluminium not containing oxygen. 3rd. Cheapening sodium. 4th. Replacing sodium by a cheaper reducing agent. Mr. Weldon exhibited the relative cost of the materials used in making aluminium as then carried on by M. Pechiney as Producing the alumina 10 per cent. " double chloride . . . . 33 " " sodium and reducing therewith . 57 " " Discussing these figures, it is seen that the cost of the alu- mina forms but a small item in the cost of the metal, since a saving of 50 per cent, in its cost would only cheapen the metal 5 per cent. A large margin is, however, left in the conversion of the alumina into the chloride, and it is here that a large saving may be expected either in cheaper methods of producing the chloride or by the substitution of some other cheaper salt for the chloride. The only other suitable compounds which might re- place the latter are the fluoride, iodide, bromide, sulphide, phos- phide, or cyanide. The fluoride has been used to some extent in the form of cryolite, but, from the impurities in the mineral and its corrosive action on the apparatus used for reduction, the metal produced is very much contaminated with iron and silicon. The bromide and iodide, no matter how produced, would always be too costly to replace the chloride. The production of the sul- phide in a suitable form from which the metal can be extracted has thus far not proved a success ; and, even if ever it be thus pro- duced in a suitable condition, it is not at all likely to be as cheap a material to use as the chloride. The phosphide and cyanide 30 ALUMINIUM. can thus far only be produced from the metal itself, and are, therefore, totally out of the question. To find a substitute for sodium as a reducing agent has been a favorite object of research among chemists for the past thirty years, and although every ele- ment occurring in any abundance or obtainable at a cheaper rate than sodium has been tried under almost all conditions, yet abso- lutely nothing has been accomplished in this direction that would entitle any one to the belief that aluminium can ever be pro- duced chemically without the use of sodium. So absorbing to those interested in the search for a substitute for sodium has the occupation proved, that the effort to cheapen sodium did not re- ceive anything like its fair share of attention. Since, of the 57 per cent, ascribed to the cost 'of sodium and reduction, 50 per cent, represents the sodium, which thus costs about 6 shillings a pound, there is seen to be a very large margin for improvements, since the raw materials for a pound of sodium do not cost over 1 or at most 2 shillings." In 1882, the cost of aluminium was materially cheapened by the application of the inventions of Mr. Webster, which, in ac- cordance with the analysis of the problem made by Mr. Weldoii, consisted principally in the cheap production of alumina and its conversion into chloride. Mr. Webster had experimented on this subject many years, and in 1881 and 1882 took out patents for his processes and organized the " Aluminium Crown Metal Company," located at Hollywood near Birmingham, where several thousand pounds were expended in plant. Business was soon commenced on a large scale, the company producing, however, niany other alloys besides those of aluminium. The business grew until it soon became the serious competitor of the French company, and practically controlled the English market. How- ever, a radical change of still greater importance in the sodium process was made in 1886 by an invention of Mr. H. Y. Cast- uer, of New York City. This gentleman conceived the plan of reducing sodium compounds in cast-iron pots, from a fused bath of caustic soda, by which the reduction is performed at a much lower temperature and the yield of sodium is very much more than by the Deville method. The application of this process on a large scale, with the use of gas furnaces and other modern HISTORY OF ALUMINIUM. 31 improvements, has lowered the cost of sodium from $1 per pound to about 20 or 25 cents. It is but just to say that Mr. Castner 7 s invention was by no means a chance discovery. For four years he worked in a large laboratory fitted up for this special purpose, and after many discouragements in trying to produce aluminium by means other than that of sodium was led finally to consider that the cheapening of this metal was the most promising method for cheapening aluminium, and after much patient, hard work, achieved well-deserved success. Mr. Castner's patent was taken out in the United States in June, 1886, and, while being the first one granted on that sub- ject in this country, was said also to be the only one taken out in the world since 1808. With the assistance of Messrs. J. H. and Henry Booth, of New York City, Mr. Castner demonstrated the process by building and operating a furnace on a somewhat large scale. This being accomplished, Mr. Castner crossed to Eng- land and met the representatives of the Webster process, with whom it was evident a combination would be especially advan- tageous to both parties ; for, with cheap aluminium chloride and cheap sodium, it was clear that a strong process could be built up. Mr. Castner then demonstrated plainly, by erecting a fur- nace and operating it for several weeks, that his process was all that he claimed for it. As the result of this success, the "Alu- minium Company, Limited" was incorporated in June, 1887, with a share capital of 400,000, a to acquire the patents and work and develop the inventions of James Webster for the manu- facture of pure alumina and certain metallic alloys and com- pounds, together with the business at present carried on by the Webster Patent Aluminium Crown Metal Company, Limited, in Birmingham, Sheffield, and London, England ; and also to ac- quire the patents and work and develop the invention of H. Y. Castner for the manufacture of sodium and potassium." Mr. Webster was paid 230,000 for the business, properties, stock, etc., of the Crown Metal Company, while 140,000 was allowed for the sodium patents. The new company appointed Mr. Cast- ner managing director, and the erection of large works was im- mediately begun at Oldbury, near Birmingham. These works were started in operation at the end of July, 1888. They cover 32 ALUMINIUM. five acres of ground, and have an annual producing capacity of 100,000 Ibs. of aluminium. This plant is, at present, the largest aluminium works in the world, and in view of the large part contributed to the establishment of this works by the genius of Mr. Castner, the methods there used are rightly called "The Deville-Castner Process." We have followed the progress of the Webster and Castner pro- cesses up to the date of starting the works at Oldbury because the continuity of the advances made in the old Deville process would hardly allow of a break in order to mention other processes aris- ing meanwhile. However, the five years since 1884 have wit- nessed not one but several revolutions in the aluminium industry. The great advances made in dynamo-electric machinery in the last decade have led to the revival of the old methods of elec- trolysis discovered by Deville and Bunsen, and to the invention of new methods of decomposing aluminium compounds electro- lytically. It will be recalled that the first small pencils of alu- minium made by Deville were obtained by electrolysis, and that he turned back to the use of the alkaline metals solely because the use of the battery to eifect the decomposition was far too costly to be followed industrially. This fact still holds true, and we cannot help supposing that if Deville had had dynamos at his command such as we have at present, the time of his death might have seen the aluminium industry far ahead of where it now is. First in point of time we notice Gratzel's process, patented in Germany in 1883 and used industrially by the "Aluminium and Magnesium Fabrik, Patent Gratzel" at Hemelingen near Bre- men. The process was essentially the electrolysis of a bath of fused aluminium salt, such as chloride or fluoride, the improve- ments on the older experiments being in details of apparatus used, the use especially of anodes of mixed carbon and alumina, and the use of dynamic electricity. Several metallurgists maintained the uselessness of the Gratzel processes, and their position was proved to be not far from the truth, for in October, 1887, the com- pany announced that the addition " Pt. Gratzel" would be drop- ped from the firm name, since they had abandoned Gratzel's pro- cesses and were making aluminium by methods devised by Herr HISTORY OF ALUMINIUM. 33 Saarburger, director of therr works. The processes of this latter gentleman not being published, we are unable to state their nature, but they are very probably electrolytic. In October, 1888, Mr. Saarburger reports that their works are producing at the rate of 12000 kilos of aluminium yearly, besides a large quantity of aluminium bronze and ferro-aluminium. The firm also works up the aluminium and its alloys into sheet, wire, tube, etc. A somewhat similar electrolytic process was patented by Dr. Ed. Kleiner, of Zurich, in 1886. Molten cryolite was decomposed by two carbon poles, the heat generated by the current first melting the cryolite and then electrolyzing it. Since the motive power in this, as in all electric processes, composes one of the chief elements for carrying on the reduction, the Kleiner Gesellschaft, formed to work this method, made an attempt to obtain water rights at the falls of the Rhine, at Schaffhausen, which would furnish 15,000 horse-power. This proposition being refused by the government, an experimental plant was started at the Hope Mills, Tyldesley, Lancashire, England, which is in operation at present; but its commercial success seems still to depend on a more economical application of the electric power and the obtaining of metal of greater purity than is usually made from cryolite. An electrolytic method, which is probably superior to both the preceding, is the invention of Mr. Chas. M. Hall, of Oberlin, Ohio, which was patented in the United States, April, 1889, but which has already been in successful operation for nearly a year. Mr. Hall is a graduate of Oberlin College, and for^ several years experimented on a small scale, overcoming many discouragements, at last perfecting the process which is now being operated by the Pittsburgh Reduction Company on Fifth Avenue, Pittsburgh ; Mr. Alfred E. Hunt, a well-known metallurgist, being president of the company. The principle involved is different from that in either the Gratzel or the Kleiner process ; it is the electric de- composition of alumina suspended or dissolved in a fused bath of the salts of aluminium and other bases, the current reducing the alumina without affecting its solvent. At present the plant is turning out 50 to 75 Ibs. of aluminium a day, and is so successful as to first cost that during 1889 they sold aluminium, guaranteed 98 per cent, pure, at $4.50 per pound, the lowest figure the metal 3 34 ALUMINIUM. had ever touched; but in November, 1889, they captured the aluminium market by cutting the price to $2.00, for which achievement Mr. Hall is to be heartily congratulated. While the electrolytic processes so far considered use a fluid bath and operate at moderate temperatures with a current of moderate intensity, there have been devised two other prominent processes which operate in a somewhat different manner and at- tain to very economical results. These primarily depend on the enormous temperature attainable by the use of a powerful electric arc, and secondarily on the reduction of alumina (which at the temperature attained becomes fluid) either by the reducing action of the carbon present or by simple electric decomposition. Which of these two agencies performs the reduction, in either process, is still an unsettled question which we will discuss later on. Before going further with the history of these two processes, Cowles* and Heroult's, it may not be inappropriate to take note of a few facts antecedent to their appearance. It is well known that Sir W. Siemens devised an electric furnace in which the heat of the arc was utilized for melting steel. In 1882, Mr. Ludwig Grabau, in Hanover, Germany, purchased a Siemens furnace for the express purpose of attempting the reduction of alumina, and after experimenting successfully for some time, modified the apparatus so as to work it continuously, and therewith made aluminium alloys; but on account of the difficulties of the pro- cess and the Jrnpurity of the alloys produced, Mr. Grabau gave up the experiments, having come to the conclusion that alumin- ium alloys to be technically valuable should be obtained in a state of almost chemical purity. In the beginning of 1885, Dr. Mierzinski, in his book on aluminium, presented some very striking remarks on the use of the electric furnace, which are so much to the point that they are well worth quoting in this connection : " The application of electricity for producing metals possesses the advantage not to be ignored that a degree of heat may be attained with it such as cannot be reached by a blowpipe or regenera- tive gas-furnace. The highest furnace temperature attainable is 2500 to 2800 C., but long before this point is reached the com- bustion becomes so languid that the loss of heat by radiation HISTORY OF ALUMINIUM. 35 almost equals the production of heat by combustion, and hinders a farther elevation of temperature. But in applying electricity the degree of heat attainable is theoretically unlimited. A fur- ther advantage is that the smelting takes place in a perfectly neutral atmosphere, the whole operation going on without much preparation and under the eyes of the operator. Finally, in ordinary furnaces the refractory material of the vessel must stand a higher heat than the substance in it, whereas by smelting in an electric furnace the material to be fused has a higher temperature than the crucible itself. Since the attempt to produce aluminium by the direct reduction of alumina by carbon is considered by metallurgists as impossible, because the temperature requisite is not attainable, the use of the electric current for attaining this end seems to be of so much the more importance." The Cowles invention was patented August 18, 1885, and was first publicly described before the American Association for the Advancement of Science, at their Ann Harbor meeting, August 28, 1885. The process is due to two Cleveland gentlemen, E. H. and A. H. Cowles, who in the development of their process associated with them Prof. Charles F. Mabery, of the Case School of Applied Science, Cleveland, as consulting chemist. The Cowles Electric Smelting and Aluminium Company, formed to work the process, erected a plant at Lockport, N. Y., where a water power of 1200 horse-power was secured, and where, among other novel apparatus, the largest dynamo in the world, made especially for this purpose by the Brush Electric Company, is in operation. Following the success of this plant in America, the Cowles Syndicate Company, organized to work the patents in England, have put in operation works at Stoke-on-Trent which have a capacity of something like 300 Ibs. of alloyed aluminium daily. Springing also from the Cowles process is the " Alumi- nium Brass and Bronze Company," of Bridgeport, Conn., which was organized in July, 1887, and controls the exclusive rights under the Cowles American patents of manufacturing the allovs of aluminium into sheet, rods, and wire. The extensive plant which this company is starting will employ 300 men, and has been erected at a cost of nearly $300,000. The principle made use of in the Cowles process is, briefly, 36 ALUMINIUM. that a powerful electric current is interrupted, the terminals being large carbon rods, and the space between having been filled with a mixture of alumina, carbon, and the metal to be alloyed, the intense heat generated in contact with this mixture causes the metal to melt and the alumina to be reduced to aluminium, which combines with the metal, while the oxygen escapes as carbonic oxide. It is interesting to note as separating the Cowles, as well as the Heroult, process from the previously mentioned electrolytic methods, that while the latter produce almost exclusively pure aluminium in their electric operation, finding it inexpedient, if not, perhaps, impossible to add other metals and form alloys at once the former experience almost the reverse of these condi- tions, and as yet are confined exclusively to the direct produc- tion of the alloys. The Heroult process was first put in practical operation on July 30th, 1888, at the -works of the Swiss Metallurgic Company (Societe Metallurgique Suisse), at Neuhausen, near Scbaffhausen. The patents for the process were granted in France and England in April and May, 1887, and in the United States in August, 1888. The company named above is composed of some of the largest metal workers in Switzerland. Previously to their adoption of this process they had experimented with Dr. Kleiner's electrolytic method, but abandoned it, and on becoming the owners of the Heroult process immediately started it up practically on a large scale, and with signal success. The process consists in electrolyzing molten alumina which has been rendered fluid by the heat of the arc, using as the positive anode a large prism of hard carbon and as the negative a sub-stratum of molten copper or iron, the arrangement of the parts being such that the process seems to proceed, when once well under way, in all respects as the simple electrolysis of a liquid. Using water power for driving the dynamos, the econom- ical production of alloyed aluminium at 4.5 francs per kilo (50 cents per pound), is said to be an assured fact. The success of this process at Neuhausen was so marked as to attract general attention, and in the latter months of 1888 several large German corporations, prominent among which was the HISTORY OF ALUMINIUM. 37 Allgemeine Electricitats Gessellschaft of Berlin, sent representa- tives to arrange for the purchase of the Heroult patents for Germany. The outcome of these examinations and negotiations was the purchase by this German Syndicate of Heroult's conti- nental patents and the founding by them and the former S\wss owners of the Aluminium Industrie Actien-Gesellschaft, with a capital of. 10,000,000 francs. In December, 1888, the new com- pany took possession at Neuhausen, and commenced the construc- tion of a plant many times larger than the original one, their plans also including the erection of foundries and mills for casting and manufacturing their alloys. Dr. Kiliani, the well- known writer on electro-metallurgical subjects, is working manager for the new company. The new plant will utilize about 3000 horse-power, and will have a capacity of 20 to 25 tons of 10 per cent, bronze daily. Besides these works, we learn that a French company, the Societe Electro-Metallurgique, has commenced the manufacture of alloys by the Heroult process, their works at Froges (Isere) being equal to a daily output of 3000 kilos of 10 per cent, bronze. Mr. Heroult was also in the United -States May- August, 1889, for the purpose of establishing a plant. The works were located at Bridgeport, Conn., and were started in August, but after run- ning a few hours the dynamo was burnt out and operations summarily stopped until the arrival of a dynamo ordered from the Oerlikon works at Zurich. This is hoped to be in place before the end of 1889,* and the works in full operation. Both the Cowles and Heroult processes have been successful in producing aluminium in alloys at a cost far below that at which pure aluminium is made, and they apparently have a good pros- pect of holding this position for some time to come. Comparing . the two processes we see that while on first sight the principle made use of appears similar, yet the different disposition of the parts and the evidently more economical working in the case of the latter seem to point to some deep-seated difference in the re- actions made use of in the two cases. However, we shall more minutely discuss these points in their proper place, suffice it to say, in summing up, that while the Cowles process undoubtedly 38 ALUMINIUM. has the merit of having been first in the field, the Heroult has the advantage of more practical and economical application. Among the many other aluminium processes and companies which have been projected within the last few years, we notice prominently the Alliance Aluminium Company of London, Eng- land, organized in the early part of 1888. Having a nominal capi- tal of 500,000, it is said to own the English, German, French, and Belgian patents of Prof. Xetto, of Dresden, for the manufacture of sodium and potassium and the reduction of cryolite thereby ; the patents of Mr. Cunningham for methods of reduction of the same metals; and methods devised by Prof. Netto and Dr. Saloman, of Essen, for producing aluminium of great purity on a commercial scale. The two latter named gentlemen are said to have invented their processes after long experimenting at Krupp's works at Essen ; and, since the apparatus used was mounted on trunnions, many rumors have been spread by the newspapers that aluminium was being made (by tons, of course) in a Bessemer con- verter by Krupp, of Essen. Prof. Netto reduces sodium by a continuous process, by allowing fused caustic soda to trickle over incandescent charcoal in a vertical retort, the apparatus contain- ing many ingenious details and giving promise of being quite economical. One method of using the sodium in reduction con- sists in the use of a plunger to which bars of sodium are attached and held at the bottom of a crucible full of molten cryolite ; another depends on the use of a revolving cylinder in which the cryolite and sodium react, and appears, more chimerical than Netto's other propositions. This latter device, however, is said to be in operation at Essen, though with what success we cannot learn. In June, 1888, "Engineering" stated that the Alliance Com- pany were located at King's Head Yard, London, E. C., and that several small reduction furnaces were being operated, each producing about 50 Ibs. of aluminium a day, estimates of the cost at which it was made giving 6 to 8 shillings per pound. In the early part of 1889 there seems to be a division of the original company. The "Alkali Reduction Syndicate, Limited" have leased ten acres of ground at Hepburn on which to erect a plant for working Cunningham's sodium patents, the sodium produced HISTORY OF ALUMINIUM. 39 going to the Alliance Company's reduction works located at Wallsend. As to the exhibit made by this company at the Paris Exhibi- tion, 1889, we will have some remarks to make later on. Ludwig Grabau, of Hanover, Germany, has made several patented improvements in producing aluminium, which are in the same direction as Prof. Netto's methods. Mr. Grabau believes that in order that aluminium may possess its most valuable quali- ties, both for use alone or in alloying, it should be of almost chemical purity ; and as the best means of attaining this end economically he has improved the sodium method 011 these three lines : 1st. Production of cheap pure aluminium fluoride. 2d. Production of cheap sodium. 3d. Reduction in such a manner that no possible impurities can enter the reduced metal, and that the sodium is completely utilized. How far Mr. Grabau has succeeded, as regards cheap produc- tion, I cannot say, but as for the purity, a sample sent the author contains 99.8 per cent, of aluminium, and is undoubtedly the purest made at present in the world. Mr. Grabau's sodium patents are now pending, but his other processes are described in full in their appropriate places. " The American Aluminium Company," of Milwaukee, Wis., was organized in July, 1887, with a capital of $1,000,000, to manu- facture aluminium by a process of Prof. A. J. Rogers. The process is kept secret, the application made for patents not being yet granted, but the means used are electrolytic and not very dif- ferent in principle from some others recently granted in England. A small experimental plant put up in the summer of 1888 has given encouraging results as to the purity of metal obtainable and the yield, and it is not improbable that if patents are granted soon the company will have* a larger plant in operation and their metal on the market in the early months of 1890. There is a company hailing from Kentucky, about whose methods no reliable information is to be had, the numerous news- paper articles which it has inspired being glaringly inaccurate and 40 ALUMINIUM. sensational, while our more staid scientific journals seem to treat it on the principle of " the least said the better." The enterprise was first brought to public notice in June, 1888, by an Associated Press dispatch, stating that by reducing common clay and cryolite in steel water-jack etted cupola furnaces, pure aluminium was ob- tained very cheaply. Two months later the ridiculous statement went the rounds of the press that this concern had exported 150 Ibs. of pure metallic aluminium to London, England, selling it at 50 cents per Ib. Since then, advertisements have appeared in the newspapers claiming them to be the only manufacturers of pure aluminium in America, oifering it at $5 per pound, and also offer- ing for sale various aluminium bronzes, ferro-aluminium, alumin- ium solders, etc. Later accounts of some methods used seem to point to the utilization of the idea of coating scrap iron with clay and " certain fluxes" and then running it down in a water- jacketted cupola, the castings being said to contain 1 J per cent, of aluminium. This method is identical with one recently patented by other parties in England and on the Continent. Whether this company produces aluminium or not is a question ojily answered by some very unreliable newspaper statements in the affirmative. The process last referred to is apparently successful in England, and may quite probably give the results claimed by this company, but of the process for making pure aluminium we can only say that it does not appear to be possible. Colonel William Frishmuth, of Philadelphia, is a German chemist whose name has been often published in connection with aluminium. Before 1860, Col. Frishmuth operated a small chemical works on North Broad Street, Philadelphia, and there followed the production of sodium by Deville's methods, furnishing it to the chemical dealers. It is quite possible that he followed Deville's methods still further, and, by means of sodium, pro- duced aluminium in small quantities. In 1877, Col. Frishmuth was operating a small electro-plating works in the northern part of Philadelphia, claiming to plate an alloy of nickel and alumin- ium from aqueous solution. While engaged in this, he persuaded some gentlemen in the metal trade to aid him financially in de- veloping a process for making aluminium, but always stipulating HISTORY OF ALUMINIUM. 41 that he be allowed to retain the secret of the process. Led on by reports of successes and promises of returns in the near future these gentlemen invested several thousand dollars with the sole result of reports of progress and fresh requests for money. After several years waiting, one, at least, of these gentlemen lost faith in the truth of Frishmuth's statements and withdrew his support, losing all that he had advanced. Other capitalists, however, were induced to step forward and put money into the concern, having nothing but the statements and promises of Frishrnuth as their security. Again others, in disgust, threw up their in- terest in the affair, never regaining a cent of what had been ad- vanced. I have been thus minute in these statements because this is a sample of the whole history of the process. In 1884, Col. Frishmuth obtained a patent for producing aluminium by simultaneously generating sodium vapor in one retort, vapor of a volatile aluminium salt in another, and mixing the vapors in a third retort, where they were to react and form aluminium. The process was never successful, and Frishmuth has since abandoned altogether the use of sodium and has been experi- menting of late years with electrolytic methods. On the obtain- ing of this patent an English syndicate sent Major Ricarde-Seaver, F.R.S.E., to this country to report on the process. Major Seaver was not altogether convinced, from what he was allowed to see, of the practicability of the furnace, and on reporting to the syndicate, a very liberal offer was made to Frishmuth, pro- posing that he come to England, erect a furnace, and demon- strate its working in a fair, clear manner, the syndicate to pay all the expenses incident to the test, including Col. Frishmuth's per- sonal expenses. This offer was refused, for what reason we need not go far to find. Since this episode other capitalists at home have advanced the funds which were asked for, and aluminium has been sold in moderate quantities, though how it is made, or whether Col. Frishmuth produces it or not, is an unsettled question. The metal sold is unquestionably of good quality, averaging as nearly as can be the same as the best French metal ; it is quite probable that with his long experience in handling the metal Col. Frishmuth is quite expert in refining and running down aluminium scrap of all kinds undoubtedly a difficult 42 ALTTMINIUM. thing to do. In 1884-5, the Philadelphia Business Census re- corded him as employing ten men and his annual product as valued at $18,000, but since then Col. Frishmuth has grown un- communicative to the census reporter, so that in 1886 it was stated in the Government Report on the Mineral Resources of the United States that no pure aluminium was made in America in that year a statement which we may accept as correct. Much public interest was directed to Frishmuth in 1884, when he cast the aluminium cap or apex of the Washington Monument. This casting is of pyramidal form, 10 inches high, 6 inches on a side of its base, and weighs 8 J pounds. An analysis of the metal in this casting is given on p. 54, and show^s it to be of a quality equal to the best French aluminium. Two aluminium companies have come to the author's notice of which I am able to give no more than the bare fact of their ex- istence. " The Aluminium Company of America 77 was incorpo- rated under the laws of New York, with a capital of $1,500,000 ; Paul R. Pohl, of Philadelphia, was styled the mineralogist and chemist. I do not think that the company has ever done anything further than to organize, offer stock, and issue a pros- pectus. It is now extinct. " The United States Aluminium Company,' 7 of East St. Louis, was incorporated in March, 1889, with a capital of $1,000,000, for the purpose of manufacturing aluminium and its alloys. The incorporators of the company, process to be used, etc., are unknown to the author. We will close this historical sketch by referring the reader back to Dr. Winckler's remarks (p. 27), and supplementing them with a notice of the exhibits of aluminium at the Paris Exposition of 1889. If, as Dr. Winckler remarks, the three international ex- hibitions in 1855, 1867, and 1878 show so many stages in its career, it is quite evident that the exposition of 1889 has shown a more promising view of the industry than any of its predecessors, excepting perhaps the first. It was not unnatural that many hopes were disappointed when the exhibit of 1878 showed so lit- tle advance over that of 1867, and when the fact became pain- fully evident that for twenty years, 1858 to 1878, very little real progress had been made in the industry. I think that if the exposition of 1878 showed anything at all, it showed that, from HISTORY OF ALUMINIUM. 43 a metallurgical standpoint, the industry was at a stand-still. Against this we place the exhibit of 1889, and the contrast is striking ; this shows not deadness but the most intense and suc- cessful activity that the industry has ever known. In place of one exhibitor, five manufacturers compete for honors. In short, this last exposition has shown the aluminium industry re-awakened and rapidly approaching its goal the placing of aluminium among the common metals. Just now, at the close of 1889, are we not almost inclined to state, in view of recent developments, that it has reached this goal ? As to the exhibits referred to, a detailed account reads as follows : Societe Anonyme pour Flndustrie de P Aluminium : In a large case, the frame of which was aluminium bronze, samples of aluminium, ferro-aluminium, aluminium bronze, forged and rolled, and numerous articles of the latter alloy. Cowles Electric Smelting and Aluminium Company : Samples of ferro-aluminium, aluminium bronze and aluminium brass of various grades, aluminium silver, and numerous useful articles made of these alloys. Brin Bros. : Samples of aluminium, with thin iron and steel castings made by its use. The Alliance Aluminium Company : Two large blocks of aluminium, cast hollow, weighing possibly 1000 pounds and 500 pounds respect- ively. The inclosing balustrade and decorations were princi- pally of aluminium or aluminium bronze. The Aluminium Company, Limited : A solid casting of aluminium bronze weigh- ing J ton, and on this a solid block of 98 per cent, aluminium weighing the same. In the corners of the case piles of ingots of 99 per cent, aluminium, 10 per cent, bronze, 5 per cent, bronze, 10 per cent, ferro-aluminium, and 20 per cent, alu- minium steel. Besides which was a 7 inch bell, springs, statues, aluminium plate, round and square tubes, wire, sheet, etc. Such were the aluminium exhibits which attracted as much interest as the historic ingot of 1855 did at its debut; and, not taking into account that Mr. HalFs process was not represented and that the German makers were debarred from exhibiting because of inter- national pique, yet the exhibit shown was one which demonstrated the great advances made in the last decade and give cause for the 44 ALUMINIUM. most sanguine hopes for the future. Indeed, it seems more than half true that already "aluminium the metal of the future, is transformed into aluminium the metal of the present." STATISTICAL. The following table shows the price at which aluminium has been sold since it was first placed on the market. Date. Place. Per kilo. Per pound. 1856 (Spring) Paris . . . . 1000 fr. $90.90 1856 (August) " . . . . 300 " 27.27 1859 " . . . . 200 " 17.27 1862 . " . . . . 130 " 11.75 1862 Newcastle . . . 11.75 1878 Paris . . . . 130 " 11.75 1886 " . . . . 12.00 1887 Bremen . . . . 8.00 1888 London .... 4.84 1889 Pittsburgh . . . 2.00 The selling price of aluminium bronze has until recently de- pended directly on the price of pure aluminium, since the bronze was made by simply uniting the two metals, but since electrical methods of obtaining the bronze directly have been used the alloy has been sold at a price for the contained aluminium much below what pure aluminium could be bought for. The ten per cent, bronze has been sold as follows : ' Date. Place. Per kilo. Per pound. 1878 Paris . .... . 18.00 fr. $1.64 1885 Cowles Bros. . . . . 4.50 " 0.40 1888 " " 3.85 " 0.35 1888 Heroult process, Neuhausen . 3.30 " 0.30 It is almost impossible to estimate how much aluminium has been made since Deville first started the industry. The following figures of annual outputs are gleaned from various sources, some of them being of doubtful accuracy. HISTORY OF ALUMINIUM. 45 kg. Ibs. a 55 = 1584 2112 2400 = 1000 4000 1650 5170 5280 . 70 . 125 . 230 . 450 . 6500 17800 A very approximate estimate of the whole amount of alumin- ium that had been produced up to 1886, made from a careful comparison and study of the above reports, gives a total of 115,000 Ibs. (52,000 kilos). Since then the Cowles Bros, are reported as having turned out 50,000-60,000 Ibs. in alloys, the Aluminium Company, Limited, have probably made as much, and the Hemelingen Fabrik, which has been in operation since 1885, is now producing 10,000-15,000 kilos yearly (22,000-33,000 Ibs.). The amount of aluminium imported and entered for consump- tion in the United States from 1870 to 1887 is as follows : 1854-56 Deville .... 25 1859 Nanterre (Deville) . . 720 1859 Rouen (Tissier Bros.) . 960 1865 France .... . 1090 1869 France .... . 455 1872 Salindres (H. Merle & Co.) . 1800 1872 England (Bell Bros.) . 750 1882 Salindres . 2350 1884 Salindres . 2400 1883 Philadelphia (Frishmutli) . 1884 " " . 1885 it . . 1885 Cowles Bros, (in alloys) . 1886 a . 1887 a . " . Year ending June 30. Quantity (pounds). Value. 1870 . . ... $ 98 1871 . 341 1872 . 1873 . 2 22 ]874 . 183 2125 1875 . .... 134 1355 1876 . 139 1412 1877 . 131 1551 1878 . 251 2978 1879 . 284 3423 1880 . 341 4042 1881 . . . . . .517 6071 1882 . 566 6459 1883 . 426 5079 1884 . . . . . 590 8416 1885 . 439 4736 1886 . . ' . .464 5297 1887 . 797 9458 1888 . 1772 16764 46 ALUMINIUM. CHAPTEE II. OCCURRENCE OF ALUMINIUM IN NATURE. THERE is no other metal on the earth which is so widely scat- tered and occurs in such abundance. Aluminium is not found metallic. Stocker* made the state- ment that aluminium occurred as shining scales in an alumina formation at St. Austel, near Cornwall, but he was in error. But the combinations of aluminium with oxygen, the alkalies, fluorine, silicon, and the acids, etc., are so numerous and occur so abund- antly as not only to form mountain masses, but to be also the bases of soils and clays. Especially numerous are the combina- tions with silicon and other bases, which, in the form of felspar and mica, mixed with quartz, form granite. These combinations, by the influence of the atmosphere, air, and water, are decomposed, the alkali is replaced or carried away, and the residues form clays. The clays form soils, and thus the surface of the earth becomes porous to water and fruitful. It is a curious fact that aluminium has never been found in animals or plants, which would seem to show that it is not necessary to their growth, and perhaps would act injuriously, if it were present, by its influence on the other materials. Most of the aluminium compounds appear dull and disagreeable, such as felspar, mica, pigments, gneiss, amphibole, porphyry, eurite, trachyte, etc. ; yet there are others possessing extraordinary lustre, and so beautiful as to be classed as precious stones. Some of these, with their formulae, are : Ruby A1 2 Q3 Sapphire A1 2 3 Garnet . (Ca.Mg.Fe.Mn)3A12Si 3 Qi2 Cyanite Al 2 Si0 5 Journ. fr. prakt. Chem., 66, p. 470. OCCURRENCE OF ALUMINIUM IN NATURE. 47 Some other compounds occurring frequently are : Turquoise A12p208.H<5A120 6 .2H 2 Lazulite (MgFe)Al*paO + Aq Wavellite 2A1 2 P 2 8 .H6A120 6 .9H2 Topaz 5Al 2 Si0 5 .A12SiF 10 Cryolite Al 2 F 6 .6NaF Diaspore H 2 A12Q 4 Beauxite H6A1*0 6 Alurainite . . . . . . A12S06.9H2Q Al unite K2S0 4 .A12c 3 12 .2H2A120 6 One would suppose that since aluminium occurs in such abund- ance over the whole earth that we literally tread it under foot, it would be extracted and applied to numberless uses, being made as abundant and useful as iron ; but such is not the case. Beauxite and cryolite are the minerals most used for producing aluminium, and their preference lies mainly in their purity. Na- tive alums generally contain iron, which must be removed by expensive processes. BEAUXITE. Beauxite is a combination between diaspor, A1 2 O 3 .3H 2 O, and brown hematite, Fe 2 O 3 .3H 2 O ; or, it is diaspor with aluminium replaced more or less by iron the larger the amount of iron, the more its color changes from white to brown. It w r as first found in France, near the town of Beaux, large deposits occurring in the departments of Var and Benches du Rhon, extending from Tarascon to Antibes. Several of these beds are a dozen yards thick, and 160 kilometers in length. Deposits are also found in the departments of 1'Herault and PArriege. Very important beds are found in Styria, at Wochein, and at Freisstritz, in Aus- tria, a newly discovered locality where the mineral is called Wocheinite. Here it has a dense, earthy structure, while that of France is conglomerate or oolitic. Deposits similar to those of France are found in Ireland at Irish Hill, Straid, and Glenravel. Further deposits are found in Hadamar in Hesse, at Klein Stein- heim, Langsdorff, and in French Guiana. The following analyses give an idea of the peculiar composi- tion of this mineral ; besides the ingredients given there are also 48 ALUMINIUM. traces of lime, magnesia, sulphuric, phosphoric, titanic and van- adic acids. a. b. c. d. e. /. A1 2 3 . . 60 75 63 16 72 87 44 4 54 1 Fe 2 G 3 . . 25 12 23 55 13 49 30 3 10 4 SiO 2 3 1.0 4 15 4 25 15 12 K 2 and Na 2 . . H 2 12.0 12.0 0.79 8.34 0.78 8.50 9.7 29 9 ff- h. i. k. I. m. A1 2 3 64.6 29.80 48 12 43 44 61 89 45 76 Fe 2 3 2.0 3.67 2.36 2 11 1 96 18 96 SiO 2 7.5 44.76 7.95 15 05 6 01 6 41 K 2 and Na 2 . . H 2 . 24 7 13 86 40 33 35 70 27 82 0.38 27 61 w. o. P- ? r. A1 2 Q3 55 61 76 3 50 85 49 02 73 00 Fe 2 3 7 17 6 2 14 36 12 90 4 26 SiO 2 4 41 11.0 5 14 10 27 2 15 K 2 and Na 2 . . H 2 32.33 26.4 0.26 28 38 0.31 25 91 18 66 Index : a and c. d. e. f> 9- h. i, k. I. m and o, and b. from Beaux (Deville). dark 1 Wocheinite ( D recnsler ). light J red brown - \ Beauxite from Feisstritz (Schnitzer). yellow white white Wocheinite (L. Mayer and 0. Wagner). Beauxite from Irish Hill. " " Co. Antrine (Spruce). " Glenravel (F. Hodges). n. " " Hadamar (Hesse) (Retzlaff). from Klein-Steinheim (Bischof). 7. from Langsdorff (I. Lang). Beauxite from Dublin, Ireland, brought to the Laurel Hill Chemical Works, Brooklyn, L. I., and there used for making alums. It is dirty white, hard, dense, compact, and in addition to the ingre- ' dients given above contains 0.59 per cent, of lime, and some titanic acid. It costs $6 per ton laid down in the works. The above analysis, made by Mr. Joiiet, is furnished me by the kindness of the superintendent of the works, Mr. Herreshoff'. OCCURRENCE OF ALUMINIUM IX NATURE. 49 As is seen from the above analyses, the percentage of alumina is very variable, and cannot be determined at all simply by in- spection, but only by an analysis, for often the best-looking speci- mens are the lowest in this base. For instance, a beauxite con- taining 62.10 A1 2 O 3 , 6.11 Fe 2 O 3 , 5.06 SiO 2 , and 20.83 H 2 O was much darker and more impure-looking than that from Wochein (A), which contained only 29.8 per cent, of alumina. Beauxite has until recently not been found in the United States, but in 1887 a deposit was discovered in Floyd County, Ga., which is described as follows in a paper read by Mr. Edward Nichols before the American Institute of Mining Engineers at their Duluth meeting, July, 1887. " Numerous float specimens, covering an area of about one- half an acre, indicate the location of the main deposit, which has thus far been opened to an inconsiderable extent only. The excavations show the beauxite to exist apparently as large masses in clay. The formation is determined by the Geological Survey of Georgia to be Lower Silurian. The surface in the immediate vicinity is covered with numerous fragments of chert, a charac- teristic rock throughout this formation in Georgia. An exami- nation of the mineral shows it to have the oolitic structure com- mon to several beauxites. It varies in color from light-salmon to dark-red, according to the content of iron sesquioxide. The light-colored specimens are comparatively soft, while the dark- colored are much harder, spots in them being harder than quartz. The chemical composition is interesting because of the presence of titanic acid, in which it resembles the mineral found in Asia Minor. It dissolves with difficulty in acids, but fuses easily with potassium acid-sulphate. Owing to the purity of the deposit, it seems likely to have a value before long for use in some alu- minium reduction process, or as a refractory material." Analyses SiO 2 Al0 8 Fe 2 3 TiO 2 H 2 CaO MgO P2Q5 4 Dark specimen. 2.800 Light specimens. 2.300 57.248 56.883 3.212 1.490 3.600 3.551 0.06J 52.211 13.504 3.520 27.721 0. 0. 50 ALUMINIUM. CRYOLITE. Cryolite was first found at Ivigtuk in Arksut-fiord, west coast of Greenland, where it constitutes a large bed or vein in gneiss. It was very rare even in mineralogical collections until 1855, when several tons were carried to Copenhagen and sold under the name of " soda mineral." It is a semi-transparent, snow-white mineral. When impure it is yellowish or reddish, even sometimes almost black. It is shining, sp. gr. 2.95, and hardness 2.5 to 3. It is brittle, not infrequently contains ferrous carbonate, sulphide of lead, silica, and sometimes columbite. It is fusible in the flame of a candle, and on treatment with sulphuric acid yields hydrofluoric acid. As will be seen further on, cryolite was first used by the soap-makers for its soda ; it is still used for making soda and alumina salts, and to make a white glass which is a very good imitation of porcelain. The Pennsylvania Salt Company in Philadelphia import it from Ivigtuk by the shipload for these purposes ; lately they have discontinued making the glass. Cyrolite is in general use as a flux. A very complete description of the deposit at Ivigtuk can be found in Hoffman's " Chemische Industrie.'' Pure cryolite contains Aluminium .13.0 Fluorine '.'.'.. . 54.5 Sodium . . 32.5 100.00 Or otherwise stated Aluminium fluoride ...... 40.25 Sodium fluoride 59.75 100.00 From the reports in the Mineral Resources of the United States we find that there was imported by the Pennsylvania Salt Company in 1887, 11,732 tons, which was valued at nearly $15 a ton. The importers say this value is too low; they sell what they call pure prepared cryolite at $125 a ton. This so called pure article was found by Prof. Rogers, of Milwaukee, to contain 2 per cent, of silica and 1 per cent, of iron. OCCURRENCE OF ALUMINIUM IN NATURE. 51 The only known deposit of cryolite in the United States is that found near Pike's Peak, Colorado, and described by "W. Cross and W. F. Hillebrand in the "American Journal of Science/' October, 1883. It is purely of mineralogical import- ance and interest, occurring in small masses as a subordinate constituent in certain quartz and feldspar veins in a country rock of coarse reddish granite. Zircon, astrophyllite, and columbite are the primary associated minerals, the first only being abundant. CORUNDUM. Until 1869, the sole sources of corundum were a few river washings in India and elsewhere, where it was found in scattered crystals. Its cost was twelve to twenty-five cents a pound. Within the last twenty years numerous mines have been opened in the eastern United States, the first discovery of which was due to Mr. W. P. Thompson, and is thus described by him :* " In 1869, in riding over a spur of the Alleghenies in Northern Georgia, I found what has proven to be an almost inexhaustible mine of corundum in the crysolite serpentine, the first instance on record of the mineral being found in situ. Previously it had been washed out of debris at Cripp's Hill, N. C., and at a mine in West Chester, Pa., both on the slopes of the crysolite ser- pentine. The clue being thus obtained accidentally, about thirty mines were shortly afterwards discovered in the same formation ; but of the thousands of tons thus far dug out the larger portion has come from the mines I discovered. " At present it can be bought at about ten dollars per ton at the mines. It is nearly pure alumina. Disapore, a hydrated aluminia, is also found in the same region and locality. Corun- dum will probably always be the principal source in America of material from which to manufacture pure aluminiun ; but in Great Britain, in all probability, manufacturers must look to alumina prepared artificially from cryolite or from sulphate of alumina." In 1887, the production of corundum in the United States was * Journal of the Society of Chemical Industry, April, 1886. 52 ALUMINIUM. practically limited to the mines of the Hampden Emery Company at Laurel Creek, Ga., and at Corundum Hill, Macon County, N. C., these mines furnishing somewhat over 600 tons. The Unionville Corundum Mines Company operate a mine at Union- ville, Chester County, Pa., but the extent of their output is not given. NATIVE SULPHATE OF ALUMINA. In the summer of 1884, a large deposit of rock called " native alum" was discovered on the Gila Eiver, Sorocco County, New Mexico, about two miles below the fork of the Little Gila, and four miles below the Gila Hot Springs. The deposit is said to extend over an area one mile square and to be very thick in places. The greater part of the mineral is impure, as is usual with native occurrences, but it is thought that large quantities are available. A company formed in Sorocco has taken up the alum-bearing ground. Through the kindness of Mr. W. B. Spear, of Phila- delphia, the author was enabled to get a specimen of the mineral. It is white, with a yellowish tinge. On examining closely it is seen to consist of layers of white, pure-looking material ar- ranged with a fibrous appearance at right angles to the lamination. These layers are about one-quarter of an inch thick. Separating them are thin layers of a material which is deeper yellow, harder and more compact. The whole lump breaks easily, and has a strong alum taste. On investigation, the fibrous material was found to be hydrated sulphate of alumina, the harder material sulphate of lime. It is probable that this deposit was the bed of a shallow lake in which the alum-bearing water from the hot springs concentrated and deposited the sulphate of alumina. Periodically, or during freshets, the Little Gila, flowing through a limestone country, bore into this lake water containing lime, which, meeting the aluminium sulphate solution, immediately caused a deposit of calcium sulphate. When the dry season came, the Little Gila dried up, the deposit of alum was made, and thus were formed the succession of layers through the deposit. Analysis showed 7 to 8 per cent, insoluble material, and the PHYSICAL PROPERTIES OF ALUMINIUM. 53 remainder corresponded to the formula A1 2 (SO 4 ) 3 .18H 2 O. A small amount of iron was present. [Further information about some of the native aluminous minerals has unavoidably fallen into the chapter describing aluminium compounds.] CHAPTER III. PHYSICAL PROPERTIES OF ALUMINIUM. COMMERCIAL aluminium is never chemically pure, and there- fore displays properties varying more or less from those of the pure metal according to the character and amount of impurities present. In this treatise, whenever the properties of aluminium are mentioned they must be understood to refer to the chemically pure metal, and not to the commercial article unless specifically stated. The impurities most frequently present in commercial alumin- ium are iron and silicon. These are found in all brands, varying in amount from 1 per cent, in the purest to 6 and even 8 per cent, in the worst. Besides these, various other impurities are found coming from accidental sources in the manufacture ; thus, some of the first metal made by Deville contained a large amount of copper (analysis 1), coming from boats of that metal which he used in his experiments. Metal made later by Deville contained zinc, coming from zinc muffles which he had borrowed and used for retorts, old retorts broken up having been used in the com- position of the new ones. More recently, aluminium has been produced by the agency of sodium in the presence of lead, which latter it takes up in small amount. Sodium is liable to remain alloyed in very small proportion, yet it is an element so easily at- tacked that it destroys some of the most valuable qualities of the aluminium. The distinct effect, however, of each of these usual impurities in modifying the physical properties of aluminium has not yet been investigated in a thoroughly satisfactory manner. 54 ALUMINIUM. A few years more, however, of increasing familiarity with and handling of the metal on a large commercial scale will, I believe, cause the effect of foreign elements on aluminium to be as plainly recognized as is now the case with carbon and the metalloids in iron. In general, we may say that silicon seems to play a role in aluminium closely analogous to that of carbon in iron ; the purest aluminium is fibrous and tough, but a small percentage of silicon makes it crystalline and brittle. Carbon, moreover, is said to be dissolved by molten aluminium and to modify its properties quite materially ; yet, if so, almost nothing more is known about its influence than this unsatisfactory statement. Here is excel- lent room for work for some investigator who, as Hampe has done with copper, will prepare the purest aluminium, and by adding to it known impurities tell us precisely, beyond doubt, how these various foreign elements affect its properties. The following analyses will show the amount of impurities pres- ent in commercial aluminium, and also, incidentally, the im- provement which has been achieved since the beginning of the industry in 1854 : 1. Deville Process . 2. " " . 3. " " . 4. " " . 5. " " . 6. " " . 7. Tissier Bros. . 8. Moriii & Co., Nanterre 9. " 10. " 11. " " 12. Merle & Co., Salindres 13. " 14. " 15. " 16. Frishmuth .. 17. " .. 18. Hall's Process .. 19. Deville-Castner . 20. Grabau Process . 21. " " Aluminium. Silicon. Iron. 88.350 2.87 2.40 92.500 0.70 6.80 92.000 0.45 7.55 92.969 2.149 4.88 94.700 3.70 1.60 96.160 0.47 3.37 94.800 0.80 4.40 97.200 0.25 2.40 97.000 2.70 0.30 98.290 0.04 1.67 97.680 0.12 2.20 96.253 0.454 3.293 96.890 1.270 1.840 97.400 1.00 1.30 97.600 0.40 1.40 97.49 1.90 0.61 97.75 1.70 0.55 98.34 1.34 0.32 99.20 0.50 0.30 99.62 0.23 0.15 99.80 0.12 0.08 PHYSICAL PROPERTIES OF ALUMINIUM. 55 Notes on the above analyses : 1. Analyzed by Salvetat. Contained also 6.38 per cent, of copper and a trace of lead. 2 and 6. Analyzed by Dumas. 3. Parisian aluminium bought in La Haag. 4. Analyzed by Salvetat. Contained also a trace of sodium. 5. Parisian aluminium bought in Bonn and analysed by Dr. Kraut. 7. Made at the works near Rouen, in 18f8, from cryolite. Analyzed by Demondeur. 8. Analyzed by Sauerwein. Contained also traces of lead and sodium. 9. Analyzed by Morin. Average of several months' work. 10, 11. Analyzed by Kraut. Represents the best product of the French works sent to the London Exhibition in 1862. 12, 13. Analyzed by Mallet. The best metal which could be bought in 1880. Purchased in Berlin by Mallet and used by him as the material which he purified and used for determining the atomic weight of aluminium. 14, 15. Analyzed by Hampe. This was the purest metal which could be bought in 1876. No. 14 contained also 0.10 per cent, of copper and 0.20 per cent, of lead. No. 15 contained 0.40 per cent, of copper and 0.20 per cent, of lead. 16. Bought in Philadelphia as Frishmuth's aluminium, in 1885, and analyzed by the author. 17. Specimen of the metal composing the tip of the Washington Monument, cast by Frishmuth. This analysis is reported by R. L. Packard in the Mineral Resources of the United States, 1883-4. 18. The best grade of metal made by this process, analyzed by Hunt & Clapp, Pittsburgh. For average analyses, etc., see description of process. 19. The best grade made by this process, exhibited at the Paris Exposition, 1889. Analyzed by Cullen. 20. Analysis by Dr. Kraut of metal being made on a commercial scale. 21. Analysis by Grabau of the purest metal yet obtained by his process. According to Rammelsberg (KerPs Handbuch) the silicon which is always found in aluminium is in part combined with it, and this combined silicon changes by treatment with hydrochloric acid into either silica, which remains, or into silicon hydride, SiH 4 , which escapes ; while another part of it is combined with the aluminium just as graphite is with iron; and this part re- mains on treatment with acid as a black mass not oxidized by ignition in the air. Two analyses of aluminium reduced from cryolite by sodium in a porcelain crucible gave i. 2. Silicon obtained as silica .... 9.55 1.85 Free silicon 0.17 0.12 Silicon escaping in SiH 4 .... 0.74 0.58 56 ALUMINIUM. One sample of aluminium analyzed by Professor Rammelsberg contained as much as 10.46 per cent, of silicon, and another sample even 13.9 per cent. The quantity of iron varied from 2.9 to 7.5 per cent. M. Dumas found that aluminium usually contains gases, about which he makes the following statements :* On submitting alu- minium in a vacuum to the action of a gradually increasing tem- perature up to the softening point of porcelain, and letting the mercury pump continue acting on the retort until it was com- pletely exhausted, considerable quantities of gas were withdrawn. The liberation of the gas from the metal seems to take place sud- denly towards a red-white heat. 200 grammes of aluminium, oc- cupying 80 c.c., gave 89.5 c.c. of gas, measured at 17 and 755 mm. pressure. The gas consisted of 1.5 c.c. carbonic acid, and 88 c.c. hydrogen. Carbonic oxide, nitrogen and oxygen were absent. The author has observed that molten aluminium will absorb large quantities of gas. On passing sulphuretted hydrogen into the melted metal for about twenty minutes some aluminium sul- phide was formed while the metal appeared to absorb the gas. On pouring, the metal ran very sluggishly with a thick edge, but when just on the point of setting gas was disengaged so actively that the crackling sound could be heard several feet away, and the thick metal became suddenly quite fluid and spread over the plate in a thin sheet. The gas disengaged seemed by its odor to contain a good proportion of sulphuretted hydrogen, although free hydrogen may have been present in it. COLOR. Deville : The color of aluminium is a beautiful white with a slight blue tint, especially when it has been strongly worked. Being put alongside silver, their color is sensibly the same. However, common silver, and especially that alloyed with copper, has a yellow tinge, making the aluminium look whiter by com- parison. Tin is still yellower than silver, so that aluminium pos- sesses a color unlike any other useful metal. * Comptes Rendue xc. 1027 (1880). PHYSICAL PROPERTIES OF ALUMINIUM. 57 Mallet : Absolutely pure aluminium is perceptibly whiter than the commercial metal ; on a cut surface very nearly pure tin- white, without bluish tinge, as far as could be judged from the small pieces examined. The purest aluminium examined by the author is that made by Grabau. On a fresh fracture it is absolutely white, but on long exposure to the air it takes a faint, almost imperceptible bluish tint. On a cut surface it has the faintest suspicion of a yellow tint, not so decided as the yellowish color of pure tin. Ordinary commercial aluminium is bluish on a fresh fracture, the tint being deeper the greater the amount of impurities it con- tains. A specimen with 10 per cent, of silicon and 5 per cent, of iron was almost as blue as lead. It is my belief that a very small percentage of copper closes the grain and whitens the fracture a little ; I have also found that chilling suddenly from a high tem- perature has the same effect. When ingots of aluminium are ex- posed a long time to damp air the thin film of oxide forming 011 them gives a more decided bluish cast to the metal, since the coating is perfectly snow-white and hence, by contrast, heightens the bluish tint of the metallic back-ground. Mourey recom- mended removing this discoloration by placing the articles first in dilute hydro-fluoric acid, 1000 parts of water to 2 of acid, and afterwards dipping in nitric acid. The oxide would thus be dissolved and the original color restored. Pure aluminium pos- sesses to the highest degree that property expressed best by the French term " eclat." It is rather difficult to see why the blue tint should be more prominent after the metal has been worked, yet I think two reasons will explain this phenomenon ; first, alu- minium is not a hard metal, and on polishing or burnishing par- ticles of dirt or foreign substances are driven into the pores of the metal, thereby altering its color slightly ; second, any metal looks whiter when its surface is slightly rough than when highly pol- ished, in the latter case it being as much the reflected color of the general surroundings as the color of the metal itself which is seen. I have never seen any highly polished white metal which did not look bluish especially when reflecting out-door light. I think this explains why opera glasses, rings, jewelry, etc., generally look bluer than the bar or ingot-metal from which they are made. 58 ALUMINIUM. Aluminium takes a very beautiful mat which keeps almost in- definitely in the air, the surface thus slightly roughened appear- ing much whiter than the original polished surface. Aluminium can be polished and burnished without much difficulty if attention is given to a few particulars which it is necessary to observe. (For methods of polishing, etc., see Chapter XIII.) FRACTURE. A cast ingot of purest aluminium has a slightly fibrous struct- ure, a section J inch thick bending twenty degrees or so from a straight line when sharply bent before showing cracks at the outside of the turn. The fracture of such an ingot is uneven, rough, and very close, often showing a curious semi-fused appear- ance, as if it had been already exposed to heat and the sharpest j joints melted down. However, only the purest varieties show these peculiarities. Metal containing 96 to 97 per cent, of aluminium begins to show a crystalline structure, breaks short, and with a tolerably level surface. Metal less than 95 per cent, pure shows large shining crystal surfaces on the fracture, the smaller crystals being on the outside of the ingot where it has been cooled most quickly, while in the centre the crystalline sur- faces may be as large as y 1 ^ inch in diameter. A specimen con- taining only 85 per cent, of aluminium broke as short as a bar of autimonial lead, with a large granular, crystalline surface. Working the metal increases its fibrousness greatly, the section of a square rolled bar of good metal looking very much like that of a low-carbon steel. HARDNESS. The purest aluminium is distinctly softer than the commercial, estimated on the scale of hardness proposed by Mohs it would be written as about 2.5, that is, a little harder than can be scratched by the nail. It is not so soft as pure tin. The presence of impurities, however, rapidly increases the hardness. While 99 per cent, aluminium can be cut smoothly with the knife and shavings turned up almost as with pure tin, yet 95 per cent, metal PHYSICAL PROPERTIES OF ALUMINIUM. 59 can hardly be cut at all, the shavings break off short and a fine grating is felt through the blade. Experience in testing various specimens of commercial alumin- ium with the knife will, I am sure, enable a person to become quite skilful in determining the purity and in separating different grades from each other. Taking this test in connection with the breaking and surface of fracture, it appears to me that these indications are as significant and can be made of as much use as the corresponding tests for iron, steel, and other metals. Mr. Joseph Richards, the author's father, having had many years' experience in testing lead, tin, zinc, and similar metals, in which the knife blade has been put to good service, has been able with very little practice to arrange a number of specimens of alumin- ium correctly according to their purity simply by noting care- fully the way they cut and the color of the cut surface. These tests will in the future, I am sure, be of great use to those hand- ling aluminium on a large scale, especially in the works where it is produced. Aluminium becomes sensibly harder after being worked, prob- ably owing to the closing of the grain, since we know that its density is also increased. SPECIFIC GRAVITY. Mallet : The specific gravity of absolutely pure aluminium was carefully determined at 4 C., and the mean of three closely agreeing observations gave 2.583. Commercial aluminium is almost always heavier than this, but the increase is not in direct proportion to the amount of im- purities present. There are two reasons why this last statement is correct; first, we cannot say what expansion or contraction may take place in forming the alloy ; second, while most of the impurities which occur are much heavier than aluminium, yet silicon, the most frequent of all, has a specific gravity of only 2.34 (Deville's determination), and therefore acts in the opposite direction to the other impurities, though not to as great an extent. The following analyses and specific gravities may give some in- formation on this point : 60 ALUMINIUM. SPECIFIC GRAVITY. Aluminium. Silicon. Iron. Observed. Calculated. 97.60 0.60 1.80 2.735 2.61 (2.64) 95.93 2.01 2.06 2.800 2.61 (2.69) 94.16 4.36 1.48 2.754 2.59 (2.74) 78. 16. 4. 2.85 2.66 It is seen in each case that the calculated specific gravity is much less than the observed, which would show contraction in volume by alloying. Indeed, this is a prominent characteristic of aluminium alloys, aluminium often taking up several per cent, of its weight of another metal without its volume being increased, the particles of the other metal seeming to pass between those of the aluminium ; thus probably accounting for the extraordinary strength and closeness of many of the aluminium alloys. This subject is treated more at length in the chapter on alloys. We can see the large contraction taking place by inspecting the numbers in parentheses under the heading "Calculated." These are computed on the supposition that the volume of the impure alu- minium is equal to that of the pure aluminium entering into it. As these numbers are also less than the observed specific gravi- ties, the extraordinary fact is shown that aluminium can absorb several per cent, of iron and silicon and yet will decrease in volume in doing so. The remarks thus far made are based on the gravity of cast metal. Aluminium increases in density by being worked ; De- ville states that metal with a specific gravity of 2.56 had this increased to 2.67 by rolling, which, he says, may explain the differences existing in its properties after being annealed or worked. He remarked further that heating this rolled metal to 100, and cooling quickly changed its specific gravity very little, lowering it to 2.65. I have observed that on heating a piece of aluminium almost to its fusing point and suddenly chilling it in water, its specific gravity was lowered from 2.73 to 2.69. The low specific gravity of aluminium, when compared to those of the other metals, is (in the words of a recent lecturer) " the physical property on which our hopes of the future usefulness of aluminium chiefly rest." The following table will facilitate this comparison : PHYSICAL PROPERTIES OF ALUMINIUM. 61 SPECIFIC GRAVITY. Water = 1. Alumin- Pounds in a Kilos in a iuin = 1. cubic foot, cubic meter. Platinum . 21.5 8.3 1344 21,500 Gold . 19.3 7.4 1206 19,300 Lead . 11.4 4.6 712 11,400 Silver . . 10.5 4.0 656 10,500 Copper . . 8.9 3.5 557 8,900 Iron and steel . 7.8 2.8 487 7,800 Tin 7.3 2.7 456 7,300 Zinc . 7.1 2.7 444 7,100 Aluminium . . 2.6 1.0 163 2,600 In comparing the price of aluminium with that of the metal it is to replace, for such purposes where the bulk of the article is fixed, such as tableware, jewelry, engineering instruments, and a large proportion of all its uses, it is important to take its low specific gravity into the account. Thus, for making spoons, alu- minium at $4 per Ib. would be as cheap as silver at $1 per lb., since the silver spoons would be four times as heavy. So for such purposes, at the prices prevailing to-day, aluminium is practically only one-tweuty-fifth as costly as silver. FUSIBILITY. Deville : Aluminium melts at a temperature higher than that of zinc, lower than that of silver, but approaching nearer to that of zinc than silver. It is, therefore, quite a fusible metal. Mallet : It seems that pure aluminium is a little less fusible than the commercial metal. Picktet determined the melting point to be 600, Heeren about 700, while Van der Weyde placed it as high as 850.* Prof. Carnelley has lately determined this point himself, and found that a sample containing J per cent, of iron melted at 700, while one with 5 per cent, of iron did not fuse completely until above 730. These numbers can be accepted as the best determinations yet made, and it results from them that iron raises the melting point and hinders fluid fusion. Since it is already conceded that silicon raises the melting point until, with * Carnelley's Tables of Melting Points. 62 ALUMINIUM. a large percentage, the metal can hardly be made fluid at any heat, it is rather puzzling to see why the absolutely pure metal should be less fusible than the commercial metal, as is remarked by Mallet. It may be that the small percentages of iron and silicon present in a high grade of commercial metal act in a man- ner contrary to the effect of larger percentages, as is known to be true in a few instances with the impurities present in other metals, but we have no definite information to bring forward on this point. VOLATILIZATION. Deville : Aluminium is absolutely fixed, and loses no part of its weight when it is violently heated in a forge fire in a carbon crucible. This statement was made in 1859, and can still be accepted as true as far as ordinary furnace temperatures are concerned. But, with the use of the electric furnace, temperatures have been at- tained at which aluminium does sensibly volatilize. In Cowles Bros, electric furnace it is stated that the aluminium is almost all produced as vapor and as such is absorbed by the copper or iron present, when these are not present it is found condensed in the cooler upper-part of the furnace. A similar experience has been met in other electric furnace processes, so that the volatilization of aluminium at these extreme temperatures may be accepted as a fact. ODOR. Deville : The odor of pure aluminium is sensibly nothing, but the metal strongly charged with silicon will exhale the odor of silicuretted hydrogen, exactly represented by the odor of cast iron. But even under these unfavorable circumstances, the smell of the metal is only appreciable to persons experienced in judging very slight sensations of this kind. TASTE. Deville : Pure aluminium has no taste, but the impure and odorous metal may have a taste like iron, in any case only very slight. PHYSICAL PROPERTIES OF ALUMINIUM. 63 MAGNETISM. Deville : I have found, as also MM. Poggendorff and Reiss, that aluminium is very feebly magnetic. SONOROUSNESS. Deville : A very curious property, which aluminium shows the more the purer it is, is its excessive sonorousness, so that a bar of it suspended by a fine wire and struck sounds like a crystal bell. M. Lissajous, who with me observed this property, has taken ad- vantage of it to construct tuning forks of aluminium, which vi- brate very well. I also tried to cast a bell, which has been sent to the Royal Institution at London at the request of my friend Rev. J. Barlow, vice-president and secretary of the institution. This bell, cast on a model not well adapted to the qualities of the metal, gives a sharp sound of considerable intensity, but which is not prolonged, as if the clapper or support hindered the sound, which, thus hindered, becomes far from agreeable. The sound produced by the ingots is, on the contrary, very pure and pro- longed. In the experiments made in Mr. Faraday's laboratory, this celebrated physicist has remarked that the sound produced by an ingot of aluminium is not simple. One can distinguish, by turning the vibrating ingot, two sounds very near together and succeeding each other rapidly, according as one or the other face of the ingot faces the observer. The bell referred to above was 20 kilos in weight and 50 centi- metres in diameter, but as Deville admits, its sound was not pleasing, and a contemporary writer, evidently not very enthusi- astic in sounding the praises of aluminium, said that while the bell was highly sonorous yet it " gave a sound like a cracked pot." I have not heard that any large bell has since been cast, but it is certain that the metal in bars has a highly musical ring. Faraday's observation has also been verified, for a recent lecturer suspended by one end a bar 6 feet long, 3J inches wide, and 1J inches thick, and on striking it a prolonged vibration ensued, two 64 ALUMINIUM. notes being recognized, A sharp and D sharp, the latter more subdued. CRYSTALLINE FORM. Deville : Aluminium often presents a crystalline appearance when it has been cooled slowly. When it is not pure the little crystals which form are needles, and cross each other in all directions. When it is almost pure it still crystallizes by fusion but with difficulty, and one may observe on the surface of the ingots hexagons which appear regularly parallel along lines which centre in the middle of the polygon. It is an error to conclude from this observation that the metal crystallizes in the rhombo- hedral system. It is evident that a crystal of the regular system may present a hexagonal section ; while on the other hand, in preparing aluminium by the battery at a low temperature, I have observed complete octahedrons which were impossible of measurement it is true, but their angles appeared equal. ELASTICITY. Deville : M. Wertheim has found that the elasticity of alumin- ium just cast is sensibly the same as that of silver; but when worked it resembles that of soft iron, becoming more rigid and elastic, and giving the sound of steel when dropped on a hard body. Mallet remarked that absolutely pure aluminium seemed to be less hardened by hammering than ordinary commercial metal. A German firm engaged in making aluminium state that by long, gradual cooling from a red heat aluminium can be made so elastic that it can even be used for hair springs for watches. Annealing by cooling quickly from a red heat makes the metal soft. Aluminium stiffens up very quickly in rolling; the author's father has found the best means of removing this is to heat the metal red hot and plunge into water. Metal thus treated becomes very soft. Fine wire quickly becomes hard in drawing, but can be annealed in the heat over an argand burner. PHYSICAL PKOPERTIES OF ALUMINIUM. 65 TENACITY. "VV. H. Barlow :* A bar of aluminium three feet long and one- quarter inch square was obtained and different parts of it sub- jected to tests for tension, compression, and transverse strain, elasticity, elastic range, and ductility. It will be seen on refer- ence to the results that the weight of a cubic inch was 0.0275 pound, showing a specific gravity of 2.688, and its ultimate ten- sile strength was about twelve tons per square inch. The range of elasticity is large, the extreme to the yielding point being one-two hundredths of the length. The modulus of elasticity is 1,000,000, the extension in samples two inches long being 2.5 per cent. Taking the tensile strength of the metal in relation to its weight, it shows a high mechanical value. These results are thus tabulated : Weight of Teusile Length of a 1 cubic foot strength bar able to sup- iu pounds. per sq.in. port its weight, in pounds. in feet. Cast iron . 444 16.500 5,351 Bronze . 525 36,000 9,893 Wrought iron . 480 50,000 15,000 Steel . . 490 78,000 23,040 Aluminium . 1H8 26,800 23,040 It thus appears that taking the strength of aluminium in rela- tion to its weight, it possesses a mechanical value about equal to that of steel of 35 tons per square inch tensile strength. Kamarscht obtained the following results as to the strength of aluminium wire : DIAMETER. TENSILE STKKNHTH, GRAMMFS. TENACITY. Kilos per sq. millimetre. 12.975 12.255 12.700 11.845 These results are far below that obtained by Barlow, which is equal to 18.92 kilos per square millimetre. The latter figure is, * Rpt. Brit. A. A. S., 1882, p. 668. f Dingier, 172, p. 55. illimetres. 1st trial. 2d trial. Meau. 0.225 661 653 657 0.205 524 506 515 0.160 307 311 309 0.145 246 252 249 66 . ALUMINIUM. however, undoubtedly nearer the truth for good aluminium, since tests of the metal made by the Deville-Castner process average 25,000 to 30,000 Ibs. per square inch, being in general higher than the figure given by Barlow. MALLEABILITY. Deville : Aluminium may be forged or rolled with as much perfection as gold or silver. It is beaten into leaves as easily as they, and a very experienced gold-beater, M. Rousseau, has made leaves as fine as those of gold or silver, which are put up in books. I know of no other useful metal able to stand this treat- ment. Mallet : With absolutely pure aluminium the malleability was undoubtedly improved, the metal yielding easily to the hammer, bearing distortion well, and flattening in two or three directions without cracking. It seemed to be sensibly less hardened by hammering than the ordinary metal of commerce. Commercial aluminium is now to be had rolled into sheets of almost any size or thickness, and at only a small advance on the price of ingot metal. The only particulars in which it differs much from other metals being that it must be annealed much oftener, and requires an extraordinarily large power to roll it. Mr. J. Richards compares the cold rolling of aluminium to the hot rolling of steel in regard to the power required ; he also finds that unless the sheet is rolled until quite hard it does not polish in the rolls. The aluminium leaf is now in regular use with gilders and decorators. It was first made by M. Degousse, of Paris, and afterwards for several years by C. Falk & Co., of Vienna. The manufacture is rather more difficult than beating out gold or silver, and requires also a pure metal to stand the working. A specimen such as is sold commercially was measured by the author. He found its thickness to be 0.000,638 millimetres or one-forty thousandth of an inch, which compares favorably with that of ordinary gold leaf. It is quite possible that if a test were made with extra pure metal, this result would easily be exceeded. PHYSICAL PROPERTIES OF ALUMINIUM. 67 This leaf was not thin enough to show any color by transmitted light. Deville has stated that aluminium can be forged with as much perfection as gold or silver, but at what heat it works best is not stated. It can readily be hammered and shaped cold, like silver or copper, but it soon stiffens up, and must be kept soft by fre- quent annealing. Aluminium probably stands third in the order of malleability of the metals, gold and silver exceeding it ; while it is probably sixth in the order of ductility, being preceded by gold, silver, platinum, iron, and copper.* DUCTILITY. Deville : Aluminium behaves very well at the drawing plate. M. Vangeois obtained, in 1855, with a metal far from being pure, wires of extreme tenuity, which were used to make aluminium passementerie. However, the metal deteriorates much in the operation, and the threads become flexible again only after an annealing very delicately performed, because of the fineness of the threads and the fusibility of the metal. The heat of the air coming from the top of the chimney over an Argand burner is sufficient to anneal them. Aluminium wire is being made at present by numbers of manufacturers, the difficulties being very few when pure metal can be procured to work with. Quite a large amount of power is required for drawing when compared with other metals. Wire as fine as 0.1 millimetre in diameter can be made without very much trouble, and the use of aluminium in this form promises large development in the near future. EXPANSION BY HEAT. Fizeau is quoted as authority for the following coefficients of linear expansion of aluminium by heat : For 1 F. For 1 C. Cast aluminium .... 0.00001234 0.00002221 Crystallized aluminium . . 0.00000627 0.00001129 * Thurston's Materials of Engineering. 68 ALUMINIUM. SPECIFIC HEAT. Deville : According to the experiments of M. Regnault, the specific heat of aluminium corresponds to its equivalent 13.75, from which we may conclude that it must be very large when com- pared with all the other useful metals. One can easily perceive this curious property by the considerable time which it takes an ingot of the metal to get cold. We might even suggest that a plate of aluminium would make a good chafing-dish. Another experiment makes this conclusion very evident. M. Paul Morin had the idea of using aluminium for a plate on which to cook eggs, the sulphur of which attacked silver so easily ; and he obtained excellent results. He noticed, also, that the plate kept its heat a much longer time than the silver one. The value of this quantity has been quoted differently by different authorities. Regnault obtained 0.2143 as the mean between and 100, while Kopp obtained 0.2020. In the first case Deville remarks that the metal he gave Regnault was unfor- tunately contaminated with copper, which would lead to the sup- position that the value obtained was somewhat below the truth ; we cannot account for the lower value obtained by Kopp. How- ever these may be, more recent and probably more accurate determinations have indicated a higher value. Mallet deter- mined the specific heat of absolutely pure aluminium to be 0.2253, which, he remarked, made its atomic heat 0.2253 X 27.02 or 6.09. Naccari* observed the specific heat at different tem- peratures to be 18 50 100 200 300 0.2135 02.164 0.2211 0.2306 0.2401 The author has determined the mean specific heat from to the melting point to be 02.85, and the latent heat of fusion 29.5 calories. ELECTRIC CONDUCTIVITY. Deville : Aluminium conducts electricity with great facility, so that it may be considered as one of the best conductors known, * Transactions "Accademia di Torino," Dec. 1887. PHYSICAL PROPERTIES OF ALUMINIUM. 69 and perhaps equal to silver. I found by Wheatstone's Bridge that it conducts eight times better than iron. M. Buff has arrived at results evidently different from mine because we have not taken the same ground of comparison. The difference is due, without doubt, to the metal which he employed containing, as is easily found in many specimens, a little cryolite and fusible materials the density of which is near that of the metal, and which were employed in producing it. The complete separation of the metal and flux is a difficult mechanical operation, but which is altogether avoided by using a volatile flux. This is a condition which must be submitted to in order to get the metal absolutely pure. The exact value expressing the electric conductivity of alumin- ium is not beyond dispute. In one place we find the following relative numbers given : * At At 100 Copper . . . . . . . 45.74 33.82 Magnesium 24.47 17.50 Aluminium 22.46 17.31 M. Margottet states it as being 51.5 if copper is 100; or 33.74 silver being 100. Professor Mattheisen determined the values as follows : Pure silver 100 Commercial copper ....... 77 Commercial aluminium ...... 33.76 Watts states that the electric conductivity of aluminium is 56.1 silver being 100. Finally, Benoitf gives the mean electric resistance and conductivity at as follows, the resistance being for a wire 1 metre long, and with a cross section of 0.2 square centimetres (a column of mercury of those dimensions giving resistances of 0.9564 Ohms or 1.0 Siemens). Ohms. Siemens. Conductivity. Silver, annealed . 0.0154 0.0161 100 Copper, " . 0.0171 0.0179 90 Gold, " . . 0.0217 0.0227 71 Aluminium, annealed . 0.0309 0.0324 49.7 Magnesium, hard . 0.0423 0.0443 36.4 * Jahresb. der Chemie, 1881, p. 94. f Thurston's Materials of Engineering. 70 ALUMINIUM. If we compare these various results we find the values given to vary as follows : Silver = 100. Copper = 100. Jahresb. d. Chemie . . . f 49.10 at I $1.18 at 100 Margottet 33.74 51.5 Mattheisen . . . 33.76 43.8 Watts 56.1 Benoit 49.7 55.2 THERMAL CONDUCTIVITY. Deville : It is generally admitted that conductivity for heat and electricity correspond exactly in the different metals. A very simple experiment made by Mr. Faraday in his laboratory seems to place aluminium very high among metallic conductors. He found that it conducted heat better than silver or copper. It is altogether probable that there was some mistake made in Faraday's experiment, since, as we have seen, aluminium is inferior to silver and copper as a conductor of electricity, and recent investigations also place it inferior to them in thermal conduc- tivity. The writer before quoted (Jahresb. d. Chemie), gives these values : At At 100 Copper ;.' 0.7198 0.7226 Magnesium ..... 0.3760 0.3760 Aluminium 0.3435 0.3619 or if the conductivity of copper is 100, that of aluminium is 47.72 at and 50.0 at 100, which it may be observed agree very closely with the values found for electric conductivity by the same investigator. Calvert and Johnson determined the ratio of its conducting power for heat with that of silver to be as 665 is to 1000, which is considerably higher than the values given for electric conductivity. The fact that these values agree in general better when referred to copper, would seem to show that the variable quantity is probably the standard silver used for com- parison, although we should have expected to meet with more trouble from the copper in this respect. CHEMICAL PROPERTIES OF ALUMINIUM. 71 CHAPTER IV. CHEMICAL PROPERTIES OF ALUMINIUM. would here repeat the remark made with regard to the physical properties, that the properties to be recorded are those of the purest metal unless specifically stated otherwise. However, the high grade of commercial metal differs very little in most of its chemical properties from the absolutely pure, so that not many reservations are necessary in applying the following properties to good, commercial metal : ACTION OF AIR. Deville : Air, wet or dry, has absolutely no action on alumin- ium. No observation which has come to my knowledge is con- trary to this assertion, which may easily be proved by any one. I have known of beams of balances, weights, plaques, polished leaf, reflectors, etc., of the metal exposed for months to moist air and sulphur vapors and showing no trace of alteration. We know that aluminium may be melted in the air with impunity, therefore air and also oxygen cannot sensibly affect it: It resisted oxidation in the air at the highest heat I could produce in a cupel furnace, a heat much higher than that required for the assay of gold. This experiment is interesting, especially when the metallic button is covered with a layer of oxide which tarnishes it, the expansion of the metal causing small branches to shoot from its surface, which are very brilliant and do not lose their lustre in spite of the oxi- dizing atmosphere. M. Woliler has also observed this property on trying to melt the metal with a blowpipe. M. Peligot has profited by it to cupel aluminium. I have seen buttons of im- pure metal cupelled with lead and become very malleable. With pure aluminium the resistance of the metal to direct oxi- dation is so considerable that at the melting point of platinum it 72 ALUMINIUM. is hardly Appreciably touched, and does not lose its lustre. It is well known that the more oxidizable metals take this property away from it. But silicon itself, which is much less oxidizable, when alloyed with it makes it burn with great brilliancy, because there is formed a silicate of aluminium. While the above observations are in the main true, yet it is now well known that objects made of commercial aluminium do after a long exposure become coated with a very thin film, which gives the surface a " dead" appearance. The coating is very similar in appearance to that forming on zinc under the same circumstances. The oxidation, however, does not continue, for the film seems to be absolutely continuous and to protect the metal underneath from further oxidation. This coating can best be removed by very dilute acid (see Mourey's receipt, p. 57), after which the surface can be burnished to its former brilliancy- It has also been found that at a high white-heat, especially at the heat of an electric furnace, aluminium burns with a strong light to alumina. It is quite probable that in this case it volatilizes first, and it is the vapor which burns. During the operation of an electric furnace a white smoke formed of invisible particles of alumina is thus formed and evolved from the furnace. Also, in melting aluminium, even the purest, it will be found that the surface seems bound and the aluminium restrained from flowing freely by a minute " skin' 7 which may probably be a mixture of oxide with metal, or perhaps of oxides of foreign metals, but, nevertheless, it is always present and is therefore indicative of oxidation taking place. It seems to protect the metal beneath it perfectly, so that, ooice formed, it gets no thicker by continued heating. Wohler first discovered that when aluminium was in the extremely attenuated form of leaf it would burn brightly in air, and burn in oxygen with a brilliant bluish-light. It is also said that thin foil will burn in oxygen, being heated by wrapping it around a splinter of wood, and fine wire also burns like iron wire, but the combustion is not continuous because the wire fuses t > > quickly. The alumina resulting is quite insoluble in acids, and as hard as corundum. CHEMICAL PROPERTIES OF ALUMINIUM. 73 ACTION OF WATER. Deville : Water has no action on aluminium, either at ordi- nary temperatures or at 100, or at a red heat bordering on the fusing point of the metal. I boiled a fine wire in water for half an hour and it lost not a particle in weight. The same wire was put in a glass-tube heated to redness by an alcohol lamp and traversed by a current of steam, but after several hours it had not lost its polish, and had the same weight. To obtain any sen- sible action it is necessary to operate at the highest heat of a reverberatory furnace a white heat. Even then the oxidation is so feeble that it develops only in spots, producing almost inap- preciable quantities of alumina. This slight alteration and the analogies of the metal allow us to admit that it decomposes water, but very feebly. If, however, metal produced by M. Rose's method is used, which is almost unavoidably contaminated with slag composed of chlorides of aluminium and sodium, the former, in presence of water, plays the part of an acid towards alu- minium, disengaging hydrogen with the formation of a subchlor- hydrate of alumina, whose composition is not known, and which is soluble in water. When the metal thus tarnishes in water one may be sure to find chlorine in the water on testing it with nitrate of silver. Aluminium leaf, however, will slowly decompose water at 100. Hydrogen is slowly evolved, the leaf loses its brilliancy, becomes discolored, and after some hours translucent. It is eventually entirely converted into gelatinous hydrated alumina. ACTION OF HYDROGEN SULPHIDE AND SULPHUR. Deville : Sulphuretted hydrogen exercises no action on alu- minium, as may be proved by leaving the metal in an aqueous solution of the gas. In these circumstances almost all the metals, and especially silver, blacken with great rapidity. Sulph-hydrate of ammonia may be evaporated on an aluminium leaf, leaving on the metal only a deposit of sulphur, which the least heat drives away. Aluminium may be heated in a glass tube to a red heat in 74 ALUMINIUM. vapor of sulphur without altering the metal. This resistance is such that in melting together polysulphide of potassium and some aluminium containing copper or iron, the latter are attacked without the aluminium being sensibly affected. Unhappily, this method of purification may not be employed because of the pro- tection which aluminium exercises over foreign metals. Under the same circumstances gold and silver dissolve up very rapidly. However, at a high temperature I have observed that it com- bines directly with sulphur to give aluminium sulphide. These properties varying so much with the temperature form one of the special characteristics of the metal and its alloys. Margottet states that hydrogen sulphide is without action on aluminium, as also are the sulphides of iron, copper, or zinc. Aluminium is said to decompose silver sulphide, Ag 2 S, setting the sulphur, however, at liberty and alloying with the silver. In regard to its indifference to the first mentioned sulphides, this would give inferential evidence that the reverse operation, i. e., the action of iron, copper, or zinc on aluminium sulphide, would be possible, as will be seen later to be apparently established by direct experiment. As to the action of sulphuretted hydrogen, the author has a different experience to quote. On passing a stream of that gas into commercial aluminium melted at a red heat, little explosive puffs were heard accompanied by a yellow light, while the dross formed on the surface, when cooled, evolved sulphuretted hydrogen briskly when dropped into water, and gave every indication of containing aluminium sulphide. It could not have been silicon sulphide, for the metal contained as large a percentage of silicon after treatment as before. Hydro- gen sulphide is also absorbed in large quantity by molten alu- minium, and mostly evolved just as the metal is about to set. Some of the gas is entangled in the solidifying metal, forming and filling numerous cavities or blow-holes. SULPHURIC ACID. Deville: Sulphuric acid, diluted in the proportion most suit- able for attacking the metals which decompose water, has no action on aluminium ; and contact with a foreign metal does not CHEMICAL PROPERTIES OF ALUMINIUM. 75 help, as with zinc, the solution of the metal, according to M. de la Rive. This singular fact tends to remove aluminium con- siderably from those metals. To establish it better, I left for several months some globules weighing only a few milligrammes in contact with the weak acid, and they showed no visible altera- tion ; however, the acid gave a faint precipitate when neutralized with aqua ammonia. Margottet : Sulphuric acid, dilute or concentrated, exercises in the cold only a very slight sensible action on aluminium, the pure metal is attacked more slowly than when it contains foreign metals. The presence of silicon gives rise to a disengagement of silicon hydride (SiH 4 ), which communicates to the hydrogen set free a tainted odor. Concentrated acid dissolves it rapidly with the aid of heat, disengaging sulphurous acid gas (SO 2 ). NITRIC ACID. Deville : Nitric acid, weak or concentrated, does not act on alu- minium at the ordinary temperature. In boiling acid solution takes place, but with such slowness that I had to give up this mode of dissolving the metal in my analyses. By cooling the solution all action ceases. On account of this property, M. Hulot obtained good results on substituting aluminium for platinum in the Grove battery. HYDROCHLORIC ACID. Deville : The true solvent of aluminium is hydrochloric acid, weak or concentrated ; but, when the metal is perfectly pure, the reaction takes place so slowly that M. Favre, of Marseilles, had to give up this way of attack in determining the heat of a com- bination of the metal. But, impure aluminium is dissolved very rapidly. At a very low temperature gaseous hydrochloric acid attacks the metal and changes it into chloride. Under these cir- cumstances iron does not seem to alter ; able, no doubt, to resist by covering itself with a very thin protecting layer of ferrous chloride. This experiment would lead me to admit that it is the acid and not the water \vhich is decomposed by aluminium ; and, 76 ALUMINIUM. in fact, the metal is attacked more easily as the acid is more con- centrated. This explains the difference of the action of solutions of hydrochloric and sulphuric acids, the latter being almost inac- tive. This reasoning applies also to tin. When the metal contains silicon it disengages hydrogen of a more disagreeable smell than that given out by iron under similar circumstances. The reason of this is the production of that remarkable body recently discovered by MM. Wohler and Buff silicuretted hydrogen. When the proportion of silicon is small, the whole is evolved as gas ; when increased a little, some remains in solution with the aluminium, and then it re- quires great care to separate the metal exactly even when the solution is evaporated to dry ness. If 3 to 5 per cent, of silicon is present, it remains insoluble mixed with a little silica, as has been cleverly proven by Wohler and Buff, by the action of hydro- fluoric acid, which dissolves the silica with evolution of hydrogen without attacking the silicon itself. On dissolving commercial aluminium there is sometimes obtained a black crystalline resi- due, which separated on a filter and dried at 200 to 300 takes fire in places; this residue is silicon mixed with some silica. The presence of silicon augments very much the facility with which aluminium is attacked by hydrochloric acid. If hydrochloric acid is present in a mixture of acids, it begins the destruction of the metal. Hydrobromic, hydriodic, hydro- fluoric acids are said to act very similarly to hydrochloric. ORGANIC ACIDS, VINEGAR, ETC. Deville : Weak acetic acid acts on aluminium in the same way as sulphuric acid, i. e., in an inappreciable degree or with extreme slowness. I used for the experiment acid diluted to the strength of strongest vinegar. M. Paul Morin left a plaque of the metal a long time in wine which contained tartaric acid in excess and acetic acid, and found the action on it quite inappreciable. The action of a mixture of acetic acid and common salt in solution in pure water on pure aluminium is very different, for the acetic acid replaces a portion of the chlorine existing in the sodium CHEMICAL PROPERTIES OF ALUMINIUM. 77 chloride, rendering it free. However, this action is very slow, especially if the aluminium is pure. The practical results flowing from these observations deserve to be clearly defined, because of the applications which may be made of aluminium to culinary vessels. I have observed that the tin so often used and which each day is put in contact with common salt and vinegar, is attacked much more rapidly than aluminium under the same circumstances. Although the salts of tin are very poisonous, and their action on the economy far from being negligible, the presence of tin in our food passes unperceived because of its minute quantity. Under the same circumstances aluminium dissolves in less quantity ; the acetate of aluminium formed resolves itself on boiling into insoluble aluminia or an insoluble sub-acetate, having no more taste or action on the body than clay itself. It is for that reason and because it is known that the salts of the metal have no appreciable action on the body, that aluminium may be considered as an absolutely harm- less metal. It may be appropriately remarked here that the rapid tar- nishing of polished aluminium articles is more frequently due to the effect of handling than to any other cause. The perspiration contains about 2 per cent, of sodium chloride and about an equal quantity of organic acids ; its action on aluminium is not very great, yet almost always sufficient to spoil a high polish and give a visible tarnish. AMMONIA. Aqua ammonia acts slowly on aluminium, producing a little alumina, part of which remains dissolved. Ammonia gas does not appear to act on the metal. CAUSTIC ALKALIES. Deville : Alkaline solutions act with great energy on the metal, transforming it into aluminate of potash or soda, setting free hydrogen. However, it is not attacked by caustic potash or soda in fusion ; one may, in fact, drop a globule of the pure metal into melted caustic soda raised almost to red heat in a 78 ALUMINIUM. silver vessel, without observing the least disengagement of hydro- gen. Silicon, on the contrary, dissolves with great energy under the same circumstances. I have employed melted caustic soda to clean siliceous aluminium. The piece is dipped into the bath kept almost at red heat. At the moment of immersion several bubbles of hydrogen disengage from the metallic surface, and when they have disappeared all the silicon of the superficial layer of aluminium has been dissolved. It only remains to wash well with water and dip it into nitric acid, when the aluminium takes a beautiful mat. Alkaline organic materials, as the saliva, have a tendency to oxidize it, but the whole effect produced is in- significant. M. Charriere has made for a patient on whom he practised tracheotomy a small tube of the metal, which remained almost unaltered although in contact with purulent matter. After a long time a little alumina was formed on it, hardly enough to be visible. Mallet : The pure metal presents greater resistance to the pro- longed action of alkalies than the impure. Aluminium leaf dissolves with extraordinary quickness in caustic alkali, leaving the iron, which is always present, undis- solved. The chemical reaction occurring indicates that aluminium acts the part of a strong acid, forming aluminates of the alkaline metals which stay in solution. Lime water attacks aluminium in a similar manner, but the resulting calcium aluminate is insoluble in water and is therefore precipitated. SOLUTIONS OF METALLIC SALTS. Deville : The action of any salt whatever on aluminium may be easily deduced from the action of its acids on that metal. We may, therefore, predict that in acid solutions of sulphates and nitrates aluminium will precipitate no metal, not even silver, as Wbhler has observed. But the hydrochloric solutions of the same metals will be precipitated, as MM. Tissier have shown. Like- wise, in alkaline solutions, silver, lead, and metals high in the classification of the elements are precipitated. It may be concluded from this that to deposit aluminium on other metals by means of the battery, it is always necessary to use acid solutions in CHEMICAL PROPERTIES OF ALUMINIUM. 79 which hydrochloric acid, free or combined, should be absent. For similar reasons the alkaline solutions of the same metals can- not be employed, although they give such good results in plating common metals with gold and silver. It is because of t these curious properties that gilding and silvering aluminium are so diffi- cult. These conclusions by Deville are confirmed only when using pure aluminium ; the impure metal, containing iron, silicon, or perhaps sodium, may produce very slight precipitates in cases where pure aluminium would produce none. Some observers have noted different results in some cases even when using alu- minium free from these impurities. We will therefore take up these cases and consider them separately. Mercury. * Aluminium decomposes solutions of mercuric chlor- ide, cyanide or nitrate, mercury separating out first then forming an amalgam with the aluminium which is immediately decom- posed by the water, the result being alumina and mercury. From an alcoholic solution of mercurous chloride the mercury is pre- cipitated more quickly at a gentle heat. A solution of mercurous iodide with potassium iodide is also reduced in like manner. Copper. *From solution of copper sulphate or nitrate alumin- ium separates out copper only after two days 7 standing, as either dendrites or octahedra ; from the nitrate it also precipitates a green, insoluble basic salt. Copper is precipitated immediately from a solution of cupric chloride ; but slower from the solution of copper acetate. The sulphate or nitrate solutions behave simi- larly if potassium chloride is also present, and the precipitation is complete in presence of excess of aluminium. Silver. *From a nitrate solution, feebly acid or neutral, alu- minium precipitates silver in dendrites, the separation only begin- ning after six hours' standing. From an ammoniacal solution of silver chloride or chromate, aluminium precipitates the silver im- mediately as a crystalline powder. fCossa confirms the statement as to the nitrate solution. Lead. *From nitrate or acetate solution the lead is slowly pre- * Dr. Mierzinski. f A. Cossa, Bull, de la Soc. Chim. 1870, p. 199. 80 ALUMINIUM. cipitated in crystals ; an alkaline solution of lead chromate gives precipitates of lead and chromic oxide. Zinc. *An alkaline solution of zinc salts is readily decomposed and zinc precipitated. Margottet states that all metallic chlorides excepting those of potassium or sodium are reduced from solution. This statement can hardly include chlorides of magnesium or lithium, since mag- nesium precipitates alumina from solutions of aluminium salts. Alkaline or ammoniacal solutions are more easily decomposed than acid solutions ; in alkaline solutions the cause being the facility with which aluminates of the alkaline are formed. Alkaline chlorides. A solution of sodium or potassium chlor- ide is not affected by pure aluminium, either cold or warm. However, aluminium which was packed in a case with saw-dust and kept wet with sea-water for two weeks was deeply corroded ; whether the result would have been the same without the pres- ence of the saw-dust, I cannot say. Aluminium salts. It is a curious fact that a solution of alu- minium chloride will attack aluminium, forming sub-chlorhydrate, with evolution of hydrogen. A solution of alum does not attack aluminium, but if sodium chloride is added it is dissolved with evolution of hydrogen. It is interesting to note that while neither of these salts alone attacks aluminium, the mixture of the two does. SODIUM CHLORIDE. Fused common salt is used as a flux for aluminium. It does not possess the property, like fluorspar, of dissolving alumina, but it is apparently without any corroding effect on the molten aluminium ; neither is it probable that it is capable of reacting alone with any aluminous material to form aluminium chloride, which might volatilize and thus cause loss of material. FLUORSPAR. This compound is said to be without action on molten alumin- ium. It makes a good flux for the metal, especially in connection * A. Cossa, Bull, de la Soc. Chim. 1870, p. 199. CHEMICAL PROPERTIES OF ALUMINIUM. 81 with cryolite or common salt, and possesses the property of dis- solving the alumina with which the metal may be contaminated and which, by encrusting small globules, hinders their reunion to a button. CRYOLITE. This salt is largely used as a flux for aluminium and also as a source of the metal. It is commonly supposed to have the prop- erty of dissolving alumina, like fluorspar, but to be without action on the metal itself. Prof. W. Hampe, however, has re- cently stated that at a temperature about the melting point of cop- per, finely-divided aluminium is rapidly dissolved, a sub-fluoride being probably formed ; but the metal " en masse" is not sensibly attacked. SILICATES AND BORATES. Neither of these classes of compounds can be used as fluxes or slags in working aluminium, since they both rapidly corrode the metal. Deville had little difficulty in decomposing these salts so completely with metallic aluminium that he isolated silicon and boron. If aluminium is melted in an ordinary glass vessel it attacks it, setting free silicon from silica, forming an aluminate with the alkali present and an alloy with the silicon set free. Alu- minium melted under borax is rapidly dissolved, an aluminium borate being formed. It is thus seen that the common metal- lurgic slags are altogether excluded from the manufacture of aluminium. NITRE. Deville : Aluminium may be melted in nitre without under- going the least alteration, the two materials rest in contact with- out reacting even at a red heat, at which temperature the salt is plainly decomposed, disengaging oxygen actively. But if the heat is pushed to the point where nitrogen, itself is disengaged, there the nitre becomes potassa, a new affinity becomes manifest, and the phenomena change. The metal then combines rapidly with the potassa to give aluminate of potash. The accompanying 82 ALUMINIUM. phenomenon of flagration often indicates a very energetic reac- tion. Aluminium is continually melted with nitre at a red heat to purify it by the oxygen disengaged, without any fear of loss. But it is necessary to be very careful in doing it in an earthen crucible. The silica of the crucible is dissolved by the nitre, the glass thus formed is decomposed by the aluminium, and the sili- cide of aluminium formed is then very oxidizable, especially in the presence of alkalies. The purification by nitre ought to be made in an iron crucible well oxidized by nitre inside. If finely divided aluminium is mixed with nitre and brought to a red heat, the metal is oxidized with the production of a fine blue flame. (Mierzinski.) ALKALINE SULPHATES AND CARBONATES. Tissier : Only 2.65 grammes of aluminium introduced into melted red-hot sodium sulphate (Na 2 SO 4 ) decomposed that salt with such intensity that the crucible was broken into a thousand pieces, and the door of the furnace blown to a distance. Heated to redness with alkaline carbonate, the aluminium was slowly oxidized at the expense of the carbonic acid, carbon was set free, and an aluminate formed. The reaction takes place without deflagration. METALLIC OXIDES. Tissier Brothers made a series of experiments on the action of aluminium on metallic oxides. Aluminium leaf was carefully mixed with the oxide, the mixture placed in a small porcelain capsule and heated in a small earthen crucible, which served as a muffle. The results were as follows : Manganese dioxide. No reaction. Zinc oxide. No reaction even at white heat. Ferric oxide. By heating to white heat 1 equivalent of ferric oxide and 3 of aluminium the reaction took place with detona- tion, and by heating sufficiently we obtained a metallic but- ton, well melted, containing 69.3 per cent, of iron and 30.7 per cent, of aluminium. Its composition corresponds very nearly to the formula AlFe. It would thus appear that the decomposition CHEMICAL PROPERTIES OF ALUMINIUM. 83 of ferric oxide will not pass the limit where the quantity of iron reduced is sufficient to form with the aluminium the alloy AlFe. Lead oxide. We mixed 2 equivalents of litharge with 1 of alu- minium, and heated the mixture slowly up to white heat, when the latter reacted on the litharge with such intensity as to produce a strong detonation. We made an experiment with 50 grammes of litharge and 2.9 grammes of aluminium leaf, when the crucible was broken to pieces and the doors of the furnace blown off. Copper oxide. Three grammes of black oxide of copper mixed with 1.03 grammes of aluminium detonated, producing a strong explosion, when the heat reached whiteness. Beketoff* reduced baryta (BaO) with metallic aluminium in excess, and obtained alloys of aluminium and barium containing in one case 24 per cent, in another 33 per cent, of barium. MISCELLANEOUS AGENTS. Phosphate of lime. Tissier Brothers heated to whiteness a mixture of calcium phosphate with aluminium leaf, without the metal losing its metallic appearance or any reaction being noted. Hydrogen. This gas appears to have no action on aluminium, except to be dissolved in it in a moderately large quantity. Chlorine. Gaseous chlorine attacks the metal rapidly. Alu- minium foil heated in an atmosphere of chlorine takes fire and burns with a vivid light. Bromine, iodine, fluorine act similarly to chlorine. Silver chloride. Fused silver chloride is decomposed by alu- minium, the liberated silver as well as the excess of aluminium being melted by the heat of the reaction. Mercurous chloride. If vapors of mercurous chloride are passed through a tube in which some hot aluminium is placed, mercury is separated out, aluminium chloride deposits in the cooler part of the tube, and the aluminium" is melted by the heat developed. * Bull, de la Soc. Chimique, 1887, p. 22. 84 ALUMINIUM. GENERAL OBSERVATIONS ON THE PROPERTIES OF ALUMINIUM. Deville : " Aluminium at a low temperature conducts itself as a metal which can give a very weak base ; in consequence, its re- sistance to acids, hydrochloric excepted, is very great. It con- ducts itself with the alkalies as a metal capable of giving a quite energetic acid, it being attacked by alkaline oxides dissolved in water. But this affinity is still insufficient to determine the decomposition of melted caustic potash. For a stronger reason it does not decompose metallic oxides at a red heat. This is why in the muffle the alloy of aluminium and copper gives black CuO, and this also accounts for the alloy of aluminium and lead being capable of being cupelled. But by a strange exception, and which does not appertain solely, I believe, to aluminium, as soon as the heat is above redness the affinities are quickly in- verted and the metal takes all the properties of silicon, decom- posing the oxides of lead and copper with the production of the aluminates. " From all the experiments which have been reported and from all the observations which have been made, we can conclude that aluminium is a metal which has complete analogies with no one of the simple bodies which we consider metals. In 1855, I pro- posed to place it alongside of chromium and iron, leaving zinc out of the group with which aluminium had been until then classed. Zinc is placed very well beside magnesium, there being intimate analogies between these two volatile metals. There may be found at the end of a memoir which M. Wohler and I pub- lished in the ' Compt. Rendue' and the ' Ann. de Chem. et de Phys./ the reasons why we are tempted to place aluminium near to silicon and boron in the carbon series, on grounds analogous to those on which antimony and arsenic are placed in the nitro- gen series." ALUMINIUM COMPOUNDS. 85 CHAPTER Y. PROPERTIES AND PREPARATION OP ALUMINIUM COMPOUNDS. IN this chapter we propose to note in rather condensed form the prominent characteristics of the various aluminium com- pounds, with an outline of the methods by which they can be produced, reserving for another chapter however, the preparation of those salts which are now being manufactured on a commer- cial scale for purposes of further treatment for aluminium. I do not propose this as a substitute for the various chemical treatises on this subject, but simply to add to the completeness of this work in order that a fair understanding of the other parts of the book may not be missed because data of this nature are not immediately at hand. Parts of this chapter are taken from M. Margottet's treatise on aluminium, in Fremy's Enclycopedie Chimique. GENERAL CONSIDERATIONS. Structure of aluminium compounds* Aluminium is a quad- rivalent element, but in its compounds always acts as a double hexad atom (Al- Al) vi , one bond or affinity thus serving to bind the two atoms together. The double atom Al 2 can thus unite with six rnonatomic elements or atomic groups, or their equiva- lent. Thus we have A1 2 3 Aluminium oxide. A1 2 (OH)6 " oxyhydrate. " chloride. The salts of aluminium usually called aluminious salts, are chemically considered as derivatives of the oxy hydrate, the hydro- gen atoms being replaced by acid radicals. Thus * R. Biedermann. Kerl and Stohmans, Handbuch, 4th ed. 86 . ALUMINIUM. A1 2 .0 6 .(N02)6 Aluminium nitrate. A12.06.(C*H30)6 " acetate. AK0 6 .(S02)3 " sulphate. A1 2 .()6.(PO)2 phosphate. The above are normal or neutral salts, all the hydrogen atoms having been replaced. Basic salts result if only part of the hy- drogen is replaced. A12.(OH)*0 2 .(C 2 H30) 2 Basic aluminium acetate. A12.(OH*)02.(SO*) " " sulphate. Aluminium is very apt to form these basic compounds and others of even greater complexity. Aluminium oxyhydrate is distinguished from most of the other basic oxides in that its hydrogen atoms are not alone replaced by acid radicals, but by metals forming aluminates. Thus Al 2 .0 6 .Na 6 Sodium aluminate. AR0 6 .Ba 3 Barium " If we consider aluminium oxyhydrate to act in these com- pounds as an acid, these are its neutral salts. Besides alu- minates of this form there are others, natural and artificial, having the general formula APRO 4 , R being diatomic. These were written on the old dualistic theory A1 2 O 3 .RO, but they are now considered as derivatives of aluminium anhydro-hydrate. Thus A1 2 2 .(OH) 2 Aluminium anhydrohydrate, Al 2 2 .(0 2 Mg) Magnesium aluminate. General methods of formation and properties. Hydrated alu- mina, which has not been too strongly heated, dissolves in strong acids forming salts which are mostly soluble in water. In the feebler acids and in all organic acids it is completely insoluble. The salts of these latter acids are formed best by decomposing solution of aluminium sulphate with the barium or lead salt of the acid in question. Alumina forms no carbonate. Most alumin- ium salts are soluble in water and rather difficult to crystallize : the few insoluble salts are white, gelatinous, and similar to the hydrate in appearance. In the neutral salts the acid is loosely held, for their solution strongly reddens litmus paper and their ALUMINIUM COMPOUNDS. . 87 action is as if part of the acid were free in the salt. For in- stance, -a solution of alum attacks iron giving off hydrogen, a soluble basic salt of aluminium being formed as well as sulphate of iron. The neutral salts of volatile acids give off acid simply by boiling their solutions, basic salts being formed. An aqueous solution of aluminium chloride loses its acid almost completely on evaporation. Gentle ignition is sufficient in most cases to completely decompose aluminium salts. Hydrated alumina dis- solves easily in caustic alkali forming soluble aluminates ; with baryta two aluminates are known, one soluble the other not ; all other known aluminates are insoluble. Neutral solutions of aluminium salts react as follows with the common reagents : Hydrogen sulphide produces no precipitate. Ammonium sulphide precipitates aluminium hydrate with sepa- ration of free sulphur. Caustic potash or soda precipitates aluminium hydrate, soluble in excess. Aqua ammonia precipitates aluminium hydrate insoluble in excess, especially in presence of ammoniacal salts. Alkaline carbonates precipitate aluminium hydrate insoluble in excess. Sodium phosphate precipitates white gelatinous aluminium phosphate, easily soluble in acids or alkalies. ALUMINIUM OXIDE. Commonly called alumina. Composition APO 3 , and contains 52.95 per cent, of aluminium when perfectly pure. Colorless corundum is a natural pure alumina, in which state it is infusible at ordinary furnace heats, insoluble in acids, has a specific gravity of 4, and is almost as hard as the diamond. To get this into solution it must be first fused with potassium hydrate or bisul- phate. The alumina made by igniting aluminium hydrate or sulphate is a white powder, easily soluble in acids if the ignition has been gentle, but becoming almost insoluble if the heat has been raised to whiteness. The specific gravity of this ignited alumina also varies with the temperature to which it has been 88 ALUMINIUM. raised ; if simply to red heat, it is 3.75 ; if to bright-redness, 3.8 ; and if to whiteness, 3.9. In the last case it acquires almost the hardness of corundum. It can be melted to a clear, limpid liquid in the oxyhydrogen blowpipe; after cooling it forms a clear glass, often crystallized. Gaseous chlorine does not act on it even at redness, but if carbon is present at the same time alu- minium chloride is formed. Similarly, although neither carbon nor sulphur, alone or mixed together, acts on aluminium, carbon bisulphide converts it into aluminium sulphide. The preparation of alumina is described at length in the next chapter. ALUMINIUM HYDRATES. There are three natural hydrates of aluminium, which may be briefly described as follows : Diaspore, formula A1 2 O 3 .H 2 O or A1 2 O 2 .(OH) 2 , containing 85 per cent, of alumina, occurs in crystalline masses as hard as quartz, with a specific gravity of 3.4. Bauxite, of the general formula A1 2 O 3 .2H 2 O or APO.(OH) 4 , with the aluminium replaced by variable quantities of iron. If perfectly pure, it would con- tain 74 per cent, of alumina. Hydrochloric acid removes from it only the iron, heated with moderately dilute sulphuric acid it gives up its alumina, a concentrated alkaline solution also dis- solves the alumina. Calcined with sodium carbonate it forms sodium aluminate without melting. Gibbsite, formula APO 3 .- 3H 2 O or AP(OH) 6 , containing when pure 65 per cent, of alu- mina, is a mineral generally stalactitic, white, and with a specific gravity of 2.4. It loses two-thirds of its water at 300 and the rest at redness. The artificial hydrates are of two kinds, the soluble and in- soluble modifications. The latter is the common hydrate, such as is obtained by adding ammonia to a solution containing alu- minium. The precipitate is pure white, very voluminous, and can be washed free from the salts with which it was precipitated only with great difficulty. Its composition is AP(OH) 6 , corre- sponding to the mineral gibbsite. It is insoluble in water, but easily soluble in dilute acids or alkali solutions. It dissolves in ALUMINIUM COMPOUNDS. 89 small quantity in ammonia, but the presence of ammonia salts counteracts this action. When dissolved in caustic potash or soda the addition of ammoniacal salts reprecipitates it. It loses its water on heating, in the same manner as gibbsite. Many other properties of this hydrate, and its manufacture on a large scale, are given in the next chapter. The soluble modification can only be made by complicated processes, too long to be described here, and is principally of use in the dyeing industries ; a full descrip- tion can be found in any good chemical dictionary. ALUMINATES. Potassium aluminate. Formula K 2 APO, crystallizes with 3 molecules of water, the crystals containing 40 per cent, alumina, 37.5 per cent, potassa and 21.5 per cent, of water. It is formed when precipitated alumina is dissolved in caustic potash, or by melting together alumina and caustic potash in a silver dish and dissolving in water. If the solution is evaporated in vacuo, bril- liant hard crystals separate out. They are soluble in water but insoluble in alcohol. Sodium aluminate has not been obtained crystallized. Ob- tained in solution by dissolving alumina in caustic soda or by fusing alumina with caustic soda or sodium carbonate and dis- solving in water. If single equivalents of carbonate of soda and alumina are used, the aluminate seems to have the composition ^a 2 APO 4 ; if an excess of soda is used, the solution appears to contain AP(ONa) 6 , or APO.3Na 2 O. If a solution of sodium aluminate is concentrated to 20 or 30 B., alumina separates out; if carbonic acid gas is passed through it, aluminium hydrate is precipitated. For a description of its manufacture on a large scale, see next chapter. Barium aluminate. Formula BaAPO. Deville prepared it by calcining a mixture of nitrate or carbonate of barium with an excess of alumina, or by precipitating sulphate of aluminium in solution by baryta water in excess. The aluminate is soluble in about 10 times its weight of water and crystallizes out on addition of alcohol. The crystals contain 4 molecules of water Gaudin obtained it by passing steam over a mixture of alumina and 90 ALUMINIUM. barium chloride, or of alumina, barium sulphate, and carbon, at a red heat. Tedesco claimed that by heating to redness a mixture of alumina, barium sulphate, and carbon, barium aluminate was ex- tracted from the residue by washing with water. He utilized this reaction further by adding solution of alkaline sulphate, bar- ium sulphate being precipitated (which was used over), while alkaline aluminate remained in solution. Calcium aluminate. Lime water precipitates completely a solution of potassium or sodium aluminate, insoluble gelatinous calcium aluminate being formed, of the formula AP(O 6 Ca 3 ) or Al 2 O 3 .3CaO. At a red heat it melts to a glass, which, treated after cooling with boiling solution of boric acid, affords a com- pound appearing to contain 2APO 3 .3CaO. (Tissier.) Lime water is also completely precipitated by hydrated alumina, the com- pound formed having the composition CaAPO 4 or Al 2 O 3 .CaO. Also, by igniting at a high temperature an intimate mixture of equal parts of aluminia and chalk, Deville obtained a fused corn- pound corresponding to the formula CaAPO 4 . Zinc aluminate occurs in nature as the mineral Gahnite, formula ZnAPO 4 . Berzelius has remarked that when a solution of zinc oxide in ammonia and a saturated solution of alumina in caustic potash are mixed, a compound of the two oxides is pre- cipitated, which is redissolved by an excess of either alkali. Copper aluminate. On precipitating a dilute solution of sodium aluminate with an ammoniacal solution of copper sulphate, the clear solution remaining contained neither copper nor aluminium. Whether the precipitate contained these combined as an alu- minate I was not able to determine. Magnesium aluminate occurs in nature as Spinell ; iron alu- minate as Hercynite ; beryllium aluminate as Chrysoberyl. I can find no certain information of their artificial production except in grains at a very high heat. ALUMINIUM CHLORIDE. Formula APC1* contains 20.2 per cent, of aluminium. The commercial chloride is often yellow or even red from the presence of iron, but the pure salt is quite white. It absorbs water very ALUMINIUM COMPOUNDS. 91 rapidly from the air. It usually sublimes without melting, especially when in small quantity, but if a large mass is rapidly heated, it may melt and even boil, but its melting point is very close to its boiling point. Its vapor condenses at 180 to 200. When sublimed it deposits in brilliant, hexagonal crystals. A current of steam rapidly decomposes it into alumina and hydro- chloric acid. Oxygen disengages chlorine from it at redness, but decomposes it incompletely. Potassium or sodium decomposes it explosively, the action commencing below redness. Anhydrous sulphuric acid converts it into aluminium sulphate. Aluminium chloride combines with many other chlorides, forming the double salts. On dissolving this salt in water, or by dissolving alumina in hydrochloric acid, a solution is obtained which on evaporation deposits crystals having the formula A1 2 C1M2H 2 O. If these crystals are heated, they decompose, losing both water and acid and leaving alumina. Thus, it is not possible to obtain anhy- drous aluminium chloride by evaporating its solution, and the anhydrous salt must be made by other methods, detailed at length in the next chapter. ALUMINIUM-SODIUM CHLORIDE. Formula Al 2 Cl 6 .2NaCl contains 14 per cent, of aluminium. The commercial salt is often yellow or brown from the presence of ferric chloride, but the pure salt is perfectly white. Its melt- ing point has been generally stated to be 180, but Mr. Baker, chemist for the Aluminium Company, of London, states that when the absolutely pure salt is warmed it melts at 125 to 130. That chemists should for thirty years have made an error of this magnitude seems almost incredible, and it would be satisfactory if Mr. Baker would advance some further information than the bare statement above. This salt volatilizes at a red heat without decomposition. It is less deliquescent in the air than aluminium chloride, and for this reason is much easier to handle on a large scale. It is recently stated that the absolutely pure salt deteri- orates less than the impure salt in the air, and the inference is drawn that perhaps the greater deliquescence of the impure salt 92 ALUMINIUM. is due to the iron chlorides present. Its solution in water behaves similarly to that of aluminium chloride ; it cannot be evaporated to dryness without decomposition, the residue consisting of alu- mina and sodium chloride. The manufacture of this double salt on a large scale is described in the next chapter. It may be prepared in the laboratory by melting a mixture of the two component salts in the proper pro- portions. A similar salt with potassium chloride may be prepared by exactly analogous reactions. ALUMINIUM-PHOSPHORUS CHLORIDE. Formula A1 2 C1 6 .PC1 5 , contains 9 per cent, of aluminium. It is a white salt, easily fusible, volatilizes only about 400 and sub- limes slowly, fumes in the air and is decomposed by water. Pro- duced by heating the two chlorides together or by passing vapor of phosphorus perchloride over alumina heated to redness. ALUMINIUM-SULPHUR CHLORIDE. Formula A1 2 C1 6 .SC1 4 , contains 12.2 per cent, of aluminium. It forms a yellow crystalline mass, fuses at 100, may be distilled without change, and is decomposed by water. May be obtained by distilling a mixture of aluminium chloride and ordinary sul- phur chloride, SCI 2 . ALUMINIUM-SELENIUM CHLORIDE. Formula Al 2 Cl 6 .SeCl 4 . Obtained by heating the separate chlor- ides together in a sealed tube, when on careful distillation the less volatile double chloride remains. It is a yellow mass, melt- ing at 100 and decomposed by water. ALUMINIUM-AMMONIUM CHLORIDE. Formula A1 2 C1 6 .3NH 3 . Solid aluminium chloride absorbs ammonia in large quantity, the heat developed liquefying the ALUMINIUM COMPOUNDS. 93 resulting compound. It may be sublimed in a current of hydro- gen, but loses ammonia thereby and becomes APC1 S .NH 8 . ALUMINIUM-CHLOR-SULPHYDRIDE. Formed by subliming aluminium chloride in a current of hy- drogen sulphide. A current of hydrogen removes the excess of the gas used, leaving on sublimation fine colorless crystals. In air it deliquesces rapidly and loses hydrogen sulphide. ALUMINIUM-CHLOR-PHOSPHYDRIDE. Apparantly of the formula 3A1 2 C1 6 .PH 3 . If phosphuretted hydrogen is passed over cold aluminium chloride very little is absorbed, but at its subliming point it absorbs a large quantity, the combination subliming and depositing in crystals. It is de- composed by water or ammonium hydrate, disengaging hydrogen phosphide. ALUMINIUM BROMIDE. Formula APBr 8 , containing 10.1 per cent, of aluminium. It is colorless, crystalline, melts at 93 to a clear fluid which boils at 260. It is still more deliquescent than aluminium chloride. At a red heat in contact with dry oxygen, it evolves bromine and forms alumina ; it is also decomposed slowly by the oxygen of the air. It dissolves easily in carbon bi-sulphide, the solution fuming strongly in the air. It reacts violently with water, the solution on evaporation depositing the compound Al 2 Br 6 .12H*O. The same result is attained by dissolving alumina in hydrobromic acid and evaporating. This hydrated chloride is decomposed by heat leaving alumina. The specific gravity of solid aluminium bromide is 2.5. This compound is obtained by heating aluminium and bromine together to redness, or by passing bromine vapor over a mixture of alumina and carbon at bright redness. 94 ALUMINIUM. ALUMINIUM IODIDE. Formula API 6 , containing 6.6 per cent, of aluminium. This compound is a white solid, fusible at 125 and boils at 350. It dissolves easily in carbon bisulphide, the warm saturated solution depositing it in crystals on cooling. It dissolves also in alcohol and ether. Its behavior towards water is exactly analogous to that of aluminium bromide. It is prepared by heating iodine and aluminium together, or by passing iodine vapor over an ignited mixture of alumina and carbon. ALUMINIUM FLUORIDE. Formula A1 2 F 6 , containing 32.7 per cent, of aluminium. It is sometimes obtained in crystals which are colorless and slightly phosphorescent. They are insoluble in acids even in boiling sul- phuric, and boiling solution of potash scarcely attacks them ; they can only be decomposed by fusion with sodium carbonate at a bright red heat. Melted with boric acid, aluminium fluoride forms crystals of aluminium borate. L. Grabau describes the aluminium fluoride which he obtains in his process, as being a white powder, unalterable in air, unaffected by keeping, insoluble in water, infusible at redness, but volatilizing at a higher temperature. Deville first produced this compound by acting on aluminium with silicon fluoride at a red heat. He afterwards obtained it by moistening pure calcined aluminium with hydrofluoric acid, drying and introduced into a tube made of gas carbon, protected by a refractory envelope. The tube was heated to bright red- ness, a current of hydrogen passing through meanwhile to facili- tate the volatilization of the fluoride. Brunner demonstrated that aluminium fluoride is formed and volatilized when hydro- fluoric acid gas is passed over red hot alumina. Finally, if a mixture of fluorspar and alumina is placed in carbon boats, put into a carbon tube, suitably protected, heated to whiteness and gaseous hydrofluoric acid passed over it, aluminium fluoride will volatilize and condense in the cooler part of the tube in fine cubical crystals, while calcium chloride remains in the boats. ALUMINIUM COMPOUNDS. 95 ALUMINIUM FLUORHYDRATE. When calcined alumina or kaolin is treated with hydrofluoric acid, alumina being in excess, soluble fluorhydrate of aluminium is formed, whiclj deposits on evaporating the solution. It has the formula A1 2 F 6 .7H 2 O, and easily loses its water when heated. ALUMINIUM-HYDROGEN FLUORIDE. If to a strongly acid solution of alumina in hydrofluoric acid alcohol is added, an oily material separates out and crystallizes, having the formula 3A1 2 F 3 .4HF.10H 2 O. If the acid solution is simply evaporated, acid fumes escape and a crystalline mass re- mains which, washed with boiling water and dried, has the for- mula 2A1 2 F 3 .HF.10H 2 O. On heating these compounds to 400 or 500 in a current of hydrogen, pure amorphous aluminium fluoride remains. The acid solution of alumina first used seems to contain an acid of the composition A1 2 F 6 .6HF, which is capa- ble of forming salts with other bases. Thus, if this solution is neutralized with a solution of soda, a precipitate of artificial cryo- lite, Al 2 F 6 .6NaF, falls. The similar potash compound is formed in the same way. ALUMINIUM-SODIUM FLUORIDE. Formula Al 2 F 6 .6NaF, containing 12.85 per cent, of alumin- ium, occurs native as cryolite, a white mineral with a waxy ap- pearance, as hard as calcite, specific gravity 2.9, melting below redness and on cooling looking like opaque, milky glass. If kept melted in moist air, or in a current of steam, it loses hydrofluoric acid and sodium fluoride and leaves a residue of pure alumina. When melted it is decomposable by an electric current or by sodium or magnesium. It is insoluble in water, unattacked by hydrochloric but decomposed by hot sulphuric acid. The native mineral is contaminated with ferrous carbonate, silica, phosphoric, and vanadic acids. An extended description of its utilization, manufacture, etc. will be found in the next chapter. 96 ALUMINIUM. ALUMINIUM SULPHIDE. Formula APS 3 , containing 36 per cent, of aluminium. The pure salt is light yellow in color and melts at a high temperature. In damp air it swells up and disengages hydrogen sulphide, form- ing a grayish white powder ; it decomposes water very actively, forming hydrogen sulphide and ordinary gelatinous aluminium hydrate. Steam decomposes it easily, at red heat forming amorph- ous alumina, which is translucent and very hard. Gaseous hydro- chloric acid transforms it into aluminium chloride. Elements having a strong affinity for sulphur reduce it, setting free aluminium, but it is doubtful if hydrogen or carburetted hydro- gen has this effect. It may be formed by throwing sulphur into red-hot alumin- ium, or by passing sulphur vapor over red-hot aluminium. Traces only of aluminium sulphide are formed by passing hydro- gen sulphide over ignited alumina, but carbon-bisulphide vapor readily produces this reaction. For details of its formation see next chapter. ALUMINIUM SELENIDE. When aluminium is heated in selenium vapor, the two elements combine with incandescence, producing a black powder. In the air this powder evolves the odor of hydrogen selenide ; in con- tact with water it disengages that gas abundantly and furnishes a red deposit of selenium along with aluminium hydrate. When a solution of an aluminium salt is treated with an alkaline poly- selenide, a flesh-colored precipitate falls, the composition of which is not known, which is decomposed at redness leaving aluminium. ALUMINIUM BORIDES. A1B 2 , containing 55.1 per cent, of aluminium, was first ob- tained by Deville and Wohler by heating boron in contact with aluminium, or on reducing boric acid with the latter metal, the action not being long continued. Also, if a current of boron tri- chloride with carbonic oxide is passed over aluminium in boats in ALUMINIUM COMPOUNDS. 97 a tube heated to redness, aluminium chloride volatilizes and there remains in the boats a crystalline mass, cleavable, and covered with large hexagonal plates of a high metallic lustre. To re- move the aluminium present in excess the mass is treated with hydrochloric acid and then by caustic soda. The final residue is composed of hexagonal tablets, very thin but perfectly opaque, of about the color of copper. These crystals do not burn in the air, even if heated to redness, but their color changes to dark-gray. They burn in a current of chlorine, giving chlorides of the two elements contained in them. They dissolve slowly in concen- trated hydrochloric acid or in solution of caustic soda; nitric acid, moderately concentrated, attacks them quickly. A1B S , containing 45 per cent, of aluminium, has been obtained by Hampe by heating aluminium with boric acid for three hours at a high temperature, carbon being carefully kept away. On cooling very slowly, the upper part of the fusion is composed 01 aluminium borate, the centre is of very hard, alumina containing a few black crystals of aluminium boride, while at the bottom is a button of aluminium also containing these crystals. To free these crystals, the aluminium is dissolved by hydrochloric acid. These crystals are the compound sought for, and contain no other impurity than a little alumina, which can be removed by boiling sulphuric acid. These purified crystals are black, but are thin enough to show a dark-red by transmitted light. Their specific gravity is 2.5, they are harder than corundum, but are scratched by the diamond. Oxygen has no action on them at a high tempera- ture, solution of caustic potash or hydrochloric acid does not attack them, boiling sulphuric acid has scarcely any action, but they dissolve completely in warm, concentrated nitric acid. If the operation by which this product is made is conducted in the presence of carbon, the compound formed contains less alu- minium and also some carbon. Its composition corresponds to the formula A1 3 C 2 B 48 , containing about 12 per cent, of aluminium and 3.75 per cent, of carbon. The crystals of this compound are yellow and as brilliant as the diamond. Their specific gravity is 2.6, hardness between that of corundum and the diamond. They are not attacked by oxygen, even at a high temperature ; hot hydrochloric or sulphuric acid attacks them only superficially, 7 98 ALUMINIUM. concentrated nitric acid dissolves them slowly but completely. They resist boiling solution of caustic potash or fused nitre, but take fire in fused caustic potash or chromate of lead. ALUMINIUM NITRIDE. Formula AIN, containing 66 per cent, of aluminium, is formed when aluminium is heated in a carbon crucible to a high tempera- ture. Mallet* obtained it in quantity by heating aluminium with dry sodium carbonate at a high heat, for several hours, in a car- bon crucible. The aluminium is partially transformed into alu- mina, some sodium vaporizes and some carbon is deposited. After cooling, there are found on the surface of the button little yellow crystals and amorphous drops, to recover which the whole is treated with very dilute hydrochloric acid. This product has the com- position AIN. Calcined in the air it slowly loses nitrogen and forms alumina. It decomposes in moist air, loses its trans- parency, becomes a lighter yellow 7 , and finally only alumina remains, the nitrogen having formed ammonia. Melted with caustic potash it disengages ammonia and forms potassium alu- minate. ALUMINIUM SULPHATE. Anhydrous. The salt obtained by drying hydrated aluminium sulphate at a gentle heat has the formula A1 2 (SO 4 ) 3 , containing 15.8 per cent, of aluminium, and of a specific gravity of 2.67. By heating this salt several minutes over a Bunsen burner it loses almost all its acid, leaving alumina. Hydrogen likewise decom- poses it at redness, forming water and sulphur dioxide and leav- ing alumina with hardly a trace of acid. Melted with sulphur, Violi states that it is transformed into aluminium sulphide, evolving sulphurous acid gas.f Hot hydrochloric acid in excess partly converts it into aluminium chloride. Hydrated. This is the ordinary aluminium sulphate; its form- ula is A1 2 (SO 4 ) 3 .18H 2 O, and it contains 8.4 per cent, of alu- * Ann. der Chemie u. Pharmacie, 186, p. 155. f Berichte des Deutschen Gesellschaft, X, 293. ALUMINIUM COMPOUNDS. 99 minium and 47 per cent, of water. It has a white, crystalline appearance and tastes like alum. It dissolves freely in water, from which it crystallizes out at ordinary temperatures with the above formula ; crystallized out at a low temperature it retains 27H 2 O, or one-half as much again. Water dissolves one-half its weight of this salt, the solution reacting strongly acid ; it is almost insoluble in alcohol. At a gentle heat it melts in its water of crystallization, then puifs up and leaves a porous mass of anhydrous sulphate which is soluble with difficulty in water. If heated to redness it leaves only alumina, the salt with 18H 2 O has a specific gravity of 1.76 ; it is the salt found in fibrous masses in solfataras, its mineralogical name being Halotrichite. A hydrated sulphate with 10H 2 O is formed and precipitated when alcohol is added to an aqueous solution of aluminium sulphate. On heating it acts similarly to the other hydrated sulphates. .Basic. On precipitating a solution of aluminium sulphate with alkaline hydrate or carbonate a series of basic salts are formed. On precipitating with ammonia, the compound formed has the formula A1 2 O 3 .SO 3 .9H 2 O, corresponding to the mineral Aluminite. If the ammonia is in insufficient quantity to entirely precipitate the solution, a precipitate is very slowly formed hav- ing the formula 3A1 2 O 3 .2SO 8 .20H 2 O. On precipitating a cold solution of alum by alkaline carbonate not in excess, a precipitate is very slowly formed having the formula 2A1 2 O 3 .SO 3 .12H 2 O. If a very dilute solution of acetate of alumina is precipitated by adding potassium sulphate, a compound deposits very slowly having the formula 2A1 2 O 3 .SO 3 .10H 2 O. Native minerals are met with of analogous composition to these precipitates : Felsobanyte, 2 A1 2 O 3 .SO 3 .10H 2 O ; Paraluminite, 2A1 2 O 3 .SO 3 .15H 2 O. By heat- ing a concentrated solution of aluminium sulphate with aluminium hydrate, and filtering cold, the solution deposits on further cooling a gummy mass having the formula A1 2 O 3 .2SO 8 .#H 2 O. On wash- ing with water it deposits a basic salt having the formula A1 2 O 3 .- SO 3 . By letting stand a very dilute solution of sulphuric acid completely saturated with aluminium hydrate, Rammelsberg ob- tained transparent crystals having the formula 3APO 8 .4SO 3 .- 30H 2 O. On boiling a solution of aluminium sulphate with zinc, Debray obtained a granular precipitate having the formula 100 ALUMINIUM. 5A1 2 O 3 .3SO 3 .20H 2 O. By leaving zinc a long time in a cold solu- tion of aluminium sulphate, a gelatinous precipitate was obtained having the formula 4A1 2 O 3 .3SO 3 .36H 2 O ; the same compound was formed if the zinc was replaced by calcium carbonate. The manufacture of aluminium sulphate from clay, aluminous earths, cryolite, beauxite, etc. is carried on industrially on a very large scale ; descriptions of the processes used may be found in any work on industrial chemistry they are too foreign to metallurgical purposes to be treated of here. ALUMS. Under this name are included a number of double salts con- taining water, crystallizing in octahedra and having the general formula R 2 SO 4 .R 2 (SO 4 ) 3 .24H 2 O, in which the first R may be potass- ium, sodium, rubidium, caesum, ammonium, thallium or even or- ganic radicals ; the second R, maybe aluminium, iron, manganese or chromium ; the acid may even be selenic, chromic or manganic, in- stead of sulphuric. We will briefly describe the most important alums consisting of double sulphates of aluminium and another metal, remarking, as with aluminium sulphate, that their prepara- tion may be found at length in any chemical treatise. POTASH ALUM. Formula K 2 SO 4 .A1 2 (SO 4 ) 3 .24H 2 O, containing 10.7 per cent, of alumina or 5.7 per cent of aluminium. Dissolves in 25 parts of water at and in two-sevenths part at 100. The solution re- acts acid. It forms colorless, transparent octahedrons, insoluble in alcohol. On exposure to air they become opaque, being covered with a white coating, which is said not to be efflorescence a loss of water but to be caused by absorption of ammonia from the air. The crystals melt in their water of crystallization, but lose it all above 100. Heated to redness it swells up strongly, be- comes porous and friable, giving the product called calcined alum ; at whiteness it loses a large part of its sulphuric acid, leaving a residue of potassium sulphate and alumina. If it is mixed with one-third its weight of carbon and calcined, the residue inflames ALUMINIUM COMPOUNDS. 101 spontaneously in the air. If a mixture of alumina and bi-sul- phate of potassium is fused and afterwards washed with warm water, a residue is obtained of anhydrous alum, or K 2 SO 4 .- A1 2 (SO 4 ) 3 . The mineral Alunite is a basic potash alum, K 2 SO 4 .- 3(A1 2 O 3 .SO 3 ).6H 2 O. AMMONIA ALUM. Formula(NH 4 ) 2 SO 4 .Al 2 (SO 4 ) 3 .24H 2 O, containing 11.3 per cent, of alumina or 6.0 per cent, of aluminium. Dissolves in 20 parts of water at and in one-fourth part at 100. When heated, the crystals swell up strongly, forming a porous mass, losing at the same time water and sulphurous acid ; if the temperature is high enough there remains a residue of pure alumina. The tem- perature necessary for complete decomposition is higher than that required for volatilising ammonium sulphate alone. SODA ALUM. Formula Na 2 SO 4 .Al 2 (SO 4 ) 8 .24H 2 O, containing 11.1 per cent, of alumina or 5.9 per cent, of aluminium. Dissolves in an equal weight of water at ordinary temperatures. The crystals effloresce and fall to powder in the air. It is insoluble in absolute alcohol. On account of its great solubility in water it cannot be separated from ferrous sulphate by crystallization, and therefore it is either contaminated with much iron or else, to be obtained pure, special expensive methods must be adopted. These difficulties cause the manufacture of soda alum to be insignificant in amount when compared with potash alum. ALUMINIUM-METALLIC SULPHATES. Sulphate of aluminium forms double sulphates with iron, man- ganese, magnesium and zinc, but these compounds are not analo- gous to the alums. They are extremely soluble in water, do not crystallize in octahedrons or any isometric forms, and their com- position is different from the alums in the amount of water of crystallization. It has been determined that the double sulphates 102 ALUMINIUM. with manganese and zinc contain 25 equivalents of water, which would permit their being considered as combinations of sulphate of aluminium, A1 2 (SO 4 ) 3 .18H 2 O, with a sulphate of the magne- sian series containing seven equivalents of water, as ZnSO 4 .7H 2 O. ALUMINIUM SELENITES. By adding a solution of selenite of soda to one of sulphate of aluminium maintained in excess, an amorphous, voluminous pre- cipitate forms having the composition 4APO 3 .9SeO 2 .3H 2 O. This substance decomposes on being heated, leaving alumina. If vary- ing quantities of selenious acid are added to this first salt, other salts of the formulas Al 2 SO 3 .3SeO 2 .7H 2 O,2Al 2 O 3 .9SeO 2 .12H 2 O, Al 2 O 3 .6SeO 2 .5H 2 O are formed. These are mostly insoluble in water and decompose on being heated, like the first. ALUMINIUM NITRATE. Formula A1 2 (NO 3 ) 6 .18H 2 O is obtained on dissolving aluminium hydrate in nitric acid. If the solution is evaporated keeping it strongly acid, it deposits on cooling voluminous crystals having the formula A1 2 (NO 3 ) 6 .15H 2 O. This salt is deliquescent, melts at 73 and gives a colorless liquid which, on cooling, becomes crystal- line. It is soluble in water, nitric acid, and alcohol ; on evapo- rating these solutions it is obtained as a sticky mass. It is easily decomposed by heat; if kept at 100 for a long time it loses half its weight, leaving as residue a soluble salt of the formula 2A1 2 O 3 .- 3N 2 O 5 .3H 2 O. Carried to 140, this residue loses all its nitric acid, leaving alumina. On this property is based a separation of alumina from lime or magnesia, si nee the nitrates of these latter bases resist the action of heat much better than aluminium nitrate. ALUMINIUM PHOSPHATES. The normal phosphate, A1 2 (PO 4 ) 2 , is obtained as a white, gelat- inous precipitate when a neutral aluminium solution is treated with sodium phosphate. It is soluble in alkalies or mineral acids but not in acetic acid. If a solution of this salt in acids is ALUMINIUM COMPOUNDS. 103 neutralized with ammonia, a basic phosphate is precipitated hav- ing the composition 3 A1 2 (OH) 3 PO 4 4- A1 2 (OH) 6 . The mineral Wavellite has this composition, with nine molecules of water. The mineral Kalait contains A1 2 (PO 4 ) 2 + A1 2 (OH) 6 + 2H 2 O, and when it is colored azure blue by a little copper it forms the Turquois. ALUMINIUM CARBONATE. ' If to a cold solution of alum a cold solution of sodium carbon- ate is added drop by drop, stirring constantly until the solution reacts feebly alkaline, a precipitate is obtained which, after being washed with cold water containing carbonic acid gas, contains when damp single equivalents of alumina and carbonic acid, A1 2 O 3 .CO 2 . If the precautions indicated are not used, the pre- cipitate contains a very small proportion of carbonic acid. ALUMINIUM BORATE. Formula 3A1 2 O 3 .BO 3 . Prepared by Ebelman by heating together alumina, oxide of cadmium, and boric acid. After three days' heating the platinum capsule containing the mixture was found covered with transparent crystals of the above com- position, hard enough to scratch quartz and having a specific gravity of 3. Troost obtained the same substance by heating alumina in the vapor of boron trichloride. Fremy prepared it by heating fluoride of aluminium with boric acid. Ebelman also obtained it by heating a mixture of alumina and borax to whiteness ; under these conditions crystals of corundum were formed at the same time. By precipitating a cold solution of alum with sodium borate, double salts are obtained containing soda, but which leave on washing with warm water two compounds having the formulae 2A1 2 O 3 .BO 3 .5H 2 O and 3A1 2 O 3 .2BO 3 .8H 2 O. If the washing is prolonged too far the two salts are completely decomposed, leaving a residue of pure alumina. ALUMINIUM SILICATES. Compounds of alumina and silica, or aluminium, silicon, and oxygen are of wide occurrence in nature. In them these bases 104 ALUMINIUM. occur in many proportions ; the following proportions of alumina to silica, A1 2 O 3 to SiO 2 , have been observed: 2-1, 3-2, 1-1, 2-3, 1-2, 1-3, 1-4, 1-8, thus varying from tri-basic silicates to pent-acid silicates. Some are anhydrous, others hydrous; in many of these silicates ferric oxide replaces varying quantities of alumina and an immense number of silicates are known containing other metallic bases besides aluminium. These by their various combinations form the basis of most rocks. APO 3 .SiO 2 , or APSiO 5 , occurs in nature as Disthene, Andalusite, and Fibrolite. They are not attacked by acids, are infusible before the blowpipe, specific gravity 3 to 3.5, and hardness about that of quartz. Al 2 O 3 .2SiO 2 .2H 2 O or Al 2 Si 2 O 7 + 2H 2 O forms kaolin or white china clay, and mixed with various impurities forms the basis of many common clays. It is produced mostly from orthoclase, a feldspar containing silica, alumina, and potash, by the decompos- ing influence of the atmosphere. The moisture and carbonic acid of the air produce the following reaction K 2 A1 2 S1 6 O 16 + 2H 2 O + CO 2 = Al 2 Si 2 O 7 .2H 2 O + K 2 CO 3 4- 4SiO 2 . Kaolin acquires a certain plasticity when mixed with water. Hydrochloric or nitric acids have no action on it, but cold sul- phuric acid dissolves its alumina setting the silica at liberty. It is infusible unless contaminated with particles of feldspar or calcium sulphate, carbonate, or phosphate. The specific gravity of kaolin is 2.3. If fused with six times its weight of caustic potash the resulting mass gives up potassium aluminate when washed with water. An analogous result is obtained with sodium carbon- ate. Pure kaolin with the formula Al 2 Si 2 O 7 .2H 2 O contains 39.4 per cent, of alumina or 20.9 per cent, of aluminium ; if it is calcined enough to drive off the water, the residue will con- tain 45.9 per cent, of alumina or 24.3 per cent, of aluminium. Common clays contain from 50 to 70 per cent, of silica and 15 to 35 per cent, of alumina, and are not often amenable to a formula. Two of somewhat constant composition have been given the formula Al 2 O 3 .3SiO 2 .4H 2 O and Al 2 O 3 .5SiO 2 .3H 2 O. PREPARATION OF ALUMINIUM COMPOUNDS. 105 CHAPTER VI. PREPARATION OF ALUMINIUM COMPOUNDS FOR REDUCTION. WE will consider this division under four heads : I. Alumina. II. Aluminium chloride and aluminium -sodium chloride. III. Aluminium fluoride and aluminium-sodium fluoride. IV. Aluminium sulphide. I. THE PREPARATION OF ALUMINA. We will treat this subject in three divisions : 1. From Aluminium Sulphate or Alums. 2. From Beauxite. 3. From Cryolite. 1. PREPARATION OF ALUMINA FROM ALUMS OR ALUMINIUM SULPHATE. Hydrated alumina can be precipitated from a solution of any aluminium salt by ammonium hydrate, an excess of which re-dis- solves a portion. Its chemical formula is ordinarily written APO 3 .- 3H 2 O or AP(OH) 6 . The aluminium hydrate thus precipitated is a pure white, very voluminous, almost pasty mass, very hard to wash. By boiling and washing with boiling water it becomes more dense, but always remains very voluminous. Washing on a fil- ter with a suction apparatus gives the best results. At a freezing temperature this hydrate changes into a dense powder which is more easily washed. On drying it shrinks very much in volume and forms dense, white pieces, transparent on the edges. When dried at ordinary temperatures it has the composition A1 2 O 3 .H 2 O. 106 ALUMINIUM. On ignition, the other molecule of water is driven off, leaving an- hydrous alumina. After gentle ignition it remains highly hygro- scopic, and in a very short time will take up from the air 15 per cent, of water. In this condition it is easily soluble in hydrochloric or sulphuric acid. On stronger ignition it becomes harder and soluble only with difficulty in concentrated acid ; after ignition at a high temperature it is insoluble, and can only be brought into solution again by powdering finely and fusing with potassium acid-sul- phate or alkaline carbonate. At ordinary furnace temperatures alumina does not melt, but in the oxy-hydrogen blow-pipe or the electric arc it fuses to a limpid liquid and appears crystalline on cooling. The precipitation in aqueous solution and subsequent ignition is not economical enough to be practised on a large scale, and for industrial purposes the aluminium sulphate or alum is ignited directly. About the easiest way to proceed is to take ammonia alum crystals, put them into a clean iron pan and heat gently, when the salt melts in its water of crystallization. When the water has evaporated, a brittle, shining, sticky mass remains, which on further heating swells up and decomposes into a dry, white powder. This is let cool, powdered, put into a crucible and heated to bright redness. All the ammonia and almost all the sulphuric acid are thus removed. The rest of the acid can be removed by moistening the mass with a solution of sodium carbonate, drying and again igniting ; on washing with water the acid is removed as sodium sulphate. The residue, however, will contain some caustic soda, which for its further use in making aluminium chlor- ide is not harmful. Potash alum can be treated in a similar way, the potassium sulphate being washed away after the first igni- tion. Still more easily and cheaply can alumina be made by ignit- ing a mixture of 4 parts aluminium sulphate and 1 of sodium carbonate. On washing, sodium sulphate is removed from the alu- mina.* Deville used the following method at Javel : Ammonia alum or even the impure commercial aluminium sulphate was calcined, the residue appearing to be pure, white alumina, but it still con- * Kerl and Stohraan, 4th Ed. p. 739. PREPARATION OF ALUMINIUM COMPOUNDS. 107 tained sulphuric acid, potassium sulphate, and a notable propor- tion of iron. This alumina is very friable, and is passed through a fine sieve and put into an iron pot with twice its weight of solution of caustic soda of 45 degrees. It is then boiled and evaporated, and the alumina dissolves even though it has been strongly calcined. The aluminate of soda produced is taken up in a large quantity of water, and if it does not show clear im- mediately a little sulphuretted hydrogen is passed in, which hastens the precipitation of the iron. The liquor is let stand, the clear solution decanted off and subjected while still warm to the action of a stream of carbonic acid gas. This converts the soda into carbonate and precipitates the alumina in a particularly dense form which collects in a space not one-twentieth of the volume which would be taken up by gelatinous alumina. This precipitate is best washed by decantation, but a large number of washings are necessary to remove all the sodium carbonate from it ; it is even well, before finishing the washing, to add a little sal- ammoniac to the wash-water in order to hasten the removal of the soda. The well-dried alumina is calcined at a red heat. *Tilghman decomposes commercial sulphate of alumina, Al 2 - (SO 4 ) 3 .18H 2 O, by filling a red-hot fire-clay cylinder with it. This cylinder is lined inside with a magnesia fettling, is kept at a red heat, the sulphate put in in large lumps, and steam is passed through the retort, carrying with it vapor of sodium chloride. This last arrangement is effected by passing steam into a cast-iron retort in which the salt named is kept melted, and as the steam leaves this retort it carries vapor of the salt with it. It is pref- erable, however, to make a paste of the sulphate of alumina and the sodium chloride, forming it into small hollow cylinders, which are well dried, and then the fire-clay cylinder filled with these. Then, the cylinder being heated to whiteness, highly superheated steam is passed over it. The hydrochloric acid gas which is formed is caught in a condensing apparatus, and there remains a mass of aluminate of soda, which is moistened with water and treated with a current of carbon dioxide and steam. By washing * Mierzinski. 108 ALUMINIUM. the mass, the soda goes into solution and hydrated alumina re- mains, which is washed well and is ready for use. Mr. Webster's process for making pure alumina at a low price is now incorporated as a part of the Aluminium Co. Ld.'s pro- cesses, but whether it is that there have been no advances made in this line during the past few years or that valuable advances have been made but are sedulously kept secret, I am unable to say. The late descriptions of the Deville-Castner processes all commence with the sentiment : In the beginning we have alu- minium hydrate. Such being the case, the only description we can give of Webster's process is one dated 1883. *Three parts of potash alum are mixed with one part of pitch, placed in a calcining furnace and heated to 200 or 250. About 40 per cent, of water is thus driven off, leaving sulphate of pot- ash and aluminium, with some ferric oxide. After heating about three hours, the pasty mass is taken out, spread on a stone floor and when cold broken to pieces. Hydrochloric acid (20 to 25 per cent.) is poured upon these pieces, placed in piles, which are turned over from time to time. When the evolution of sulphu- retted hydrogen has stopped , about five per cent, of charcoal- powder or lampblack, with enough water to make a thick paste, is added. The mass is thoroughly broken up and mixed in a mill, and then worked into balls of about a pound each. These are bored through to facilitate drying, and heated in a drying chamber at first to 40, then in a furnace from 95 up to 150. The balls are then kept for three hours at a low red heat in retorts while a mixture of two parts steam and one part air is passed through, so that the sulphur and carbon are converted into sulphurous oxide and carbonic oxide, and thus escape. The current of gas carries over some potassium sulphate, ferrous sulphate, and alumina, and is therefore passed through clay condensers. The residue in the retorts consists of alumina and potassium sulphate ; it is removed, ground to fine powder in a mill, treated with about seven times its weight of water, boiled in a pan or boiler by means of steam for about one hour, then allowed to stand till cool. The solution containing the potassium sulphate * Austrian Patent, Sept. 28, 1882 ; English patent, No. 2580, 1881. Ding- ier, 1883, vol. 259, p. 86. PREPARATION OF ALUMINIUM COMPOUNDS. 109 is run off and evaporated to dryness, the alumina is washed and dried. The potassium sulphate, as a by-product, is said to pay one-half the cost of the process. This deposit contains about 84 per cent, of alumina, while that obtained by the old process of precipitation has only 65 per cent. Thus a large saving is effected in cost and 19 per cent, more alu- mina is obtained. In addition to this, the whole of the by-pro- ducts are recovered, consisting of potassium sulphate, sulphur (which is used in making sulphuric acid), and aluminate of iron. 2. PREPAEATION OF ALUMINA FROM BEAUXITE. At Salindres, the alumina used in the Deville process is ob- tained from beauxite by the following processes, which are in general use for extracting pure alumina from this mineral.* Beauxite is plentiful enough in the south of France, principally in the departments of Herault, Bouches-du-Khone, and Var. It contains at least seventy-five per cent, alumina. To separate the alumina from ferric oxide, it is treated with carbonate of soda, under the influence of a sufficiently high temperature, the alumina displacing the carbonic acid and forming an aluminate of soda, APO 3 .3Na 2 O, while the ferric oxide remains unattacked. A simple washing with water then permits the separation of the former from the insoluble ferric oxide. The beauxite is first finely pul- verized by means of a vertical mill-stone, then intimately mixed with some sodium carbonate. The mixture is made, for one opera- tion, of 480 kilos, beauxite. 300 " sodium carbonate of 90 alkali degrees. This mixture is introduced into a reverberatory furnace, resem- bling in form a soda furnace, and which will bear heating strongly. The mass is stirred from time to time, and it is kept heated until all the carbonate has been attacked, which is recognized by a test being taken which does not effervesce with acids. The operation lasts from five to six hours. The aluminate thus obtained is separated from ferric oxide by a washing with warm water. This washing is made at first with * Fremy's Ency. Chimique. 110 ALUMINIUM. a feeble solution which has served for the complete exhaustion of the preceding charge, which was last washed with pure water, forming thus this feeble solution. This gives, on the first leach- ing, solutions of aluminate concentrated enough to be called strong liquor, which are next treated by the current of carbonic acid gas to precipitate the hydrated alumina. The charge is next washed with pure water, which completely removes the aluminate ; this solution is the weak liquor, w r hich is put aside in a special tank, and used as the first leaching liquor on the next charge treated. This treatment takes place in the following apparatus (see Fig. 1) : B is a sheet-iron vessel, in the middle of which is a metallic Fig. 1, B 1-f.vYTfpe o grating, F, on which is held all round its edges, by pins, a cloth, serving as a filter. The upper part of this vessel is called sim- ply the filter. A ought to be closed by a metallic lid held on firmly by bolts. To work the apparatus, about 500 kilos of the PREPARATION OF ALUMINIUM COMPOUNDS. Ill charge to be washed is placed on the filter cloth, the lid is closed, then the steam-cock / of the reservoir A is opened. In A is the weak solution from the last washing of the preceding charge. The pressure of the steam makes it rise by the tube T into the filter; another jet of steam, admitted by the cock 6, rapidly warms the feeble liquor as it soaks into the charge. After filter- ing through, the strong liquor is drawn off by turning the stop- cock G. The weak solution of the reservoir A is put into the filter in successive portions, and not all at once ; and after each addition of solution has filtered through, its strength in B. is taken, before any more solution is run in ; then, when the solu- tion marks 3 to 4, it is placed in a special tank for weak liquor, with all that comes through afterwards. Just about this time, the weak liquor of the reservoir A is generally all used up, and is replaced by pure water introduced by the tube d. All the solu- tions which filtered through, marking over 3 to 4 B., are put together, and form the strong liquor which marks about 12 B. This extraction of the aluminate being completed by the pure water, the residue on the filter is taken out, and a new operation may be commenced. The strong liquor is introduced into a vessel having an agita- tor, where a strong current of carbonic acid gas may precipitate the alumina from it. The gas is produced by small streams of hydrochloric acid continuously falling on some limestone con- tained in a series of earthenware jars. The precipitation vessel is called a baratte. The carbonic acid after having passed through a washing flask, is directed to a battery of three barattes, where the precipitation is worked methodically, so as to precipitate com- pletely the alumina of each baratte, and utilize at the same time all the carbon dioxide produced. In order to do this, the gas always enters first into a baratte in which the precipitation is nearest completion, and arrives at last to that in which the solution is freshest. When the gas is not all absorbed in the last baratte, the first is emptied, for the precipitation in it is then completed, and it is made the last of the series, the current being now directed first into the baratte which was previously second, while the newly charged one is made the last of the series. The process is thus kept on continuously. The apparatus used is shown in Fig. 2. 112 ALUMINIUM. Each baratte holds about 1200 litres of solution, and the complete precipitation of all the alumina in it takes five to six hours. A mechanical agitator stirs the contents continually, and a current of steam is let into the double bottom so as to keep the tempera- Fig. 2. a. Charging pipe. 6. Steam pipe. c. Steam drip. d. CO 2 enters. /. Discharge pipe. A. Agitator, made of iron rods. (7. Tank in which the precipitate settles. B. "Baratte body. D. Steam jacket. ture of the solution about 70. The precipitated alumina and the solution of sodium carbonate which remain are received in a vat placed beneath each baratte. The solution is decanted off clear, after standing, and then evaporated down to dry ness, regenerating the sodium carbonate used in treating the beaux ite to make the alumiuate, less the inevitable losses inseparable from all indus- trial operations. The deposit of alumina is put into a conical strainer to drain, or else into a centrifugal drying machine, which rapidly drives out of the hydrated alumina the solution of sodium carbonate which impregnates it ; a washing with pure water in the drier itself terminates the preparation of the alumina. At PREPARATION OF ALUMINIUM COMPOUNDS. 113 the works at Salindres, a part of this alumina is converted into sulphate of alumina, which is sold, the remainder being used for the aluminium manufacture. After washing in the dryer, the alumina presents this composition : Alumina ....... 47.5 Water . . . . . . . . 50.0 Sodium carbonate . . . . . 2.5 Behnke* produces alumina by igniting beauxite or a similar mineral with sodium sulphate, carbon, and ferric oxide, using for each equivalent of alumina present at least one equivalent of alkali and one-half an equivalent of ferric oxide. The mixture is heated in a muffle or reverberatory furnace. The fritted prod- uct is ground, exposed to the air, and washed with water. Sod- ium aluminate goes into solution along with some sodium sul- phate, while ferrous sulphide and undecomposed material remains as a residue. By passing carbonic acid gas or gases from com- bustion through the solution, the alumina is precipitated. The residue spoken of is roasted, the sulphurous oxide given off utilized, and the residue used over in place of fresh ferric oxide. R. Lieberf proposes to treat beauxite, aluminous iron ore, etc. in a somewhat similar way. These materials are to be ground fine, mixed with sodium chloride and magnesium sulphate (Kieser- ite), moistened with water, and pressed into bricks or balls. These are dried and put into a retort heated red-hot by generator gas. Hydrochloric acid gas is first given off 4 , sodium sulphate and magnesium chloride being formed. In a further stage of the process sulphurous oxide is evolved, the alumina reacting on the sodium sulphate to form sodium aluminate. The latter is washed out of the residue, and its alumina precipitated by the ordinary methods. H. MullerJ proposes to extract the alumina from silicates con- taining it by mixing them with limestone, dolomite, or magnesite, also with alkali caustic, carbonate, or sulphate (in the last case also with carbon), and heating the mixture to bright-redness. * German Patent (D. R. P.), No. 7256. f German Patent (D. R. P.), No. 5670. | German Patent (D. R. P.), No. 12,947. 114 ALUMINIUM. Alkaline aluminate is washed out of the resulting mass, while the residue, consisting of lime, magnesia, iron oxide, etc., is mixed with water-glass and moulded into artificial stone. Common salt is said not to react on beauxite if fused with it alone, but will decompose it if steam is used. Tilghman* first used this reaction in 1847. It is said that it was also used at Nanterre and Salindres previously to 1865. A mixture of sodium chloride and beauxite was treated in a closed retort and steam passed through, or, better, in a reverberatory furnace and steam passed over it, at a high temperature. Much sodium chloride must have been lost by the latter arrangement. The fused mass was treated with water, when sodium aluminate dissolved out. R. Wagnerf proposed to make a solution of sodium sulphide, by reducing sodium sulphate by carbon bisulphide, and to boil the beauxite in it. The sulphuretted hydrogen evolved was to be absorbed by ferric hydrate ; while the sodium aluminate was converted into soda and alumina by any of the ordinary methods. According to Lowig's experiments, solution of sodium alu- minate can be precipitated by calcium, barium, strontium, or magnesium hydrates, forming caustic soda and hydrated alumina, the latter being precipitated, together with lime, baryta, strontia, or magnesia. The precipitate is washed by decantation and then divided into two portions, one of which is dissolved in hydro- chloric acid, the other made into a mush with water and gradually added to the solution of the first half until the filtrate shows only a very little alumina in solution. Chloride of calcium, barium, strontium, or magnesium has been formed, and the alumina all precipitated. Dr. K. J. Bayer has made an improvement in the process of extracting alumina from beauxite, which has received great com- mendation from those directly interested in the business, and who may be supposed to have proved its merits. Dr. Bayer thus describes it :J Beauxite is fused with sodium carbonate or sul- phate, and the solution obtained by washing, containing sodium * Polytechnisehes Journal, 106, p. 196. f Wagner's Jahresb., 1865, p. 332. t Stahl und Eisen, Feb. 1889, p. 112. PREPARATION OF ALUMINIUM COMPOUNDS. 115 aluminate, is not decomposed by carbonic acid as formerly, but by the addition of aluminium hydrate with constant stirring. The decomposition of the solution goes on until the quantity of alumina remaining in solution is to the sodium protoxide as 1 to 6. This precipitation takes place in the cold, and the pul- verulent aluminium hydrate separated out is easily soluble in acids. The alkaline solution remaining is concentrated by evap- oration, taken up by ground beauxite, dried, calcined, and melted, and thus goes through the process again. The use of this caustic soda solution containing alumina is thus much more profitable than using soda, because by using the latter only 75 per cent, of the beauxite used is utilized, whereas by the former all the alu- mina dissolved by the solution is obtained again. 3. PREPARATION OF ALUMINA FROM CRYOLITE. By the dry way. The following method was invented by Julius Thomson ; the description is taken principally from Mier- zinski's "Fabrikation des Aluminiums:" The cryolite is pul- verized, an easy operation, and to every 100 parts, 130 to 150 parts of chalk are added, and a suitable quantity of fluorspar is also used, which remains in the residue on washing after ignition. More chalk is used than is theoretically necessary, in order to make the mass less fusible and keep it porous. But, to avoid using too much chalk merely for this purpose, a certain quantity of coke may be put into the mixture. It is of the first im- portance that the mixture be very intimate and finely pulverized. It is of greater importance that the mixture be subjected to just the proper well-regulated temperature while being calcined. The cryolite will melt very easily, but this is to be avoided. On this account, the calcination cannot take place in an ordinary smelting furnace, because, in spite of stirring, the mass will melt at one place or another, while at another part of the hearth it is not even decomposed, because the heat at the fire-bridge is so much higher than at the farther end of the hearth. Thomson con- structed a furnace for this special purpose (see Figs. 3 and 4), in which the flame from the fire first went under the bed of the fur- nace, then over the charge spread out on the bed, and finally in 116 ALUMINIUM. a flue over the roof of the hearth.. The hearth has an area of nearly 9 square metres, being 4 metres long and 2.5 metres wide. It is charged twelve times each day, each time with 500 kilos of mixture, thus roasting 6000 kilos daily, with a consumption of 800 kilos of coal. The waste heat of the gases escaping from Fig. 4. the furnace is utilized for drying the soda solution to its crystal- lizing point, and the gases finally pass under an iron plate on which the chalk is dried. In this furnace the mass is ignited thoroughly without a bit of it melting, so that the residue can be fully washed with water. The decomposition takes place according to the formula Al 2 F 6 .6NaF + 6CaCO 3 - Al 2 3 .3Na 2 O + 6CaF 2 + 6CO 2 , the resultant product containing aluminate of soda, soluble in PREPARATION OF ALUMINIUM COMPOUNDS. 117 water, and insoluble calcium fluoride. The reaction commences at a gentle heat, but is not completed until a red heat is reached. Here is the critical point of the whole process, since a very little raising of the temperature above a red heat causes it to melt. However, it must not be understood that the forming of lumps is altogether to be avoided. These lumps would be very hard and unwork- able when cold, but they can be broken up easily while hot, so that they may be drawn out of the furnace a few minutes before the rest of the charge is removed, and broken up while still hot without any trouble. The whole charge, on being taken out, is cooled and sieved, the hard lumps which will not pass the sieve are ground in a mill and again feebly ignited, when they will become porous and may be easily ground up. However, the formation of these lumps can be avoided by industrious stirring of the charge in the furnace. A well-calcined mixture is porous, without dust and without lumps which are too hard to be crushed between the fingers. We would here remark that mechanical furnaces of similar construction to those used in the manufacture of soda, potash, sulphate of soda, etc., are more reliable and give the best results if used for this calcination. The mixture, or ashes, as the workmen call it, is drawn still hot, and washed while warm in conical wooden boxes with double bottoms, or the box may have but one bottom, with an iron plate about 76 milli- metres above it. A series of such boxes, or a large apparatus having several compartments, may be so arranged that the wash- ing is done methodically, i. e., the fresh water comes first in con- tact with a residue which is already washed nearly clean, and the fresh charge is washed by the strong liquor. This is known as the " Lessiveur rnethodique," and an apparatus constructed espe- cially for this purpose is described in Dingier 186, 376, by P. J. Havrez, but the subject is too general and the description too long to be given here. A very suitable washing apparatus is also that of Schank, used in the soda industry for washing crude soda, and described in " Lunge's Handbook of the Soda Industry," Book II. p. 410. Since the ashes are taken warm from the fur- nace the washing water need not be previously heated, but the final wash-water must be warmed, as the ashes have been cooled down by the previous washings. As soon as the strong liquor 118 ALUMINIUM. does not possess a certain strength, say 20 B., it is run over a fresh charge and so brought up. The solution contains sodium aluminate. The carbon dioxide necessary for precipitating the hydrated alumina may be made in different ways. The gases coming from the furnace in calcining the cryolite might be used if they were not contaminated with dust ; and there is also the difficulty that exhausting the gases from the furnace would interfere with the calcination. It has also been recommended to use the gases from the fires under the evaporating pans, by exhausting the air from the flues and purifying it by washing with water. This can only be done where the pans are fired with wood or gas. However, the lime-kiln is almost exclusively used to furnish this gas. The kiln used is shaped like a small blast furnace. Leading in at the boshes are two flues from five fire-places built in the brickwork of the furnace, and the heat from these calcines the limestone. The gases are taken off by a cast-iron down-take at the top. At' the bottom of the furnace, corresponding with the tap hole in a blast furnace, is an opening, kept closed, from which lime is with- drawn at intervals. A strong blast is blown in just above the entrance of the side flues, and by keeping up a pressure in the furnace, leakings into it may be avoided. The gas is sucked away from the top by a pump, which forces it through a cleaning apparatus constructed like a wash-bottle, and it is then stored in a gasometer. Instead of the pump, a steam aspirator may be used, which is always cheaper and takes up less room. The precipitation with carbonic acid gas is made by simply forcing it through a tube into the liquid. The apparatus used at Salindres is oue of the most improved forms. (See p. 112.) The precipitate is granular, and settles easily. However, it is not pure hydrated alumina, but a compound of alumina, soda, carbonic acid, and water, containing usually about Alumina 45 per cent. Sodium carbonate . . . . . . 20 " Water 35 " The sodium carbonate can be separated by long-continued boil- ing with water, but by this treatment the alumina becomes very gelatinous and very difficult of further treatment. The precip- PREPARATION OF ALUMINIUM COMPOUNDS. 119 itate was formerly separated on linen filters, but centrifugal machines are now preferred. The evaporated solution gives a high grade of carbonate of soda free from iron. The heavy resi- due which is left after the ashes have been lixiviated consists of calcium fluoride with small quantities of ferric oxide, lime, un- decomposed cryolite, and aluminate of soda, and has not been utilized for any purpose. R. Biederrnan* states that if steam is passed over molten cryo- lite at a white heat, hydrofluoric acid gas and sodium fluoride are formed and driven over, while a white, pure crystalline mass of alumina remains. Utilization of aluminous fluoride slags. At Nanterre, DeviDe used the following process for utilizing in one operation the slags from the aluminium manufacture and the residues from the so- dium manufacture. " The slags from making aluminium contain 60 per cent, of sodium chloride and 40 per cent, of insoluble matter; the former can be removed by a single washing. The insoluble material is almost entirely aluminium fluoride, with a little alumina and un- clecomposed cryolite. When fluorspar is used as a flux, the sodium chloride in the slag is in part replaced by calcium chloride ; but, in general, all the fluorine in the slag is found combined with the aluminium, which shows the great affinity between these two elements. The residues left in the sodium retorts deteriorate quickly when exposed to the air, and contain ordinarily, according to my analysis Carbon 20.0 Carbonate of soda . . . . . . .14.5 Caustic soda ........ 8.3 Sulphate of soda 2.4 Carbonates of lime and iron ..... 29.8 Water 25.0 100.0 "To utilize these two materials, 5 to 6 parts of the sodium residues are mixed carefully with one part of the washed slag, and the whole calcined at a red heat. The fusion becomes pasty ; * Kerl and Stohman, 4th Ed., p. 819. 120 ALUMINIUM. it is cooled and washed, when aluminate of soda goes into solu- tion and on treatment with carbon dioxide gives sodium carbonate and alumina. According to my laboratory experiments 1000 grammes of sodium residues 160 " " washed slags have given 110 " " calcined alumina 225 " " dry sodium carbonate. " The residue left on washing the fusion weighs about one-half the weight of the soda residues used, and contains Carbon . . . 30.0 Calcium fluoride . . . . . . . 32.0 Alumina . . . . . . . . .0.6 Various other materials ...... 37.4 " The latter item is formed of ferric oxide, oxide of manganese, a little silica and some oxysulphide of calcium. 7 ' Decomposition of cryolite in the wet way. Devi lie used the fol- lowing method at Javel, which he thus describes : " In the Greenland cryolite there are to be found numerous pieces containing siderite (ferrous carbonate). It is necessary to extract all these pieces before using the mineral as a flux in pro- ducing the aluminium. The rejected fragments are then utilized by pulverizing them finely, mixing with about three-fourths of their weight of pure, burnt lime and the whole carefully slaked. After the slaking, water is added in large quantity, and the ma- terial is heated in a large cast-iron vessel by means of a steam- coil. A reaction takes place at once, and is complete if the pro- cess is well conducted. Some insoluble aluminate of lime may be formed, but it can be recovered from the residue by digesting it with some solution of carbonate of soda. The residue re- maining is calcium fluoride, which settles easily, and the clear liquor decanted off contains aluminate of soda, from which alumina can be precipitated as before. The calcined alumina ob- tained may contain iron when the cryolite used contains a large amount of ferrous carbonate. It has appeared to me that the latter mineral may be decomposed by the lime, and some prot- oxide of iron be thus dissolved by the soda in small quantity. PREPARATION OF ALUMINIUM COMPOUNDS. 121 " We make alumina by this method at Nanterre only because it utilizes the impure pieces of cryolite and works in conveniently with the previously-described processes for utilizing the slags." An ingenious modification of the above process was devised by Sauerwein. The first reaction is the same, five parts of finely- powdered cryolite being boiled with four parts of burnt lime, as free as possible from iron, producing a solution of sodium alumin- ate and a residue of insoluble calcium fluoride. Tissier recom- mended using two parts of cryolite to one of lime, but with these proportions only about one-third of the aluminium in the cryolite is converted into soluble aluminate. Hahn claims that complete decomposition takes place by using 100 parts of cryolite to 88 parts of burnt lime. The solution is settled, washed by decan- tation, and these washings put with the strong solution first poured off; the next w r ashings are reserved for the fresh wash- water of another operation. The solution of sodium aluminate is then boiled with a quantity of cryolite equal to the amount first used, when sodium fluoride is formed and alumina precipi- tated. This operation is in no way difficult, only requiring a little more attention than the first. The alumina thus made is very finely divided. The reactions involved are : Al 2 F 6 .61NaF + 6CaO= Al 2 O 3 .3Na 2 O + 6CaF 2 . Al 2 F 6 .6NaF + Al 2 O 3 .3Na 2 O -f 6H 2 O== 2(A1 2 O 3 .3H 2 O) + 12NaF. During this last operation it is best to add an excess of cryo- lite, and keep the liquid in motion to prevent that mineral from caking at the bottom. Lead is the best material to make these precipitating tanks of, since iron would contaminate the alumina. The precipitate is washed as in the previous operation. The so- lution of sodium fluoride is boiled with the requisite quantity of burnt lime, which converts it into caustic soda, NaOH, which is separated from the precipitated calcium fluoride by decantation and washing. In the establishment of Weber, at Copenhagen, where at one time all the cryolite produced in Greenland was received, the mineral was decomposed by acid. Hydrochloric acid attacks the mineral slowly, but sulphuric acid immediately dissolves the sod- ium fluoride, with disengagement of hydrofluoric acid ; gelatin- 122 ALUMINIUM. ous aluminium fluoride separates out and is attacked more slowly. The cryolite requires nearly 1J parts of sulphuric acid to dissolve it, the reaction being The solution is evaporated and crystallized, when the sodium sul- phate crystallizes out and the mother liquor is treated for its alumina. This method is too costly when compared with more recent processes to be used at present. According to Schuch* very finely-powdered cryolite is dis- solved by a large excess of hot dilute soda solution, but is thrown down unaltered when carbonic acid gas is passed through the solution. An excess of concentrated soda liquor converts the mineral into sodium aluminate and sodium fluoride, the former being soluble but the latter almost insoluble in the soda solution. II. THE PREPARATION OF ALUMINIUM CHLORIDE AND ALUMINIUM-SODIUM CHLORIDE. Anhydrous aluminium chloride cannot be made by evaporating the solution of alumina in hydrochloric acid, for, as we have seen, decomposition of the salt sets in, hydrochloric acid is evolved and alumina remains. The same phenomena occur on evaporat- ing a solution of the double chloride. These anhydrous chlorides are prepared by a method discovered by Oerstedt, applicable to producing a number of similar metallic chlorides, which consists in passing a current of dry chlorine gas over an ignited mixture of alumina and carbon. Wohlerf proceeded as follows in preparing the aluminium chloride which was used in his early experiments: "Alumina is mixed w r ith charcoal powder and made plastic with oil. Cylin- ders of about 5 millimetres diameter are made of this paste, placed in a crucible with charcoal powder and heated until no more combustible gases distil. After cooling the crucible the ; * Poly tech ni sch es Journal, 166, p. 443. f Pogg. Aim., 11, p. 146. PREPARATION OF ALUMINIUM COMPOUNDS. 123 cylinders are taken out, and a porcelain or glass tube open at both ends filled with them. This is then placed in a combustion furnace, connected at one end with a chlorine generator, and at the other with a tubular extension from the further end of which the gases escape, either into the air or into a flask filled with milk of lime. When the whole apparatus is ready, and filled with well-dried chlorine gas, the tube is heated to glowing, when alu- minium chloride is formed and condenses in the extension of the tube/ 7 Deville paid great attention to the production and purification of aluminium chloride; the following is his account of the pro- cesses used at Javel : Manufacture on a small scale. " I took 5 kilos of alumina and mixed it with 2 kilos of carbon and a little oil ; the paste was made into balls and ignited at a bright-red heat. The compact, coke-like mass resulting was broken in pieces and put, with its powder, into a stoneware retort, C (Fig. 5), having a capacity of Fig. 5. about 10 litres, and terminating in a neck, D. This retort was put in a furnace and heated to redness, while a current of dry chlorine gas passed in by the tube A. During the first few moments considerable quantities of water vapor escape from the neck. When aluminium chloride distils, as is shown by dense, white fumes, a porcelain or stoneware funnel, E, is adjusted to the neck D, and kept in place by filling the joint with fine asbestos and then luting it over with a little potter's clay mixed with hair. 1 24 ALUMINIUM. Against this funnel fits a globular vessel, F, the joint being made tight in a similar way. This apparatus condenses and holds all the chloride distilled. However fast the chlorine may pass into the retort, it is so well absorbed during three-fourths of the opera- tion that not a trace is mixed with the carbonic oxide escaping. However, the gas always fumes a little because of a small quantity of silicon chloride being formed by the chlorine and carbon attack- ing the sides of the retort, or from chloride of sulphur or a little chloroxycarbonic acid. When the globe F is filled it is taken away to extract the coherent, crystalline aluminium chloride it contains, and is replaced immediately by another. During one operation three jars were thus filled, and altogether a little over 10 kilos of chloride obtained. In the retort there remained almost a kilo of coke mixed with alumina in the proportion of two of carbon to one of alumina, making 330 grammes of the latter remaining unattacked out of 5 kilos. This coke contains also some double chloride of alumina and potassium and a little calcium chloride, which render it deliquescent. This residue was washed, mixed with a fresh quantity of alumina, and employed in a new operation." Manufacture on a large scale. " In applying this process on a large scale, the oil and carbon were replaced by tar, the alembic by a gas-retort and the glass receiver by a small brick chamber lined with glazed tiles. The alumina was obtained by calcining ammonia alum in iron pots ; the residue obtained by one calcina- tion at a bright-red heat was mixed with pitch, to which a little charcoal dust was added. The paste was well mixed, introduced into iron pots, covered carefully and heated until all vapors of tar ceased burning. The aluminous carbon is used while it is still hot, if possible, as it is quite hygroscopic. (This aluminous car- bon conducts electricity wonderfully well ; it is the best electrode to use in inaking aluminium by the battery, since its alumina regenerates the bath.) The residue is hard, porous, and cracked, and contains sulphur from the sulphuric acid of the alum, a little iron, phosphoric acid in small quantity, a perceptible proportion of lime, and finally potash, which is always present in alums made from clay. The chlorine gas used was conducted by lead pipes and passed over calcium chloride before being used. The PREPARATION OF ALUMINIUM COMPOUNDS. 125 retort used was of about 300 litres capacity, and was placed ver- tically in a sort of chimney, C (Fig. 6), the flame circulating all around it. In the bottom was a square opening, x, about 20 centimetres square, which could be closed by a tile kept in place Fig. 6. by a screw, V. A porcelain tube pierced the sides of the furnace and entered the retort at ; it was protected from the flame by a fire-clay cylinder inclosing it. At the top, the retort was closed by a tile, Z, of refractory brick, in the centre of which was made a square opening, W, of 10 to 12 centimetres side. Finally, an opening, X y placed 30 centimetres below the plate Z, gave issue to the vapors distilled, conducting them into the chamber L. This condension chamber was about 1 metre cube ; it had one wall of bricks in common with the furnace, thus keeping it rather hot. The other walls should be thin and set with close joints and very little mortar. The cover, M, was movable; it and the sides of the chamber were of glazed tiles. An opening 20-30 centimetres square in the lower part of the chamber communicated with flues lined with lead, for a little chloride was drawn into them. The uncondensed gas passed to a chimney. " To work such an apparatus it is necessary, first of all, to dry 126 ALUMINIUM. it with the greatest care in all its parts, especially the condensa- tion chamber. The retort is slowly heated and is left open at Z until it is judged quite dry, and is then filled with red-hot, freshly calcined mixture of carbon and alumina. The top cover is then replaced and the fire urged until the retort is at a dark-red heat all over. Finally, chlorine is passed in, but the opening at Wis kept open ; the gas is allowed to pass into the condensation chamber only when fumes of aluminium chloride appear very abundantly at W. When the operation proceeds right, almost all the aluminium chloride is found attached in a dense, solid mass to the cover M. I have taken out at one time a plate weigh- ing almost 50 kilogrammes, which was less than 10 centimetres thick ; it was made up of a large number of sulphur-yellow crys- tals penetrating each other and looking like stalactites and long soda crystals. When it is judged that the material in the retort is almost exhausted, the hole x is opened, the residue scraped out, and fresh mixture put in. During the operation there should be no white vapors coming from the condensation chamber, but the odor of the gas will always be sharp because of the silicon chloride present, formed unavoidably by the chlorine attacking the retort. A gas retort, handled well, should last continuously two or three months, or even more. The furnace should be con- structed so as to permit its easy replacement without much expense. When in use, the retort is closely watched through spy- holes in the wall, and any cracks which may appear promptly plastered up, if not large, with a mixture of fine asbestos and soda glass." Purification of aluminium chloride. " It often happens that the chloride obtained is not pure, either from the nature of the apparatus employed, or from neglect of the many precautions which should be taken. In this case, to purify it, it is heated in an earthen or cast-iron vessel with fine iron turnings. When the hydrochloric acid, hydrogen and permanent gases are driven from the apparatus, it is closed and heated hotter, which produces a light pressure under which influence the aluminium chloride melts and enters into direct contact with the iron. The ferric chloride, which is as volatile as aluminium chloride, is transformed into ferrous chloride, which is much less volatile, and the aluminium PREPARATION OF ALUMINIUM COMPOUNDS. 127 chloride can be obtained pure by being volatilized away or dis- tilled in an atmosphere of hydrogen." When the processes just described were put in use at the chemi- cal works at La Glaeiere, great care had to be taken to avoid letting vapors and acid gases escape into the air, since the works were surrounded by dwellings. To avoid these inconveniences, the vapor of aluminium chloride was made to enter a heated space in which was sodium chloride, in order to produce the less vola- tile double chloride ; but the apparatus choked up so persistently that the attempt was given up. It then occurred to Deville to put sodium chloride into the mixture itself in the retort. The same apparatus was used as before, except that the large gas-retort had to be replaced by a smaller earthen one which could be heated much hotter, the grate being carried half way up the retort.* The condensation chamber had to be replaced by a small earthen vessel. The double chloride produced is fusible at about 200, and is quite colorless when pure, but colored yellow by iron. It is, moreover, very little altered in dry air when in compact masses and can be easily handled. When the double chloride is obtained quite pure, it gives up its aluminium completely when reduced by sodium. The following description by M. Margottetf will show the form of apparatus used in 1882 by the French company carrying on the Deville process at Salindres : The double chloride may be obtained in the same manner as the simple chloride ; it is sufficient to put some common salt, NaCl, into a mixture of alumina and carbon, and, on heating this mixture strongly, there is formed by the action of the chlorine, aluminium-sodium chloride, which distils at a red heat and con- denses in a crystalline mass at about 200. The hydrated alu- mina obtained in the preceding operation is mixed with salt and finely pulverized charcoal, in proper proportions, the whole is sifted, and a mixture produced as homogeneous as possible ; then it is agglomerated with water and made into balls the size of the * It was when first using this process that Deville borrowed some zinc re- torts from the Vielle Montagne works, and since they contained a little zinc in their composition the aluminium made for a while was quite zinciferrous. f Fremy's Ency. Chimique. 128 ALUMINIUM. fist. These balls are first dried in a drying stove, at about 150, then calcined at redness in retorts, where the double chloride should commence to be produced just as the balls are completely dried. These retorts are vertical cylinders of refractory earth, each one is furnished with a tube in its lower part for the intro- duction of chlorine, and with another towards its upper end for the exit of the vapor of double chloride. (See Fig. 7.) A lid Fig. 7. carefully luted during the operation with a mixture of fine clay and horse-dung serves for the charging and discharging of the retort. The double chloride is condensed in earthen pots like flower pots, made of ordinary clay, and closed by a well-luted cover, into which passes a pipe of clay to conduct the gas result- ing from the operation into flues connected with the main chimney. Each retort is heated by a fire, the flame of which circulates all round it, and permits keeping it at a bright red heat. An operation is conducted as follows : The retort is filled with stove dried balls, the lid is carefully luted, and the retort is heated gently till all the moisture is driven off. This complete desiccation is of great importance, and requires much time. Then chlorine, furnished by a battery of three generating vessels, is passed in. During the first hours, the gas is totally absorbed by the balls; the double chloride distils regularly for about three hours, and runs PREPARATION OF ALUMINIUM COMPOUNDS. 129 into the earthen pots where it solidifies. Toward the end, the distillation is more difficult and less regular, and the chlorine is then only incompletely absorbed. After each operation there re- mains a little residue in the retort, which accumulates and is re- moved every two days, when two operations are made per day. One operation lasts at least twelve hours, and a retort lasts some- times a month. The double chloride is kept in the pots in which it was condensed until the time it is to be used in the next operation ; it is almost chemically pure, save traces of iron, and is easy to keep and handle. The following estimate was made by Wurtz, in 1872, showing the cost of a kilo of aluminium-sodium chloride as made by the above process : Anhydrous alumina 0.59 kilos (5) 86 fr. per 100 kilos = fr. 50.7 cent. Manganese dioxide 3.74 " " 14 " Hydrochloric acid 15.72 " " 3 " Coal 25.78 " " 1.40 Wages Expenses 52.3 47.1 23.8 38.0 Total 2 " 48.0 " This is equal to about 22J cents per pound. An average of 10 kilos of this was used to produce one kilo of aluminium, which shows a yield of only 70 per cent, of the contained aluminium, and an increased cost of 67 cents on every pound of aluminium from the imperfection of reduction. In this respect there certainly seems large room for improvement. The largest plant ever erected for the manufacture of alu- minium-sodium chloride is that of the Aluminium Co. Ltd. at Oldbury near Birminghajn, England. The plant was commenced in the latter part of 1887, and was in working order in July, 1888. The process is in principle identical with that used at Salindres, but the whole is on such a large commercial scale that the appara- tus deserves description. Twelve large regenerative gas furnaces are used, in each of which are placed five horizontal fire-clay retorts about 10 feet in length, into which the mixture is placed. These furnaces are in two rows, of six each, along each side of a building about 250 feet long, leaving a clear passage down the centre 50 feet wide- 9 130 ALUMINIUM. Above this central passage is a platform swung from the roof, which carries the large lead mains to supply chlorine to the re- torts ; opposite each retort is a branch pipe controlled by a valve. The valves are designed so that the chlorine must pass through a certain depth of (non-aqueous) liquid, thus regulating the flow and preventing any back pressure in the retort from forcing vapor into the main. The opposite or back ends of the retorts are fitted with pipes which convey the vapor of the double chlor- ide into cast-iron condensers and thence into brick chests or boxes, the outsides or ends of which are closed by wooden doors fitting tightly. Convenient openings are arranged for clearing out the passages, which may become choked because of the quickness with which the double chloride condenses. On looking down the centre of the building it presents the appearance of a double bank of gas retorts for making ordinary illuminating gas, except that the retorts are only one high. The chlorine plant is on a correspondingly large scale, the usual manganese-dioxide method being employed and the spent liquor regenerated by Weldon's process. The chlorine gas is stored in large gasometers from which it is supplied to the retorts at a certain pressure. The mixture for treatment is made by mixing hydrated alumina with common salt and carbon in the form of charcoal powder or lamp-black. This being well mixed is moistened with water, thrown into a pug-mill from which it is forced out as solid cylinders, and cut into about 3 inch lengths by a workman. The lumps are then piled on top of the large chlor- ide furnaces to dry. In a few hours they are hard enough to allow handling, and are put into large wagons and wheeled to the front of the retorts. When the retorts are at the proper temperature for charging, the balls are thrown in until the retort is quite full, the fronts are then put up and luted tightly with clay, and the charge left alone for about four hours, during which the water of the hydrated alumina is completely expelled, the rear end of the retort being disconnected from the condensing chamber, which must be kept perfectly dry, and connected directly with the chimney. At the end of this time the chlorine is turned on and the retort con- nected with the receiver. At first the chlorine passed in is all PREPARATION OF ALUMINIUM COMPOUNDS. 131 absorbed by the charge and only carbonic oxide escapes into the boxes, where it is ignited and burns, thus warming them up. After a certain time dense fumes are evolved, and then the con- densers are shut tightly and the uncondensed gases pass into the chimney. The chlorine is passed in for 72 hours in varying quantity, the boxes at the rear being opened from time to time by the workmen to note the progress of the distillation. The greater part of the double chloride liquefies and trickles down to the floor of the chambers, but a portion sublimes and condenses on the walls as a yellow crystalline powder. These chambers are emptied from time to time and the contents packed away in air- tight wooden chests that it may keep without absorbing moisture from the air. At the end of the distillation the chlorine valves are closed and the condenser boxes cleaned out ; the retorts are also opened at their front end and the residue raked out. This residue consists of a small quantity of alumina, charcoal and salt, and is remixed in certain proportions with fresh material and used over again. The retorts are then immediately re-charged and the operations repeated. Each set of five retorts produces about 1600 to 1800 Ibs. in one operation, or say 3500 Ibs. per week. The twelve furnaces are therefore capable of producing easily 1,500,000 Ibs. of double chloride per annum. Since 10 Ibs. of this salt are required to produce 1 Ib. of aluminium, the capacity of the works is thus seen to be 150,000 Ibs. or over of metal per year. This last remark as to the proportion of chloride required to form the metal will show the absolute necessity there is to keep iron from contaminating the salt. This gets in, in varying pro- portions, from the iron in the materials used and in the fire-clay composing the retort, and exists as ferrous and ferric chlorides. Exercising the utmost care as to the purity of the alumina and charcoal used, and after having the retorts made of a special fire- clay containing a very small percentage of iron, it was found impossible to produce a chloride on a large scale containing less than 0.3 per cent, of iron. This crude chloride is highly deliques- cent and varies in color from light yellow to dark red the color depending not so much on the absolute amount of iron present as on the proportion of iron present as ferric salt, which has a high 132 ALUMINIUM. color. Since practically all the iron present in the salt passes into the aluminium, it is seen that the latter would contain 3 per cent, or more of iron. For some time the only way to obviate this difficulty was to resort to purifying the aluminium, by which the content of iron was finally reduced to 2 per cent. Mr. Castner has since perfected a process for purifying the double chloride by which only 0.01 per cent, of iron is left in it. The principle employed in doing this is described in the patent claims* to be the reduction of the iron salts to metallic iron by melting the chloride (single or double) with a quantity of metallic alumin- ium or sodium sufficient for this purpose. The purified chloride is quite white and far less deliquescent than the crude salt, which seems to indicate that the iron chlorides have a large share in ren- dering the crude salt so deliquescent. The purified chloride is preserved by melting and running into tight iron drums. The success of the manufacture of the double chloride is said to depend on the proportions of the mixture, the temperature of the furnace, the quantity of chlorine introduced and the details of construction of the retorts ; but very little information on these points has been made public. The following figures may give some idea of the quantities of materials used : The production of 100 Ibs. of double chloride is said to require Common salt 357 Ibs. Hydrated alumina . . . . . 491 " Chlorine gas . 674 " Coal 1800 " The salt and hydrated alumina are therefore mixed in about the same proportions as those indicated by the formula which represents the reaction APO 3 + 2NaCl + 3C + 6C1 = APCl 6 .2NaCl + 3CO. for if we assume the hydrated alumina used to contain 90 per cent, of that compound, the 491 Ibs. of it used would correspond to very nearly the amount of salt said to be used. As to the cost of this double chloride, so many uncertain elements enter into it that it cannot be satisfactorily estimated from the data at * U. S. Patent, No. 409668, Aug. 27, 1889. PREPARATION OF ALUMINIUM COMPOUNDS. 133 hand. We are informed, however,* that the double chloride used represents 43 per cent, of the cost of aluminium to this company. If we place the total cost at 8 shillings per Ib. this would indicate a trifle over 4 pence per Ib. as the cost of the double chloride. I think it is probably not over 3 pence. H. A. Gadsden,f of London, has patented a method of obtain- ing aluminium in which the aluminium chloride used is obtained by a method similar in all respects to the process as described by Deville except that the corundum or beauxite used is mixed with about 10 per cent, of sodium or potassium fluoride and a small quantity of fluorspar. After this has been mixed and calcined it is pulverized, 10 per cent, of charcoal dust added, made into balls and heated in a muffle until pasty. Taken out of the muf- fle they are then put into a retort, heated highly, and chlorine gas passed over them, when aluminium chloride distils. Count R. de MontgelasJ patents a process for producing alu- minium chloride and the double chloride with sodium, in which the only difference from the preceding methods is that molasses is used instead of pitch for moulding the mixture into balls, the mixture otherwise containing alumina, charcoal, and sodium chlor- ide, and it is claimed that by regulating the heat at which chlorine is passed over this mixture, previously calcined, aluminium chlor- ide can be volatilized while aluminium-sodium chloride remains in the retort. The use of horizontal retorts is recommended, and these certainly possess advantages over the vertical ones, but I am unable to say if this process has the merit of being the pioneer in this direction. Prof. Chas. F. Mabery, of the Case School of Applied Science, Cleveland, patented and assigned to the Cowles Bros, the process of making aluminium chloride, consisting in passing dry chlorine or hydrochloric acid gas over an alloy of aluminium and some other metal kept in a closed vessel at a temperature sufficient to volatilize the aluminium chloride formed, which is caught in a condenser. Or, hydrochloric acid gas is passed through an elec- * Zeitschrift des Vereins Deutscher Ingenieure, 1889, p. 301. f German Patent (D. R. P.) No. 27572 (1884). J English Patent, Nos. 10011, 10012, 10013, Aug. 4, 1886. U. S. Patent, Oct. 26, 1886. 134 ALUMINIUM. trically heated furnace in which alumina is being decomposed by carbon, a condenser being attached to the opposite end of the furnace. Mr. Paul Curie* states that aluminium chloride can be made by passing vapors of carbon disulphide and hydrochloric acid either simultaneously or successively over ignited alumina or clay. The first forms aluminium sulphide which the latter converts into the volatile chloride, which distils. H. W. AVarrenf recommends the following process as of gen- eral application in producing anhydrous metallic chlorides : Petroleum is saturated with either chlorine or hydrochloric acid gas, both gases being soluble in it to a large extent, particularly the latter gas. This operation is performed at a low temperature, as more of the gases is then dissolved. The oxide of the metal, alumina for instance, is put into large earthenware retorts and raised to red heat. The saturated oil is then boiled and its vapor passed into the retort. On contact with the oxide a strong reac- tion commences, fumes of aluminium chloride are at once evolved and distil into a condenser, the operation being continued until no more white fumes appear. Then fresh alumina is supplied, and the reaction continues. The aluminium chloride may be purified from any oil by gentle application of heat. Mr. War- ren also used naphthaline chloride with advantage, as also chloride of carbon, but their high price rendered them unable to compare with petroleum in economy. Aluminium bromide can be simi- larly prepared by substituting bromine for chlorine. Camille A. Faure, of New York, the well-known inventor of the Faure storage battery, has patented^ a process for producing aluminium chloride which is very similar to the above method. The manipulation is described as follows : An oxygenated ore of aluminium is brought to about a red heat by bringing it, in a furnace, into direct contact with the flame. When at proper heat the flame is cut off and a gas containing carbon and chlorine in- troduced. A mixture of petroleum vapor or a similar hydro- * Chemical News, 1873, p. 307. f Chemical News, April 29, 1887. t U. S. Patent, No. 385345, July 3, 1888. PREPARATION OF ALUMINIUM COMPOUNDS. 135 carbon with hydrochloric acid gas is preferred. Vaporized chloride of aluminium immediately passes off into a condenser. In a paper written by Mr. Faure, and read before the French Academy of Sciences by M. Berthelot,* it was stated that the aim of this process was to suppress the prominent disadvantages of the older methods : viz., cost and wear and tear of retorts, great consumption of fuel, slowness of the operation, large amount of labor, and cost of the chlorine. For this purpose the chlorine is replaced by hydrochloric acid gas and the carbon by a hydro- carbon, Since all pure hydrocarbons are decomposed at a red heat with deposition of carbon the process would appear impracticable, but a proper mixture of hydrochloric acid gas and naphtha- line vapor is said not to decompose by the highest temperature alone, a new compound being formed, a sort of naphthaline chlo- ride, which is exceedingly corrosive and powerful enough to attack any oxide and convert it into chloride. To carry out the process a gas furnace with large bed is used. On this is spread a layer of small pieces of beauxite about two feet deep. The flame comes in over the ore, passes downward through it and through numerous holes arranged in the hearth, and thence to a chimney. In this way the heat of the gases is well utilized, while the layer of beauxite is heated to whiteness on top and to low-red at the bottom. The flames are then turned off and the mixture of naphthaline and hydrochloric acid vapors passed upward through the bed, and by their reaction producing aluminium chloride, which is diverted by suitable flues into a condenser. It is claimed that by careful fractional condensation the chlorides of silicon, iron, calcium, etc., formed from impurities in the beauxite, can be easily separated, that of silicon being more volatile and those of iron and calcium less volatile than aluminium chloride. As naph- thaline is a bye product from gas-works, it is claimed that it can be bought for 1| cents per lb., and that only J of a Ib. is used per lb. of aluminium chloride produced. It is also claimed that one furnace, with two men to work it, will produce 4000 Ibs. of chloride a day. The estimated cost of the chloride is about 1 J cents per pound, of which 17 per cent, is for beauxite, 47 per * July 30, 1888. 136 ALUMINIUM. cent, for hydrochloric acid, 27 per cent, for naphthaline, and 9 per cent, for labor. Mr. Faure has been experimenting in the vicinity of New York during the last few months, and is sanguine of having the process at work commercially in 1890. (See further, Chap. XL) In all the processes for producing aluminium chloride so far considered the use of common clay was not recommended, since silicon chloride is formed as well as aluminium chloride. The only method proposed for using clay for this purpose is that of M. Dullo, nearly twenty years ago, and which cannot have been very successful, since it has not been heard of in operation. We will repeat his remarks, however, for there is still a large field open in the utilization of clay for the manufacture of aluminium, and since the metal is becoming so cheap the manufacturers are not above looking for and utilizing the cheapest raw material available. * " Aluminium chloride may be obtained easily by direct treat- ment of clay. For this purpose a good clay, free from iron and sand, is mixed with enough water to make a thick pulp, to which are added sodium chloride and pulverized carbon. For every 100 parts of dry clay there are taken 120 parts of salt and 30 of car- bon. The mixture is dried and broken up into small fragments, which are then introduced into a red-hot retort traversed by a current of chlorine. Carbonic oxide is disengaged, while at the same time aluminium chloride and a little silicon chloride are formed. It is not necessary that the chlorine should be absolutely dry, it may be employed just as it comes from the generator. The gas is absorbed very rapidly, because between the aluminium and silicon there are reciprocal actions under the influence of which the chemical actions are more prompt and energetic. The alu- minium having for chlorine a greater affinity than silicon has, alu- minium chloride is first formed, and it is only when all the alu- minium is thus transformed that any silicon chloride is formed. When the latter begins to form the operation is stopped, the in- candescent mixture is taken out of the retort and treated with water. The solution is evaporated to dryness to separate out a * Bull, de la Soc. Chem. 1860, vol. v. p. 472. PREPARATION OF ALUMINIUM COMPOUNDS. 137 small quantity of silica which is in it, the residue is taken up with water, and aluminium-sodium double chloride remains when the filtered solution is evaporated to dry ness." "We must say of M. Dullo's suggestions that it is the general experience that the more volatile silicon chloride is formed first ; it is also very improbable that a solution of aluminium-sodium chloride can be evaporated without decomposition. III. THE PREPARATION OF ALUMINIUM FLUORIDE AND ALUMINIUM-SODIUM FLUORIDE. (CRYOLITE.) Natural cryolite is too impure for use in many operations which aim to produce very pure aluminium. Schuh has proposed boil- ing the mineral in solution of soda. Under certain conditions sodium aluminate is formed (see p. 1 22), but if the solution of soda is dilute the liquor remains clear after taking up the cryolite, and on passing a current of carbonic acid gas through it aluminium- sodium fluoride is precipitated. In this way the pure double fluoride can be separated from impure cryolite. Berzelius recommended preparing artificial cryolite by decom- posing aluminium hydrate by a solution of sodium fluoride and hydrofluoric acid, the hydrate being added to the liquid until its acidity was just neutralized : A1 2 O 3 .3H 2 O -f 6NaF + 6HF = Al 2 F 6 .6NaF -f 6H 2 O. If a solution of sodium fluoride alone is used, half the alu- minium and half the sodium will remain in the solution as sod- ium aluminate : 2A1 2 O 3 .3H 2 O + 12NaF = Al 2 F 6 .6NaF + Al 2 O 3 .3Na 2 O + 3H 2 O. Deville states that on adding sodium chloride to a solution ob- tained by dissolving alumina in an excess of hydrofluoric acid, a precipitate of cryolite is obtained. Since cryolite is hardly at- tacked at all by hydrochloric acid, it is probable that the reaction occurring is A1 2 F 6 + 6HF + 6NaCl = Al 2 F 6 .6NaF + 6HC1. 138 ALUMINIUM. The process which Deville recommended as best, however, is the treatment of a mixture of calcined alumina and carbonate of soda, mixed in the proportions in which their bases exist in cryo- lite, by an excess of pure hydrofluoric acid : A1 2 O 3 + 3Na 2 CO 3 + 12HF = Al 2 F 6 .6NaF + SCO 2 + 6H 2 O. 100 parts of pure alumina requiring 310 parts of sodium carbonate and 245 of anhydrous hydrofluoric acid, there being 410 parts of cryolite formed. On drying the mass and melting it there results a limpid, homogeneous bath having all the characteristics of cryo- lite, being reduced by sodium or by an electric current, which would not result from a mere mixture of alumina and sodium fluoride melted together. Deville also states that when anhydrous aluminium chloride is heated with sodium fluoride in excess, a molten bath results of great fluidity, and on cooling and dissolving away the excess of sodium fluoride by repeated washings the residue is similar to cryolite, while the solution contains no trace of any soluble alu- minium salt : A1 2 C1 6 + 12NaF = Al 2 F 6 .6NaF + 6NaCl. It is evident, however, that the above reaction would be the re- verse of a profitable one, and is therefore not of economical utility. Pieper* patents a very similar reaction but operates in the wet way. A solution of aluminium chloride is decomposed by adding to it a suitable quantity of sodium fluoride in solution. Sodium chloride is formed and cryolite precipitated, as in the last reaction given. By adding different proportions of sodium fluoride solu- tion precipitates of double salts are obtained containing varying proportions of the two fluorides. The use of aluminium chloride in solution would dispense with the objection made to Deville's analogous method, and this process would very probably produce cryolite quite cheaply. Brunerf produced aluminium fluoride by passing hydrofluoric acid gas in the required quantity over alumina heated red hot in a platinum crucible : APO 3 + 6HF = A1 2 F 6 + 3H 2 O. German Patent (D. R. P.), No. 35212. f p gg- Annalen, 98, p. 488. PREPARATION OF ALUMINIUM COMPOUNDS. 139 Deville* states that it can be made by melting together equiva- lent quantities of cryolite and aluminium sulphate : APF 6 .6NaF + AP(SO 4 ) 3 .tfH 2 O = 2A1 2 F 6 + 3Na 2 SO 4 + o:H 2 O. On washing the fusion, sodium sulphate goes into solution. It is also stated that hydrochloric acid gas acting on a mixture of fluorspar arid alumina at a high temperature will produce alumin- ium fluoride : APO 3 + 3CaF 2 + 6HC1 = APF 6 + 3CaCP + 3H 2 O. The calcium chloride would be partly volatilized and the re- mainder washed out of the fusion. Hautefeuillef obtained crystallized aluminium fluoride by pass- ing hydrofluoric acid gas and steam together over red-hot alumina. Ludwig Grabau, of Hanover, bases his process of producing aluminium on the reduction of aluminium fluoride (see Chap. X.), which is prepared on a commercial scale by the following inge- nious methods : JThe process is based on the conversion of aluminium sulphate into fluoride by reaction with cryolite, the fluoride being after- wards reduced by sodium in such manner that a double fluoride of sodium and aluminium' results which is used over again, thus forming a continuous process. The purest obtainable cryolite is used to start the process, after which no more is needed, the ma- terial supplying the aluminium being its sulphate, which can be obtained cheaply in large quantities and almost perfectly pure. The process is outlined by the reactions APF 6 .6NaF + AP(SO 4 ) 3 = 2APF 6 + 3Na 2 SO 4 2 APF 6 4- 6Na= 2 Al + Al 2 F 6 .61S T aF. It is thus seen that theoretically the cryolite would be exactly re- produced, but the losses and incomplete reactions unavoidable in practice would cause less to be obtained and necessitate the con- tinual addition of fresh cryolite; since, however, it is not desired to base the process on the continual use of cryolite, because of the * Ann. de Chim. et de Phys. [3], 61, p. 333 ; [3], 49, p. 79 f Idem, [4 J, 4, p. 153. t German Patent (D. R. P.) No. 48535, March 8, 1889. 140 ALUMINIUM. impurities in that mineral, an indirect process is used consisting of two reactions, in place of the first given above, in which theoretically a larger quantity of cryolite is finally obtained than is used to begin with. This is operated by introducing fluorspar into the process, the base of which goes out as calcium sulphate or gypsum and so supplies the fluorine needed. In practice, a solution of aluminium sulphate is heated with powdered fluorspar (obtained as pure as possible and further cleaned by treatment with dilute hydrochloric acid). The alu- minium sulphate will not be entirely converted into fluoride, as has been previously observed by Friedel, but about two-thirds of the sulphuric acid is replaced by fluorine, forming a fluor- sulphate of aluminium. This latter compound remains in solution, while gypsum and undecomposed fluorspar remain as a residue and are filtered out. A1 2 (SO 4 ) 3 + 2CaF 2 = A1 2 F 4 (SO 4 ) + 2CaSO 4 . This solution is concentrated and mixed with cryolite in such proportion that the alkali in the latter is just equivalent to the sulphuric acid in the fluor-sulphate. The mass is dried and ignited, and the product washed and dried. 3A1 2 F 4 (SO 4 ) + Al 2 F 6 .6NaF= 4A1 2 F 6 + 3Na 2 SO 4 . On reduction with sodium, the 4 molecules of aluminium fluoride, treated with sodium as by the reaction given, produce 2 molecules of the double fluoride. It is thus seen that after allowing for reasonable losses in the process there is much more cryolite pro- duced than is used, and the excess can be very profitably sold as pure cryolite, being absolutely free from iron or silica. IV. THE PREPARATION OF ALUMINIUM SULPHIDE. Until the researches of M. Fremy, no other method of pro- ducing aluminium sulphide was known save by acting on the metal with sulphur at a very high heat. Fremy was the first to open up a different method, and it may be that his discoveries will yet be the basis of successful industrial processes. In order PREPARATION OF ALUMINIUM COMPOUNDS. 141 to understand just how much he discovered we here give all that his original paper contains concerning this sulphide.* " We know that sulphur has no action on silica or boric oxide, magnesia, or alumina. I thought that it might be possible to replace the oxygen by sulphur if I introduced or intervened a second affinity, as that of carbon for oxygen These decomposi- tions produced by two affinities are very frequent in chemistry ; it is thus that carbon and chlorine, by acting simultaneously on silica or alumina, produce silicon or aluminium chloride, while either alone could not decompose it ; a similar case is the decom- position of chromic oxide by carbon bisulphide, producing chrom- ium sesquisulphide. Reflecting on these relations, I thought that carbon bisulphide ought to act at a high heat on silica, magnesia, and alumina, producing easily their sulphides. Experi- ment has confirmed this view. I have been able to obtain in this way almost all the sulphides which until then had been produced only by the action of sulphur on the metals. " To facilitate the reaction and to protect the sulphide from the decomposing action of the alkalies contained in the porcelain tube which was used, I found it sometimes useful to mix the oxides with carbon and to form the mixture into bullets resem- bling those employed in the preparation of aluminium chloride. I ordinarily placed the bullets in little carbon boats, and heated the tube to whiteness in the current of vaporized carbon bisul- phide. The presence of divided carbon does not appear useful in the preparation of this sulphide. " The aluminium sulphide formed is not volatile ; it remains in the carbon boats and presents the appearance of a melted vitreous mass. On contact with water it is immediately decom- posed. APS 3 + 3H 2 O= APO 3 + 3H 2 S. " The alumina is precipitated, no part of it going into solution. This precipitated alumina is immediately soluble in weak acids. The clear solution, evaporated to dryness, gives no trace of alumina. It is on this phenomenon that I base the method of analysis. * Ann. de Chem. et de Phys. [3] xxxviii. 312. 142 ALUMINIUM. u Aluminium sulphide being non-volatile, it is always mixed with some undecomposed alumina. It is, in fact, impossible to entirely transform all the alumina into sulphide. I have heated less than a gramme of alumina to redness five or six hours in carbon bisulphide vappr, and the product was always a mixture of alumina and aluminium sulphide. The reason is that the sulphide being non-volatile and fusible coats over the alumina and prevents its further decomposition. The alumina thus mixed with the sulphide, and which has been exposed to a red heat for a long time, is very hard, scratches glass, and is in grains which are entirely insoluble in acids. By reason of this property I have been able to analyze the product exactly, for on treating the product with water and determining on the one hand the sulphu- retted hydrogen evolved, and on the other the quantity of soluble alumina resulting, I have determined the two elements of the compound. One gramme of my product contained 0.365 grrn. of aluminium sulphide, or 36.5 per cent., the remainder being undecomposed alumina." The composition of this sulphide was Aluminium ..... 0.137 grm. = 37.5 per cent. Sulphur 0.228 " = 62.5 " 0.365 " 100.0 " The formula APS 3 requires Aluminium .36.3 per cent. Sulphur , 63.7 " The above is the substance of Fremy's investigations and results. Reichel* next published an account of further experi- ments in this line. He found that by melting alumina and sul- phur together no reaction ensued. In the case of magnesia, the sulphide was formed if carbon was mixed with the magnesia and sulphur, but this change did not alter the alumina. Hydrogen gas passed over a mixture of alumina and sulphur likewise gave negative results. Sulphuretted hydrogen passed over ignited alu- mina did not succeed. By filling a tube with pure alumina, pass- ing in hydrogen gas and the vapor of carbon bisulphide, the heat- ing being continued until carbon bisulphide condensed in the * Jahresb. der Chemie, 1867, p. 155. PREPARATION OF ALUMINIUM COMPOUNDS. 143 outlet tube, and then hydrogen being passed through until the tube was cold, a product was obtained containing aluminium sul- phide and undecomposed alumina. In 1886, I made a series of experiments on the production and reduction of aluminium sulphide. Alumina, either alone or mixed with carbon or with carbon and sulphur, was put in porce- lain or carbon boats into a hard glass or porcelain tube. This was then heated and vapor of carbon bisulphide passed over it. The product was analyzed according to Fremy's directions. The proportion of aluminium sulphide obtained in the product varied from 13 to 40 per cent. The best result was obtained at the highest heat almost whiteness. The presence of sulphur or car- bon, or both together, mixed with the alumina did not promote to any degree the formation of a richer product. The conditions for obtaining the best results seem to be high heat and fine divis- ion of the alumina to facilitate its contact with the carbon bisulphide vapor. The product was light -yellow when not mixed with carbon, easily pulverized, and evolved sulphuretted hydrogen gas energetically when dropped into water. Since car- bon bisulphide can now be manufactured at a very low price, say 2 to 3 cents per lb., it is not impossible that it may be found pro- fitable to produce aluminium from its sulphide. In such a case, large retorts would be used, a stirring apparatus would facilitate the formation of a richer product, and the unused carbon bisul- phide could be condensed and saved. M. Comenge,* of Paris, proposed to prepare aluminium sul- phide by using a clay retort similar to those used in gas-works, filling it one-half its length with charcoal or coke and the other half with alumina. The retort being heated to redness, sulphur is introduced at the coke end, when in contact with the carbon it forms carbon bisulphide, which acts upon the alumina at the other end, producing the sulphide. Messrs. Reillon, Montague, and Bourgerelf obtained a patent in England for producing aluminium, in which aluminium sul- phide is obtained by mixing powdered alumina with 40 per cent. * English Patent, 1858, No. 461. f English Patent, No. 4756, March 28, 1887. 144 ALUMINIUM. of its weight of charcoal or lampblack and formed into a paste with a sufficient quantity of oil or tar. This is then calcined in a closed vessel and an aluminous coke obtained. This is broken into pieces, put into a retort, and treated with carbon bisulphide vapor. The inventors state that the reaction takes place accord- ing to the formula 2Al 2 O 3 -f-3C + 3CS 2 =2Al 2 S 3 -f 6CO. Petitjean* states that if alumina is mixed with tar or turpen- tine and ignited in a carbon-lined crucible, and the coke obtained mixed intimately with sulphur and carbonate of soda and ignited a long time at bright redness, there results a double sulphide of aluminium and sodium, from which aluminium can be easily extracted. It has been statedf that if aluminium fluoride is heated with calcium sulphide, aluminium sulphide results. F. LauterbornJ also makes the same claim in a patent twenty years later, but the possibility of this reaction taking place is not yet beyond ques- tion. CHAPTER VII. THE MANUFACTURE OF SODIUM. SOME years ago, in order to treat fully of the metallurgy of aluminium, it would have been as necessary to accompany it with all the details of the manufacture of sodium as to give the details of the reduction of the aluminium, because the manufac- ture of the former was carried on solely in connection with that of the latter. But now sodium has come out of the list of chemical curiosities and has become an article of commerce, used for many other purposes than the reduction of aluminium, though that is still its chief use. So we regard the manufacture of sodium as a separate metallurgical subject, still intimately con- * Polytechnisches Central. Blatt., 1858, p. 888. t Chemical News, 1860. J German Patent (D. R. P.), No. 14495 (1880). THE MANUFACTURE OF SODIUM. 145 nected with that of aluminium, but yet so far distinct from it as to deserve a metallurgical treatise of its own. Davy to Devllle (1808-1855). Sodium was first isolated by Davy by the use of electricity in the year 1808.* Later Gay Lussac and Thenard made it by de- composing at a very high temperature a mixture of sodium car- bonate and iron filings, f In 1808, also, Curaudau announced that he had succeeded in producing potassium or sodium without using iron, simply by decomposing their carbonates by means of animal charcoal. Briinner, continuing this investigation, used instead of animal charcoal the so-called black flux, the product obtained by calcining crude tartar from wine barrels. He was the first to use the wrought-iron mercury bottles. The mixture was heated white hot in a furnace, the sodium volatilized, and was condensed in an iron tube screwed into the top of the flask, which projected from the furnace and was cooled with water. In Briinner's experiments he only obtained three per cent, of the weight of the mixture as metallic sodium, the rest of the metal being lost as vapor. Donny and Mareska gave the condenser the form which with a few modifications it retains to-day. It was of iron, 4 millimetres thick, Fl S- 8 - and was made in the shape of a book, having a length of about 100 centi- metres, breadth 50, and depth 6 (see Fig. 8). This form is now so well known that a further description is unnecessary. With this condenser the greatest difficulty of the process was removed, and the operation could be carried on in safety. This apparatus was devised and used by Donny and Mareska in 1854, with the supervision of Deville. * Phil. Trans., 1808. f Recherches Physico-chemiques, 1810. 10 146 ALUMINIUM. Devitte's Improvements at Javel (1 855). The followiDg is Deville's own description of the attempts which he made to reduce the cost of producing sodium. As far as we can learn these experiments were commenced in 1854, but the processes about to be given are those which were carried out at Javel, March to June, 1855. As the description contains so many allusions to the difficulties met not only in producing but also in handling and preserving sodium, its perusal is yet of value to all concerned in this subject, although the actual methods here described have been superseded by much more economical ones. Properties of sodium. The small equivalent of sodium and the low price of sodium carbonate should long since have caused it to be preferred to potassium in chemical operations, but a false idea prevailed for a long time concerning the difficulties accom- panying the reduction. When I commenced these researches the cost of sodium was at least double that of potassium. In this connection I can quote from my memoir published in the Ann. de China, et de Phys., Jan. 1, 1855 : "I have studied with care the preparation of sodium and its properties with respect to oxygen and the air, in order to solve the difficulties which ac- company its reduction and the dangers of handling it. In this latter respect, sodium is not to be compared to potassium. As an example of how dangerous the latter is, I will relate that being used to handle sodium and wishing once to replace it with potassium, the simple rubbing of the metal between two sheets of paper sufficed to ignite it with an explosion. Sodium may be beaten out between two sheets of paper, cut and handled in the air without accident if the fingers and tools used are not wet. It may be heated with impunity in the air, even to its fusing point, without taking fire, and, when melted, oxidation takes place slowly, and only at the expense of the moisture of the air. I have even concluded that the vapor alone of sodium is inflam- mable, but the vivid combustion of the metal can yet take place at a temperature which is far below its boiling point, but at which the tension of the metallic vapors has become sensible." I will add to these remarks that sodium possesses two considerable ad- vantages : it is obtained pure at the first operation, and, thanks THE MANUFACTURE OF SODIUM. 147 to a knack which I was a long time in finding out, the globules of the metal may be reunited and treated as an ordinary metal when melting and casting in the air. I have thus been able to dispense with the distillation of the raw products in the manu- facture an operation which had become to be believed necessary, and which occasioned a loss of 50 per cent, or so on the return without appreciable advantage to the purity of the metal. The manufacture of sodium is in no manner incumbered by the carbu- retted products, or perhaps nitrides, which are very explosive and render the preparation of potassium so dangerous. I ought to say, however, that by making potassium on a large scale by the processes I am about to describe for sodium, Rousseau Bros, have diminished the dangers of its preparation very much, and practise the process daily in their chemical works. Method employed. The method of manufacture is founded on the reaction of carbon on alkaline carbonate. This method has been very rarely applied to sodium, but is used every day for producing potassium. Briinner's process is, in fact, very difficult to apply, great trouble being met, especially, in the shape of con- denser used. It is Donny and Mareska who have mastered the principles which should guide in constructing these condensers. Composition of mixtures used. The mixture which has given me excellent results in the laboratory is Sodium carbonate . . . * . . 717 parts. Wood charcoal . . . . . * . . 175 " Chalk 108 " 1000 Dry carbonate of soda is used, the carbon and chalk pulverized, the whole made into a paste with oil and calcined in a crucible. The end of a mercury bottle, cut off, serves very well, and can be conveniently closed. Oil may be used altogether in place of char- coal, in which case the following proportions are used : Sodium carbonate 625 parts. Oil 280 " Chalk 95 " That a mixture be considered good, it should not melt at the temperature at which sodium is evolved, becoming liquid at this 148 ALUMINIUM. point, and so obstructing the disengagement of the gas.* But it should become pasty, so as to mould itself evenly against the lower side of the iron vessel in which it is heated. The considerable latent heat required by carbonic oxide and sodium in assuming the gaseous state is one cause of cooling which retards the com- bustion of the iron. When soda salt is introduced in place of dried soda crystals, the mixture, whatever its composition, always melts, the gases making a sort of ebullition, the workmen saying that the apparatus "sputters." This behavior characterizes a bad mixture. It has been demonstrated to me that the economy made at the expense of a material such as carbonate of soda, the price of which varies with its strength in degrees, and which forms relatively a small portion of the cost of sodium, is annulled by a decrease of 20 to 25 per cent, in the return of sodium. The oil used ought to be dry and of long flame. It acts as a reducing agent, and also furnishes during the whole operation hydrogenous gases, and even, towards the close, pure hydrogen, which help to carry the sodium vapor rapidly away into the condenser, and to protect the condensed metal from the destructive action of the carbonic oxide. Oil renders a similar service in the manufacture of zinc. The role of the chalk is easy to understand. By its infusibility it decreases the liability of the mixture to melt. Further, it gives off carbonic acid, immediately reduced by the carbon present to carbonic oxide. Now, the sodium ought to be carried rapidly away, out of the apparatus, because it has the property of decomposing carbonic oxide, which is simultaneously formed, within certain limits of temperature, especially if the sodium is disseminated in little globules and so presents a large surface to the destructive action of the gas. It is necessary, then, that the metallic vapors should be rapidly conducted into the con- denser and brought into the liquid state not into that state com- parable to " flowers of sulphur," in which the metal is very oxidizable because of its fine division. A rapid current of gas, even of carbonic oxide, actively carries the vapors into the con- * It seems plain, however, granting that vapors would be evolved most freely from a perfectly infusible charge, that a pasty condition, such as is recom- mended in the next sentence, would be the worst possible state of the charge for evolving gas, being manifestly inferior to a completely fluid bath. J. W. R. THE MANUFACTURE OF SODIUM. 149 denser, which they keep warm and so facilitate the reunion of the globules of sodium. At La Glaciere and Nanterre a mixture was used in which the proportion of chalk, far from being dimin- ished, was, on the contrary, increased. The proportions used were Sodium carbonate . . . .40 kilos = 597 parts. Oil 18 " = 269 " Chalk 9 " = 134 " 67 " 1000 This quantity of mixture ought to give 9.4 kilos of sodium, melted and cast into ingots, without counting the metal di- vided and mixed with foreign materials, of which a good deal is formed. This return would be one-seventh of the weight of the mixture or one-quarter of the sodium carbonate used. Use of these mixtures. The carbonate of soda, charcoal, and chalk ought to be pulverized and sieved, well mixed and again sieved in order to make a very intimate mixture; the mixture ought to be used as soon as possible after preparing, that it may not take up moisture. The mixture may be put just as it is into the apparatus where it should furnish sodium, but it may very advantageously be previously calcined so as to reduce its volume considerably, and so permit a greater weight being put into the same vessel. I believe that whenever this calcination may be made with economy, as with the waste heat of a furnace, a gain is made by doing so, but the procedure is not indispensable. However, the utility of it may be judged when it is stated that a mercury bottle held 2 kilos of non-calcined mixture, but 3.6 kilos were put into one when previously calcined. These two bottles heated in the same fire for the same time gave quantities of sodium very nearly proportional to the weight of soda in them. In working under the direction of a good workman, who made the bottles serve for almost four operations, I have been able to obtain very fine sodium at as low a price as 9.25 francs per kilo ($0.84 per pound). In the manufacture of sodium by the continuous process, where the materials may be introduced red hot into the apparatus, this preliminary calcination is a very economical operation. 150 ALUMINIUM. Apparatus for reducing, condensing, and heating. M. Briin- ner had the happy idea of employing mercury bottles in manu- facturing potassium, thus the apparatus for reduction was in the hands of any chemist, and at such a low price that any one has been able to make potassium without much trouble. These bot- tles are equally suitable for preparing sodium, and the quantity which may be obtained from such apparatus and the ease with which they are heated, are such that they might have been, used a long time for the industrial manufacture, except for two reasons which tend to increase the price of these bottles continually. For some time a large number of bottles have been sent to the gold workers of Australia and California, also large quantities have been used in late years in preparing the alkaline metals ; these two facts have diminished the number to such a point that from 0.5 to 1 franc the price has been raised to 2.5 or 3 francs. It has thus become necessary to replace them, which has been done by substituting large wrought iron tubes which have the added advantage of being able to be worked continuously. I will first describe the manufacture in mercury bottles, which may still be very advantageously used in the laboratory, and after- wards the continuous production in large iron cylinders as now worked industrially. Manufacture in mercury bottles. The apparatus needed is com- posed of a furnace, a mercury bottle, and a condenser. The form of furnace most suitable is a square shaft, C (Fig. 9)? the sides of which are refractory brick, while the grate G ought to have movable grate bars, the furnace being connected above with a chimney furnishing good draft. The flue F, connecting with the chimney, should have a damper, R, closing tightly and should lead exactly from the centre of the top of the shaft, thus dividing the draft equally all over the grate. Coke is charged through lateral openings at 0. A small opening closed by a brick should be left a short distance above the grate bars, in order to poke down the coke around the bottle should it not fall freely. The space between the grate and bottle should always be full of fuel in order to keep the iron of the bottle from being burnt. In front of the furnace is a square opening, P, closed with an iron plate, which has a hole in it by which the tube T issues from the furnace. 151 THE MANUFACTURE OF SODIUM. The mercury bottle is supported on two refractory bricks, cut on their top side to the curve of the bottle. These should be Fig. 9. at least 20 centimetres high, to maintain between the grate and bottle a convenient distance. The illustration gives the vertical dimensions correctly, but the horizontal dimensions are somewhat shortened. There should be at least 12 centimetres between the bottle and the sides of the furnace. However, all these dimen- sions should vary with the strength of the chimney draft and the kind of fuel used ; the furnace should be narrower if the draft is very strong and the coke dense. The iron tube T 7 , which may conveniently be made of a gun barrel, is either screwed into the bottle or it may be simply fitted and forced into place, provided it holds tightly enough. It should be about 5 to 6 centimetres long, and should project scarcely 1 centimetre from the furnace. The end projecting should be tapered off in order to fit closely into the neck of the condenser. The condenser is constructed with very little deviation from that given by Donny and Mareska (see Fig. 8, p. 145). I have tried my best to make this apparatus as perfect as possible, but have always reverted to the form described by those authors ; yet even the very small differences I have made are indispensable and must be rigidly adhered to if it is wished to get the best 152 ALUMINIUM. Fig. 10. results obtainable. Two plates of sheet iron, 2 to 3 millimetres thick, are taken and cut into the shape indicated by Fig. 10. One plate, A, remains flat except at the point C, where it is drawn by hammering into a semi-cylindrical neck of about 25 millime- tres inside diameter. This corresponds with a similar neck in the other plate, so that on joining the two there is a short cylinder formed. The edges of the plate A are raised all around the sides about 5 to 6 millimetres, so that when the two plates are put together the longitudinal section from D to C is as in Fig. 11. As to the end, in one form the edge was not turned up, leav- Fig. 11. Fig. 12. Fig. 13. Fig. 14. ing the end open as in Fig. 12. Another form, which I use when wishing to let the sodium accumulate in the condenser till it is quite full, is made by turning up the edge at the end all but a small space left free, thus giving the end the appearance of Fig. 13, this device also being shown in Fig. 10. The gas evolved during the reaction then escapes at the hole 0. The most rational arrangement of the apparatus is that shown in Fig. 14. In this condenser the lower part, instead of being horizontal, is inclined, and the end having two openings, and #', the sodium trickles out at the lower one as it condenses, while the gas escapes by the slightly larger upper opening. In placing the plates together, the raised edges are washed with lime so as to form a good joint with the flat plate, and the plates are kept together by strong pressure grips. To conduct the operation, the bottles are filled entirely with THE MANUFACTURE OF SODIUM. 153 mixture, the tube T adjusted, and then placed on the two sup- ports, there being already a good bed of fire on the grate. The front is put up, the shaft filled with coke, and the damper opened. The gases disengaged from the bottle are abundant, of a yellow color ; at the end of half an hour white fumes of carbonate of soda appear. The condenser should not yet be attached, but it should be noted if any sodium condenses on a cold iron rod pushed into the tube, which would be indicated by it fuming in the air. As soon as this test shows that sodium is being produced the condenser is attached and the fire kept quite hot. The condenser soon becomes warm from the gases passing through it, while the sodium condenses and flows out at the end D (Fig. 9). It is received in a cast-iron basin L, in which some non- volatile petroleum is put. When at the end of a certain time the con- denser becomes choked, it is replaced by another which has been previously warmed up to 200 or 300 by placing it on top of the furnace. If the closed condenser is used, care must be taken to watch when it becomes full, on the point of running from the upper opening, and the condenser then replaced and plunged into a cast-iron pot full of petroleum at a temperature of 150. The sodium here melts at the bottom of this pot and is ladled out at the end of the day. The oil is generally kept up to 150 by the hot condensers being plunged in constantly. The pot ought to have a close cover, to close it in case the oil takes fire ; the ex- tinction of the fire can thus be assured and no danger results. If the oil fires just as a condenser is being introduced, the sodium is run out in the air without igniting, the only drawback being that the condenser must be cleaned before using again. This method occasions a large loss of oil, however, and has been completely abandoned for the other form of condensers. When the opera- tion proceeds well only pure sodium is obtained, the carbonized products which accompany in so provoking a manner the pre- paration of potassium not occurring in quantity sufficient to cause any trouble. Before using a condenser a second time it is put on a grating over a basin of petroleum and rubbed with a chisel- pointed tool in order to remove any such carbonized products. From time to time this material is collected, put into a mercury bottle, and heated gently. The oil first distils, and is condensed 154 ALUMINIUM. in another cold bottle. The fire is then urged, a condenser at- tached, and the operation proceeds as with a fresh charge, much sodium being thus recovered. The raw sodium is obtained from the bottles in quantities of over half a kilo ; it is perfectly pure, dissolving in absolute al- cohol without residue. It is melted and moulded into ingots just as lead or zinc. The operation I have described is executed daily, and only once has the sodium ignited. To prevent such accidents it is simply necessary to keep water away from the ap- paratus. The reduction of carbonate of soda and the production of sodium are such easy operations that when tried by those con- versant with the manufacture of potassium or who have read about the difficulties of the production of sodium, success is only gained after several attempts the failure being due solely to ex- cess of precautions. The reduction should be carried on rapidly, so that a bottle charged with two kilos of mixture may be heated and emptied in, at most, two hours. It is unnecessary to prolong the operation after the yellow flame stops issuing from the con- denser, for no more sodium is obtained and the bottle may fre- quently be destroyed. The temperature necessary for the re- duction is not so high as it has been so far imagined. M. Rivot, who has assisted in these experiments, thinks that the bottles are not heated higher than the retorts in the middle of the zinc fur- naces at Vielle Montagne. I have been even induced to try cast- iron bottles, but they did not resist the first heating, without doubt because they were not protected from the fire by any luting or covering. But I was immediately successful in using cast-iron bottles decarburised by the process used for making malleable castings. The mercury bottles heated without an envelope ought to serve three or four operations when entrusted to a careful workman. Besides all these precautions, success in this work de- pends particularly on the ability and experience of the workman, who can at any time double the cost of the sodium by careless- ness in managing the fire. . Continuous manufacture in cylinders. It might be thought that by increasing proportionately in all their parts the dimensions of the apparatus just described it would be easy to produce much larger quantities of sodium. This idea, which naturally presented THE MANUFACTURE OF SODIUM. 155 itself to me at once, has been the cause of many unfruitful at- tempts, into the details of which I will not enter. I must, how- ever, explain some details which may appear insignificant at first sight, but which were necessitated during the development of the process. For instance, it will perhaps look irrational for me to keep the same sized outlet tubes and condensers that were used with the mercury bottles, for tubes five times as large ; but I was forced to adopt this arrangement after trying the use of tubes and condensers of all sizes ; indeed, it is fortunate for the suc- cess of the operation that this was so, for it became very injurious to the workmen to handle the large and weighty apparatus in the face of a large sodium flame. The mixture of sodium carbonate and carbon is made in the manner already described. I would say again that a previous strong calcination of the materials presents a great advantage, not only because it permits putting a much larger weight into the retorts at once but also that, being more compact, the mixture will not rise as powder and be violently thrown out of the strongly- Fig. 15. heated retorts. The mixture should also be calcined as needed and used to fill the tubes while still red hot. When cold, un- calcined mixture is used, it is put into large cartridges of thick paper or canvas, 8 centimetres diameter and 35 centimetres long. 156 ALUMINIUM. The furnace and tubes are shown in section in Fig. 15. The tubes Tare 120 centimetres long, 14 centimetres inside diameter, and 10 to 12 millimetres in thickness. They are formed from one piece of boiler iron, bent and welded along one side. The iron plate P which closes one end is about 2 centimetres thick, and pierced on one of its edges quite close to the side of the cylinder by a hole in which is screwed or fitted an iron tube, L, 5 to 6 centimetres long and 15 to 20 millimetres inside diameter, and tapering off at the end to fit into the condenser neck. The other end of the tube is closed by an iron plug, 0, terminated by a knob. The welded side of the tube is kept uppermost. These iron tubes should not, like the mercury bottles, be heated in the bare fire ; it is necessary to coat them with a resistant luting which is itself enveloped by a refractory jacket 1 centimetre thick, 22 centimetres interior diameter, and the same length as the retorts. This protection is commenced by plastering the retorts over with a mixture of equal parts of raw clay and stove ashes, which have been made into a paste with water and as much sand worked into the mixture as it will take without losing its plas- ticity, also adding some horse manure. This luting should be dried slowly, and the tube thus prepared is introduced into the refractory jacket, the open space between the two being filled with a powdered refractory brick. Finally, luting is put on the iron plate P 9 so that no part of it is exposed to the flame. The furnace I have used is a reverberatory, but I do not re- commend its use without important modifications because it does not realize all the conditions of easy and economic heating. The grate is divided into two parts by a little wall of refractory brick, on which the middle of the reduction cylinders rests. The tubes are thus seen to be immediately over the bed of fuel. The top of the bridge is a little higher than the upper edge of the cylinders, this and the very low arch making the flame circulate better all around the tubes. A third cylinder might easily be placed above these two, and be heated satisfactorily, without any more fuel be- ing burnt. This reverberatory receives on its bed the mixtures to be calcined, placed in cast-iron or earthen pots according to their composition. When the furnace is kept going night and day pro- ducing sodium, the temperature rises on the bed to clear cherry- THE MANUFACTUKE OF SODIUM. 157 red, and experience has shown that other reducing cylinders might be placed there, under such conditions, and be heated sufficiently for the reduction. All that I have said of the manufacture of sodium in mercury bottles applies equally to its manufacture in cylinders. The only difference consists in the charging and discharging, and I have only to add several precautions to be taken. On introducing the cartridges containing uncalcined mixture, only 8 to 9 kilos can be heated at once ; double as much can be used of previously calcined mixture. The plug is put in place, not so tightly that it cannot easily be taken out again ; a little luting stops all leakages which show themselves. The reduction lasts about four hours. When it is finished, a little water is thrown on the plug 0, and it is easily loosened and removed. On looking into the cylinder, the cartridges are seen to have kept their shape, but have shrunken so much that their diameter is only about 2 to 3 centimetres ; they are very spongy. This shows that the mixture has not melted ; the remainder is principally lime and carbon, and free from sodium carbonate. While opening the cylinder, a bright-red-hot iron is thrust into the outlet tube L, to keep dirt from getting into it, and it is kept in until the charging is finished. The cartridges are put in by means of semi-cylin- drical shovels. The sudden heating of the mixture disengages soda dust from uncalcined mixtures, which is very disagreeable to the workmen. The cylinders are closed, and when the sodium flame appears at the outlet tube the condenser is attached, and the operation proceeds as already described. The envelopes of the cylinders are thick enough to prevent the distillation of the sodium being in any way affected by the accidental causes of cooling of the fire. So when fresh fuel is charged or the door of the reverberatory is opened causing the draft to cease almost entirely in the fire-place, the operation should not suffer by these intermittences provided that they are not too prolonged. In short, when operating in cylinders, the production of sodium is easier, less injurious to the workmen, and less costly in regard to labor and fuel than when working with mercury bottles. At times, after working a fortnight with many interruptions dangerous for the apparatus, my experiment 158 ALUMINIUM. has been suddenly ended. The furnace was intact; the envelopes of the tubes were split open, and the luting on the tubes found to be compact and coherent but without traces of fusion, showing perfect resistance. The iron tubes meanwhile had not suffered inside or out, and seemed as though they would last indefinitely. I attribute this success to the particular care given to the com- position of the jackets, and to the perfection with which the tubes had been welded. Only on one of the tubes was a very slight crack found on a part not the most highly heated, and not suffi- cient to cause the tube to be discarded. Tissier Bros* method of procedure (1856). As related in the historical treatment of the subject (p. 22), Deville charged the Tissier Bros, with appropriating from him the process for the continuous production of sodium in cylinders, which, as just given, was devised during the experiments at Javel. On the other hand, the Tissier Bros, asserted their right to the process, patenting it, and using it in the works started at Rouen in the latter part of 1 855. The following details are taken from Tissier's " Recherche de F Aluminium," only such being selected as sup- plement Deville's description which has just been given. The sodium carbonate is first well dried at a high temperature, then mixed with well-dried pulverized charcoal and chalk, ground to the finest powder, the success of the operation depending on the fineness of this mixture. The proportions of these to use are various. One simple mixture is of Sodium carbonate 566 Coal .244 Chalk . 95 Coke 95 1000 Another contains Sodium carbonate .615 Coal 277 Chalk 108 1000 The addition of chalk has the object of making the mixture less fusible and more porous, but has the disadvantage that the THE MANUFACTURE OF SODIUM. 159 residue remaining in the retort after the operation is very impure, and it is impossible to add any of it to the succeeding charge ; and also, some of it being reduced to caustic lime forms caustic alkali with some sodium carbonate, which is then lost. When the mixture is well made it is subjected to a preliminary calcin- ation. This is done in cast-iron cylinders, two of which are placed side by side in a furnace and heated to redness (see Fig. 16). This is continued till all the moisture, carbonic acid, and Fig. 16. any carburetted hydrogen from the coal cease coming off. The mass contracts, becomes white and somewhat dense, so that a larger amount of the mixture can now be treated in the retorts where the sodium is evolved. As soon as the outcoming gases burn with a yellow flame, showing sodium coming off, the calcin- ation is stopped. The mixture is then immediately drawn out on to the stone floor of the shop, where it cools quickly and is then ready for the next operation. This calcination yields a mixture which without any previous reactions is just ready to evolve sodium when brought to the necessary temperature. This material is made into a sort of cylinder or cartridge and put into the decomposition retorts (see Fig. 15). The charging should be done quickly. The final retorts are of wrought-iron, since cast-iron would not stand the heat. At each end this retort is closed with wrought-iron stoppers and made tight with fire-clay. Through one stopper leads the pipe to the condenser, the other stopper is the one removed when the retort is to be recharged. These retorts are placed horizontally in rows in a furnace. Usu- ally four are placed in a furnace, preferably heated by gas, such as the Siemens regenerative furnace or Bicheroux, these being 160 ALUMINIUM. much more economical. In spite of all these precautions the retorts will be strongly attacked, and in order to protect them from the destructive action of a white heat for seven or eight hours they are coated with some kind of fire-proof material. The best for this purpose is graphite, which is made into cylin- ders inclosing the retorts, and which can remain in place till the furnace is worn out. These graphite cylinders not only protect the iron retorts, but prevent the diffusion of the gaseous products of the reaction into the hearth, and so support the retorts that their removal from the furnace is easily accomplished. Instead of these graphite cylinders the retorts may be painted with a mixture that melts at white heat and so enamels the outside. A mixture of alumina, sand, yellow earth, borax, and water-glass will serve very well in many cases. We would remark that the waste gases from this furnace can be used for the calcining of the mixture, or even for the reduction of the aluminium by sodium where the manufacture of the former is connected with the making of the sodium. As for the reduction of the sodium, the retort is first heated to redness, during which the stopper at the condenser end of the retort is left off. The charge is then rapidly put in, and the stopper at once put in place. The reaction begins almost at once and the operation is soon under full headway, the gases evolved burning from the upper slit of the condenser tube with a flame a foot long. The gases increase in volume as the operation con- tinues, the flame becoming yellower from sodium and so intensely bright as to be insupportable to look at. Now has come the moment when the workman must quickly adapt the condenser to the end of the tube projecting from the retort, the joint being greased with tallow or paraffin. The sodium collects in this in a melted state and trickles out. The length of the operation varies, depending on the intensity of the heat and the quantity of the mixture ; a charge may sometimes be driven over in two hours, and sometimes it takes eight. We can say, in general, that if the reaction goes on quickly a somewhat larger amount of sodmm is obtained. The higher the heat used, however, the quicker the retorts are destroyed. The operation requires con- tinual attention. From time to time, a workman with a prod THE MANUFACTURE OF SODIUM. 161 opens up the neck of the condenser. But if care is not taken the metal overflows ; if this happens, the metal overflowing is thrown into some petroleum, while another man replaces the con- denser with an empty one. The operation is ended when the evolution of gas ceases and the flame becomes short and feeble, while the connecting tube between the retort and condenser keeps clean and does not stop up. As soon as this occurs, the stopper at the charging end is removed, the charge raked out into an iron car, and a new charge being put in, the operation continues. After several operations the retorts must be well cleaned and scraped out. The sodium thus obtained is in melted bits or drops, mixed with carbon and sodium carbonate. It must, there- fore, be cleaned, which is done by melting it in a wrought-iron kettle under paraffin with a gentle heat, and then casting it into the desired shapes. The sodium is kept under a layer of oil or any hydrocarbon of high boiling point containing no oxygen. Tissier gives the reaction as Na'CO 3 4- 2C= SCO + 2Na. The sodium is condensed, while the carbonic oxide, carrying over some sodium, burns at the end of the apparatus. This would all be very simple if the reaction of carbonic oxide on sodium near the condensing point did not complicate matters, pro- ducing a black, infusible deposit of sodium monoxide (Na 2 O) and carbon, which 011 being melted always gives rise to a loss of sodium. Devillds Improvements at La Glacier e (1857). At this works Deville tried the continuous process of manu- facturing sodium in cylinders on a still larger scale, with the fol- lowing results, as described by Deville himself: We made no change in the composition of the mixtures used from those already described, or in the form or size of the iron tubes or the method of condensation ; but we worked with six cylinders at a time in a furnace similar to the puddling furnaces of M. Guadillot, the tubes being protected by refractory envelopes. The cylinders were so arranged on the hearth that the flame bathed all parts of their surface. A low brick wall extends down the 11 162 ALUMINIUM. centre of the hearth, supporting the middle of the cylinders, which extend across it. The hearth is well rammed with refractory sand, and the space between it and the bottom of the cylinders serves as a passage way for most of the flame. Our six cylinders worked satisfactorily for five days. We were able to observe that they were all heated with remarkable uniformity, and that the heat was sufficient all round them. It also appeared that the rear end of the cylinders required only a hermetic seal. Indeed, as soon as the operation was well under way and sodium distilling off, some of it condensed and oxidized in the cool parts of the apparatus, forming a sort of plug of carbonate and carbides of sodium which the vapor and gases could no longer penetrate. We were thus able for a long time to distil sodium away from one of our tubes which was entirely opened at the rear. This new furnace worked so well that we were hopeful of com- plete success when an accident happened which compelled the stopping of the experiment. The iron tubes had been ordered 1.20 metres long, the size of the hearth calculated accordingly, but they were delivered to us only 1.05 metres long. We made use of these, with the result that the rear ends became red-hot during the operation and allowed sodium vapors to leak through. These leaked through the luting, and escaping into the furnace melted the envelopes very rapidly. In another attempt, in which this fault was avoided, we were unsuccessful because the envelopes gave way at the first heating up, both they and the iron tubes being of inferior quality. We were considerably inconvenienced by the failure of these experi- ments, which caused considerable expense and gave no very de- finite results. Just then a new sort of apparatus was devised, a description of which is given later on. It will be seen that we were compelled to employ tubes of very small value, so that their destruction in case of accident involved no great loss, and to heat each one by an independent fire, so that the stoppage or de- struction of one cylinder would not necessitate the stoppage or endanger the safety of the neighboring ones. Cast-iron vessels. Deville tried at La Glaciere, as well as at Javel, to utilize cast-iron vessels for producing sodium. Deville THE MANUFACTURE OF SODIUM. 163 states the difficulties which caused their use to be unsuccessful to be as follows : The result was always unfavorable. Sodium is obtained, but as soon as its production becomes rapid the vessel melts and the operation is quickly ended. This follows because the temperature necessary for the production of the metal is far from being suffi- cient for producing it in large quantities at once ; and we know that this is the one condition for condensing the sodium well and obtaining it economically. This observation led me to think that by diminishing very much the temperature of the furnace, large apparatus of cast-iron with large working surface could be used, thus making at a time a large amount of metallic vapor which could be condensed in recipients of ordinary size. The whole large apparatus would thus have the output of a smaller one worked at a higher temperature. My experience has shown me that in large sized tubes heated to a low temperature there is formed in a given time about as much sodium as from a single mercury bottle at a much higher heat. This is the reason why larger condensers are not necessary with the larger tubes. Be- fore knowing this fact, I tried a large number of useless experi- ments to determine the size of condensers suitable for large ap- paratus. It is on this principle that I have long been endeavor- ing to make sodium without working at high temperatures and using less costly and more easily protected apparatus. Improvements used at Natiterre (1859). The method used here was exactly that already described, the improvements being solely in details of the apparatus. These are described by Devil le as follows : The experiments made at Javel and the continuous process used at Glaciere have shown us in the clearest manner the abso- lute necessity of efficient protection for the iron cylinders, for without this protection the method cannot be practised with economy. Further, experiments in this direction are very costly, for the failure of a tube stops the working of a large number of cylinders and often compromises the brick work of the furnace itself. We therefore came to the conclusion that for making the 164 ALUMINIUM. small quantity of sodium we required, 300 to 500 kilos a month, it would be better to employ smaller apparatus independent of each other and easy to replace. The iron tubes are made of thinner iron and at very little expense, by taking a sheet of iron, curving it into a cylinder and rivetting the seam. This tube resembles very closely those used at Javel, shown in Fig. 15, but of smaller dimensions. It is closed at each end by cast-iron plugs, one of which has a hole for the outlet tube. These cylinders are filled with sodium mixture and placed in furnaces of the form of Fig. 9, except it is neces- sary to have openings in the back and front of the furnace so that the cast-iron plugs closing the cylinders may be outside, to prevent their melting. We used coke at first for fuel, fed around the cylinders, but M. Morin has since placed the tubes out of direct contact with the fuel, uses soft coal, and heats the tubes by contact with the flame and by radiation. In the latest form used, two cylinders are placed in each furnace, and, in general, they serve for two or three operations. All that has been said in con- nection with the manufacture in mercury bottles is immediately applicable to the manufacture in cylinders of this kind, the capaci- ties of which may vary from two to six or eight litres, without any change in the manner of using them. We have, however, adopted altogether condensers of cast iron. The neck is cylin- drical and belongs only to one-half of the apparatus, the neck end of the other plate being bevelled and fitting closely against a recess in the other plate. The foregoing shows the sodium industry as it was perfected by Deville, in 1859, and as it remained for twenty-five years without sensible change. The cost of sodium by this process is stated to have been, in 1872, as follows : Manufacture of one kilo of sodium. Soda . . .9.35 kilos @ 32 fr. per 100 kilos = 3 fr. 9 cent. Coal . . .74.32 " "1.40" " " =1" 4 " Wages . . . . 1 " 73 " Expenses . . . 3 " 46 " Total . . . . 11 " 32 " which is equal to $1 per Ib. The larger part of the expense ac- count is the cost of retorts or tubes in which the operation takes THE MANUFACTURE OF SODIUM. 165 place, and which are so quickly destroyed that the replacing of them forms nearly one-quarter of the cost of the metal. Minor Improvements (18591888). R. Wagner* uses paraffin in preference to paraffin oil in which to keep the sodium after making it. Only pure paraffin, which has been melted a long time on a water bath, and all its water driven off, can be used. The sodium to be preserved is dipped in the paraffin melted on a water bath and kept at no higher heat than 55, and the metal is thereby covered with a thick coat of paraffin which protects it from oxidation, and may then be put up in wooden or paper boxes. When the metal is to be used, it is easily freed from paraffin by simply warming it, since sodium melts at 95 to 96 C., and the paraffin at 50 to 60. The reduction of potassium carbonate by carbon requires a much less degree of heat than that of sodium carbonate, and, therefore, many attempts have been made to reduce potassium and sodium together, under circumstances where sodium alone would not be reduced. Dumasf added some potassium carbonate to the regular sodium mixture ; and separated the sodium and potassium from each other by a slow, tedious oxidation. R. Wag- nerj made a similar attempt. He says that not only does the reduction of both metals from a mixture of their carbonates with carbon work easier than sodium carbonate alone with carbon, but even caustic soda may be used with potassium car- bonate and carbon. Also, the melting point of potassium and sodium alloyed is much lower than that of either one alone, in consequence of which their boiling point and the temperature required for reduction are lower. J. B. Thompson and W. White specify mixing dry sodium carbonate with a liquid carbonaceous material, preferably tar, driving off all volatile matter in iron pots at a low heat, and then distilling in a tubular fire-clay retort connected with a tightly- closed receiver containing a little paraffin oil to insure a non- oxidizing atmosphere, and also provided with a small escape pipe * Dingier, 1883, p. 252. f Handbuch der Angewandten Chernie, 1830, ii. 345. J Dingier, 143, 343. English Patent 8426, June 11, 1887. 166 ALUMINIUM. for carbonic oxide. This process gave great prospects of suc- cess when tried in the laboratory, but on a manufacturing scale it failed for the reason (assigned by Mr. Thompson) that the sheet- iron tray, designed to keep the material from attacking the retort, absorbed carbon at about 1000 and fused, after which no sodium was produced, since the material took up silica from the retort, absorbing so much that the carbon no longer decomposed it. H. S. Blackmore,* of Mount Vernon, U. S. A., patents the fol- lowing process of obtaining sodium : 27 parts calcium hydrate, 31 " ferric oxide, 31 " dry sodium carbonate, 10 " charcoal are intimately mixed and subjected to a red heat for 20 minutes, afterwards to a white heat. Caustic soda is first produced, the carbon reduces the ferric oxide, producing iron, which in its turn reduces the caustic soda and sodium vapors distil. The residue consists of ferric oxide and lime, and is slaked and used over. O. M. Thowlessf of Newark, N. J., claims to place a retort in a furnace, providing it on one side with an arm through which carboniferous material can be supplied, on the other side with a similar arm (surrounded by flues), into which caustic soda or sodium carbonate is charged a valve controlling their flow into the retort. Outside the furnace and on top of it is a flat conden- ser into which the sodium vapor passes. G. A. Jar vis J patents the replacement of the iron tubes or crucibles used in the manufacture of sodium, by fire-clay appara- tus lined with basic material, such as strongly burnt magnesia with 10 per cent, of fluorspar. Castner's Process (1886). The first public announcement of this process was through one of the New York daily journals, and as the tone of the article is above that of the usual newspaper reports, and the expectations contained in it have been subsequently more than realized, we * English Patent 15156, Oct. 22, 1888. f English Patent 12486 (1887). t English Patent 4842, March 31, 1888. New York World, May 16, 1886. THE MANUFACTURE OF SODIUM. 167 cannot better introduce a description of this process than by quoting the paragraph referred to : "When sodium was reduced in price to $1.50 per Ib. it was thought to have touched a bottom figure, and all hope of making it any cheaper seemed fruitless. This cheapening was not brought about by any improved or new process of reduction, but was owing simply to the fact that the aluminium industry required sodium, and by making it in large quantities its cost does not exceed the above-mentioned price. The retail price is now $4.00 per Ib. The process now used was invented by Briinner, in 1808, and up to the present time nothing new or original has been patented except three or four modifications of his process which have been adopted to meet the requirements of using it on a large scale. Mr. H. Y. Castner, whose laboratory is at 218 West Twentieth Street, New York, has the first patent ever granted on this subject in the United States, and the only one taken out in the world since 1808. Owing to negotiations being carried on, Mr. Castner having filed applications for patents in various foreign countries, but not having the patents granted there yet, we are not at liberty to state his process fully. The metal is re- duced and distilled in large iron crucibles, which are raised automatically through apertures in the bottom of the furnace, where they remain until the reduction is completed and the sodium distilled. Then the crucible is lowered, a new one con- taining a fresh charge is substituted and raised into the furnace, while the one just used is cleaned and made ready for use again. The temperature required is very moderate, the sodium distilling as easy as zinc does when being reduced. Whereas by previous processes only one-third of the sodium in the charge is obtained, Mr. Castner gets nearly all, for the pots are nearly entirely empty when withdrawn from the furnace. Thus the great items of saving are two or three times as much metal extracted from a given amount of salt, and cheap cast-iron crucibles used instead of ex- pensive wrought-iron retorts. Mr. Castner expects to produce sodium at 25 cents per Ib., thus solving the problem of cheap aluminium, and with it magnesium, silicon, and boron, all of which depend on sodium for their manufacture. Thus the pro- duction of cheap sodium means much more than cheap aluminium. 168 ALUMINIUM. Mr. Castner is well known in New York as a chemist of good stand- ing, and has associated with him Mr. J. H. Booth and Mr. Henry Booth, both well known as gentlemen of means and integrity." The following are the claims which Mr. Castner makes in his patent : * 1. In a process for manufacturing potassium or sodium, per- forming the reduction by diffusing carbon in a body of alkali in a state of fusion at moderate temperatures. 2. Performing the reduction by means of the carbide of a metal or its equivalent. 3. Mechanically combining a metal and carbon to increase the weight of the reducing material, and then mixing this product with the alkali and fusing the latter whereby the reducing material is held in suspension throughout the mass of fused alkali. 4. Performing the deoxidation by the carbide of a metal or its equivalent. For an explanation of the principles made use of in the above outlined process we will quote from a lecture delivered by Mr. Castner at the Franklin Institute, Philadelphia, October 12th, 1886. That Institution has since bestowed on Mr. Castner one of its gold medals as a recognition of the benefit to science ac- cruing from his invention. " In the ordinary sodium process, lime is added to the reducing mixture to make the mass refractory, otherwise the alkali would fuse when the charge is highly heated, and separate from the light, infusible carbon. The carbon must be in the proportion to the sodium carbonate as four is to nine, as is found needful in practice, so as to assure each particle of soda in the refractory charge having an excess of carbon directly adjacent or in actual contact. Notwithstanding the well-known fact that sodium is reduced from its oxide at a degree of heat but slightly exceeding the reducing point of zinc oxide, the heat necessary to accomplish reduction by this process and to obtain even one-third of the metal in the charge, closely approaches the melting point of wrought iron. " In my process, the reducing substance, owing to its composi- tion and gravity, remains below the surface of the molten salt, * U. S. Pat. No. 342897, June 1, 188(5. Hamilton Y. Castner, New York. THE MANUFACTURE OF SODIUM. 169 and is, therefore, in direct contact with the fused alkali. The metallic coke of iron and carbon contains about 30 per cent, carbon and 70 per cent, iron, equivalent to the formula FeC 2 . I prefer to use caustic soda, on account of its fusibility, and mix with it such quantity of so-called ' carbide' that the carbon con- tained in the mixture shall not be in excess of the amount theo- retically required by the following reaction : 3NaOH + FeC 2 = 3Na + Fe + CO 4- CO 2 + 3H ; or, to every 100 Ibs. of pure caustic soda, 75 Ibs. of ' carbide/ containing about 22 Ibs. of carbon. " The necessary cover for the crucible is fixed stationary in each chamber, and from this cover a tube projects into the con- denser outside the furnace. The edges of the cover are convex, those of the crucible concave, so that when the crucible is raised into position and held there the tight joint, thus made prevents all leaking of gas or vapor. Gas is used as fuel, and the reduction begins towards 1000 C. As the charge is fused, the alkali and reducing material are in direct contact, and this fact, together with the aid rendered the carbon by the fine iron, in withdrawing oxygen from the soda, explains why the reduction is accom- plished at a moderate temperature. Furthermore, by reducing from a fused mass, in which the reducing agent remains in sus- pension, the operation can be carried on in crucibles of large diameter, the reduction taking place at the edges of the mass, where the heat is greatest, the charge flowing thereto from the centre to take the place of that reduced. " I am enabled to obtain fully 90 per cent, of the metal in the charge, instead of 30 per cent, as formerly. The crucibles, after treatment, contain a little carbonate of soda, and all the iron of the ' carbide' still in a fine state of division, together with a small percentage of carbon. These residues are treated with warm water, the solution evaporated to recover the carbonate of soda, while the fine iron is dried, and used over again for ( carbide. 7 r ' Mr. Castner having demonstrated in his New York laboratory the success of his process, went to England, and for several months during the winter of 1886-7 was engaged in building and working a large sodium furnace. This was successfully car- 170 ALUMINIUM. ried out near London, the inventor being assisted by Mr. J. Mac- Tear, F.C.S., who, in March, 1887, read a description of this furnace and the results obtained before the Society of Chemical Industry. During the working of this furnace it was inspected by many chemical and metallurgical authorities, who were com- pletely satisfied as to its success. As the furnace now used differs in a few details from the one j ust referred to, it may be well to extract the essential particulars from Mr. MacTear's paper on the ground that the importance of this invention justifies a com- plete discussion of its development : " Since Mr. Castner's paper upon his process, which was read before the Franklin Institute of Philadelphia, October 12th, 1886, several slight changes in the mode of carrying on this process have been made. These have been brought about by the experience gained from the actual working of the process upon a commercially large scale. " The reactions by which the sodium is produced are some- what difficult to describe, as they vary somewhat according to the mixture of materials and temperature employed in the reduc- tion. The mixture and temperature which it is now preferred to use is represented by the reaction : 6NaHO + FeC 8 - 2Na 2 CO 3 + 6H -f Fe + 21Na. " In place of using an actual chemical compound of iron and carbon, as expressed by the above reaction, a substitute or equiva- lent is prepared as follows : To a given quantity of melted pitch is added a definite proportion of iron in a fine state of division. The mixture is cooled, broken up into lumps, and cooked in large crucibles, giving a metallic coke consisting of carbon and iron, the proportions of each depending upon the relative quantities of pitch and iron used. This metallic coke, after being finely ground, provides a substance having the iron and carbon in a like propor- tion to an iron carbide, and from which neither the iron nor car- bon can be separated by mechanical means. The fine iron is conveniently prepared by passing carbonic oxide and hydrogen in a heated state, as obtained from an ordinary gas producer, over a mass of oxide of iron commercially known as i purple ores/ heated to a temperature of about 500 C. THE MANUFACTURE OF SODIUM. 171 " In producing sodium, caustic soda of the highest obtainable strength is used, and there is mixed with it a weighed quantity of the so-called ' carbide/ sufficient to furnish the proper amount of carbon to carry out the reaction indicated above. The cruci- bles in which this mixture is treated are made of cast-steel, and are capable of containing a charge of 15 Ibs. of caustic soda, together with the proper proportion of the i carbide/ " After charging a crucible with the above mixture, it is placed in a small furnace where it is kept at a low heat for about thirty minutes, during which time the mass fuses, boils violently, and a large part of the hydrogen is expelled by the combined action of the iron and carbon, the ' carbide/ owing to its gravity, remaining in suspension throughout the fused soda. At the end of the time stated, the contents of the crucible have subsided to a quiet fusion. The crucible is then lifted by a pair of tongs on wheels and placed upon the platform of the elevating gear, as shown in the drawing, and raised to its position in the heating chamber of the main distilling furnace. The cover which remains stationary in the furnace has a convex edge, while the crucible has a groove round the edge into which the edge of the cover fits. A little powdered lime is placed in the crucible groove just before it is raised, so that when the edges of the cover and crucible come together they form a tight joint, and at the same time will allow the crucible to be lowered easily from the chamber when the operation is finished, to give place to another containing a fresh charge. From the cover projects a slanting tube (see Fig. 17), connected with the condenser. The condenser is provided with a small opening at the further end to allow the escape of hydrogen, and has also a rod fixed (as shown), by means of which any obstruction which may form in the tube during distillation, may be removed. After raising a crucible in its place in the furnace, the hydrogen escaping from the condenser is lighted, and serves to show by the size of the flame how the operation is progressing in the crucible, the sodium actually distilling soon after the cru- cible is in its place. The temperature of the reduction and dis- tillation has been found to be about 823 C. The gas coming off during the first part of the distillation has been analyzed and found to consist of pure hydrogen. An analysis of the gas 172 ALUMINIUM. disengaged when the operation was almost completed, gave as a result, hydrogen 95 per cent., carbonic oxide 5 per cent. It Fig. 17. has been found advisable to use a little more ' carbide' than the reaction absolutely requires, and this accounts for the presence of the small quantity of carbonic oxide in the expelled gas, the free carbon acting upon the carbonate formed by the reaction, thus giving off carbonic oxide and leaving a very small percentage of the residue in the form of peroxide of sodium. This small amount of carbonic oxide rarely combines with any of the sodium in the tube, and so the metal obtained in the condensers is pure, and the tubes never become choked with the black compound. In the preparation of potassium a little less ' carbide' is used than the reaction requires, thus no carbonic oxide is given off, and all danger attached to the making of potassium is removed. After the reduction and distillation the crucible is lowered from the furnace and the contents poured out, leaving the crucible ready to be recharged. The average analyses of the residues show their composition to be as follows: THE MANUFACTURE OF SODIUM. 173 Carbonate of soda ...... 77 per cent. Peroxide of sodium . . . . . 2 " Carbon . 2 " Iron 19 " " The average weight of these residues from operating upon charges of 15 Ibs. caustic soda and 5J Ibs. of carbide is 16 Ibs. These residues are treated either to produce pure crystallized carbonate of soda or caustic soda, and the iron is recovered and used again with pitch in the formation of the ' carbide/ From this residue weighing 16 Ibs., is obtained 13 Ibs. of anhydrous carbonate of soda, equivalent to 9.4 Ibs. caustic soda of 76 per cent. " Operating upon charges as above mentioned the yield has been Sodium, actual . , ? . 2.50 Ibs. Theory 2.85 Ibs. Soda carbonate, actual . 13.00 Ibs. " 13.25 Ibs. " The average time of distillation in the large furnace has been 1 hour 30 minutes, and as the furnace is arranged for three cru- cibles, 45 Ibs. of caustic soda are treated every 90 minutes, pro- ducing 7 J Ibs. of sodium and 39 Ibs. of carbonate of soda. The furnace is capable of treating 720 Ibs. of caustic soda daily, giving a yield in 24 hours of 120 Ibs. of sodium and 624 Ibs. of anhydrous carbonate of soda. The furnace is heated by gas which is supplied by a Wilson Gas Producer, consuming 1 cwt. of fuel per hour. The small furnace in which the crucibles are first heated requires about J cwt. per hour. The following esti- mate of cost, etc., is given from the actual running of the furnace working with the above charges for 24 hours : *. d. 720 Ibs. of caustic soda @ 11 per ton * . V . 3 10 10 150 Ibs. of " carbide" @ \d. per Ib. . . .064 Labor ... . . . * . ^ . 1 Fuel .... . . . . . 17 Re-converting 624 Ibs. of carbonate into caustic, at a cost of about 5 per ton on the caustic pro- duced, say . . ... . . .100 Total . ... 6 14 2 Deducting value of 475 Ibs. of caustic recovered 268 Cost of 120 Ibs. of sodium ... .4 Cost per pound 85^. 174 ALUMINIUM. " Regarding the item of cost relating to the damage caused to the crucibles by the heat, this question has been very carefully gone into, some of the crucibles have been used upwards of fifty times, and from present indications of their condition there is no doubt that they can continue to be used at least 150 times more before they become unfit for further use. In considering 200 operations to be the life of a crucible, the item of damage or wear and tear amounts to less than lc/. per Ib. on the sodium produced, and if we take the furnace tear and wear at the same rate of Id. per Ib., we will see that the tear and wear of plant is only one-twelfth of that incurred in the ordinary process. It is upon these facts that Mr. Castner bases his claim to be able to produce sodium by his process upon the large scale, at a cost of less than Is. per Ib. The advantages of this process will be apparent to any one at all familiar with the manufacture of these metals as conducted heretofore. The first and most important end gained is their cheap production, and this is owing chiefly to the low heat at which the metals are produced, the quick- ness of the operation, non-clogging of the conveying tubes, and a very small waste of materials. The process furthermore admits of being carried on upon a very large scale, in fact it is intended ultimately to increase the size of the crucible so as to make the charges consist of 50 Ibs. of caustic soda. Crucibles of cast iron have been found quite suitable, and it is intended in future to use crucibles made of this material in place of the more expensive steel." Immediately on the demonstration of this success, a company was formed to unite Mr. Castner's sodium process with Mr. Webster's improvements in the production of aluminium chlor- ide. The Aluminium Co., Ltd., first appeared before the public in June, 1887, and at the first meeting in the following September it was decided to build works at once. These were begun at Oldbury, near Birmingham, and were in working operation by the end of July, 1888. The furnaces here erected are larger than the one just described, and altogether have a producing capacity of nearly a ton of sodium a day. The following details respecting this latest plant and its working are taken mostly from an address delivered before the Society of Arts, March 13, 1889, by Mr. THE MANUFACTURE OF SODIUM. 175 William Anderson, and from a discourse at the Royal Institu- tion, May 3, 1889, by Sir Henry Roscoe, president of the company. There are four large sodium furnaces, each holding five pots or crucibles and heated by gas, applied on the regenerative prin- ciple. A platform about five feet above the floor allows the workmen to attend to the condensers, while the lifts on which the pots are placed sink level with the floor. The crucibles used are egg-shaped, about 1 8 inches diameter at their widest part and 24 inches high ; when joined to the cover the whole apparatus is about 3 feet in height. The covers have vertical pipes passing through the top of the furnace, forming a passage for the intro- duction of part of the charge, and also a lateral pipe connecting with the condenser. The whole cover is fixed immovably to the roof of the furnace and is protected by brickwork from ex- treme heat ; but it can easily be removed when necessary. The natural expansion of the vessels is accommodated by the water pressure in the hydraulic lifts on which the pots stand. When the lift is lowered and sinks with the lower part of the crucible to the floor level, a large pair of tongs mounted on wheels is run up, and catching hold of the crucible by two projections on its sides it is carried away by two men to the dumping pits, on the edge of which it is turned on its side, the liquid carbonate of soda and finely divided iron which form the residue are turned out, and the inside is scraped clean from the opposite side of the pit, under the protection of iron shields. When clean inside and out, it is lifted again by the truck and carried back to the furnace, re- ceiving a fresh charge on its way. It is then put on the platform and lifted into place, having still retained a good red heat. It takes only 1J to 2 minutes to remove and empty a crucible, and only 6 to 8 minutes to draw, empty, recharge, and replace the five crucibles in each furnace. The time occupied in reducing a charge is one hour and ten minutes. It is thus seen that one bank of crucibles yields 500 pounds of sodium in twenty-four hours, the battery of four furnaces produces about a ton in that time. The shape of the condenser has been altogether changed. In- stead of the flat form used on the furnace at London (see Fig. 17), 176 ALUMINIUM. which resembled the condenser used in the Deville process, a peculiar pattern is used which is quite different. It consists in a tube-shaped cast-iron vessel 5 inches in diameter, nearly 3 feet long over all, and having a slight bend upwards at a point about 20 inches from the end. At this bend is a small opening in the bottom, which can be kept closed by a rod dropping into it ; this rod, passing through a tight-fitting hole above, can be raised or lowered from outside. Thus the sodium can either run out con- tinually into small pots placed beneath the opening or can be al- lowed to collect in the condenser until several pounds are present, then a small potful run out at once, by simply lifting the iron rod. The outer end of the condenser is provided with a lid, hinged above, which can be thrown back out of the way when required. This lid also contains a small peep-hole covered with mica. In the top of the condenser just before the end is a small hole through 'which the hydrogen and carbonic oxide gases es- cape when the end is closed, burning with the yellow sodium flame. The bend in the condenser is not acute enough to prevent a bar being thrust through the end right into the outlet tube pro- jecting from the furnace, thus allowing the whole passage to be cleaned out should it become choked up. Previous to drawing the crucibles from the furnace for the purpose of emptying them and recharging, the small pots containing the metal distilled from one charge are removed and empty ones put in their place. Those removed each contain on an average about 6 Ibs. of sodium, or 30 Ibs. from the whole furnace. When sufficiently cool, petro- leum is poured on top of the metal in the pots, and they are wheeled on a truck to the sodium casting shop, where the sodium is melted in large pots heated by oil baths and cast either into large bars ready to be used for making aluminium or into smaller sticks to be sold. The sodium is preserved under an oil such as petroleum, which does not contain oxygen in its composition, and the greatest care is taken to protect it from water. Special care is taken to keep the temperature of the furnace at about 1000 C., and the gas and air-valves are carefully regulated so as to maintain as even a temperature as possible. The covers remain in the furnace from Sunday night to Saturday afternoon, and the crucibles are kept in use till worn out, when new ones, THE MANUFACTURE OF SODIUM. 177 previously heated red-hot, are substituted without interrupting the general running of the furnace. These bottom halves of the crucibles are the only part of the plant liable to exceptional wear and tear, and their durability is found to depend very much on the soundness of the casting, because any pores or defects are rapidly eaten into and the pot destroyed. The average duration of each crucible is now 750 Ibs. of sodium, or 125 charges. Apropos of the reaction involved in the reduction, it has prob- ably been observed that Mr. MacTear proposes a different form- ula from that suggested by Mr. Castner. Mr. Weldon remarked that when a- mixture of sodium carbonate and carbon was heated the carbon did not directly reduce the soda, but at a high tem- perature the mixture gives off vapors of oxide of sodium (Na 2 O) part of which dissociates into free oxygen and sodium vapor ; as soon as this dissociation takes place the carbon ,takes up the oxygen, forming carbonic oxide, and thus, by preventing the re- combination of the sodium and oxygen, leaves free sodium vapors. Dr. Kosman, speaking in "Stahl und Eisen," January, 1889, on Castner's process, gives the following explanation of the reac- tions taking place : Ten kilos of caustic soda and 5 kilos of carbide (containing 1.5 kilos of carbon) give the following reaction : 4NaOH + FeC 2 = Na 2 CO 3 + Fe + 4H -f CO + 2Na, and half the sodium in the mixture is obtained. Ten kilos of caustic soda and 10 kilos of carbide (containing 3 kilos of carbon) give this reaction 2NaOH + FeC 2 = NaCO + Fe + 2H + CO + Na, and half the sodium in the mixture is again obtained. If 20 kilos of caustic soda and 15 kilos of carbide are mixed, both the above reactions take place, but if the ignition is con- tinued, the sodium carboxyd (NaCO) reacts on the sodium car- bonate according to the reaction Na 2 CO 3 + NaCO 3Na + 2CO 2 , and the entire reaction may be represented by 3NaOH + FeC 2 = 3Na -f Fe + 3H + CO + CO 2 , and all the sodium in the mixture is obtained. This is the reaction first proposed by Mr. Castner (see p. 169), 12 1 78 ALUMINIUM. and the proportions indicated by it gave him the largest return of sodium. Mr. MacTear, however, states that the reaction which takes place is conditioned largely by the temperature, and that at 1000 C. it is probably to be represented by 6NaOH + FeC 2 ~ 2Na*CO + 6H + Fe + 2Na, which is essentially the same as that given by Sir Henry Roscoe in his discourse, viz : 3NaOH + C- Na 2 C0 3 + 3H + Na. This reaction would require 18f Ibs. of carbide to 50 Ibs. of caustic soda, and since the sodium carbonate is easily converted back into caustic by treatment with lime, the production of so much carbonate is offset by the ease with which the reaction takes place, and the added advantage that the gas evolved with the sodium is solely hydrogen, thus allowing the reduction to proceed in an atmosphere of that gas, and reducing the production of the usual deleterious sodium carbides to a minimum. A further discussion of this subject will come up in consider- ing Netto's process. Netto's Process (1887). Dr. Curt Netto, of Dresden, has taken out patents in several European countries,* which have been transferred to and are pre- sumably being operated by the Alliance Aluminium Company, of London (see p. 38). The process is continuous, and is based on the partial reduction of caustic soda by carbon. Dr. Netto observes that carbon will reduce caustic soda at first at a red heat, but a white heat is necessary to finish the reduction, the explana- tion being that the reaction is at first 4NaOH + C = Na 2 CO 3 + 2H 2 4- CO + Na 2 , and that the carbonate is only reduced at a white heat. To avoid any high temperature, the first reaction only is made use of, the carbonate being removed and fresh caustic supplied continuously, and without interrupting the operation or admitting air into the retort in which the reduction takes place. A vertical cast-iron retort, protected by fire-clay coating, is * German patent (D. R. P.) 45105 ; English patent, October 26, 1887, No. 14602. THE MANUFACTURE OF SODIUM. 179 surrounded by flues. The flame after heating the retort passes under an iron pot in which the caustic soda is kept melted, and situated just above the top of the retort. This pot has an outlet tube controlled by a stop-cock, by which the caustic may be dis- charged into a funnel with syphon-shaped stem fastened into the top of the retort. There is also a syphon-shaped outlet at the bot- tom of the retort, through which the molten sodium carbonate and bits of carbon pass. A hole with tight lid in the upper cover is provided for charging charcoal. A tube passes out just beneath the upper cover, connecting with a large condenser of the shape used by Deville (see Fig. 18). In operating, the retort is heated Fig. 18. to bright redness, filled one-third with best wood charcoal, and then molten caustic soda tapped from the melting pot into the funnel, the feed being so regulated that the funnel is kept full and the retort closed. The lower opening is kept closed until enough 180 ALUMINIUM. sodium carbonate has accumulated to lock the syphon passage air tight. When after several hours' working the charcoal is almost all used up, the supply of caustic soda is shut off for a time and the retort recharged through the opening in the upper lid, when the operation goes on as before. The sodium carbonate produced is easily purified from carbon by solution. Since sodium vapor at a high temperature is very corrosive, all rivets and screw joints must be avoided in making the retort. On this account, the out- let tubes should be cast in one piece with the retort. The process of O. M. Thowless, Newark, IS". J.,* is essentially identical with Netto's process. REDUCTION OF SODIUM COMPOUNDS BY ELECTRICITY. The decomposition of fused sodium chloride by the electric current seems to promise the economic production of sodium, for not only is this metal formed but chlorine is obtained as a by- product, its value reducing very much the cost of the operation. P. Jablochoff has devised the following apparatus for decom- posing sodium or potassium chlorides. f (Fig. 19.) The arrangement is easily understood. The salt to be decom- posed is fed in by the funnel into the kettle heated by a fire beneath. The positive pole evolves chlorine gas, and the negative pole evolves vapor of the metal, for, as the salt is melted, the heat is sufficient to vaporize the metal liberated. The gas escapes through one tube and the metallic vapor by the other. The vapor is led into a condenser and solidified. Prof. A. J. Rogers, of Milwaukee, Wis., has made a number of attempts to reduce sodium compounds electrolytically, using as a cathode a bath of molten lead and producing an alloy of lead and sodium which he makes use of for the reduction of aluminium compounds. Although these attempts are hardly past the experi- mental stage, yet the record of the results obtained may very probably be interesting and valuable to other investigators in this line. Prof. Rogers reasons that from the known heat of combination * U. S. Patent, Nos. 380775, 380776, April 4, 1888. f Mierzinski. THE MANUFACTURE OF SODIUM. 181 of sodium and chlorine (4247 calories per kilo of sodium) there is enough potential energy in a pound of coal to separate nearly two pounds of sodium, if any mode of applying the combustion of the coal to this end without loss could be devised. If, however, Fig.|19. this energy is converted into mechanical work, this again into electrical energy, and this latter used to decompose sodium chlor- ide, we can easily compute the amount of coal to be used in a steam boiler to produce a given amount of sodium by electrolysis. Now, if the electric current could be applied without loss in de- composing sodium chloride, 1 electric horse-power (746 Watts) would produce about 8 Ibs. of sodium in 24 hours. But as in practice one mechanical horse-power applied to a dynamo yields only 80 or 90 per cent, of an electric horse-power, and as about 4 Ibs. of coal are used per indicated horse-power per hour, from 105 to 120 Ibs. of coal would be required per day to produce this result, or about 15 Ibs. per Ib. of sodium. Since, however, there is a transfer resistance in the passage of the electric current through the molten electrolyte, more than this will be required, in propor- tion to the amount of current thus absorbed. 182 ALUMINIUM. The temperature of fusion of sodium chloride is given by Car- nelly as 776 C., but Prof. Rogers remarks that the fusing point may be lowered considerably by the presence of other salts ; for instance, it melts about 200 lower if a small amount of calcium chloride or potassium chloride is present. We will quote the results of some experiments as given by Prof. Rogers.* " The following results were obtained among many others by using a Grove battery, a Battersea crucible to hold the sodium chloride, a carbon anode and an iron cathode terminating in a tube of lime placed in the melted salt. As soon as metallic sodium escaped and burnt at the surface of the liquid the current was stopped. A little sodium was oxidized but a considerable amount was found in the tube in metallic state. In six experi- ments the amount of sodium obtained was from 50 to 85 per cent, of the theoretical amount, averaging 65 per cent. It thus seemed that, with suitable apparatus, from 5 to 6 Ibs. of sodium could be obtained in 24 hours per electric horse-power. Thus, if there were no practical difficulties in the construction of the crucibles and other apparatus involved, nor in working continu- ously on a large scale, the metal could be obtained at small cost. Various forms of crucibles were used and attempts made to distil the metal when formed at the negative electrode (sodium volatili- zing at about 900C.), but the sodium vapor carries with it a large amount of sodium chloride as vapor, and the distillation is attended with difficulty. " During the last three years I have experimented on the re- duction of sodium chloride using molten negative electrodes and especially lead. Lead, tin, zinc, cadmium and antimony all readily alloy with sodium, a large part of which can be recovered from the alloys by distillation in an iron crucible. They can be heated to a higher temperature than pure sodium in acid crucibles with- out the sodium attacking the crucible. In the following experi- ments a dynamo machine was used to supply the current. "Experiment 1. A current averaging 72 amperes and 33 volts was passed through molten sodium chloride contained in two crucibles arranged in series, for two hours. Each contained 30 * Proceedings of the Wisconsin Natural History Society, April, 1889. REDUCTION THEORETICALLY CONSIDERED. 183 Ibs. of salt ; in the first was put 104 grammes of tin, in the second 470 grammes of lead, each serving as cathode and connection being made through the bottom of the crucible. A carbon anode passed through the cover and extended to within three inches of the molten cathode. The crucible containing the tin was nearer the fire and consequently hotter, and had an average potential across the electrodes of 12 volts, while that containing the lead cathode was 21 volts. When at the end of two hours the carbons were removed and the crucibles cooled and broken open, the lead alloy was found to contain 96 grammes of sodium, or 17 per cent. There was about 90 grammes of sodium found in the tin alloy, or between 45 and 50 per cent. Both these alloys rapidly oxidized in the air, and when thrown into water the action was very energetic, in the case of the tin alloy the liberated hydrogen being ignited, and after the reaction the metals were found at the bottom of the vessel in a finely divided state. Both these alloys reduce cryolite or aluminium chloride." In Prof. Rogers' further experiments cryolite was added to the bath, so that sodium was produced and aluminium formed in one operation. (See under " Electrolytic Processes/ 7 Chap. XI.) CHAPTER VIII. THE REDUCTION OF ALUMINIUM COMPOUNDS FROM THE STANDPOINT OF THERMAL CHEMISTRY. THE branch of chemical science called thermal chemistry may be said to be yet in its infancy. Although an immense mass of thermal data has been accumulated, yet the era of great gener- alizations in this subject has not yet been reached ; and although we know with a fair degree of accuracy the heat of combination of thousands of chemical compounds, including nearly all the common ones, yet the proper way to use these data in predicting the possibility of any proposed reaction remains almost unknown. The principal barriers in the way are two : 1st, the unknown quantities entering into almost every chemical reaction thermally 184 ALUMINIUM. considered, i. e., the heat of combination of elementary atoms to form molecules of the elements ; 2d, the uncertainty as regards the critical temperature at which a given exchange of atoms and consequent reaction will take place. We will explain what is meant by these statements. To illustrate, let us consider the case of hydrogen uniting with oxygen to form water according to the formula 2(H H) + (O - O) = 2 H 2 where (H H) and (O = O) represent respectively molecules of hydrogen and oxygen. Now, as 1 kilo of hydrogen unites with 8 of oxygen to form 9 of water, setting free 34462 units of heat (calories), if we take the atomic weights in the above reaction as representing kilos, we shall have the thermal value of the reaction 4 X 34462 = + 137848 calories. But this quantity is evidently the algebraic sum of the heat evolved in the union of 4 kilos of hydrogen atoms with 32 kilos of oxygen atoms, and the heat absorbed in decomposing 4 kilos of hydrogen gas into atoms, and 32 kilos of oxygen gas into atoms. These two latter quanti- ties are unknown, though a few chemists have concluded from studies on this question that they are probably very large. It has been calculated that the reaction H + H (H H) sets free 240,000 calories, and O + O (O O) sets free 147,200 calories ; but no assurance can be placed on these numbers. If they were approximately true, then 4H + 2O = 2H 2 O would set free about 773,000 calories. If these quantities are really anything like so large, and if they are at sometime determined with precision, thermo - chemical principles and conclusions will be greatly modified. Meanwhile, predictions based on the data we have lose all possibility of certainty, and so we need to keep in mind in our further discuss- ion that our deductions at the best can be no more than prob- abilities. Further, suppose that we mix 1 kilo of hydrogen gas and 8 kilos of oxygen gas, put them in a tight vessel and keep them at the ordinary temperature. No reaction will take place in any length of time, even though 34,462 calories would be set REDUCTION THEORETICALLY CONSIDERED. 185 free thereby. The explanation of this is probably that the atoms of hydrogen and oxygen are so firmly bound to each other in the molecules, that the dissimilar atoms have not strength of affinity sufficient to break away in order to combine. However this may be, it is well known that a spark only is necessary to cause an explosive combination of the gases under the above conditions, the temperature of the spark expanding the gases coming in contact with it, causing the atoms to swing with more freedom in the molecules, and as soon as two atoms of hydrogen come within the sphere of attraction of an atom of oxygen and form a molecule of water, the heat liberated is immediately communi- cated to the adjacent atoms, and almost instantaneously the entire gases have combined. The same principle undoubtedly holds true in cases of reduction. Carbon may be mixed with litharge and the mixture left in the cold forever without reacting, but at a certain temperature the carbon will abstract the oxygen. The temperatures at which reactions of this nature will take place are often determined experimentally, but I know of no theo- retical grounds on which they can rationally be calculated. There are other points which are somewhat indeterminate in these discussions, such as the influence of the relative masses of the reacting bodies, their physical states, i. e. y solid, liquid or gaseous, also the influence of the physical conditions favoring the formation of a certain compound, but the nature of the subject and the meagreuess of data in the particular phenomenon of reduction, render it inexpedient if not impracticable to take these points into consideration. Starting with the above remarks in view, we will consider the heat generated by the combination of aluminium with certain other elements, as has been determined experimentally, and study from a comparison with the corresponding thermal data for other elements, what possibilities are shown for reducing these alumin- ium compounds. The heat generated by the combination of aluminium with the different elements is given as follows ; the first column giving the heat developed by 54 kilos of aluminium (representing Al 2 ), and the second the heat per atomic weight of the other element, e. g. } per 16 kilos of oxygen. 186 ALUMINIUM. Element. Oxygen Chlorine Bromine Iodine Sulphur Compound. A1 2 C1 6 Al 2 ! 6 Calories. 391,600 392,600 321,960 239,440 140,780 124,400 Calories. 130,500 130,900 53,660 39,900 23,460 41,467 Authority. Bertholet. Bailie & Fery. Thomsen. Let us consider the theoretical aspect of the reduction of Alumina. The heat given out by other elements or compounds which unite energetically with oxygen is as follows, the quantity given being that developed by combination with 16 kilos (rep- resenting one atomic weight) of oxygen. Element. Compound. Calories. Aluminium A1 2 O 3 130,500 Sodium Na 2 99,760 Potassium K a O 100,000 (?) Barium BaO 124,240 Strontium SrO 128,440 Calcium CaO 130,930 Magnesium MgO 145,860 Manganese . . . . MnO 95,000 (?) Silicon SiO 2 110,000 Zinc ZnO 85,430 Iron . . . . . . . Fe^ 3 63,700 Lead PbO 50,300 Copper CuO 37,160 Cu*O 40,810 Sulphur SO 2 35,540 Hydrogen H 2 68,360 Carbon CO 29,000 " CO 2 48,480 Carbonic anhydride .... CO 2 67,960 Potassium cyanide .... KCyO 72,000 On inspecting this list we find magnesium to be the only metal surpassing aluminium, while calcium is about the same. This would indicate that the reaction APO 3 + 3Mg = Al 2 + 3MgO * Bertholet's number represented the formation of the hydrated oxide, A1 2 3 .3H 2 0, and, for want of knowing the heat of hydration, has been gener- ally used as the heat of formation of A1 2 OV Recently, J. B. Bailie and C. Fe>y (Ann. de China, et de Phys., June, 1889, p. 250) have, by oxidizing aluminium amalgam, obtained the above figure for the heat of formation of A1 2 3 , and determined that the heat of hydration is 3000 calories, which would make the heat of formation of the hydrated oxide 395,600. REDUCTION THEORETICALLY CONSIDERED. 187 would, if it were possible to bring the alumina and magnes- ium in the proper conditions for reacting, develop about (145,860130,500) x 3 - 46,080 calories, and points to the possibility of reducing alumina by nascent, molten, or vaporized magnesium, under certain unknown con- ditions. It may be that molten alumina would be reduced by vapor of magnesium, but experiment only could establish or deny the possibility of the reaction. Even if this took place, it would probably not be of practical importance. We notice further the fact that sodium or potassium could not reduce alumina without heat being absorbed in large quantity, and it is interesting to remember that some of the first attempts at isolating aluminium by using potassium were made on alumina, and were unsuccessful, so that it is practically acknowledged that while these metals easily reduce other aluminium compounds (according to reactions which are thermally possible, as we shall see later on) yet they cannot reduce alumina, under any conditions so far tried. When we consider the case of reduction by the ordinary re- ducing agents, hydrogen, carbon, or potassium cyanide, we are confronted in every case with large negative quantities of heat, i. e., deficits of heat. So large do these quantities appear that it is very small wonder that the impossibility of these reductions oc- curring under any conditions has been strongly affirmed. For instance APO 3 4- 6H = AP + 3H*0 would require (130500 68360) X 3 186,420 calories. A1 2 O 3 + 3C = AP + 3CO 304,500 calories. APO 3 + 1JC = Al 2 + HCO 2 246,060 calories. APO 8 + 3KCy AP + 3KCyO 175,500 calories. APO 3 + 3CO = AP + 3CO 2 187,620 calories. From these figures, however, we beg leave to.disclairn predicting the absolute impossibility of the reactions taking place ; the figures simply point to the probable impossibility of the reaction, or to its possibility only under very exceptional conditions. This position can be strengthened by considering that the reaction 188 ALUMINIUM. ZnO -f C a. Zn + CO requires 56,430 cal. Fe 2 O 3 -f 3C - Fe 2 + SCO " 104,100 cal. PbO + C = Pb + CO " 21,300 cal. yet these reactions are a matter of every day experience. If it be claimed that ferric oxide and litharge are really reduced by car- bonic oxide, according to the reactions Fe"O + SCO = Fe 2 + SCO 2 developing 12,780 cal. PbO 4- CO - Pb CO 2 " 17,660 and therefore that the reduction is possible because thermally positive, yet ZnO + CO = Zn + CO 2 requires 17,470 cal. and we still have before us a thermally negative reaction, which is practically carried out. It is thus apparent that the reduction of alumina by the com- mon reducing agents is, thermally considered, not an absolutely impossible question but one which presents, possibly, as much greater difficulty over the reduction of zinc oxide or iron ore as the heat deficit is greater in one case than in the other. The question may be asked, " On what grounds has it been calculated that carbon will reduce alumina at a temperature of 10000 C. ?" I have seen this statement in print, and was for some time at a loss to understand how this result was obtained, but came finally to the conclusion that it must have been deduced from the following premises : The reaction A1 2 O 3 + 3C * Al 2 + SCO shows a deficit of 304500 calories. If, therefore, 304500 heat units can in some way be added to the alumina and carbon, then they might probably be induced to react. Evidently then, if we heat these substances they absorb a certain number of heat units for every degree rise of temperature, and at some certain temperature will have absorbed the required number of heat units to induce the reaction. The calculation seems to have been made thus Weight of alumina X specific heat. 102 x 0.2 20.4 Weight of carbon x specific heat. 36 X 0.25 - 9. Caloric capacity per degree 29.4 calories. REDUCTION THEORETICALLY CONSIDERED. 189 The temperature to which the alumina and carbon must be heated in order to absorb 304,500 calories must be 30450 2 =s 10350 C. 29.4 There are several sources of error which will be immediately pointed out in this calculation. For instance, specific heats are known to increase with the temperature, while in the case of carbon its specific heat at a red heat is known to be about 0.46. Making this correction alone would reduce the temperature needed to about 8200 C. That this method of figuring is not entirely unreasonable seems probable when we apply it to the reduction of oxide of zinc by carbonic oxide ; for, in the case of the reaction, ZnO + CO = Zn + CO 2 , the temperature calculated would be (sr^^lSrSlr = TTT = 1020 > whichisver y close to the observed temperature. Yet we are constrained to regard this coincidence as fortuitous, since the same calculations for other oxides do not agree with the observed values. The method, if applied to the reduction of alumina by carbonic oxide, would give about 4500 C. ; but it is certain, from what we know of the dissociation of carbonic acid by heat, that far below this temperature carbonic oxide loses almost all its affinity for oxygen, and this result must be rejected as mythical. The result obtained for reduction by carbon, forming CO, is open to a similar objec- tion, owing to the fact that at very high temperatures carbonic oxide also is dissociated, but the dissociation takes place so slowly and to such a small degree within observable temperatures, that it is not impossible that alumina may be reduced by carbon at temperatures within the above-named limits. The reduction of alumina by hydrogen, calculated by this method, would take place at 4500, but since water is dissociated at high temperatures, this figure is open to the same criticism as that obtained for carbonic oxide. The lowest calculated value for the temperature of reduction of alumina is given by potas- sium cyanide, for the reaction Al 2 a H- 3KCy = Al 2 + 3KCyO 190 ALUMINIUM. would require an addition of 175,600 cal., which would necessi- tate heating the substances to about 3000 (using the most prob- able value for the specific heat of potassium cyanide 0.2). Whether potassium cyauate (KCyO) dissociates sensibly at this temperature I cannot say, but the fact remains that if the tem- peratures calculated by this method are worthy of any credibility at all, they point to potassium cyanide as likely to reduce alumina at a lower temperature than either hydrogen, carbonic oxide, or carbon. As the basis of our discussion of the reduction of aluminium chloride, bromide, or iodide, we give a table of the heat developed by the combination of some of the elements with one atomic weight (in kilos) of each of these haloids. Element. Com- pound. Calories. Com- pound. Calories. Com- pound. Calories. Aluminium . . . Potassium .... A1 2 C1 6 KC1 NaCl 53,660 305,600 97,690 AFBr 5 KBr NaBr 40,000 95,300 85,700 Al 2 ! 6 KI Nal 23,460 80,100 69,000 Lithium .... LiCl Bad 2 93,810 97,370 BaBr 2 85,000 Strontium .... Calcium .... Magnesium . . . Manganese . . . SrCl* Cad 2 MgCl 2 MnCl 2 ZnCl 2 92,270 84,910 75,500 56,000 ( 50,600f SrBr 2 CaBr' ZnBr* 78,900 70,400 (43, 100J { 40,640f Znl 8 f30,000t 1 26,600 Lead .... PbCl 2 \ 48, 600* 41,380 PbBi-2 ^37,500* 32,200 Pbl 2 124,500 20,000 Mercury .... Tin Hg z Cl 2 SnCl 2 41,275 40,400 Hg 2 Br 2 34,150 Hg 2 ! 2 24,200 Fed 2 41,000 FeBr 2 24,000 Pel 2 8,000f Cu 2 Cl 2 32,875 Cu 2 Br 2 25,000 Cu 2 ! 2 16,000 Hydrogen .... Hd 22,000 HBr 8,400 HI 6,000 * Thomson. f Andrews, t Jahresbericht der Chemie, 1878, p. 102. On inspecting this table we notice that, in general, all the metals down to zinc develop more heat in forming chlorides and very probably also in forming bromides and iodides. A reaction, then, between aluminium chloride and any of these metals, form- ing aluminium and a chloride of the metal, would be exothermic, which means, generally speaking, that if aluminium chloride and SEDUCTION THEORETICALLY CONSIDERED. 191 any one of these metals were heated together to the critical point at which the reaction could begin, the reaction would then pro- ceed of itself, being continued by the heat given out by the first portions which reacted. Zinc seems to lie on the border line, and the evidence as to whether zinc will practically reduce these aluminium compounds is still contradictory, as may be seen by ex- amining the paragraphs under " Reduction by Zinc." (Chap. XII.) Of the first six metals mentioned in the table after aluminium, Duly potassium and sodium are practically available. The reac- tion A1 2 C1 6 + 6K = Al 2 + 6KC1 develops 311,640 cal. APC1 6 + 6Na = Al 2 + 6NaCl develops 264,180 cal. and the result of this strong disengagement of heat is seen when, on warming these ingredients together, the reaction once com- menced at a single spot all external heat can be cut off, and the resulting fusion will become almost white hot with the heat de- veloped. In fact, the heat developed in the second reaction would theoretically be sufficient to heat the aluminium and sodium chloride produced to a temperature between 3000 and 4000 C. Magnesium should act in a similar manner, though not so vio- lently, since A1 2 C1 6 + 3Mg = Al 2 + 3MgCl 2 develops 131,000 cal. And manganese possibly also, since A1 2 C1 6 + 3Mn .= Al 2 + 3MnCl develops 14,040 cal. The reduction of aluminium chloride, bromide, or iodide by hydrogen is thermally strongly negative, which would indicate a very small possibility of the conditions ever being arranged so as to render the reaction possible. For instance, taking the most probable case, A1 2 C1 6 + 6H = Al 2 + 6HC1 requires 189,960 calories. More- over, a calculation similar to those made on the reduction of alumina by carbon would show a theoretical temperature of 2500 C. necessary to cause the reaction, if the energy required were added in the shape of heat. The only probable substitutes for sodium in reducing alumin- 192 ALUMINIUM. ium chloride are thus seen to be magnesium (whose cost will probably be always greater than that of aluminium), manganese (which may sometime be used in the form of ferro-manganese for producing ferro-aluminium), and zinc (whose successful applica- tion to this purpose would be a most promising advance in the metallurgy of aluminium). The heat of combination of fluorides is unknown, and so what would be an inquiry of interest with regard to these salts is out of our reach. We know, however, from experiment, that sodium will displace aluminium in its fluoride, developing a great deal of heat in the reaction, so that it is probable that the thermal relations of elements towards fluorine are similar to those towards chlorine. We can venture nothing further than this general observation. In order to discuss the thermal relations of aluminium sul- phide, we will make use of the following data, the heat developed being per atomic weight (32 kilos) of sulphur combining : Element. Compound. Calories. Aluminium A1 2 S 3 41,467 Potassium K 2 S 103,700 Sodium Na 2 S 88,200 Calcium CaS 92,000 Strontium SrS 99,200 Magnesium . . . . . MgS 79,600 Manganese MnS 46,400 Zinc ZnS 41,326 Iron FeS 23,576 Copper Cu*S 20,270 Lead PbS 20,430 Hydrogen R2S 4,740 Carbon CS* 26,010 These figures point to the easy reduction of aluminium sul- phide by potassium, sodium, or magnesium, and possibly by manganese and zinc. The other metals would require exceptional conditions, perhaps of temperature, for their action. It is in- teresting to note, as illustrating the many difficult points to be mastered by a consistent theory of the thermo-chemistry of re- duction, that two observers at least have determined (probably from the deposition of the metals from solution by hydrogen REDUCTION THEORETICALLY CONSIDERED. 193 sulphide), that the order of the affinity of the metals for sulphur is first the alkaline metals, then the others in the following order: copper, lead, zinc, iron, manganese, and then aluminium and magnesium with the remark that the affinities of the latter two for sulphur appear quite insignificant. We are unable to sug- gest the meaning of the discrepancy here seen, it may be that when the metals are in solution some other circumstances beside the heat of combination may have the controlling influence in deciding which one of the metals would be first precipitated, such as the degree of acidity of the solution, etc. It is altogether probable that in reactions in the dry way, by heat, the order of affinity of the metals for sulphur would more nearly correspond to the order seen in the heats of combination. The reduction of aluminium sulphide by hydrogen is seen to appear highly improbable. Before closing this study of the thermal aspect of the reduction of aluminium compounds, it may be interesting to notice some of the reactions which are of use in the aluminium industry. It is well known that while chlorine gas can be passed over ignited alumina without forming aluminium chloride, and while carbon can be in contact with alumina at a white heat without reducing it, yet the concurrent action of chlorine and carbon will change the alumina into its chloride, a compound with a lower heat of formation. Thus A1 2 O 3 -f 3C = Al 2 -f 3CO requires 304,500 cal. But A1 2 O 3 -f 3C 4- 6C1 = A1 2 C1 6 + 3CO requires a quantity of heat equal to the 304500 cal. minus 321960, the heat of forma- tion of aluminium chloride, or in other words 17360 cal. is evolved, showing that the reaction is one of easy practicability. If it be inquired whether there is not some chloride which would act on alumina to convert it into chloride, we would remark that if we can find a chloride whose heat of formation is as much greater than the heat of formation of the corresponding oxide as the heat of formation of aluminium chloride is greater than that of alumina, then such a chloride might react. To be more particular, to convert alumina into aluminium chloride, a deficit of 391600 13 194 ALUMINIUM. 321960 or 69640 calories must be made up. If we know of an element which in uniting with 3 atom weights (48 kilos) of oxygen gives out 69640 calories more heat, or a still greater excess, than in uniting with 6 atom weights (213 kilos) of chlor- ine, then the chloride of that element might perform the reaction. Now 6Na + 3O = 3Na 2 O evolves 299,280 cal. and 6Na + 6C1 = 6NaCl evolves 586,140 cal. leaving evidently a balance of 286,860 calories in the opposite direction to what we are looking for. And so for every metal except aluminium, I find the heat of formation of its chloride greater t than that of an equivalent quantity of its oxide. The only element which I know of which possesses the opposite prop- erty is hydrogen, for 6H + 3O _ 3H 2 O evolves 205,080 cal. and 6H + 6C1 = 6HC1 evolves 132,000 cal. and therefore the reaction AW +6HC1 - A1 2 C1 6 +3H 2 O would evolve according to our calculations (205,080 132,000) 69640 or 3440 calories, and would be thermally considered a pos- sible reaction. Moreover, as a secondary effect, the water formed is immediately seized by the aluminium chloride, for the reaction A1 2 C1 6 +3H 2 O A1 2 C1 6 .3H 2 O evolves 153,690 cal. and thus increases the total heat developed in the decomposition of the alumina to 158,130 calories. The result of this reaction is therefore the hydrated chloride, which is of no value for re- duction by sodium, since when heated it decomposes into alumina and hydrochloric acid again, that is, it will decompose before giving up its water, and the water if undecomposed, or the acid if it decomposes, simply unites with the sodium without affecting the alumina. The immense heat of hydration, 1 53,690 calories, is so much greater than that of any other known substance, that it is in vain that we seek for any material which might abstract the water and leave anhydrous aluminium chloride. Analogous to the reaction by which aluminium chloride is REDUCTION THEORETICALLY CONSIDERED. 195 formed from alumina is the reaction made use of for obtaining aluminium sulphide, yet with some thermal considerations of a different and highly interesting kind. If a mixture of alumina and carbon is ignited and, instead of chlorine, sulphur vapor is passed over it, no aluminium sulphide will be formed. An ex- planation of this fact is seen on discussing the proposed reaction thermally. APO 3 + 3C + 38 = APS 3 + SCO requires 180,200 cal. It will be remembered that the similar reaction with chlorine evolved 17,360 calories ; the quantity causing this diiference is the heat of combination of aluminium sulphide, which is 321,960 124,400 _ 197,560 calories less than that of alu- minium chloride, changing the excess of 17,360 calories into a deficit of 180,200 calories. This large negative quantity shows a priori that the reaction could be made to occur only under ex- ceptional conditions, and its uon -occurrence under all conditions so far tried gives evidence of the utility of the study of thermo- chemistry, at least as a guide to experiment. However, while carbon and sulphur cannot convert alumina into aluminium sul- phide, carbon bisulphide can, for a current of the latter led over ignited alumina converts it into aluminium sulphide. The reac- tion taking place is APO 3 + 3CS 2 = APS 3 + 3COS. Now, since carbon and sulphur by themselves could not perform the reaction, we should be very apt to reason that a compound of carbon and sulphur would be still less able to do so, since the heat absorbed in dissociating the carbon-sulphur compound would cause a still greater deficit of heat. But here is precisely the ex- planation of the paradox. Carbon bisulphide is one of those compounds, not frequent, which has a negative heat of formation ( 26,010 calories), i. e., heat is absorbed in large quantity in its formation, and therefore, per contra, heat is given out in the same quantity in its decomposition. The heat of formation of carbon oxysulphide being 37,030 calories, we can easily compute the thermal value of the reaction just given. 196 ALUMINIUM. Heat absorbed. Decomposition of alumina ..... 391,600 cal. Heat developed. Decomposition of carbon bisulphide . 78,030 Formation of carbon oxysulphide . . 111,090 " of aluminium sulphide . . 124,400 313,520 " Deficit of heat . . . . 78,080 " It is thus seen that the reaction with carbon bisulphide is less than one-half as strongly negative as the reaction with carbon and sulphur alone, and in accordance with this we have the fact that aluminium sulphide is produced when carbon bisulphide vapor is passed over alumina heated white hot, while it is still further interesting to note that the presence of carbon mixed with the alumina is of no aid at all to the reaction. CHAPTER IX. REDUCTION OF ALUMINIUM COMPOUNDS BY MEANS OF POTASSIUM OR SODIUM. THE methods comprised under this heading may be con- veniently divided into three classes : I. Methods based on the reduction of aluminium chloride or aluminium-sodium chloride. II. Methods based on the reduction of cryolite. III. Methods based on the reduction of aluminium fluoride. I. The methods here included can be most logically presented by taking them in chronological order. Oersted? s Experiments (1824). After Davy's unsuccessful attempts to isolate aluminium by the battery, in 1807, the next chemist to publish an account of REDUCTION BY POTASSIUM OR SODIUM. 197 attempts in this direction was Oerstedt, who published a paper in 1824 in a Swedish periodical.* Oersted t's original paper is thus translated into Berzelius's '' Jahresbericht :"f " Oerstedt mixes calcined and pure alumina, quite freshly pre- pared, with powdered charcoal, puts it in a porcelain retort, ignites and leads chlorine gas through. The coal then reduces the alumina, and there results aluminium chloride and carbonic oxide, and perhaps also some phosgene, COC1 2 ; the aluminium chloride is caught in the condenser and the gases escape. The sublimate is white, crystalline, melts about the temperature of boiling water, easily attracts moisture, and evolves heat when in contact with water. If it is mixed with a concentrated potass- ium amalgam and heated quickly, it is transformed ; there results potassium chloride, and the aluminium unites with the mercury. The new amalgam oxidizes in the air very quickly, and gives as residue when distilled in a vacuum a lump of metal resembling tin in color and lustre. In addition, Oerstedt found many re- markable properties of the metal and of the amalgam, but he holds them for a future communication after further investiga- tion." Oerstedt did not publish any other paper, and -the next advance in the science is credited to Wohler, whom all agree in naming as the true discoverer of the metal. Wohler's Experiments (1827). In the following article from PoggendorfFs Annalen,J Wohler reviews the article of Oerstedt's given above, and continues as follows : " I have repeated this experiment of Oerstedt, but achieved no very satisfactory result. By heating potassium amalgam with aluminium chloride and distilling the product, there remained behind a gray, melted mass of metal, but which, by raising the heat to redness, went oif as green vapor and distilled as pure * Oversigt over det K. Danske Videnskabemes Selkabs Forhandlingar og dels Medlemmers Arbeider. May, 1824, to May, 1825, p. 15. f Berz. Jahresb. der Chemie, 1827, vi. 118. t Pogg. Ann., 1827, ii. 147. 198 ALUMINIUM. potassium. I have therefore looked around for another method or way of conducting the operation, but, unpleasant as it is to say it, the reduction of the aluminium fails each time. Since, how- ever, Herr Oerstedt remarks at the end of his paper that he did not regard his investigations in aluminium as yet ended, and already several years have passed since then, it looks as if I had taken up one of those researches begun auspiciously by another (but not finished by him), because it promised new and splendid results. I must remark, however, that Herr Oerstedt has indi- rectly by his silence encouraged me to try to attain to further results myself. Before I give the art how one can quite easily reduce the metal, I will say a few words about aluminium chloride and its production (see p. 1 22). "I based the method of reducing aluminium on the reaction of aluminium chloride on potassium, and on the property of the metal not to oxidize in water. I warmed in a glass retort a small piece of the aluminium salt with some potassium, and the retort was shattered with a strong explosion. I tried then to do it in a small platinum crucible, in which it succeeded very well. The reaction is always so violent that the cover must be weighted down, or it will be blown off; and at the moment of reduction, although the crucible be only feebly heated from outside, it sud- denly glows inside, and the platinum is almost torn by the sudden shocks. In order to avoid any mixture of platinum with the reduced aluminium, I next made the reduction in a porcelain crucible and succeeded then in the following manner : Put in the bottom of the crucible a piece of potassium free from carbon and oil, and cover this with an equal volume of pieces of aluminium chloride. Cover, and heat over a spirit lamp, at first gently, that the crucible be not broken by the production of heat inside, and then heat stronger, at last to redness. Cool, and when fully cold put it into a glass of cold water. A gray powder separates out, which on nearer observation, especially in sunlight, is seen to con- sist of little flakes of metal. After it has separated, pour off the solution, filter, wash with cold water, and dry ; this is the alu- minium." In reality, this powder possessed no metallic properties, and moreover, it contained potassium and aluminium chloride, which REDUCTION BY POTASSIUM OR SODIUM. 199 gave to it the property of decomposing water at 100. To avoid the loss of aluminium chloride by volatilization at the high heat developed during the reaction, Liebig afterwards made its vapor pass slowly over some potassium placed in a long glass tube. This device of Liebig is nearly the arrangement which Wohler adopted later, in 1845, and which gave him much better results. Wohler' s Experiments (1845). The following is Wohler' s second paper, published in 1845 : * " On account of the violent incandescence with which the re- duction of aluminium chloride by potassium is accompanied, this operation requires great precautions, and can be carried out only on a small scale. I took for the operation a platinum tube, in which I placed aluminium chloride, and near it some potassium in a platinum boat. I heated the tube gently at first, then to redness. But the reduction may also be done by putting potass- ium in a small crucible which is placed inside a larger one, and the space between the two filled with aluminium chloride. A close cover is put over the whole and it is heated. Equal volumes of potassium and the aluminium salt are the best proportions to employ. After cooling, the tube or crucible is put in a vessel of water. The metal is obtained as a gray metallic powder, but on closer observation one can see even with the naked eye small tin- white globules, some as large as pins' heads. Under the micro- scope magnifying two hundred diameters the whole powder resolves itself into small globules, several of which may sometimes be seen sticking together, showing that the metal was melted at the moment of reduction. A beaten out globule may be again melted to a sphere in a bead of borax or salt of phosphorus, but rapidly oxidizes during the operation, and if the heat is continued disap- pears entirely, seeming either to reduce boric acid in the borax bead or phosphoric acid in the salt of phosphorus bead. I did not succeed in melting together the pulverulent aluminium in a crucible with borax, at a temperature which would have melted cast-iron, for the metal disappeared entirely and the borax became * Liebig's Annalen, 53, 422. 200 ALUMINIUM. a black slag. It seems probable that aluminium, being lighter than molten borax, swims on it and burns. The white metallic globules had the color and lustre of tin. It is perfectly malleable and can be hammered out to the thinnest leaves. Its specific gravity, determined with two globules weighing 32 milligrammes, was 2.50, and with three hammered-out globules weighing 34 milligrammes, 2.67. On account of their lightness these figures can only be approximate. It is not magnetic, remains white in the air, decomposes water at 100, not at usual temperatures, and dissolves completely in caustic potash (KOH). When heated in oxygen almost to melting, it is only superficially oxidized, but it burns like zinc in a blast-lamp flame." These results of Wohler's, especially the determination of spe- cific gravity, were singularly accurate when we consider that he established them working with microscopic bits of the metal. It was just such work that established Wbhler's fame as an investi- gator. However, we notice that his metal differed from alumin- ium as we know it in several important respects, in speaking of w r hich Deville says : " All this time the metal obtained by Wohler was far from being pure ; it was very difficultly fusible, owing without doubt to the fact that it contained platinum taken from the vessel in which it had been prepared. It is well known that these two metals combine very easily at a gentle heat. Moreover it decomposed water at 100, which must be attributed either to the presence of potassium or to aluminium chloride, with which the metal might have been impregnated : for aluminium in pre- sence of aluminium chloride in effect decomposes water with evolution of hydrogen." After Wohler's paper in 1845, the next improvement is that introduced by Deville in 1854-55, and this is really the date at which aluminium, the metal, became known and its true proper- ties established. Deville' s Experiments (1854). The results of this chemist's investigations and success in ob- taining pure aluminium were first made public at the seance of the French Academy, August 14, 1854, and included mention of REDUCTION BY POTASSIUM OR SODIUM. 201 an electrolytic method of reduction (see Chap. XI.), as well as of following on reduction by sodium.* " The following is the best method for obtaining aluminium chemically pure in the laboratory. Take a large glass tube about four centimetres in diameter, and put into it 200 to 300 grammes of pure aluminium chloride free from iron, and isolate it between two stoppers of amianthus (fine, silky asbestos). Hydrogen, well dried and free from air, is brought in at one end of the tube. The aluminium chloride is heated in this current of gas by some lumps of charcoal, in order to drive off hydrochloric acid or sulphides of chlorine or of silicon, with which it is always impregnated. Then there are introduced into the tube porcelain boats, as large as possible, each containing several grammes of sodium, which w r as previously rubbed quite dry between leaves of filter paper. The tube being full of hydrogen, the sodium is melted, the alu- minium chloride is heated and distils, and decomposes in contact with the sodium with incandescence, the intensity of which can be moderated at pleasure. The operation is ended when all the sodium has disappeared, and when the sodium chloride formed has absorbed so much aluminium chloride as to be saturated with it. The aluminium which has been formed is held in the double chloride of sodium and aluminium, Al 2 Cl 6 .2NaCl, a compound very fusible and very volatile. The boats are then taken from the glass tube, and their entire contents put in boats made of re- tort carbon, which have been previously heated in dry chlorine in order to remove all silicious and ferruginous matter. These are then introduced into a large porcelain tube, furnished with a pro- longation and traversed by a current of hydrogen, dry and free from air. This tube being then heated to bright redness, the alu- minium-sodium chloride distils without decomposition and con- denses in the prolongation. There is found in the boats, after the operation, all the aluminium which had been reduced, collected in at most one or two small buttons. The boats when taken from the tube should be nearly free from aluminium-sodium chloride and * Ann. de Phys. et de Chem., xliii. 24. 202 ALUMINIUM. also from sodium chloride. The buttons of aluminium are united in a small earthen crucible which is heated as gently as possible, just sufficient to melt the metal. The latter is pressed together and skimmed clean by a small rod or tube of clay. The metal thus collected may be very suitably cast in an ingot mould." The later precautions added to the above given process were principally directed towards avoiding the attacking of the crucible, which always takes place when the metal is melted with a flux, and the aluminium thereby made more or less siliceous. The year following |the publication of these results, this laboratory method was carried out on a large scale at the chemical works at Javel. Devilled Methods (1855). The methods about to be given are those which were devised in Deville's laboratory at the Ecole Normale, during the winter of 1854-55, and applied on a large scale at Javel, during the spring of 1855 (March-July). The Emperor Napoleon III. defrayed the expenses of this installation. Descriptions of the methods used for producing alumina, aluminium chloride and sodium at Javel can be found under their respective headings (pp. 106, 120, 123, 146). We here confine our description to the mode of reducing the aluminium chloride by sodium, and the re- marks incident thereto. The process has at present only an his- toric interest, as it was soon modified in its details so as to be almost entirely changed. The following is Deville's description : " Perfectly pure aluminium. To obtain aluminium perfectly pure it is necessary to employ materials of absolute purity, to reduce the metal in presence of a completely volatile flux, and finally never to heat, especially with a flux, in a siliceous vessel to a high temperature." "Pure materials. The necessity of using absolutely pure materials is easy to understand ; all the metallic impurities are concentrated in the aluminium, and unfortunately I know no absolute method of purifying the metal. Thus, suppose we take an alum containing 0.1 per cent, of iron and 11 per cent, of alumina; the alumina derived from it will contain 1 per cent. REDUCTION BY POTASSIUM OR SODIUM. 203 of iron, and supposing the alumina to give up all the aluminium in it, the metal will be contaminated with 2 per cent, of iron." " Influence of flux or slag. The flux, or the product of the reaction of the sodium on the aluminous material, ought to be volatile, that one may separate the aluminium by heat from the material with which it has been in contact, and with which it remains obstinately impregnated because of its small specific gravity." " Influence of the vessel. The siliceous vessels in which alu- minium is received or melted give it necessarily a large quantity of silicon, a very injurious impurity. Silicon cannot be separated from aluminium by any means, and the siliceous aluminium seems to have a greater tendency to take up more silicon than pure alu- minium, so that after a small number of remeltings in siliceous vessels the metal becomes so impure as to be almost infusible." In order to avoid the dangers pointed out above, Deville recom- mended following scrupulously the following details in order to get pure aluminium. " Reduction by solid sodium. The crude aluminium chloride placed in the cylinder A (Fig. 20), is vaporized by the fire and Fig. 20. passes through the tube to the cylinder J5, containing 60 to 80 kilos of iron-nails heated to a dull-red heat. The iron retains as relatively fixed ferrous chloride, the ferric chloride and hydro- chloric acid which contaminate the aluminium chloride, and like- wise transforms any sulphur dichloride (SCI 2 ) in it into ferrous chloride and sulphide of iron. The vapors on passing out of B through the tube, which is kept at about 300, deposit spangles of ferrous chloride, which is without sensible tension at that tern- 204 ALUMINIUM. perature. The vapors then enter D, a cast-iron cylinder in which are three cast-iron boats each containing 500 grms. of sodium. It is sufficient to heat this cylinder barely to a dull-red heat in its lower part, for the reaction once commenced disengages enough heat to complete itself, and it is often necessary to take away all the fire from it. There is at first produced in the first boat some aluminium and some sodium chloride, which latter combines with the excess of aluminium chloride to form the volatile aluminium- sodium chloride, Al 2 Cl 6 .2NaCl. These vapors of double chloride condense on the second boat and are decomposed by the sodium into aluminium and sodium chloride. A similar reaction takes place in the third boat when all the sodium of the second has disappeared. When on raising the cover it is seen that the sodium of the last boat is entirely transformed into a lumpy black material, and that the reactions are over, the boats are taken out, immediately replaced by others, and are allowed to cool covered by empty boats. In this first operation the reaction is rarely complete, for the sodium is protected by the layer of sodium chloride formed at its expense. To make this disappear, the contents of the boats are put into cast-iron pots or earthen crucibles, which are heated until the aluminium chloride begins to volatilize, when the sodium will be entirely absorbed and the aluminium finally remains in contact with a large excess of its chloride, which is indispensable for the success of the operation. Then the pots or crucibles are cooled, and there is taken from the upper part of their contents a layer of sodium chloride almost pure, while underneath are found globules of aluminium which are separated from the residue by washing with water. Unfortunately, the water in dissolving the aluminium chloride of the flux exercises on the metal a very rapid destructive action, and only the globules larger than the head of a pin are saved from this washing. These are gathered together, dried, melted in an earthen crucible, and pressed together with a clay rod. The button is then cast in an ingot mould. It is important in this operation to employ only well purified sodium, and not to melt the aluminium if it still contains any sodium, for in this case the metal takes fire and burns as long as any of the alkaline metal remains in it. In such a REDUCTION BY POTASSIUM OR SODIUM. 205 case it is necessary to remelt in presence of a little aluminium- sodium chloride. " Such is the detestable process by means of which were made the ingots of aluminium sent to the Exhibition (1855). To com- plete my dissatisfaction at the process, pressed by time and ignor- ant of the action of copper on aluminium, I employed in almost all my experiments reaction cylinders and boats of copper, so that the aluminium I took from them contained such quantities of this metal as to form a veritable alloy. Moreover, it had lost almost all ductility and malleability, had a disagreeable gray tint, and finally at the end of two months it tarnished by becoming covered with a black layer of oxide or sulphide of copper, which could only be removed by dipping in nitric acid. But, singular to relate, an ingot of virgin silver which had been put along- side the aluminium that the public might note easily the dif- ference in color and weight of the two metals, was blackened still worse than the impure aluminium. Only one of the bars exhibited, which contained no copper, remained unaltered from the day of its manufacture till now (1859). It was some of this cupreous aluminium that I sent to Mr. Regnault, who had asked me for some in order to determine its specific heat. I had cau- tioned him at the time, of the number and nature of the impuri- ties which it might contain, and the analysis of M. Salvetat, which is cited in the memoir of Regnault, accords with the mean composition of the specimens that I had produced and analyzed at that time (see p. 54, Analysis 1). It is to be regretted that I gave such impure material to serve for determinations of such splendid precision ; I was persuaded to do so only by the entreaties of M. Regnault who could not wait until I prepared him better. It is also this cupreous aluminium which M. Hulot has called t hard aluminium/ in a note on the physical properties of this metal which he addressed to the Academy. Hulot has remarked that this impure metal, which is crystalline in structure, after having been compressed between the dies of the coining press may lose its crystalline structure, to which it owes its brittleness, and become very malleable. It possesses then such strength that it works well in the rolls of a steel-rolling mill. Further, this 206 ALUMINIUM. ' hard aluminium' becomes quite unalterable when it has thus lost its texture." " Reduction by sodium vapor. This process, which I have not perfected, is very easy to operate, and gave me very pure metal at the first attempt. I operate as follows : I fill a mercury bot- tle with a mixture of chalk, carbon, and carbonate of soda, in the proportions best for generating sodium. An iron tube about ten centimetres long is screwed to the bottle, and the whole placed in a wind furnace, so that the bottle is heated to red-white and the tube is red to its end. The end of the tube is then intro- duced into a hole made in a large earthen crucible about one- fourth way from the bottom, so that the end of the tube just reaches the inside surface of the crucible. The carbonic oxide (CO) disengaged burns in the bottom of the crucible, heating and drying it ; afterwards the sodium flame appears, and then pieces of aluminium chloride are thrown into the crucible from time to time. The salt volatilizes and decomposes before this sort of tuyere from which issues the reducing vapor. More aluminium salt is added when the vapors coming from the crucible cease to be acid, and when the flame of sodium burning in the atmosphere of aluminium chloride loses its brightness. When the operation is finished, the crucible is broken and there is taken from the walls below the entrance of the tube a saline mass composed of sodium chloride, a considerable quantity of globules of aluminium, and some sodium carbonate, which latter is in larger quantity the slower the operation was performed. The globules are detached by plunging the saline mass into water, when it becomes necessary to notice thp reaction of the water on litmus. If the water be- comes acid, it is renewed often ; if alkaline, the mass impregnated with metal must be digested in nitric acid diluted with three or four volumes of water, and so the metal is left intact. The globules are reunited by melting with the precautions before given." Deville's Process (1859). The process then in use at Nanterre was based on the use of aluminium-sodium chloride, which was reduced by sodium, with cryolite or fluorspar as a flux. The methods of preparing each REDUCTION BY POTASSIUM OR SODIUM. 207 of these materials were carefully studied out at the chemical works of La Glaciere, where from April 1856, to April 1857, the manufacture of aluminium was carried on by a company formed by Deville and a few friends, and from thence proceeded the actual system which was established at Nanterre under the direction of M. Paul Morin when the works at La Glaciere were closed. The methods of preparation of alumina, aluminium- sodium chloride and sodium used at Nanterre are placed under their respective headings (pp. 120, 127, 161, 163). In the first year that the works at Nanterre were in operation there were made Aluminium-sodium chloride .... 10,000 kilos. Sodium ........ 2,000 " Aluminium 600 " The metal prepared improved constantly in quality, M. Morin profiting continually by his experience and improving the prac- tical details constantly, so that the aluminium averaged, in 1859, 97 per cent. pure. (See Analysis 9, p. 54.) As to the rationale of the process used, aluminium chloride was replaced by aluminium-sodium chloride because the latter is less deliquescent and less difficult of preservation ; but the small amount of moisture absorbed by the double chloride is held very energetically, at a high temperature giving rise to some alumina, which incloses the globules of metal with a thin coating, and so hinders their easy reunion to a button. Deville remarked that the presence of fluorides facilitated the reunion of these globules, which fact he attributed to their dissolving the thin coat of alu- mina ; so that the employment of a fluoride as a flux became necessary to overcome the effect produced primarily by the alu- minium-sodium chloride holding moisture so energetically. De- ville gives the following account of the development of these im- provements : " The facility with which aluminium unites in fluorides is due without doubt to the property which these possess of dissolving the alumina on the surface of the globules at the moment of their formation, and which the sodium is unable to reduce. I had experienced great difficulty by obtaining small quantities of metal poorly united, when I reduced the aluminium- 208 ALUMINIUM. sodium chloride by sodium ; M. Rammelsberg, who often made the same attempts, tells me he has had a like experience. But I am assured by a scrupulous analysis that the quantity of metal reduced by the sodium is exactly that which theory indicates, although after many operations there is found only a gray pow- der, resolving itself under the microscope into a multitude of small globules. The fact is simply that aluminium-sodium chlor- ide is a very poor flux for aluminium. MM. Morin, Debray, and myself have undertaken to correct this bad effect by the in- troduction of a solvent for the alumina into the saline slag which accompanies the aluminium at the moment of its formation. At first, we found it an improvement to condense the vapors of alu- minium chloride, previously purified by iron, directly in sodium chloride, placed for this purpose in a crucible and kept at a red heat. We produced in this way, from highly colored material, a double chloride very white and free from moisture, and furnish- ing on reduction a metal of fine appearance. We then intro- duced fluorspar (CaF 2 ) into the composition of the mixture to be reduced, and we obtained good results with the following propor- tions : Aluminium-sodium chloride . . . 400 grammes. Sodium chloride 200 " Calcium fluoride 200 " Sodium . , ". . . . . t . 75 to 80 " "The double chloride ought to be melted and heated almost to low red heat at the moment it is employed, the sodium chloride calcined and at a red heat or melted, and the fluorspar pulver- ized and well dried. The double chloride, sodium chloride and calcium fluoride are mixed and alternated in layers in the crucible with sodium. The top layer is of the mixture, and the cover is sodium chloride. Heat gently, at first, until the reaction ends, and then to a heat about sufficient to melt silver. The crucible, or at least that part of it which contains the mixture, ought to be of a uniform red tint, and the material perfectly liquid. It is stirred a long time and cast on a well dried, chalked plate. There flows out first a very limpid liquid, colorless and very fluid, then a gray material, a little more pasty, which contains alu- REDUCTION BY POTASSIUM OR SODIUM. 209 minium in little grains, and is set aside, and finally a button with small, metallic masses which of themselves ought to weigh 20 grms. if the operation has succeeded well. On pulverizing and sieving the gray slag, 5 or 6 grms. of small globules are ob- tained, which may be pressed together by an earthen rod in an ordinary crucible heated to redness. The globules are thus re- united, and when a sufficient quantity is collected the metal is cast into ingots. In a well-conducted operation, 75 grms. of sodium ought to give a button of 20 grms. and 5 grms. in grains, making a return of one part aluminium from three of sod- ium. Theory indicates one to two and a half, or 30 grms. of aluminium from 75 of sodium. But all the efforts which have been made to recover from the insoluble slag the 4 or 5 grms. of metal not united but easily visible with a glass, have been so far unsuccessful. There is, without doubt, a knack, a particular manipulation on which depends the success of an operation which would render the theoretical amount of metal, but we lack it yet. These operations take place, in general, with more facility on a large scale, so that we may consider fluorspar as be- ing suitable for serving in the manufacture of aluminium in cru- cibles. We employed very pure fluorspar, and our metal was quite exempt from silicon. It is true that we took a precaution which is necessary to adopt in operations of this kind ; we plastered our crucibles inside with a layer of aluminous paste, the composition of which has been given in ' Ann. de Chim. et de Phys.' xlvi. 195. This paste is made of calcined alumina and an aluminate of lime, the latter obtained by heating together equal parts of chalk and alumina to a high heat. By taking about four parts calcined alumina and one of aluminate of lime well pulverized and sieved, moistening with a little water, there is obtained a paste with which the inside of an earthen crucible is quickly and easily coated. The paste is spread evenly with a porcelain spatula, and compressed strongly until its surface has become well polished. It is allowed to dry, and then heated to bright redness to season the coating, which does not melt, and protects the crucible completely against the action of the aluminium and fluorspar. A crucible will serve several times in succession provided that the new material is put in as soon as the previous 14 210 ALUMINIUM. charge is cast. The advantages of doing this are that the mix- ture and the sodium are put into a crucible already heated up, and so lose less by volatilization because the heating is done more quickly, and the crucible is drier than if a new one had been used or than if it had been let cool. A new crucible should be heated to at least 300 or 400 before being used. The saline slag contains a large quantity of calcium chloride, which can be washed away by water, and an insoluble material from which aluminium fluoride can be volatilized. "Yet the operation just described, which was a great improve- ment on previous ones, requires many precautions and a certain skill of manipulation to succeed every time. But nothing is more easy or simple than to substitute cryolite for the fluorspar. Then the operation is much easier. The amount of metal produced is not much larger, although the button often weighs 22 grammes, yet if cryolite can only be obtained in abundance in a continuous supply, the process which I will describe will become most eco- nomical. The charge is made up as before, except introducing cryolite for fluorspar. In one of our operations we obtained, with 76 grms. of sodium, a button weighing 22 grms. and 4 grms. in globules, giving a yield of one part aluminium to two and eight-tenths parts sodium, which is very near to that indicated by theory. The metal obtained was of excellent quality. However, it contained a little iron coming from the aluminium chloride, which had not been purified perfectly. But iron does not injure the properties of the metal as copper does ; and, save a little bluish coloration, it does not alter its appearance or its resistance to physical and chemical agencies. " After these attempts we tried performing the reduction simply on the bed of a reverberatory furnace, relying on the immediate reaction of sodium on the double chloride to use up these mate- rials before they could be perceptibly wasted by the furnace gases. This condition was realized in practice with unlooked-for success. The reduction is now made on a somewhat considerable scale at the Nanterre works, and never, since commencing to operate in this way, has a reduction failed, the results obtained being always uniform. The furnace now used has all the relative dimensions of a soda furnace. In fact, almost the temperature of an ordinary REDUCTION BY POTASSIUM OR SODIUM. 211 soda furnace is required that the operation may succeed per- fectly. The absolute dimensions of the furnace, however, may vary with the quantity of aluminium to be made in one opera- tion, and are not limited. With a bed of one square metre sur- face, 6 to 10 kilos of aluminium can be reduced at once ; and since each operation lasts about four hours and the furnace may be recharged immediately after emptying it of the materials just treated, it is seen that, with so small a bed, 60 to 100 kilos of alu- minium can be made in twenty-four hours without any difficulty. In this respect, I think the industrial problem perfectly solved. The proportions which we employed at first were Aluminium-sodium chloride (crushed) . . 10 parts. Fluorspar . . . . . . . 5 " Sodium (in ingots) . . . . . 2 " " As aluminium is still very dear, it is necessary to direct great attention to the return from the materials used, and on this point there is yet much progress to be made. We ascertained many times that the return was always a little better, and the reunion of the metal to a single ingot a little easier, when cryolite was substituted for fluorspar, the price of the former, after having been high, being now lowered to 350 francs per tonne (about $75 per long ton). For this reason we can now use cryolite instead of fluorspar, and in the same proportions. W^e can also recover alumina from this cryolite by treating the slags (see p. 119). The double chloride and pulverized cryolite are now mixed with the sodium in small ingots, and the mixture thrown on to the bed of the heated-up furnace. The dampers are then shut, to prevent as much as possible access of air. Very soon a lively reaction begins, with the production of such heat that the brick sides of the furnace, as well as the materials on the hearth, are made bright red-hot. At this heat the mixture is almost com- pletely fused. Then it is necessary to open the damper and direct the flame on the bed in such manner as to heat the bath equally all over and unite the reduced aluminium. When the operation is considered ended, a casting is made by an opening in the back of the furnace and the slag is received in cast-iron pots. At the end of the cast the aluminium arrives in a single jet, which unites 212 ALUMINIUM. into a single lump at the bottom of the still-liquid slag. The gray slag flowing out last should be pulverized and sieved, to extract the divided globules of aluminium, 200 to 300 grammes of which can sometimes be extracted from one kilo of gray slag. The pulverization of the slag is in all cases indispensable in its subsequent treatment for extracting its alumina. The slag is of two kinds, one fluid and light, which covered the bath, and is rich in sodium chloride ; the other less fusible and pasty, gray in color, which is more dense and lies in contact with the aluminium. The coloring material producing the gray ness is carbon, coming either from the sodium or from the oil which impregnated it, or finally from the vapor of the oil. I attribute the slight pastiness of this slag to a little alumina dissolved by the fluorides. This slag contains about Sodium chloride . . . . . .60 parts. Aluminium fluoride . . . . . . 40 " and on washing it the former dissolves while the latter remains, mixed with a little cryolite or alumina. This is the alumina which had been dissolved or retained in the bath of fluoride. It will be remarked that the bath of slag contains no other fluoride than aluminium fluoride, which does not attack earthen crucibles or siliceous materials in general except at a very high tempera- ture. It is for this reason that the hearth and other parts of the furnace resist easily a fluoride slag containing only aluminium fluoride, which has not the property of combining with silicon fluoride at the expense of the silica of the bricks as sodium fluoride does in like circumstances. In our operations, cryo- lite is used only as a flux. In the process of reduction based on cryolite alone, the sodium fluoride resulting is, on the contrary, very dangerous to crucibles, and it is due to that fact especially that the aluminium absorbs a large quantity of silicon, which always happens with this method. In fact, it is well known that metallic silicon can be prepared in this way by prolonging the operation a little." Deville closes his account of the aluminium industry in 1859 with these words : " Many things yet remain to us to do, and we can scarcely say now that we know the true qualities of the REDUCTION BY POTASSIUM OR SODIUM. 213 substances we employ. But the matter is so new, is harassed with so many difficulties even after all that has been done, that our young industry may hope everything from the future when it shall have acquired experience. I ought to say, however, that the aluminium industry is now at such a point that if the uses of the metal are rapidly extended it may change its aspect with great rapidity. One may ask to-day how much a kilo of iron would cost if a works made only 60 to 100 kilos of it a month, if large apparatus were excluded from this industry, and iron obtained by laboratory processes which would permit it to be- come useful only by tedious after-treatment. Such will not be the case with aluminium, at least with the processes just described. In fact, in all I undertook, either alone or with my friends, I have always been guided by this thought that we ought to adopt only such apparatus as is susceptible of being immediately en- larged, and to use only materials almost as common as clay itself for the source of the aluminium." The Devitte Process (1882). The process just described reached a fair degree of perfection at Nanterre, under the direction of M. Paul Morin. Afterwards, some of the chemical operations incidental to the process were car- ried on at the works of the Chemical Manufacturing Company of Alais and Carmargue, at Saliudres (Gard), owned by H. Merle & Co. At a later date the whole manufacture was removed to this place, while the Societe Anonyme de 1'Aluminium, at Nan- terre, worked up the metal and placed it on the market. The Salindres works, about 1880, went under the management of A. R. Pechiney & Co., and under the personal attention of M. Pechiney the Deville process has reached its present state of per- fection. The following account is taken mostly from M. Mar- gottet's article on aluminium in Fremy's Encyclopedic Chimique. An outline of the process, as it now stands, may very appro- priately be given at this place, although detailed descriptions of the preliminary processes for preparing the materials for reduc- tion are given under the appropriate headings (see pp. 109, 127). The primary material to furnish the aluminium is beauxite. 214 ALUMINIUM. To obtain the metal it is necessary to proceed successively through the following operations : I. Preparation of the aluminate of soda, and solution of this salt to separate it from the ferric oxide contained in the beauxite. II. Precipitation of hydrated alumina from the aluminate of soda by a current of carbon dioxide ; washing the precipitate. III. Preparation of a mixture of alumina, carbon, and salt, drying it, and then treating with gaseous chlorine to obtain the double chloride of aluminium and sodium. IV. Lastly, treatment of this chloride by sodium to obtain aluminium. The principal chemical reactions on which this process rests are the following : Formation of aluminate of soda by calcining beauxite with sodium carbonate (AlFe) 2 O s .2H 2 O + 3Na 2 CO 3 = Al 2 O 3 .3Na 2 O 4- Fe 2 O s 4- 2H 2 4- 3C0 2 . Formation of alumina by precipitating the aluminate of soda with a current of carbon dioxide Al 2 O 3 .3]N T a 2 O 4- 3CO 2 + 3H 2 O = A1 2 O 3 .3H 2 O 4- 3Na 2 CO 3 . Formation of aluminium sodium chloride by the action of chlor- ine on a mixture of alumina, carbon, and sodium chloride APO 3 4- 30 + 2]NaCl + 6C1 = Al 2 Cl 6 .2NaCl + 3CO. Reduction of this double chloride by sodium Al 2 Cl 6 .2NaCl 4- 6Na = 2A1 4- 8NaCl. As observed before, we will here consider only the last opera- tion. The advances made since 1859 are mostly in matters of detail, which every one knows are generally the most important part of a process; and so, although a few of the details may be repeated, yet we think it best not to break the continuity of this description by excising those few sentences which are nearly identical in the two accounts. The difficulty of this operation, at least from an industrial point of view, is to get a slag fusible enough and light enough to let the reduced metal easily sink through it and unite. This [REDUCTION BY POTASSIUM OR SODIUM. 215 result has been reached by using cryolite, a white or grayish mineral originally from Greenland, very easy to melt, formula APF 6 .6NaF. This material forms with the sodium chloride re- sulting from the reaction a very fusible slag, in the midst of which the aluminium collects well, and falls to the bottom. In one operation the charge is now composed of 100 kilos ...... Aluminium-sodium chloride. 45 " -Cryolite. 35 " Sodium. The double chloride and cryolite are pulverized, the sodium, cut into small pieces a little larger than the thumb, is divided into three equal parts, each part being put into a sheet-iron bas- ket. The mixture of double chloride and cryolite, being pulver- ized, is divided into four equal parts, three of these are respectively put in each basket with the sodium, the fourth being placed in a Fig. 21. basket by itself. The reduction furnace (see Fig. 21) is a little furnace of refractory brick, with an inclined hearth and a vaulted roof. This furnace is strongly braced by iron tie-rods, because of the concussions caused by the reaction. The flame may at any given moment be directed into a flue outside of the hearth. At the back part of the furnace, that is to say, on that side towards which the bed slopes, is a little brick wall which is built up for each reduction and is taken away in operating the running out of the metal and slag. A gutter of cast-iron is placed immediately 216 ALUMINIUM. in front of the wall to facilitate running out the materials. All this side of the furnace ought to be opened or closed at pleasure by means of a damper. Lastly, there is an opening for charging in the roof, closed by a lid. At the time of an operation the furnace should be heated to low redness, then are introduced in rapid succession the contents of the three baskets containing sodium, etc., and lastly the fourth containing only double chloride and no sodium. Then all the openings of the furnace are closed and a very vivid reaction accompanied by dull concussions imme- diately takes place. At the end of fifteen minutes, the action subsides, the dampers are opened, and the heat continued, mean- while stirring the mass from time to time with an iron poker. At the end of three hours the reduction is ended, and the metal collects at the bottom of the liquid bath. Then the running out is proceeded with in three phases : First. Running off the upper part of the bath, which consists of a fluid material completely free from reduced aluminium and constituting the white slag. To run this out a brick is taken away from the upper course of the little wall which terminates the hearth. These slags are received in an iron wagon. Second. Running out the aluminium. This is done by opening a small orifice left in the bottom of the brick wall, which was temporarily plugged up. The liquid metal is received in a cast-iron melting pot, the bottom of which has been previously heated to redness. This aluminium is immediately cast in a series of small rectangular cast-iron moulds. Third. Running out of the rest of the bath, which constitutes the gray slags. These were, like the white slags, formed by the sodium chloride and cryolite, but they contain, in addition, isolated glob- ules of aluminium. To run these out, all the bricks of the little wall are taken away. This slag is received in the same melting pot into which the aluminium was run, the latter having been already moulded. Here it cools gradually, and after cooling there are always found at the bottom of the pot several grains of metal. In a good operation there are taken from one casting 10.5 kilos of aluminium, which is sold directly as commercial metal. The following data as to the expense of this process may be very appropriately inserted here, giving the cost at Salindres in 1872, in which year 3600 kilos are said to have been made. REDUCTION BY POTASSIUM OR SODIUM. 217 *Manufacture of one kilo of aluminium. Sodium . . . 3.44 kilos @ 11.32 fr. per kilo = 38 fr. 90 cent. Aluminium-sodium chloride . . 10.04 " 2.48 " " = 24 Cryolite . . . 3.87 " 61.0 " 100 kilos = 2 Coal .... 29.17 " 1.40 " " =0 Wages .... 1 Costs . 90 36 41 80 88 Total . . . . 69 " 25 " This must be increased ten per cent, for losses and other ex- penses, making the cost of aluminium 80 fr. per kilo, and it is sold for 100. ($9.00 per Ib.) According to a statement in the ' Bull, de la Soc. de ^Industrie Mine-rale/ ii., 451, made in 1882, Salindres was then the only place in which aluminium was being manfactured. Niewerttts Process (1883). This method can be regarded as little more than a suggestion, since it follows exactly the lines of some of Deville's earlier ex- periments. Although theoretically very advantageous, yet in practice it has probably been found far inferior in point of yield of metal and expense to the ordinary sodium processes. The patent is said to be taken out in the United States and other countries in the name of H. Niewerth, of Hanover, and is thus summarized : fA compound of aluminium, with chlorine or fluorine, is brought by any means into the form of vapor, and conducted, strongly heated, into contact with a mixture of 62 parts sodium carbonate, 28 coal, and 10 chalk, which is also in a highly heated condition. This mixture disengages sodium, which reduces the gaseous chloride or fluoride of aluminium, the nascent sodium being the reducing agent. In place of the above mixture other suitable mixtures which generate sodium may be employed, or mixtures may also advantageously be used from which potassium is generated. * A. Wurtz, Wagner's Jaresb., 1874, vol. xxi. f Sci. Am. Suppl., Nov. 17, 1883. 218 ALUMINIUM. Gadsden's Patent (1883). H. A. Gadsden, of London, and E. Foote,* of New York, were granted a patent based on the principle of heating in a retort sodium carbonate and carbonaceous matter, or any suitable mixture for generating sodium, and conducting the vapor of sodium produced into another retort, lined with carbon, in which aluminium chloride, or aluminium-sodium chloride or cryolite has been placed and heated. The second English patent claims to heat a mixture which will generate sodium, in one retort, and pass chlorine over a mixture of carbon and alumina, thus gen- erating aluminium chloride, in another retort, and then mixing the two vapors in a third retort or reaction chamber. Frishmuitis Process (1884). This was patented in the United States in 1884 (U. S. Pat. 308,152, Nov. 1884). In what the originality of the process consists, in view of Deville's publications and even in view of the processes just mentioned, we cannot see, and we simply acquiesce blindly to the mysterious penetration of our Patent Office Board. However, Col. Frishmuth himself admits, in 1887, having aban- doned the sodium process ; it is therefore probable that the dif- ficulties of the method did not permit its competing with the more roundabout but more easily-conducted operation with solid sodium. A simple transcript of the claims in his patent will give a sufficiently extended idea of the reactions proposed to be used. 1. The simultaneous generation of sodium vapor and a vola- tile compound of aluminium in two separate vessels or retorts, and mingling the vapors thus obtained in a nascent (!) state in a third vessel, wherein they react on each other. 2. The sodium vapor is produced from a mixture of a sodium compound and carbon, or some other reducing agent ; and the aluminous vapor from aluminous material.- 3. The simultaneous generation of sodium vapor and vapor of * English patents 1995 and 4930 (1883) ; German patent 27,572 (1884). REDUCTION BY POTASSIUM OR SODIUM. 219 aluminium chloride or aluminium fluoride ; or of sodium vapor and aluminium-sodium chloride. 4. Converting the aluminous material to a vapor by heating it in a retort with sodium chloride, and subjecting it at the same time to chlorine gas ; mingling the vapor of aluminium-sodium chloride thus obtained with vapor simultaneously generated from sodium carbonate and carbon. H. von Groudllier y s Improvement (1885). This suggestion as to the way of performing the reduction by sodium is the subject of the English patent 7858, June 29, 1885. Dr. Fischer remarks on it, in i Wagner's Jahresbericht' for 1885, that " it is apparently wholly worked out at the writing-table." The patentee, Hector von Grousillier, Springe, Hanover, thus describes his invention : " In order to avoid the difficulties ordinarily met with in the use of aluminium-sodium chloride to obtain aluminium, I raise the volatilizing point of aluminium chloride by performing its reduction, either chemically or electrolytically, under pressure in a strong, hermetically-closed vessel lined with clay or magnesia and provided with a safety valve." The Deville-Castner Process (1886). This latest development of the old Deville process is now operated by the Aluminium Company, Limited, at their large new works at Oldbury, near Birmingham, England. The plant covers nearly five acres of ground, and adjoins Chance Bros/ large chemical works, from which the hydrochloric acid used is obtained and the waste soda-liquors returned, by means of large pipes connecting the two plants. The company is thus in posi- tion to obtain acid and dispose of its by-products to very good advantage. The principle on which the process works is similar to its predecessor, in being the reduction of aluminium-sodium chloride by sodium, but it improves on the other in the cheaper production of both these materials. For instance, the alumina used is obtained and converted into double chloride by Mr. Web- 220 ALUMINIUM. ster's processes, by which it is probable that this salt does not cost over 3d. per Ib. (see p. 133), as against 12d., the cost at Salindres ; further, by Mr. Castner's sodium process it is acknowledged that the sodium costs only about 9d. per Ib., as against 48d, or $1, as formerly. Since 10 Ibs. of the chloride and 3 Ibs. of sodium are required to produce 1 Ib. of aluminium, the average saving in these two items, over the old process, is somewhere about 75 per cent. The works contain a sodium building, in which are four large sodium furnaces, each capable of producing over 500 Ibs. of that metal in twenty-four hours ; the sodium is also remelted and stored in the same building (see p. 166). The double chloride furnaces are in a building 250 feet by 50 feet wide, there being 12 furnaces each containing 5 retorts. The total output of double chloride is an average of 5000 Ibs. per day. (See p. 129.) Connected with this building is a chlorine plant of the largest size, capable of supplying about a ton and a half of chlorine a day. In a separate building are two reverberatory furnaces in which the final reduction takes place and the aluminium is pro- duced. Besides these, there are a rolling mill, wire mill, and foundry on the grounds. From the quantity of sodium and double chloride produced, we can see that the works can produce about 500 Ibs. of aluminium a day or 150,000 Ibs. a year, with some sodium left over for sale or other purposes. The mode of conducting the reduction is not very different from that practised at Salindres. There are two regenerative reverberatory furnaces used, one about twice as large as the other. The larger furnace has a bed about six feet square, slop- ing towards the front of the furnace through which are several openings at different heights. The charge for this furnace con- sists of 1200 Ibs. of double chloride, 350 Ibs. of sodium, and 600 Ibs. of cryolite for a flux. The chloride is in small pieces, the cryolite is in powder, and the sodium is cut into thin slices by a machine. These ingredients are put into a revolving wooden drum placed on a staging over the furnace, and are there thoroughly mixed. The drum is then opened and turned, when the contents fall into a small wagon beneath. The fur- nace having been raised to the required temperature, all the REDUCTION BY POTASSIUM OR SODIUM. 221 clampers are shut and the car is moved on a track immediately over a large hopper placed in the roof of the furnace. The hop- per being opened the charge is dumped in and drops on to the centre of the hearth. The reaction is immediate and the whole charge becomes liquid in a very short time. After a few minutes, heating gas is again turned on and the furnace kept moderately hot for two or three hours. The reaction has been Al 2 Cl 6 .2NaCl + 6Na = Al 2 + SNaCl and the aluminium gathers under the bath of cryolite and sod- ium chloride. One of the lower tap holes is then opened with a bar, and the aluminium run out into moulds. When the metal has all run out it is followed by slag, which flows into iron wagons. The openings are then plugged up and the furnace is ready for another charge. The charge given produces usually 115 to 120 Ibs. of aluminium, the whole operation lasting about 4 hours. The large furnace could thus produce 840 Ibs. in 24 hours, and the smaller one half that quantity. The first portion of metal running out is the purest, the latter portions and especially that entangled in the slag on the hearth, and which has to be scraped out, containing more foreign substances. This impure metal is about one-fourth of all the aluminium in the charge. The purity of the metal run out depends directly on the purity of the chloride used. If the double chloride contains 0.2 per cent, of iron the metal produced will very probably contain all of it, or 2 per cent. Using the double chloride purified by Mr. Castner's new method (see p. 132), by which the content of iron is reduced to 0.05 per cent, or less, aluminium can be made con- taining less than 0.5 per cent, of iron and from 99 to 99.5 per cent, of aluminium. Professor Roscoe exhibited at one of his lectures a mass of metal weighing 116 Ibs., being one single run- ning from the furnace, and which contained only 0.3 per cent, silicon and 0.5 per cent. iron. In practice, the metal from 8 or 10 runnings is melted dow r n together to make a uniform quality. Taking the figures given, it appears that the metal run out rep- resents 70 per cent, of the aluminium in the charge, and 80 per cent, of the weight which the sodium put in should reduce, but since an indeterminate weight is sifted and picked from the slag, 222 ALUMINIUM. it is probable that the utilization of the materials is more perfect than the above percentages. However, this seems to be the part of the old Devi lie process least improved upon in these new works, for there seems to be plenty of room for improvement in perfecting the utilization of materials especially in regard to loss of sodium by volatilization, which undoubtedly takes place and which can possibly be altogether prevented. CHAPTER. X. REDUCTION OF ALUMINIUM COMPOUNDS BY MEANS OF POTASSIUM OR SODIUM (continued). II. The methods based on the reduction of cryolite can be most conveniently presented in chronological order. Rose's Experiments (1855). We will here give H. Rose's entire paper, as an account of this eminent chemist's investigations written out by himself with great detail, describing failures as well as successes, cannot but be of value to all interested in the production of aluminium.* " Since the discovery of aluminium by Wohler, Deville has re- cently devised the means of procuring the metal in large, solid masses, in which condition it exhibits properties with which we were previously unacquainted in its more pulverulent form as procured by Wohler's method. While, for instance, in the lat- ter state it burns vividly to white earthy alumina on being ignited, the fused globules may be heated to redness without perceptibly oxidizing. These differences may be ascribed to the greater amount of division on the one hand and of density on the other. * Pogg. Annalen, Sept. 1855. REDUCTION BY POTASSIUM OR SODIUM. 223 According to Deville, however, Wohler's metal contains platinum, by which he explains its difficulty of fusion, although it affords white alumina by combustion. Upon the publication of De- ville's researches I also tried to produce aluminium by the decom- position of aluminium-sodium chloride by means of sodium. I did not, however, obtain satisfactory results. Moreover, Prof. Rammelsberg, who followed exactly the method of Deville, ob- tained but a very small product, and found it very difficult to prevent the cracking of the glass-tube in which the experiment was conducted by the action of the vapor of sodium on aluminium chloride. It appeared to me that a great amount of time, trouble, and expense, as well as long practice, was necessary to obtain even small quantities of this remarkable metal. " The employment of aluminium chloride and its compounds with alkali chlorides is particularly inconvenient, owing to their volatility, deliquescence, and to the necessity of preventing all ac- cess of air during their treatment with sodium. It very soon oc- curred to me that it would be better to use the fluoride of alu- minium instead of the chloride ; or rather the combination of the fluoride with alkaline fluorides, such as we know them through the investigations of Berzelius, who pointed out the strong affinity of aluminium fluoride for sodium fluoride and potassium fluoride, and that the mineral occurring in nature under the name of Cryo- lite was a pure compound of aluminium fluoride and sodium fluoride. " This compound is as well fitted for the preparation of alu- minium by means of sodium as aluminium chloride or aluminium sodium chloride. Moreover, as cryolite is not volatile, is readily reduced to the most minute state of division, is free from water and does not attract moisture from the air, it affords peculiar ad- vantages over the above-mentioned compounds. In fact, I succeeded with much less trouble in preparing aluminium by exposing cryolite together with sodium to a strong red heat in an iron crucible, than by using aluminium chloride and its compounds. But the scarcity of cryolite prevented my pursuing the experi- ments. In consequence of receiving, however, from Prof. Krantz, of Bonn, a considerable quantity of the purest cryolite at a very 224 ALUMINIUM. moderate price ($2 per kilo), I was enabled to renew the investi- gation. " I was particularly stimulated by finding, most unexpectedly, that cryolite was to be obtained here in Berlin commercially at an inconceivably low price. Prof. Krantz had already informed me that cryolite occurred in commerce in bulk, but could not learn where. Shortly after, M. Rudel, the manager of the chemical works of H. Kunheim, gave me a sample of a coarse white powder large quantities of which were brought from Greenland, by \vay of Copenhagen, to Stettin, under the name of mineral soda, and at the price of $3 per centner. Samples had been sent to the soap boilers, and a soda-lye had been extracted from it by means of quicklime, especially adapted to the preparation of many kinds of soap, probably from its containing alumina. It is a fact, that powdered cryolite is completely decomposed by quicklime and water. The fluoride of lime formed contains no alumina, which is all dissolved by the caustic soda solution ; and this, on its side, is free from fluorine, or only contains a minute trace. I found this powder to be of equal purity to that received from Prof. Krantz. It dissolved without residue in hydrochloric acid (in platinum vessels) ; the solution evaporated to dryness with sul- phuric acid, and heated till excess of acid was dissipated, gave a residue which dissolved completely in water, with the aid of a little hydrochloric acid. From this solution, ammonia precipi- tated a considerable quantity of alumina. The solution filtered from the precipitate furnished, on evaporation, a residue of sulphate of soda, free from potash. Moreover, the powder gave the well- known reactions of fluorine in a marked degree. This powder was cryolite of great purity : therefore the coarse powder I first obtained was not the form in which it was originally produced. It is now obtainable in Berlin in great masses ; for the prepara- tion of aluminium it must, however, be reduced to a very fine powder. " In my experiments on the preparation of aluminium, which were performed in company with M. Weber, and with his most zealous assistance, I made use of small iron crucibles, 1J inches high and If inches upper diameter, which I had cast here. In these I placed the finely divided cryolite between thin layers of REDUCTION BY POTASSIUM OR SODIUM. 225 sodium, pressed it down tight, covered with a good layer of potass- ium chloride (KC1), and closed the crucible with a well-fitting porcelain cover. I found potassium chloride the most advan- tageous flux to employ ; it has the lowest specific gravity of any which could be used, an important point when the slight density of the metal is taken into consideration. It also increases the fusibility of the sodium fluoride. I usually employed equal weights of cryolite and potassium chloride, and for every five parts of cryolite two parts of sodium. The most fitting quantity for the crucible was found to be ten grammes of powdered cryo- lite. The whole was raised to a strong red heat by means of a gas-air blowpipe. It was found most advantageous to maintain the heat for about half an hour, and not longer, the crucible being kept closely covered the whole time ; the contents were then found to be well fused. When quite cold the melted mass is removed from the crucible by means of a spatula, this is facilitated by striking the outside with a hammer. The crucible may be employed several times, at last it is broken by the hammer blows. The melted mass is treated with water, when at times only a very minute evolution of hydrogen gas is observed, which has the same unpleasant odor as the gas evolved during solution of iron in hydrochloric acid. The carbon contained in this gas is derived from a very slight trace of naphtha adhering to the sodium after drying it. On account of the difficult solubility of sodium fluor- ide, the mass is very slowly acted on by water, although the insolubility is somewhat diminished by the presence of the potass- ium chloride. After twelve hours the mass* is softened so far that it may be removed from the liquid and broken down in a porcelain mortar. Large globules of aluminium are then discov- ered, weighing from 0.3 to 0.4 or even 0.5 grammes, which may be separated out. The smaller globules cannot well be separated from the undecomposed cryolite and the alumina always produced by washing, owing to their being specifically lighter than the latter. The whole is treated with nitric acid in the cold. The alumina is not dissolved thereby, but the little globules then first assume their true metallic lustre. They are dried and rubbed on fine silk muslin ; the finely powdered, undecomposed cryolite and alumina pass through, while the globules remain on the gauze. 15 226 ALUMINIUM. The mass should be treated in a platinum or silver vessel, a por- celain vessel would be powerfully acted on by the sodium fluoride. The solution, after standing till clear, may be evaporated to dry- ness in a platinum capsule, in order to obtain the sodium fluoride, mixed however with much potassium chloride. The small globules may be united by fusion in a small well-covered porcelain crucible, under a layer of potassium chloride. They cannot be united without a flux. They cannot be united by mere fusion, like globules of silver, for instance, for though they do not appear to oxidize on ignition in the air, yet they become coated with a scarcely perceptible film of oxide, which prevents their running together into a mass. This fusion with potassium chloride is always attended with a loss of aluminium. Buttons weighing 0.85 gramme lost, when so treated, 0.05 gramme. The potassium chloride when dissolved in water left a small quantity of alumina undissolved, but the solution contained none. Another portion of the metal had undoubtedly decomposed the potassium chloride ; and a portion of this salt and aluminium chloride must have been volatilized during fusion (other metals, as copper and silver, behave in a similar manner Pogg. Ixviii. 287). I therefore followed the instructions of Deville, and melted the globules under a stratum of aluminium-sodium chloride in a covered porcelain crucible. The salt was melted first, and then the globules of metal added to the melted mass. There is no loss, or a very trifling one of a few milligrammes of metal, by this pro- ceeding. When the aluminium is fused under potassium chloride its surface is not perfectly smooth, but exhibits minute concavities ; with aluminium-sodium chloride this is not the case. The readi- est method of preparing the double chloride for this purpose is by placing a mixture of alumina and carbon in a glass tube, as wide as possible, and inside this a tube of less diameter, open at both ends, and containing sodium chloride. If the spot where the mixture is placed be very strongly heated, and that where the sodium chloride is situated, more moderately, while a current of chlorine is passed through the tube, the vapor of aluminium chloride is so eagerly absorbed by the sodium chloride that none or at most a trace is deposited in any other part of the tube. If the smaller tube be weighed before the operation, the amount REDUCTION BY POTASSIUM OR SODIUM. 227 absorbed is readily determined. It is not uniformly combined with the sodium chloride, for that part which is nearest to the mixture of charcoal and alumina will be found to have absorbed the most. " I have varied in many ways the process for the preparation of aluminium, but in the end have returned to the one just de- scribed. I often placed the sodium in the bottom of the crucible, the powdered cryolite above it, and the potassium chloride above all. On proceeding in this manner, it was observed that much sodium was volatilized, burning with a strong yellow flame, which never occurred when it was cut into thin slices and placed in alternate layers with the cryolite, in which case the process goes on quietly. When the crucible begins to get red hot, the tem- perature suddenly rises, owing to the commencement of the de- composition of the compound ; no lowering of the temperature should be allowed, but the heat should be steadily maintained, not longer, however, than half an hour. By prolonging the process a loss would be sustained, owing to the action of the potassium chloride on the aluminium. Nor does the size of the globules increase on extending the time even to two hours ; this effect can only be produced by obtaining the highest possible temperature. If the process be stopped, however, after five or ten minutes of very strong heat, the production is very small, as the metal has not had sufficient time to conglomerate into globules, but is in a pulverulent form and burns to alumina during the cooling of the crucible. No advantage is gained by mixing the cryolite with a portion of chloride before placing it between the layers of sodium, neither did I increase the production by using aluminium-sodium chloride to cover the mixture instead of potassium chloride. I repeatedly employed decrepitated sodium chloride as a flux in the absence of potassium chloride, without remarking any important difference in the amount of metal produced, although a higher temperature is in this case required. The operations may also be conducted in refractory unglazed crucibles made of stoneware, and of the same dimensions, although they do not resist so well the action of the sodium fluoride at any high heats, but fuse in one or more places. The iron crucibles fuse, however, when exposed to a very high temperature in a charcoal fire. The prod- uct of metal was found to vary very much, even when operating 228 ALUMINIUM. exactly in the manner recommended and with the same quantities of materials. I never succeeded in reducing the whole amount of metal contained in the cryolite (which contains only 13 per cent of aluminium). By operating on 10 grammes of cryolite, the quantity I always employed in the small iron crucible, the most successful result was 0.8 grm. But 0.6 or even 0.4 grm. may be considered favorable ; many times I obtained only 0.3 grm., or even less. These very different results depend on various causes, more particularly, however, on the degree of heat obtained. The greater the heat the greater the amount of large globules, and the less amount of minutely divided metal to oxidize during the cooling of the crucible. I succeeded once or twice in reducing nearly the whole of the metal to one single button weighing 0.5 grm., at a very high heat in a stoneware crucible. I could not always obtain the same heat with the blowpipe, as it depended in some degree on the pressure in the gasometer in the gas-works, which varies at different hours of the day. The following experi- ment will show how great the loss of metal may be owing to oxidation during the slow cooling of the crucible and its contents : In a large iron crucible were placed 35 grms. of cryolite in alter- nate layers with 14 grms. of sodium and the whole covered with a thick stratum of potassium chloride. The crucible, covered by a porcelain cover, was placed in a larger earthen one also covered, and the whole exposed to a good heat in a draft furnace for one hour and cooled as slowly as possible. The product in this case was remarkably small, for 0.135 grm. of aluminium was all that could be obtained in globules. The differences in the amounts reduced depend also in some degree on the more or less suc- cessful stratification of the sodium with the powdered cryolite, as much of the latter sometimes escapes decomposition. The greater the amount of sodium employed, the less likely is this to be the case ; however, owing to the great difference in their prices, I never employed more than 4 grms. of sodium to 10 grms. of cryolite. In order to avoid this loss by oxidation I tried another method of preparation : Twenty grms. of cryolite were heated intensely in a gun-barrel in a current of hydrogen, and then the vapor of 8 grms. of sodium passed over it. This was effected simply by placing the sodium in a little iron tray in a part of the gun-barrel REDUCTION BY POTASSIUM OR SODIUM. 229 without the fire, and pushing it forward when the cryolite had attained a maximum temperature. The operation went on very well, the whole being allowed to cool in a current of hydrogen. After the treatment with water, in which the sodium fluoride dis- solved very slowly, I obtained a black powder consisting for the most part of iron. Its solution in hydrochloric acid gave small evidence of aluminium. The small amounts I obtained, how- ever, should not deter others from making these experiments. These are the results of first experiments on which I have not been able to expend much time. Now that cryolite can be pro- cured at so moderate a price, and sodium by Deville's improve- ments will in future become so much cheaper, it is in the power of every chemist to engage in the preparation of aluminium, and I have no doubt that in a short time methods will be found afford- ing a much more profitable result. " To conclude, I am of opinion that cryolite is the best adapted of all the compounds of aluminium for the preparation of this metal. It deserves the preference over aluminium-sodium chlor- ide or aluminium chloride, and it might still be employed with great advantage even if its price were to rise considerably. The attempts at preparing aluminium direct from alumina have as yet been unattended with success. Potassium and sodium appear only to reduce metallic oxides when the potash and soda produced are capable of forming compounds with a portion of the oxide remaining as such. Pure potash and soda, with whose properties we are very slightly acquainted, do not appear to be formed in this case. Since, however, alumina combines so readily with the alkalies to form aluminates, one would be inclined to believe that the reduction of alumina by the alkali metals should succeed. But even were it possible to obtain the metal directly from alu- mina, it is very probable that cryolite would long be preferred should it remain at a moderate price, for it is furnished by nature in a rare state of purity, and the aluminium is combined in it with sodium and fluorine only, which exercise no prejudicial in- fluence on the properties of the metal, whereas alumina is rarely found in nature in a pure state and in a dense, compact condition, and to prepare it on a large scale, freeing it from those substances 230 ALUMINIUM. which would act injuriously on the properties of the metal, would be attended with great difficulty. "The buttons of aluminium which I have prepared are so malleable that they may be beaten and rolled out into the finest foil without cracking on the edges. They have a strong metallic lustre. Some small pieces, not globular, however, were found in the bottom of the crucible, and occasionally adhering to it, which cracked on being hammered, and were different in color and lustre from the others. They were evidently not so pure as the greater number of globules, and contained iron. On sawing through a large button weighing 3.8 grammes, it could readily be observed that the metal for about half a line from the exterior was brittle, while in the interior it was soft and malleable. Sometimes the interior of a globule contained cavities. With Deville, I have occasion- ally observed aluminium crystallized. A large button became striated and crystalline on cooling. Deville believes he has observed regular octahedra, but does not state this positively. According to my brother's examination, the crystals do not belong to any of the regular forms. As I chanced on one occasion to attempt the fusion of a large, flattened-out button of rather im- pure aluminium, without a flux, I observed before the heat was sufficient to fuse the mass, small globules sweating out from the surface. The impure metal being less fusible than pure meta^ the latter expands in fusing and comes to the surface." Experiments of Percy and Dick (1855). After the publication of Rose's results, widespread attention was directed toward this field, and it was discovered that some six months previously Dr. Percy, in England, had accomplished almost similar results, and had even shown a specimen of the metal to the Royal Institution, but with the singular fact of exciting very little attention. These facts are stated at length in the following paper written by Allan Dick, Esq., which appeared in November, 1855, two months after the publication of H. Rose's paper : * * Phil. Mag., Nov. 1855. DEDUCTION BY POTASSIUM OR SODIUM. 231 " In the last number of this magazine was the translation of a paper by H. Rose, of Berlin, describing a method of preparing aluminium from cryolite. Previously, at the suggestion of Dr. Percy, I had made some experiments on the same subject in the metallurgical laboratory of the School of Mines, and as the results obtained agree very closely with those of Mr. Rose, it may be interesting to give a short account of them now, though no detailed description was published at the time, a small piece of metal prepared from cryolite having simply been shown at the weekly meeting of the Royal Institution, March 30, 1855, accom- panied by a few words of explanation by Faraday. " Shortly after the publication of Mr. Deville's process for preparing aluminium from aluminium chloride, I tried along with Mr. Smith to make a specimen of the metal, but we found it much more difficult to do than Deville's paper had led us to anticipate, and had to remain contented with a much smaller piece of metal than we had hoped to obtain. It is, however, undoubt- edly only a matter of time, skill, and expense to join successful practice with the details given by Deville. Whilst making these experiments, Dr. Percy had often requested us to try whether cryolite could be used instead of the chlorides, but some time elapsed before w r e could obtain a specimen of the mineral. The first experiments were made in glass tubes sealed at one end, into which alternate layers of finely powdered cryolite and sodium cut into small pieces were introduced, and covered in some instances with a layer of cryolite, in others by sodium chloride. The tube was then heated over a gas blowpipe for a few minutes till de- composition had taken place and the product was melted. When cold, on breaking the tube, it was found that the mass was full of small globules of aluminium, but owing to the specific gravity of the metal and flux being nearly alike, the globules had not col- lected into a button at the bottom. To effect this, long-continued heat would be required, which cannot be given in glass tubes owing to the powerful action of the melted fluoride on them. To obviate this difficulty, a platinum crucible was lined with magnesia by ramming it in hard, and subsequently cutting out all but a lining. In this, alternate layers of cryolite and sodium were placed, w r ith a thickish layer of cryolite on top. The cruci- 232 ALUMINIUM. ble was covered with a tight-fitting lid, and heated to redness for about half an hour over a gas blowpipe. When cold it was placed in water, and after soaking for some time the contents were dug out, gently crushed in a mortar, and washed by decan- tation. Two or three globules of aluminium, tolerably large considering the size of the experiment, were obtained along with a large number of very small ones. The larger ones were melted together under potassium chloride. Some experiments made in iron crucibles were not attended with the same success as those of Rose, no globules of any considerable size remained in the melted fluorides ; the metal seemed to alloy on the sides of the crucible, which acquired a color like zinc. It is possible that this differ- ence may have arisen from using a higher temperature than Rose, as we made these experiments in a furnace, not over the blowpipe. Porcelain and clay crucibles were also tried, but laid aside after a few experiments, owing to the action of the fluorides upon them, which in most cases was sufficient to perforate them completely." Deville's Methods (1856-8). * " I have repeated and confirmed all the experiments of Dr. Percy and H. Rose, using the specimens of cryolite which I obtained from London through the kindness of MM. Rose and Hofmann. I have, furthermore, reduced cryolite mixed with sodium chloride by the battery, and I believe that this will be an excellent method of covering with aluminium all the other metals, copper in particular. Anyhow, its fusibility is considerably in- creased by mixing it with aluminium-sodium chloride. Cryolite is a double fluoride of aluminium and sodium, containing 13 per cent, of aluminium and having the formula APF 6 .6NaF. I have verified these facts myself by many analyses. "In reducing the cryolite I placed the finely-pulverized mix- ture of cryolite and sodium chloride in alternate layers with sodium in a porcelain crucible. The uppermost layer is of pure cryolite, covered with salt. The mixture is heated just to com- plete fusion, and, after stirring with a -pipe-stem, is let cool. On * Ann. de Chem. et de Phys. [3], xlvi. 451. REDUCTION BY POTASSIUM OB SODIUM. 233 breaking the crucible, the aluminium is often found united in large globules easy to separate from the mass. The metal always contains silicon, which increases the depth of its natural blue tint and hinders the whitening of metal by nitric acid, because of the insolubility of the silicon in that acid. M. Rose's metal is very ferruginous. I have verified all M. Rose's observations, and I agree with him concerning the return of metal, which I have always found very small. There are always produced in these operations brilliant flames, which are observed in the scoria float- ing on the aluminium, and which are due to gas burning and exhaling a very marked odor of phosphorus. In fact, phosphoric acid exists in cryolite, as one may find by treating a solution of the mineral in sulphuric acid with molybdate of ammonia, accord- ing to H. Rose's reaction. "M. Rose has recommended iron vessels for this operation, because of the rapidity with which alkaline fluorides attack earthen crucibles and so introduce considerable silicon into the metal. Unfortunately, these iron crucibles introduce iron into the metal. This is an evil inherent in this method, at least in the present state of the industry. The inconveniences of this method result in part from the high temperature required to complete the operation, and from the crucible being in direct contact with the fire, by which its sides are heated hotter than the metal in the crucible. The metal itself, placed in the lower part of the fire, is hotter than the slag. This, according to my observations, is an essentially injurious condition. The slag ought to be cool, the metal still less heated, and the sides of the vessel where the fusion occurs ought to be as cold as possible. The yield from cryolite, according to Rose's and my own observations, is also very small. M. Rose obtained from 10 of cryolite and 4 of sodium about 0.5 of aluminium. This is due to the affinity of fluorine for alu- minium, which must be very strong not only with relation to its affinity for sodium but even for calcium, and this affinity appears to increase with the temperature, as was found in my laboratory. Cryolite is most convenient to employ as a flux to add to the mixture which is fused, especially when operating on a small scale. " The argument which decided the company at Nanterre not to 234 ALUMINIUM. adopt the method of manufacture exclusively from cryolite was the report of M. de Chancourtois, mining engineer, who had just returned from a voyage to Greenland. According to the verbal statements of this gentleman, the gite at Evigfcok is accessible only during a very short interval of time each year, and, because of the ice fields, can only be reached then by a steamboat. The workmen sent from Europe to blast and load up the rock have scarcely one or two months of work possible. The local work- men remain almost a whole year deprived of all communication with the rest of the world, without fresh provisions or fuel other than that brought from Europe in the short interval that naviga- tion is open. The deposit itself, which is scarcely above sea- level, can be easily worked with open roof, but the neighborhood of the sea in direct contact with the vein, the unorganized man- ner of working, and the lack of care in keeping separate the metalliferous portions of the ore all combine to render the mineral very costly and further developments underground almost impossible. " It is therefore fortunate that cryolite is not indispensable, for no one would wish to establish an industry based on the employ- ment of a material which is of uncertain supply." Tissier Bros.' Method (1857). The process adopted in the works at Amfreville, near Rouen, directed by Tissier Bros., is essentially that described by Percy and Rose. The method of operating is given by the Tissier Bros, themselves in their book as follows : " After having finely powdered the cryolite, it is mixed with a certain quantity of sodium chloride (sea salt), then placed between layers of sodium used in the proportions given by M. Rose, in large refractory crucibles. These are heated either in a rever- beratory furnace or in a wind furnace capable of giving a tempera- ture high enough to melt the fluoride of sodium produced by the reaction. As the sodium fluoride requires a pretty high tempera- ture to fuse it, the heat will necessarily be higher than that re- quired in the reduction of the double chloride of aluminium and sodium. When the contents of the crucible are melted, so as to REDUCTION BY POTASSIUM OR SODIUM. 235 be quite liquid, the fusion is poured into cast-iron pots at the bottom of which the aluminium collects in one or several lumps." Tissier Bros, claimed the following advantages for the use of cryolite : . " Cryolite comes to us of a purity difficult to obtain with the double chloride of aluminium and sodium, to which it exactly corresponds ; and since, thanks to the perfection we have attained in using it, the return of aluminium is exactly correspondent to the amount of sodium used in reduction, it is easily seen what immense advantages result from its employment. The double chloride deteriorates in the air, it gives rise in the works to vapors more or less deleterious and corrosive, and its price is always high. Cryolite can be imported into France at a price so low that we have utilized it economically for making commercial carbonate of soda; it remains unaltered in the air, emits no deleterious vapors, and its management is much more easy than that of the double chloride. Moreover, on comparing the residues of the two methods of reduction, the manufacture from double chloride leaves sodium chloride, almost without value, while the manu- facture from cryolite leaves sodium fluoride, which may be con- verted for almost nothing into caustic soda or carbonate, and so completely cancels the cost of the cryolite from the cost of the aluminium. The most serious objection which can be made to using cryolite is that the sources of the mineral being up to the present very limited, the future prospect of aluminium lies neces- sarily in the utilization of clays and their transformation into aluminium chloride ; but, admitting that other sources of cryolite may not be discovered hereafter, the abundance of those which exist in Greenland will for a long time to come give this mineral the preference in the manufacture of aluminium." The most serious difficulty which this process had to meet, and which it could not overcome, was the high content of silicon in the metal produced. A specimen of their aluminium made in 1859 contained 4.4 per cent, of silicon alone (see p. 54, Analy- sis 7).* The firm at Rouen went out of business about 1863 or 1865, I am unable to give the exact date. From that time * The analysis should read 0.8 iron and 4.4 silicon, not 0.8 silicon and 4.4 iron. 236 ALUMINIUM. until quite recently, it has been considered that the best use of cryolite is as a flux in the preparation of aluminium from alu- minium-sodium chloride, in which case the slag is not sodium fluoride but aluminium fluoride, which acts but slightly on the containing vessel. WoMer>s Modifications (1856). "Wohler suggested the following modifications of Deville's pro- cess of reducing cryolite in crucibles, by means of which the reduction can be performed in an earthen crucible without the metal produced taking up silicon. * " The finely pulverized cryolite is mixed with an equal weight of a flux containing 7 parts sodium chloride to 9 parts potassium chloride. This mixture is then placed in alternate layers with sodium in the crucible, 50 parts of the mixture to 10 of sodium, and heated gradually just to its fusing point. The metal thus ob- tained is free from silicon, but only one-third of the aluminium in the cryolite is obtained." In spite of the small yield, this method was used for some time by Tissier Bros. Gerhard's Furnace (1858). This furnace was devised for the reduction of aluminium either from aluminium-sodium chloride or from cryolite, the object being to prevent loss of sodium by ignition. It was invented and patented by W. F. Gerhard.f " It consists of a reverberatory furnace having two hearths, or of two crucibles, or of two rever- beratory furnaces, placed one above the other and communicating by an iron pipe. In the lower is placed a mixture of sodium with the aluminium compound, and in . the upper a stratum of sodium chloride, or of a mixture of this salt and cryolite, or of the slag obtained in a previous operation. This charge, when melted, is made to run into the lower furnace in quantity suffi- cient to completely cover the mixture contained therein, and so to protect it from the air. The mixture thus covered is reduced as by the usual operation." * Ann. der Chem. und Pharm. 99,255. f Eng. Pat. 1858, No. 2247. EEDUCTION BY POTASSIUM OR SODIUM. 237 Whether a furnace was ever put up and operated on this prin- ciple the author cannot say. It is possible that it may have been used in the English manufactories started in 1859 and 1860 at Battersea and Newcastle-on-Tyne. Thompson and White's Patent (1887). * J. B. Thompson and W. White recommend heating a mixture of 3 parts sodium and 4 parts of cryolite to 100, whereby the sodium becomes pasty and the whole can be well kneaded together with an iron spatula. When cold, 4 parts of aluminium chloride are added, and the mixture put into a hopper on top of a well-heated reverberatory furnace, with a cup-shaped hearth. The charge is dropped into the furnace and the reaction takes place at once. To produce alloys, this patent claims that 16 parts of cryolite are mixed with 5 parts of sodium, the metal added before reduction and the mixture treated as above, by which means explosions are avoided. The preliminary heating to 100 is effected in a jacketed cast-iron pot connected with a circulating boiler. Hampers Experiment (1888). fDr. W. Hampe failed to produce aluminium bronze by treat- ing cryolite with sodium in the presence of copper. A mixture of 44 grammes finely divided copper, 15 " sodium, in small pieces, 100 " finely powdered cryolite, was melted rapidly in a carbon-lined crucible. There were no sounds given out such as usually accompany other reductions by sodium, but much sodium vapor was given off. The copper but- ton contained only traces of aluminium. Netto's Process (1887). Dr. Curt Netto, of Dresden, patented in England and Germany, in spring and autumn of 1887, processes for producing sodium * English Patent 8427, June 11, 1887. f Chemiker Zeitung (Cothen), xii. p. 391. 238 ALUMINIUM. and potassium and methods of using them in producing alu- minium. His experiments were made in conjunction with Dr. Salomon, of Essen, and the fact that the experimental apparatus was put up in Krupp's large steel works at Essen gave rise to reports that the latter had taken up the manufacture of alu- minium by some new and very successful process, intending to use it for alloys in making cannon.* In the latter part of 1888 we hear of the formation of the Alliance Aluminium Co. of London, England, capitalized at 500,000, purposing to manufacture potassium, sodium and aluminium, and owning the English, French, German, and Belgian patents of Dr. Netto for the production of those metals, also the processes of a Mr. Cunningham for the same purpose, also a pro- cess for the production of artificial cryolite by the regeneration of slags (provisionally protected by its inventor, Mr. Forster, of the Lonesome Chemical Works, Streatham), and, lastly, a process invented by Drs. Netto and Salomon by which aluminium can be raised to the highest standards of purity on a commercial scale. A note accompanying the above announcement stated that the exhaustive experiments made at Essen had satisfactorily demon- strated the practicability of the processes, and that the company had already contracted with the cryolite mines of Greenland for all the cryolite the company would need. In June, 1888,f we learn that the Alliance Aluminium Com- pany had in operation a small aluminium plant at King's Head Yard, London, E. C., and that when the process was in con- tinuous operation the cost of the metal was set down at 6 shil- lings per pound. It is probable that the metal exhibited in the Paris Exposition of 1889 was produced at this place. In April, 1889,J it was stated in the scientific journals that ten acres of ground had been leased at Hepburn on which to produce sodium by Capt. Cunningham's process. The sodium produced is to be sent to Wallsend to be used by the Alliance Aluminium Company, who are erecting a large works at that place. * American Register, Paris, August, 1888. f Engineering, June 1, 1888. J E. and M. J., April 27, 1889. REDUCTION BY POTASSIUM OR SODIUM. 239 As for Capt. Cunningham's sodium processes, they are ap- parently identical with Dr. Netto's. Cunningham's aluminium process* consists in melting the sodium to be used with lead, in order to facilitate the submerging of the sodium under the molten aluminium salt. The alloy is cast into bars and added piece by piece to the bath of molten aluminium salt on the hearth of a reverberatory furnace. After the reaction the mixture separates by specific gravity into lead, containing a little aluminium, and aluminium containing a little lead, the slag floating on top of all. Aluminium is known to have so small an attraction for lead that this result becomes possible. Dr. Netto recommends several processes, the one used at Lon- don being the following : f One hundred parts of cryolite and 30 to 100 parts of sintered sodium chloride are melted at a red heat in a well-covered clay crucible. (Another arrangement, and apparently a better, is to melt this mixture on the hearth of a reverberatory furnace and to tap it into a deep, conical ladle, in which the succeeding opera- tions proceed as about to be described.) As soon as the bath is well fused, 35 parts of sodium at the end of a rod, and covered over by a perforated concave plate, is quickly pushed down to the bottom of the crucible. The plate mentioned fits across the whole section of the crucible at its lower part, so that the fusible, easily volatile sodium, being vaporized, is divided into very fine streams as it passes upwards through the bath, and is all utilized before it reaches the surface. In this way the reaction is almost instantaneous, and the contents can be poured out at once into iron pots, where, on cooling, the metal is found as a large lump at the bottom. It is further observed that to avoid explosions on introducing the sodium it should have in it no cavities which might contain moisture or hydrocarbons. In consequence of the reaction being over so quickly, and the heat set free in the reduction, the syrupy fusion becomes thin as water, and the aluminium disseminated through the mass collects together completely, so that the slag * English Patent, 16727, Dec. 5, 1887. f German Patent (D. R. P.) 45198, March 26, 1887. 240 ALUMINIUM. contains no particles visible to the eye. Since the reduction, pouring, and cooling take place so quickly, the aluminium is not noticeably redissolved by the bath, thus insuring a high return of metal. By using 35 parts of sodium to 100 parts of cryolite, 10 parts of aluminium are obtained. Since the cryolite contains 1 3 per cent, of aluminium, the return is 77 per cent, of the amount of metal in the cryolite ; since 35 parts of sodium should theo- retically displace 14 parts of aluminium, the return is 71 per cent, of the amount 'which the sodium should produce. Dr. Netto claims that this is double the return formerly obtained from cryo- lite. The metal produced is said to be from 98.5 to 99 per cent, pure. The apparatus erected at Krupp's works at Essen, which was described by the newspapers as similar to a Bessemer converter, was constructed and operated as follows : A large iron cylinder is pivoted at the centre in a manner similar to a Bessemer con- verter. Passing through the centre of the cylinder, longitudi- nally, is a large iron tube in which generator gas is burnt to heat the vessel. To heat it up, it is placed erect, connection made with the gas-main, while a hood above connects with the chimney. On top of the cylinder, a close valve communicates with the in- terior, for charging, and at the other end is a tap-hole. The charge of cryolite being put in, the flame is passed through the central, tube until the mineral is well fused. Then solid or melted sodium is passed in at the top, the valve is screwed tight, the gas shut off, and the whole cylinder is rotated several times until reduction is complete, when it is brought upright, the tap- hole opened and slag and metal tapped into a deep iron pot, where they separate and cool. Aluminium thus made could not but contain much iron, even up to 14 per cent., it is said, which would prevent its use for any purpose except alloying with iron. To procure pure aluminium, the vessel would have to be properly fettled. Dr. Netto also devised an arrangement similar to Heaton's apparatus for making steel. It consisted of a large, well-lined vessel on trunnions, the bottom of which was filled to a certain depth with sodium, then a perforated aluminium plate placed like a false bottom over it, On pouring molten cryolite into the SEDUCTION BY POTASSIUM OR SODIUM. 241 vessel the aluminium plate prevented the sodium from rising en masse to the surface of the cryolite. After the reaction was over, the vessel was tilted and the slag and metal poured out into iron pots. The modification of the crucible method appears to be the most feasible of Netto's processes, and is probably now being used at Wallsend by the Alliance Aluminium Company. Outside esti- mates of the cost of aluminium to this company place it at $1.50 to $2 per pound. They were selling in the latter part of 1889 at 11, 13, and 15 shillings per pound, according to quality. III. There is only one patentee claiming particularly the reduction of aluminium fluoride by sodium Ludwig Grabau, of Hann- over, Germany. His patents on this subject are immediately preceded by others on a method of producing the aluminium fluoride cheaply, which are described on p. 139, and the inventor is at present engaged on a process which will furnish him with cheap sodium. Mr. Alexander Siemens is authority for the statement that a plant was in operation in the Spring of 1889, in Hannover, producing aluminium by this process on a commercial scale. The principal object of Mr. Grabau's endeavors has been to produce metal of a very high degree of purity. To this end every precaution is taken to procure pure materials and to pre- vent contamination during reduction. We will quote from a paper written by Mr. Grabau* and also from his patent specifi- cations^ the following explanation of the process : " The purifying of impure aluminium is accompanied by so many difficulties that it appears almost impossible. It is there- fore of the greatest importance to so conduct the operation that every impurity is excluded from the start. Molten aluminium compounds, whether a flux is added or not, attack any kind of refractory vessels and become siliceous, if these vessels are made * Zeitschrift fiir angewandte Chemie, 1889, vol. 6. t German Pat. (D. R. P.) 47031, Nov. 15, 1887. English Pat. 15593, Nov. 14, 1887. U. S. Patents 386704, July 24, 1888 ; and 400449, April 2, 1889. 16 242 ALUMINIUM. of chamotte or like materials, or if made of iron they become ferruginous. These impurities are reduced in the further pro- cesses and pass immediately into the aluminium as iron, silicon, etc. Evidently the case is altered if an aluminium compound which is infusible can be used advantageously. Aluminium fluor- ide is infusible and also retains its pulverized condition when heated up to the temperature needed for its use ; it can therefore be heated in a vessel of any kind of refractory material or even in a metallic retort without danger of taking up any impurity. " Further, it is necessary for succeeding in producing alu- minium that the reduced metal shall unite to a large body after the reduction. For this purpose all previous processes use fluxes, and usually cryolite. But cryolite is impure and therefore here is a source of many of the impurities in commercial aluminium. Dr. K. Kraut, of Hannover, has observed that, according to the recent analyses of Fresenius and Hintz, commercial cryolite contains 0.80 to 1.39 per cent, of silicon and 0.11 to 0.88 per cent, of iron, and that these impurities inter-penetrate the mineral in such a manner as to be often only visible under the micro- scope and therefore totally impossible of removal by mechanical means. It is thus seen that the avoidance of the use of any flux is of great importance as far as producing pure metal is con- cerned, as well as from an economic standpoint. " By the following process it is also possible to reduce alu- minium fluoride by sodium without the vessel in which reduction takes place being attacked either by the aluminium-sodium fluor- ide formed or by the reduced aluminium. For this purpose the aluminium fluoride and sodium are brought together in such proportions that after the reaction there is still sufficient alumin- ium fluoride present to form with the sodium fluoride resulting from the reaction a compound having the composition of cryolite. The reaction, therefore, will be 2APF 6 + 6Na = ~2A1 + APF 6 .6NaF. " Using these proportions, the aluminium fluoride must be pre- viously warmed up to about 600, in order that when it is show- ered down upon the melted sodium the reaction may commence without further application of heat. The aluminium fluoride REDUCTION BY POTASSIUM OR SODIUM. Fig. 22. 243 244 ALUMINIUM. remains granular at this temperature and therefore remains on top of the melted sodium, like saw-dust or meal upon water, and under its protection the reaction proceeds from below upwards an important advantage over the usual method of pouring molten aluminium compounds on to sodium, in which the lighter sodium floats to the top and burns to waste. If solid sodium is used in my process the aluminium fluoride must be somewhat hotter on being poured into the reduction vessel, or about 700. For carrying out the process the reduction vessel must be artificially cooled, so as to form a lining by chilling some of the aluminium- sodium chloride formed by the reaction, on the inner walls. This lining is in no wise further attacked by the contents of the vessel, nor can it evidently supply to them any impurity. " The furnace A (Fig. 22) with grate B and chimney C serves for heating the iron retorts D and jE", which are coated with chamotte and protected from the direct action of the flame by brick work. The vessel D serves for heating the aluminium fluoride, and is provided with a damper or sliding valve beneath. The sodium is melted in E, and can be emptied out by turning the cock h. The water-jacketed reduction vessel is mounted on trunnions to facilitate emptying it. The retorts are first heated dark red-hot, and D is filled with the convenient quantity of aluminium fluor- ide. When this has become red hot, as is shown by a small quantity of white vapor issuing from it, the required quantity of sodium is put into E. This melts very quickly, and is then im- mediately run into the reduction vessel by opening the stop-cock h. As soon as it is transferred, the slide at the base of the retort D is pulled out and the whole quantity of aluminium fluoride falls at once upon the sodium and the reaction begins. As be- fore remarked, the granular form of the aluminium fluoride keeps it on top of the sodium, so that the latter is completely covered during the whole reaction. This prevents almost alto- gether any waste of sodium by volatilization. Dr. K. Kraut testifies to an operation which he witnessed in which the return showed 83 per cent, of the sodium to have been utilized. An efficiency in this respect of over 90 per cent, has been occasionally reached, while the average is 80 to 90. Ad. Wurtz states that the average of several years' working of the Deville process REDUCTION BY POTASSIUM OR SODIUM. 245 showed only 74.3 per cent, of the quantity of aluminium pro- duced which the sodium used could have given. " During the reaction a very high temperature is developed, so that the cryolite formed becomes very fluid but is chilled against the sides of the vessel to a thickness of a centimetre or more. This crust is a poor conductor of heat, and is neither attacked by the fluid cryolite nor by^he aluminium. In consequence of the great fluidity of the bath, it is possible for the aluminium to unite into a body without the use of any flux. The reaction b.emg over, which is accomplished with the above proportions of materials in a few sec'onds, and the vessel having been shaken briskly backwards and forwards a few times to facilitate the settling of the aluminium, the whole is turned on the trunnions and emptied into a water-jacketed iron pot where it cools. The crust of cryolite inside the reduction vessel is left there, and the apparatus is ready for another operation." M. Grabau, in a private communication to the author, sums up the advantages of his process, including the production of the aluminium fluoride, as follows : 1. The process is not dependent on natural cryolite, which is expensive, impure and not easily purified. 2. The raw material aluminium sulphate can be procured in large quantities and of perfect purity. 3. The aluminium fluoride is produced by a wet process, which offers no difficulties to production on a large scale. 4. The fluorspar may be completely freed from foreign metals by washing with dilute acid ; any silica present is not injurious, as it remains undissolved in the residue during the reactions. 5. The cryolite formed in each reduction contains no impuri- ties, and an excess of it is produced which can be sold. 6. The reduction of aluminium fluoride by my method gives a utilization of 80 to 90 per cent, of the sodium used, which is much more than can be obtained by other processes. 7. Aluminium fluoride is infusible, and can therefore be heated in a vessel of any refractory material without taking up any impurities. It is also unchanged in the air, and can be kept unsealed for any length of time without deteriorating in the least. 246 ALUMINIUM. 8. No flux has to be added for reduction, the use of impure flux being a frequent cause of impurity of the metal. In point of fact, M. Grabau has succeeded in producing several hundred pounds of aluminium averaging over 99 J per cent. pure. Dr. Kraut reports an analysis of an average specimen with 99.62 per cent, of aluminium (see Analysis 20, p. 54), and metal has been made as pure as 99.8 per cent., a jrtece of which has been kindly forwarded the author by M. Grabau, and I freely admit it to be the finest specimen of aluminium I have ever seen. If M. Gra- bau's statement that he can produce metal of this purity without difficulty on a commercial scale and at* a price low enough to compete with the other commercial brands be realized, we will freely accord that gentleman the prize not for cheap, but for pure aluminium ; cheap aluminium is yet to come. CHAPTER XI. REDUCTION OF ALUMINIUM COMPOUNDS BY THE USE OF ELECTRICITY. As preliminary to the presentation of the various electrolytic methods which have been proposed or used, it may be profitable to review briefly the principles of electro-metallurgy as they apply to the decomposition of aluminium compounds. The atomic weight of aluminium being 27, its chemical equiv- alent, or the weight of it equal in combining power to one part of hydrogen, is 9. Therefore a current of quantity sufficient to liberate 1 part of hydrogen in a certain time would produce 9 parts of aluminium in the same time, according to the funda- mental law of electric decomposition. It has been determined that a current of 1 ampere acting for one second, liberates 0.00001035 grammes of hydrogen ; therefore it will produce or set free from combination in the same time, 0.00009315 grammes of aluminium. This is the electro-chemical equivalent of alu- minium. Now, from thermo-chemical data we know that the amount of energy required to set free a certain weight of alu- REDUCTION BY THE USE OF ELECTRICITY. 247 minium will vary with the compound from which it is produced ; but the above equivalent is independent of the compound decom- posed, therefore there must be some varying factor connected with the quantity of the current to account for the different amounts of work which the current does in decomposing dif- ferent compounds of the same element. This is exactly in accordance with the principles of the mechanical or thermal equivalent of the electric current, for the statement "a current of one ampere/' while it expresses a definite quantity of electricity, yet carries no idea of the energy represented by that current ; we must know against what resistance or with what force that quantity is moved, and then we can calculate its mechanical equiv- alent. Now, a current of 1 ampere flowing against a resistance of 1 ohm, or in other words, with a moving force or intensity of 1 volt, represents a quantity of energy in one second equal to 0.00024 calories of heat or to 0.1 kilogrammetres of work, and is therefore nearly T |~g- of a horse power. Therefore we can cal- culate the theoretical intensity of current necessary to overcome the affinities of any aluminium compound for which we know the appropriate thermal data. For instance, when aluminium forms its chloride (see p. 190) ' ^ = 5960 calories are de- veloped per kilo of aluminium combining; consequently the liberating of 0.00009315 grammes of aluminium (its electro- chemical equivalent), requires the expenditure of an amount of energy equal to 0.00009315 x 5.960 * 0.000555 calories. Since a current of 1 ampere at an intensity of 1 volt represents only 0.00024 calories, the intensity of current necessary to decompose aluminium chloride is theoretically = 2.3 volts. In a 0.00024 similar manner we can calculate that to decompose alumina would ,. f f 391600 0.00000009315 require an electro-motive force ot X - o4 2.8 volts. These data would apply only to the substances named in a fused anhydrous state ; with hyd rated aluminium chloride in solution, a far greater electro-motive force would be necessary. If we had the thermal data we could also calculate the intensity of current necessary to decompose the sulphate, nitrate, acetate, 248 ALUMINIUM. etc., in aqueous solution ; but, failing these, we can reason from analogy that it would be several volts in each case. To utilize such calculations, we must bear in mind exactly what they represent. To decompose fused aluminium chloride, for instance, not only must the current possess an intensity of 2.3 volts but it must in addition have power enough above this to overcome the transfer resistance of the electrolyte ; i. e., to force the current through the bath from one pole to the other. So, then, 2.3 volts would be the absolute minimum of intensity which would produce decomposition, and the actual intensity practically re- quired would be greater than this, varying with the 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 distance, a current of a certain intensity will always produce decomposition. The objection is immediately made that in most cases no metal is ob- tained at all, which is true not because none is produced but because it is often dissolved by secondary actions as quickly as it is produced. I need but refer to the historic explanation of the decomposition of caustic soda in aqueous solution, although we have cases hardly parallel to this in which the electrolyte itself dissolves the separated metal. How about the case of aqueous solutions? Water requires a minimum electro-motive force of 1.5 volts to decompose it, and hence a prominent electrician remarked of a compound which theoretically required over 2 volts that its decomposition in aque- ous solution would involve the decomposition of the water and therefore was impossible. This remark is only partly true ; for, caustic soda requires over 2 volts, yet if mercury is present to absorb the sodium as it is set free and protect it from the water, we will obtain sodium while the water is decomposed at the same time. The truth seems to be that if two substances are present which require different electro-motive force to decompose them, a current of a certain intensity will decompose the one requiring least force without affecting the other at all ; but, if it is of an REDUCTION BY THE USE OF ELECTRICITY. 249 intensity sufficient to decompose the higher compound, then the current will be divided in some ratio between the two, decompos- ing them both. This theory would render theoretically possible the decomposition of aluminium salts in aqueous solution, with a waste of power proportional to the amount of water decomposed at the same time ; but whether any aluminium would be obtained would be contingent on the secondary action of the water on the aluminium. Pure aluminium in mass is not acted on by water, but the foil is rapidly eaten away by boiling water. The state of division of the metal, then, determines the action of water on it, and it is altogether probable that the reason why aluminium has not been easily and beyond question deposited from aqueous solu- tion is that, like sodium, it is attacked as soon as isolated, the acidity of the solution converting the hydrate formed back into the salt, or else simply the hydrate remaining. Unfortunately, mercury does not exercise the same function with aluminium as with sodium, for water attacks its amalgam with aluminium, and so destroys the metal. It is possible that if some analogous sol- vent could be found which protected the aluminium from the action of water, the deposition from aqueous solution could be made immediately successful. Perhaps some of the devices about to be described have successfully overcome these difficulties, but if so the proof of this has never been verified by any good authority, nor has the author seen any so-called aluminium plating (from aqueous solution) which really was so. Further remarks as to the amount of aluminium theoretically obtainable per horse- power, etc. etc., will come up in connection with the various processes. The consideration of these processes falls naturally under two heads : I. Deposition from aqueous solution. II. Decomposition of fused aluminium compounds. I. DEPOSITION OF ALUMINIUM FROM AQUEOUS SOLUTION. The status of this question is one of the curiosities of electro- metallurgic science. Evidently attracted by the great reward to be 250 ALUMINIUM. earned by success, many experimenters have labored in this field, have recommended all sorts of processes, and patented all kinds of methods. We have inventors affirming in the strongest manner the successful working of their methods, while other experimenters have followed these recipes, and tried almost every conceivable arrangement, yet report negative results. To show that it is quite possible that many strong affirmations may be made in good faith, I have only to mention the fact that in March, 1863, Mr. George Gore described in the Philosophical Magazine some experiments by which he deposited coatings of aluminium from aqueous solu- tions, and afterwards, in his text book of Electro-metallurgy, asserts that he knows of no successful method of doing this thing. Mr. Gore found that he was in error the first time and was manly enough to acknowledge it. So, if we take the position of many eminent authorities that aluminium cannot by any methods so far advanced be deposited from aqueous solution, we will have to admit that the proposers of the following processes are probably misled by their enthusiasm in affirming so strongly that they can do this thing. Yet the problem is not impossible of solution, and I will simply assert again my previous statement, that no good authority testifies to the success of any process so far ad- vanced, neither have I seen any so-called aluminium plating (from aqueous solution) which really was aluminium. Messrs. Thomas and Tilly* coat metals with aluminium and its alloys by using a galvanic current and a solution of freshly precipitated alumina dissolved in boiling water containing potass- ium cyanide, or a solution of freshly calcined alum in aqueous potassium cyanide ; also from several other liquids. Their patent covers the deposition of the alloys of aluminium with silver, tin, copper, iron, silver and copper, silver and tin, etc. etc., the positive electrode being of this metal or alloy. M. Corbelli, of Florence, f deposits aluminium by electrolyzing a mixture of rock alum or sulphate of alumina (2 parts) with calcium chloride or sodium chloride (1 part) in aqueous solution (7 parts), the anode being mercury placed at the bottom of the * English Patent, 1855, No. 2756. f English Patent, 1858, No. 507. REDUCTION BY THE USE OF ELECTRICITY. 251 solution and connected to the battery by an iron wire coated with insulating material and dipping its uncovered end into the mer- cury. The zinc cathode is immersed in the solution. Aluminium is deposited on the zinc, as a blackish powder or as a thin, com- pact sheet, and the chlorine which is liberated at the anode unites with the mercury, forming calomel. J. B. Thompson* reports that he has for over two years been depositing aluminium on iron, steel, and other metals, and driving it into their surfaces at a heat of 500 F., and also depositing aluminium bronze of various tints, but declines to state his process. George Gore,f the noted electrician, recommended the following procedure for depositing aluminium on copper, brass, or Ger- man silver : " Take equal measures of sulphuric acid and water, or one part sulphuric acid, one part hydrochloric acid and two parts of w r ater, put into it half an ounce of pipe clay to the pint of dilute acid and boil for an hour. Take the clear, hot liquid and immerse in it an earthen porous cell containing sulphuric acid diluted with ten times its bulk of water, together with a rod or plate of amal- gamated zinc. Connect the zinc with the positive wire of a Smee battery of three or four elements connected for intensity. The article to be coated, well cleaned, is connected with the nega- tive pole and immersed in the hot clay solution. In a few min- utes a fine, white deposit of aluminium will appear all over its surface. It may then be taken out, washed quickly in clean water, wiped dry, and polished. If a thicker coating is required, it must be taken out as soon as the deposit becomes dull, washed, dried, polished, and re-immersed, and this must be repeated at intervals as often as it becomes dull, until the required thickness is obtained. It is necessary to have the acid well saturated by boiling, or no deposit will be obtained." Mierzinski asserts that Dr. Gore was mistaken when he sup- posed this deposit to be aluminium, and in Gore's Text Book of Electro-metallurgy no mention is made of these experiments, the * Chem. News, xxiv. 194 (1871). f Philosophical Magazine, March, 1863. 252 ALUMINIUM. author thereby acknowledging the error. As to what the deposit could have been, we are left to conjecture, since no explanation has been advanced by Dr. Gore ; it may possibly have been sili- con, mercury, or zinc, as all three of these were present besides aluminium. J. A. Jeancon* has patented a process for depositing alumin- ium from an aqueous solution of a double salt of aluminium and potassium of specific gravity 1.161 ; or from any solution of an aluminium salt, such as sulphate, nitrate, cyanide, etc., concen- trated to 20 B. at 50 F. He uses a battery of four pairs of Smee's or three Bunsen's cells, with elements arranged for in- tensity, and electrolyzes the solutions at 140 F. The first solu- tion will decompose without an aluminium anode, but the others require such an anode on the negative pole. The solution must be acidulated slightly with acid corresponding to the salt used, the temperature being kept at 140 F. constantly. M. A. Bertrandf states that he deposited aluminium on a plate of copper from a solution of double chloride of aluminium and ammonia, by using a strong current, and the deposit was capable of receiving a brilliant polish. Jas. S. Haurd,J of Springfield, Mass., patented the electrolysis of an aqueous solution formed by dissolving cryolite in a solution of magnesium and mauganous chlorides. John Braun decomposes a solution of alum, of specific gravity 1.03 to 1.07, at the usual temperature, using an insoluble anode. In the course of the operation, the sulphuric acid set free is neu- tralized by the continual addition of alkali ; and-, afterwards, to avoid the precipitation of alumina, a non-volatile organic acid, such as tartaric, is added to the solution. The intensity of the current is to be so regulated that for a bath of 10 to 20 litres two Bunsen elements (about 20 centimetres high) are used. Dr. Fred. Fischer || stated that Braun's proposition was con- trary to his experience. By passing a current of 8 to 9 volts and * Annual Record of Science and Industry, 1875. f Chem. News, xxxiv. 227. t U. S. Patent, 228,900, June 15, 1880. German Patent, No. 28,760 (1883). II Zeitschrift des Vereins Deutsche Ingenieurs, 1884, p. 557. REDUCTION BY THE USE OF ELECTRICITY. 253 50 amperes, using from 0.1 to 10 amperes per sq. centimetre of cathode, with various neutral and basic aluminium sulphate solu- tions, with and without organic acids, he obtained no aluminium. He obtained a black deposit of copper sulphide on the copper anode, which had apparently been mistaken by Braun for alu- minium. Moses G. Farmer* has patented an apparatus for obtaining aluminium electrically consisting of a series of conducting cells in the form of ladles, each ladle having a handle of conducting material extending upwards above the bowl of the next succeed- ing ladle ; each ladle can be heated separately from the rest ; the anodes are hung in the ladles, being suspended from the handles of the preceding ladles, the ladles themselves being the cathodes. M. L. Senetf electrolyzes a saturated solution of aluminium sulphate, separated by a porous septum from a solution of sodium chloride. A current is used of 6 to 7 volts and 4 amperes. The double chloride, APCl 6 .2NaCl, is formed, then decomposed, and the aluminium liberated deposited on the negative electrode. It has later been remarked of this process that it has not had the wished-for success on a large scale. Col. Frismuth, Philadelphia, purports to plate an alloy of nickel -and aluminium. He uses an ammoniacal solution, prob- ably of their sulphates. The plating certainly resembles nickel, but whether it contains aluminium the author has not been able to determine. Baron Overbeck and H. Xeiwerth, of Hannover, J have patented the following process : An aqueous or other solution of an or- ganic salt of aluminium is used, or a mixture of solutions which by double decomposition will yield such salt. Or a mixture of a metallic chloride and aluminium sulphate may be used, this yielding nascent aluminium chloride, which the current splits up immediately into aluminium and chlorine. Herman Rienbold gives the following recipe, stating that it furnishes excellent results : 50 parts of potash alum are dissolved * U. S. Patent, No. 315,266, April, 1885. f Cosmos les Mondes, Aug. 10, 1885. J English Pat., Dec. 15, 1883, No. 5756. Jeweller's Journal, September, 1887. 254 ALUMINIUM. in 300 parts of water, and to this are added 10 parts of aluminium chloride. The whole is then heated to 200 F., cooled, and then 39 parts of potassium cyanide added. A weak current should be used. It is stated that the plating, when polished, will be found equal to the best silver plating. " Iron/ 7 noticing this process, remarks, "there are a number of formula? for electro-plating with aluminium, but few appear to have attained to practical utility in the arts, for the reason that there is no special demand for such processes. All the qualities that are possessed by an electro-de- posit of aluminium are possessed to an equal or superior degree by other metals, silver, nickel, platinum, etc. Furthermore, it obstinately refuses to take and to retain a high lustre." This criticism is a little overdrawn, since the one quality in which alu- minium is superior to silver not blackening by contact with sulphurous vapor is not mentioned. Under the name of Count R. de Montegelas, of Philadelphia, several patents have been taken out in England for the electrol- ysis of aqueous solutions, which may be summarized as follows : * Alumina is treated with hydrochloric acid, and aluminium chloride obtained in solution. The liquid is then placed in a vessel into which dip a suitable anode and a cathode of brass or copper. On passing an electric current through the bath the iron present in the liquid is first deposited, and as soon as this deposi- tion ceases (as is apparent by the change of color of the deposit) the liquid is decanted into another similar bath, and to it is added about fifty per cent, by weight of the oxide of either lead, tin or zinc. On sending a current through this bath, aluminium to- gether with the metal of the added oxide is said to be deposited on the cathode. fA rectangular vessel is divided into two unequal compartments by a vertical porous partition, into the smaller of which is placed a saturated solution of common salt, in which is immersed a brass or copper electrode, into the larger is put a solution of aluminium chloride, immersed in which is an aluminium electrode. On pass- ing the current the latter solution, which is normally yellow, is * English Patent, Aug. 18, 1886, No. 10607. f English Patent, Feb. 3, 1887, No. 1751. REDUCTION BY THE USE OF ELECTRICITY. 255 gradually decolorized and converted into a solution of aluminium- sodium chloride. When colorless, this solution is taken out and the aluminium deposited in a similarly arranged vessel. The double chloride solution is placed in the larger compartment, with an electrode of brass, copper, or a thin plate of aluminium, while the smaller compartment contains a carbon electrode dipping into a solution of salt and surrounded by fragments of a mixture of salt and double chloride, fused together in equal parts. The author has been given several ounces of a very fine, metal- lic powder said to have been made by these processes, and which is certainly aluminium. As I am not satisfied, however, that the specimen is really authentic, I feel justified in suspending a final expression of opinion on the process. A. Walker, of Tarnowitz, has patented the following methods of procedure : * a. Pure commercial hydrate is dissolved in nitric acid free from chlorine, in slight excess, and tartaric acid added. The liquid is let clear for some time, any potassium bi-tartrate, which may be formed from small quantities of potassium adhering to the hydrate, filtered out, and the clear solution electrolyzed. There is added to the solution during electrolysis organic acid as formic, acetic, citric, oxalic or, better, absolute alcohol. b. A solution of aluminium nitrate, as far as possible free from alkalies and sulphuric acid, is decomposed by a strong dynamic current in baths arranged in series, using platinized plates as anode and cathode. With a weak current of 0.02 to 0.05 amperes to a square centimetre, the aluminium separates out on the cathode as a deep black deposit, sticking close to the copper. The cathode is lifted from the solution, freed from small quanti- ties of alumina coating it by gentle rinsing, and then the deposit washed off by a strong jet of water. The powder obtained is washed further with clear, cold water particularly free from so- dium chloride, and dried by gentle heating in the air. H. C. Bullf proposes to manufacture aluminium alloys by using the metal to be alloyed with aluminium as a cathode in a * German Pat. (D. R. P.) 40,626 (1887.) f English Pat., 10199 A. (1887). 256 . ALUMINIUM. bath of aluminium sulphate, the anode being either of aluminium or of an insoluble substance. When enough aluminium is de- posited, the cathode is taken out and melted down. C. A. Burghardt and W. J. Twining, of Manchester, England, have patented the following methods : *To a solution of sodium or potassium aluminate containing about 7.2 oz. of aluminium per gallon are added 4 pounds of 95 percent, potassium cyanide dissolved in a quart of water, and then gradually 2J pounds of potassium bi-carbonate. The whole is boiled 12 hours and made up to a gallon. The bath is used at 175 F. with aluminium or platinum anode and a carbon or copper cathode. The addition of a little free hydrocyanic acid insures a bright deposit when articles are being plated. fTwo and one-half kilos of aluminium sulphate in solution is precipitated by ammonia, and then re-dissolved by adding 1 J kilos of caustic soda dissolved in a litre of water ; the alumina is thus slightly in excess. Then hydrocyanic acid is added until a slight precipitate appears. This solution, warmed to 80, is used as a bath from which aluminium is to be deposited. {The bath is prepared by dissolving alumina in a solution of chloride of copper, and treating further with caustic soda or potash for the purpose of causing the aluminium and copper to combine together. The precipitate, dissolved in hydrocyanic acid and diluted, forms a bath of double cyanide, which when electrolyzed deposits an alloy of aluminium and copper. Besides the processes so far described, patents have been taken out in England by Gerhard and Smith, Taylor,|| and Coulson,Tf the details of which have not been accessible to the author. Over against all these statements and claims of enthusiastic inventors, let me place a few cool statements from authorities who have given much time and attention to elucidating the subject. Sprague** states his inability to deposit aluminium electrically from solution. * English Pat., July 2, 1887, No. 9389. f German Pat. (D. R. P.), 45,020 (1887). J English Pat., Oct. 28, 1887, No. 2602. No. 16,653(1884). || No. 1991 (1855). 1 No. 2075 (1857). ** Sprague's Electricity, p. 309. REDUCTION BY THE USE OF ELECTRICITY. 257 Dr. Clemens Winekler* states that he has spent much time in trying all methods so far proposed, and comes to the conclusion that aluminium cannot be deposited by electricity in the wet way. Dr. Geo. Goref although having once proposed a method which he said attained this end, yet in his later work on Electro-metal- lurgy does not mention his former proposition, and quotes ap- parently as coinciding with his own opinion, the words of Sprague and Winekler given above. Dr. S. MierzinskiJ states, in 1883, that "the deposition of aluminium from an aqueous solution of its salt has not yet been accomplished." Dr. "W. Hampe claims to have shown that the electrolysis of aqueous aluminous solutions, although frequently patented, is not to be expected. From which we would infer that he could not testify to it ever having been done. Alexander Watt|| holds that the electrolytic production of aluminium from solution is very improbable. He tried acid solutions, alkaline solutions, cyanide combinations, etc., under most varied conditions, without any result. Finally, I will quote from a letter of my good friend Dr. Justin D. Lisle, of Springfield, O., who with ample means at his disposal, an enthusiasm bred of love for scientific truth and talent to guide him in his work, has reached the following results : " I have tried in almost every conceivable way to deposit it (alu- minium) from aqueous solution by electricity, using from 1 pint cells to 60 gallon cells successively ; the cells were connected for quantity and for intensity ; acid and neutral solutions were used ; carbon, platinum, and copper electrodes ; porous cups and dia- phragms, were all thoroughly tried without the slightest deposit of metal. In some cases alumina was deposited, which has led me to think that aluminium was primarily deposited, and owing to the fine state in which it existed was promptly oxidized." * Journal of the Chem. Soc., X. 1134. f Text book of Electro-metallurgy, t Die Fabrikation des Aluminiums. Chem. Zeit. (Cothen), XL 935. H London Electrical Review, July, 1887. 17 258 ALUMINIUM. II. THE ELECTKIC DECOMPOSITION OF FUSED ALUMINIUM COMPOUNDS. This subdivision of the electrolytic methods includes all the electric processes which have given practical results. Under this head come Davy's first attempts to decompose alumina, in 1807, Deville's first success in producing pure aluminium, in 1854, and GratzePs application of the dynamo-electric machine, in 1883, which introduced the first radical improvement the aluminiun in- dustry had known for twenty-five years. It is hardly too much to say that if the long sought for method of turning the potential energy of coal directly into electric energy ever be accomplished, these electrolytic methods will be beyond doubt the future means of bringing aluminium in price among the common metals. There seem to be two ways of operating, as mentioned on p. 34, in the first of which the liquid compound is decomposed at moderate temperatures, such that the containing vessel can be heated to, in an ordinary fire, and in which almost all the current is utilized in decomposing the electrolyte f in the other enormous temperatures are reached by means of interrupting a powerful current, and a large part of the electric energy is converted into heat, while the decomposition may be partly electrolytic and partly a chemical reaction made possible by this extreme tempera- ture. As it is impossible in one or two cases to draw this line, and since the practical requirements of the two methods of pro- cedure are in most respects identical, we will consider the fol- lowing processes in their chronological order, except in one or two cases where very similar ones are placed together. Davy's Experiment (1810). Sir Humphry Davy, in his Brompton Lecture before the Royal Philosophical Society,* described the following attempt to decompose alumina and obtain the metal of this earth. He * Philosophical Transactions, 1810. REDUCTION BY THE USE OF ELECTRICITY. 259 connected an iron wire with the negative pole of a battery con- sisting of 1000 double plates. The wire was heated to whiteness and then fused in contact with some moistened alumina, the opera- tion being performed in an atmosphere of hydrogen. The iron became brittle, whiter, and on being dissolved in acid gave a solution from which was precipitated alumina, identical with that used. Duvivier's Experiment (1854). M. Duvivier* states that by passing an electric current from eighty Bunsen cells through a small piece of laminated disthene between two carbon points, the disthene melted entirely in two or three minutes, the elements which composed it were* partly disunited by the power of the electric current, and some alumin- ium freed from its oxygen. Several globules of the metal separated, one of which was as white and as hard as silver. Bunsen' s and Devitte's Methods (1854). A method of decomposing aluminium-sodium chloride by the battery was discovered simultaneously by Deville in France and Bunsen in Germany, in 1854, and is nothing else but an applica- tion of the process already announced by Bunsen of decomposing magnesium chloride by the battery. Deville gives the more minute account, and we therefore quote his description of the process. f" It appears to me impossible to obtain aluminium by the battery in aqueous solutions. I should believe this to be an absolute impossibility if the brilliant experiments of M. Bunsen in the preparation of barium, chromium and manganese did not shake my convictions. Still I must say that all the processes of this description which have recently been published for the preparation of aluminium have failed to give me any results. Every one knows the elegant process by means of which M. Bunsen has lately produced magnesium, decomposing fused mag- * The Chemist, Aug. 1854. f Ann. de Chem. et de Phys. [3], 46, 452 ; Deville's de 1' Aluminium. 260 ALUMINIUM. nesium chloride by an electric current. The illustrious professor at Heidelberg has opened up a method which may lead to very interesting results. However, the battery cannot be used for de- composing aluminium chloride directly, which does not melt, but volatilizes at a low temperature ; it is, therefore, necessary to use some other material which is fusible and in which aluminium alone will be displaced by the current. I have found this salt in the double chloride of aluminium and sodium, which melts towards 185, is fixed at a somewhat high temperature, although volatile below the fusing point of aluminium, and thus unites all the desirable conditions. " I put some of this double chloride into a porcelain crucible separated imperfectly into two compartments by a thin leaf of porcelain, and decomposed it by means of a battery of five ele- ments and carbon electrodes. The crucible was heated more and more as the operation progressed, for the contents became less and less fusible, but the heat was not carried past the melting point of aluminium. Arrived at this point, after having lifted out the diaphragm and electrodes, I heated the crucible to bright redness and found at the bottom a button of aluminium, which was flattened out and shown to the Academy in the Seance of March 20, 1854. The button was accompanied by a considerable quan- tity of carbon, which prevented the union of a considerable mass of shot-metal. This carbon came from the disintegration of the very dense gas-retort carbon electrodes ; in fact, the positive elec- trode was entirely eaten away in spite of its considerable thick- ness. It was evident, then, that this apparatus, although similar to that adopted by Bunsen for manufacturing magnesium, would not suit here, and the following is the process which after many experiments I hold as best. " To prepare the bath for decomposition, I heat a mixture of 2 parts aluminium chloride and 1 part sodium chloride, dry and pulverized, to about 200 in a porcelain capsule. They combine with disengagement of heat, and the resulting bath is very fluid. The apparatus which I use for the decomposition comprises a glazed porcelain crucible, which as a precaution is placed inside a larger one of clay. The whole is covered by a porcelain cover pierced by a slit to give passage to a large thick leaf of KEDUCTION BY THE USE OF ELECTRICITY. 261 platinum, which serves as the negative electrode; the lid has also a hole through which is introduced, fitting closely, a well- dried porous cylinder, the bottom of which is kept at some dis- tance from the inside of the porcelain crucible. This porous vessel encloses a pencil of retort carbon, which serves as the positive electrode. Melted double chloride is poured into the porous jar and into the crucible so as to stand at the same height in both vessels ; the whole is heated just enough to keep the bath in fusion, and there is passed through it the current from several Bunsen cells, two cells being strictly sufficient. The annexed diagram shows the crucibles in section. Fig. 23. " The aluminium deposits with some sodium chloride on the platinum leaf; the chlorine, with a little aluminium chloride, is disengaged in the porous jar and forms white fumes, which are prevented from rising by throwing into the jar from time to time some dry, pulverized sodium chloride. To collect the aluminium, the platinum leaf is removed when sufficiently charged with the saline and metallic deposit ; after letting it cool, the deposit is rubbed off and the leaf placed in its former position. The 262 ALUMINIUM. material thus detached, melted in a porcelain crucible, and after cooling washed with water, yields a gray, metallic powder, which by melting several times under a layer of the double chloride is reunited into a button." Bunsen* adopted a similar arrangement. The porcelain cru- cible containing the bath of aluminium-sodium chloride kept in fusion was divided into two compartments in its upper part by a partition, in order to separate the chlorine liberated from the alu- minium reduced. He made the two electrodes of retort carbon. To reunite the pulverulent aluminium, Bunsen melted it in a bath of the double chloride, continually throwing in enough sodium chloride to keep the temperature of the bath about the fusing point of silver. As we have seen, Deville, without being acquainted with Bun- sen's investigations, employed the same arrangement, but he abandoned it because the retort carbon slowly disintegrated in the bath, and a considerable quantity of double chloride was lost by the higher heat necessary to reunite the globules of aluminium after the electrolysis. Deville also observed that by working at a higher temperature, as Bunsen has done, he obtained purer metal, but in less quantity. The effect of the high heat is that silicon chloride is formed and volatilizes, and the iron which would have been reduced with the aluminium is transformed into ferrous chloride by the aluminium chloride, and thus the aluminium is purified of silicon and iron. Plating aluminium on copper. The same bath of double chlor- ide of aluminium and sodium may be used for plating alumin- ium in particular on copper, on which Capt. Caron experimented with Deville. Deville says : " To succeed well, it is necessary to use a bath of double chloride which has been entirely purified from foreign metallic matter by the action of the battery itself. When aluminium is being deposited at the negative pole, the first portions of metal obtained are always brittle, the impurities in the bath being removed in the first metal thrown down ; so, when the metal deposited appears pure, the piece of copper to be plated is attached to this pole and a bar of pure aluminium to the posi- * Pogg. Annalen, 97, 648. KEDUCTION BY THE USE OF ELECTRICITY. 263 live pole. However, a compact mixture of carbon and alumina can be used instead of the aluminium anode, which acts similarly to it and keeps the composition of the bath constant. The tem- perature ought to be kept a little lower than the fusing point of aluminium. The deposit takes place readily and is very ad- herent, but it is difficult to prevent it being impregnated with double chloride, which attacks it the moment the piece is washed. The washing ought to be done in a large quantity of water. Cryolite might equally as well be used . for this operation, but its fusibility should be increased by mixing with it a little double chloride of aluminium and sodium and some potassium chloride." Le Chatellier's Method (1861). The subject of this patent* was the decomposition of the fused double chloride of aluminium and sodium, with the particular object of coating or plating other metals, the articles being at- tached to the negative pole. About the only novelty claimed in this patent was the use of a mixture of alumina and carbon for the anode, but we see from the previous paragraph that this was sug- gested by Deville several years before ; the only real improve- ment was the placing of this anode inside a porous cup, in order to prevent the disintegrated carbon from falling into the bath. Monckton's Patent (1862). Moncktonf proposes to pass an electric current through a re- duction chamber, and in this way to raise the temperature to such a point that alumina will be reduced by the carbon present. We clearly see in this the germ of several more-recently patented processes. Gaudirfs Process (1869). GaudinJ reduces aluminium by a process to which he applies the somewhat doubtful title of economic. He melts together * English Patent, 1861, No. 1214. f English Patent, 1862, No. 264. $ Moniteur Scientifique, xi. 62. 264 ALUMINIUM. equal parts of cryolite and sodium chloride, and traverses the fused mass by a galvanic current. Fluorine is evolved at the positive pole, while aluminium accumulates at the negative. Kagensbuscti s Process (1872). Kagensbusch,* of Leeds, proposes to melt clay with fluxes, then adding zinc or a like metal to pass an electric current through the fused mass, isolating an alloy of aluminium and the metal, from which the foreign metal may be removed by distilla- tion, sublimation, or cupellation. Berthaufs Proposition (1879). Up to this time, all the proposed electric processes were con- fined to the use of a galvanic current, the cost of obtaining which was a summary bar to all ideas of economical production. About this period dynamo-electric machines were being introduced into metallurgical practice, and Berthaut is the first we can find who proposes their use in producing aluminium. The process which he patentedf is otherwise almost identical with Le Chatellier's. Grated? 8 Process (1883). This process^ has little claim to originality, except in the de- tails of the apparatus. A dynamo-electric current is used, the electrolyte is fused cryolite or double chloride of aluminium and sodium, and the anodes are of pressed carbon and alumina none of which points are new. However, the use of melting pots of porcelain, alumina, or aluminium, and making them the negative electrode are points in which innovations are made. In a furnace are put two to five pots, according to the power of the dynamo used, each pot having a separate grate. The pots are preferably of metal, cast-steel is used, and form the negative electrodes. The positive electrode, K (Fig. 24), can be made of * English Patent, 1872, No. 4811. f English Patent, 1879, No. 4087. t German Patent (D. R. P.); No. 26962 (1883). REDUCTION BY THE USE OF ELECTRICITY. 265 a mixture of anhydrous alumina and carbon pressed into shape and ignited. A mixture of alumina and gas-tar answers very well ; or it can even be made of gas-tar and gas-retort carbon. Fig. 24. During the operation little pieces of carbon fall from it and would contaminate the bath, but are kept from doing so by the mantle, G. This isolating vessel, G 9 is perforated around the lower part at g, so that the molten electrolyte may circulate through. The tube O 1 conducts reducing gas into the crucible, which leaves by the tube O 2 . This reducing atmosphere is im- portant, in order to protect from burning any metal rising to the surface of the bath. The chlorine set free at the electrode, K, partly combines with the alumina in it, regenerating the bath, but some escapes, and, collecting in the upper part of the sur- rounding mantel, Gr, is led away by a tube connecting with it. Instead of making the electrode, K, of carbon and alumina, it may simply be of carbon, and then plates of pressed alumina and carbon are placed in the bath close to the electrode, K, but not connected with it. Also, in place of making the crucible of metal 266 ALUMINIUM. and connecting it with the negative pole, it may be made of a non-conducting material, clay or the like, and a metallic electrode as, for instance, of aluminium plunged into the bath. In a later patent,* Gratzel states that the bath is decomposed by a current of comparatively low tension if magnesium chloride be present ; the chlorides of barium, strontium, or calcium act similarly. Prof. F. Fischerf maintains as impracticable the use of plates of pressed alumina and carbon, which can, further, only be opera- tive when they are made the positive electrode, and then their electric resistance is too great. The incorporation into them of copper filings, saturation with mercury, etc., gives no more prac- tical results. There are also volatilized at the anodes considerable quantities of aluminium chloride, varying in amount with the strength of the current. Large works were erected near Bremen by the Aluminium und Magnesiumfabrik Pt. Gratzel, zu Hemelingen, in which this process was installed. License was also granted to the large chemical works of Schering, at Berlin, to operate it. R. Bieder- mann, in commenting on the process in 1886,J stated that the results obtained so far were not fully satisfactory, but the diffi- culties which had been met were of a kind which would certainly be overcome. They were principally in the polarization of the cathode, by which a large part of the current was neutralized. By using proper depolarizing substances this difficulty would be removed. The utilization of the chlorine evolved would also very much decrease the expenses. A more suitable slag, which collected the aluminium together better, was also desirable. Finally, the metal produced was somewhat impure, taking up iron from the iron pots and silicon from the clay ones, to obviate which Biedermann recommended the use of lime or magnesia vessels. Prof. Fischer, as we have seen, maintained the uselessness of GratzePs patent claims, and his later expression of this opinion * English Patent, 14325, Nov. 23, 1885. U. S. Patent, 362441, May 3, 1887. f Wagner's Jahresbericht, 1884, p. 1319 ; 1887, p. 376. J Kerl und Stohinan, 4th ed., p. 725. [REDUCTION BY THE USE OF ELECTRICITY. 267 in 1887 drew a reply from A. Saarburger,* director of the works at Hemelingen, to the eifect that since October, 1887, they had abandoned the Gratzel process and were making aluminium at present by methods devised by Herr Saarburger; in consequence of which fact the directors of the company decided in January, 1888, to drop the addition Pt. Gratzel from the firm name. The methods now in use at Hemelingen are kept secret, but the author is informed by a friend in Hamburg that they are using a modified Deville sodium process. Herr Saarburger informed me in October, 1888, that they were producing pure aluminium at the rate of 12 tons a year, besides a large quantity sold in alloys. An attractive pamphlet issued by this firm sets forth precautions to be used in making aluminium alloys, together with a digest of their most important properties, which we shall have occasion to quote from later in considering those alloys. Kleiner's Process (1886). This was devised by Dr. Ed. Kleiner of Zurich, Switzerland, and has presumably been patented in most of the European States. The English patent is dated 1886.f The first attempts to operate it were at the Rhine Falls, Schaffhausen, and were promising enough to induce Messrs. J. G. Nethers, Sons & Co., proprietors of an iron works there, to try to obtain water rights for 1500 horse power, announcing that a company (the Kleiner Gesell- schaft) with a capital of 12,000,000 francs was prepared to under- take the enterprise and build large works. The proposition is said to have met with strong opposition from the hotel-keepers and those interested in the Falls as an attraction for tourists, and the government declined the grant, considering that the pictu- resqueness of the falls would be seriously affected. This is the reason given by those interested in the process for it not being carried out in Switzerland, it being then determined to start a works in some part of England where cheap coal could be ob- tained, and test the process on a large scale. A small experi- * Verein der Deutsche Ingenieure, Jan. 26, 1889. f English Patents, 8531, June 29, 1886, and 15322, Nov. 24, 1886. 268 ALUMINIUM. mental plant was then set up in the early part of 1887 on Far- rington Road, London, where it was inspected by many scientific men, among them Dr. John Hopkinson, F.R.S., who reported on the quantitative results obtained ; a description of the process as here operated was also written up for " Engineering." With the co-operation of Major Ricarde-Seaver a larger plant was put up at Hope Mills, Tydesley, in Lancashire, where the process was inspected and reported on by Dr. George Gore, the electrician. After his report we learn that the patents have been acquired by the Aluminium Syndicate, Limited, of London, a combination of capitalists among whom are said to be the Rothschilds. The latest reports state that the process is still in the experimental stage, although Dr. Kleiner considers that the present results will justify working on a commercial scale in the near future. The aluminium compound used is commercial cryolite. It is stated that the native mineral from Greenland contains on an average, according to Dr. Kleiner's analysis, 96 per cent, of pure cryolite, the remainder being moisture, silica, oxides of iron and manganese. As pure cryolite contains 13 per cent, of aluminium, the native mineral will contain 12J per cent., all of which Dr. Kleiner claims to be able to extract. It is further remarked that as soon as sufficient demand arises, an artificial cryolite can be made at much less cost than that of the native mineral, which now sells at 18 to 20 a ton. The rationale of the process consists in applying the electric current in such a way that a small quan- tity of it generates heat and keeps the electrolyte in fusion, while the larger quantity acts electrolytically. Dry, powdered cryolite is packed around and between carbon electrodes in a bauxite- lined cavity ; on passing a current of high tension (80 to 100 volts) through the electrodes, the cryolite is quickly fused by the heat of the arc and becomes a conductor. As soon as the electrolyte is in good fusion the tension is lowered to 50 volts, the quantity being about 150 amperes, the arc ceases and the decomposition proceeds regularly for two or three hours until the bath is nearly exhausted. The evolved fluorine is said to attack the beauxite and by thus supplying aluminium to the bath extends the time of an operation. In the first patent the negative carbon was inserted through the bottom of the melting cavity, the positive dipping REDUCTION BY THE USE OF ELECTRICITY. 269 into the bath from above, but it was found that while the ends of the positive carbon immersed in the cryolite were unattacked, the part immediately over the bath was rapidly corroded. In the second patent, therefore, the positive electrode was circular and entirely immersed in the cryolite, connection being made by ears which projected through the side of the vessel. As the car- bons are thus fixed, .the preliminary fusion is accomplished by a movable carbon rod suspended from above, passing through the circular anode and used only for this purpose. The bath being well fused and the current flowing freely between the fixed car- bons, the rod is withdrawn. The carbons are said to be thus perfectly protected from corrosion, and able to serve almost in- definitely. The melting pots finally used were ordinary black- lead crucibles, which are not usually injured at all, since the fused part of the cryolite does not touch them, and they last as many as 300 fusions. After the operation, the carbons are lifted out of the bath and the contents cooled. When solid, the crucibles are inverted and the contents fall out. This residue is broken to coarse powder, the nodules of aluminium picked out, melted in a crucible and cast into bars. The coarse powder is then ground to fine dust. This powder is more or less alkaline and contains a greater or less excess of fluoride of sodium in proportion to the amount of aluminium which has been taken out. If only a small proportion of the metal has been extracted and the powder con- tains only a small excess of sodium fluoride, it is used again with- out any preparation in charging the crucibles ; but if as much as 5 or 6 per cent, of aluminium has been removed and the powder, therefore, contains a large excess of sodium fluoride, it is washed with water for a long time to remove that salt, which slowly dis- solves. The solution is reserved, while the powder remaining is unchanged cryolite, and is used over. Dr. Gore states that if the powder, electrodes and crucible are perfectly dry, there is no escape of gas or vapor during the process ; but if moisture is pre- sent, a small amount only of fumes of hydrofluoric acid appear, and that there is no escape of fluorine gas at any time. If this is so, it is rather difficult to see where the fluorine with which the alu- minium is combined goes to. If the vessel were lined with beauxite, it might be retained by this lining, but in the experi- 270 ALUMINIUM. ments seen by Dr. Gore, a plumbago crucible was used (which re- mained unattacked) and cryolite only. It is certainly a mystery how any aluminium could be produced without fluorine vapors being liberated. Dr. Kleiner hopes to soon dispense with the interruption of the process, washing, etc., by regenerating cryolite in the crucible itself and so making the process continuous. One of the great advantages claimed is that the aluminium is obtained in nodules, and not in fine powder ; if it was, it could not all be collected because it is so light, some of it would float upon the water during the washing process and be lost, and even when collected it could not be dried and melted without considerable loss. It has been found impossible in practice to obtain all the alu- minium from a given quantity of cryolite in less than two fusions, for the sodium fluoride collecting in the bath hinders the produc- tion of the metal. The proportion extracted by a single fusion de- pends upon its duration. In the operations at Tydesley, a fusion lasting 24 hours separated only 2J per cent, of aluminium, whereas the cryolite contained 12 J per cent. At this rate, to ex- tract the whole in two operations would require two fusions of 60 hours each. As to the output, on an average a current of 38 electric horse power deposited 150 grammes of aluminium per hour, being a little over 3 grammes per horse-power. Since a current of 50 volts and 150 amperes, such as was stated above as 50 x 1 50 the current in each pot, is equal to or 10 electric H. P., it is probable that the 38 H. P. current mentioned must have been used for four crucibles. Now, the output of four crucibles, each with a current of 150 amperes, should have been 0.00009135 X 150 x 4 s= 0.0548 grammes per second or 197.3 grammes per hour ; the difference between this and the amount actually ob- tained, or 47.3 grammes, is the amount of aluminium which was produced and then afterwards lost either as fine shot-metal or powder or dissolved again by corroding elements in the bath. To calculate how the output of 3 grammes per electric H. P. per hour compares with the quantity of metal which this amount of energy should be able to produce, we need to know the heat of formation of cryolite, or we could form some idea if we knew even that of aluminium fluoride, but thermal data with regard to REDUCTION BY THE USE OF ELECTRICITY. 271 fluorides are entirely lacking, since free fluorine is needed as the basis of their experimental determination. As fluorine has lately been isolated, it may not be long before some of these figures are determined, and then the calculations referred to can be made. In the mean time we can observe no further than that about 75 per cent, of the metal produced in the bath is obtained and weighed, and that the high potential of the current seems to indicate a considerable loss of power in overcoming resistances other than that of decomposition, a loss greater than is met with in. other somewhat similar operations. As to the purity of the metal obtained, the process is met at the outset by the silica and iron oxide in the cryolite, which are probably all reduced with the first few grammes of aluminium thrown down. This can possibly be remedied by using a purer artificial cryolite ; the impurities cannot generally be separated from the natural mineral. Then there are impurities of a similar nature coming from the carbons used, and which are generally present if especial pains are not taken to get very pure materials for making them. Dr. Kleiner's early attempts produced metal of 85 to 95 per cent, purity, but he now states that it is uniformly 95 to 98 per cent., and being put on the market in competition with other commercial brands. It appears, however, from a con- sideration of the preceding data, that unless great improvements have since been made in several details, the process will not enable the metal produced to be sold at 16 shillings a pound (the present selling price), and pay expenses. Lossier's Method. *This is a device for decomposing the natural silicates by electricity and obtaining their aluminium. The bath is com- posed of pure aluminium fluoride or of a mixture of this salt and an alkaline chloride, and is kept molten in a round bottomed crucible placed in a furnace. The electrodes are of dense carbon and are separated in the crucible by a partition reaching beneath the surface of the bath. The positive electrode is furnished with * German Patent (D. R. P.), No. 31089. 272 ALUMINIUM. a jacket or thick coating of some aluminium silicate, plastered on moist and well dried before use. When the current is passed, the aluminium fluoride yields up its fluorine at this pole and its aluminium at the other. The fluorine combines with the alumin- ium silicate, forming on the one hand aluminium fluoride, which regenerates the bath, on the other silicon fluoride and carbonic oxide, which escape as gases. The metal liberated at the negative pole is lighter than the fused bath, and therefore rises to the surface. M. Grabau cites as one of the recommendations of aluminium fluoride for use in his process (p. 242), that it is quite infusible, so it would appear that Lossier has made a mistake in supposing that it could be melted alone in a crucible. It would, however, make a very fusible bath when the alkali chloride was added. It is probable that the carrying out of this method would develop great trouble from the attacking of the crucible by the very corrosive bath, the disintegration of the carbons, which would cause much trouble at the negative pole especially, and the oxida- tion of the fluid aluminium on the surface of the bath. I cannot learn that the process has ever been attempted on a large scale. Omholfs Furnace. I. Omholt and the firm Bottiger and Seidler, of Gossnitz, have patented the following apparatus for the continuous electrolysis of aluminium chloride : * The bed of a reverberatory furnace is divided by transverse partitions into two compartments, in each of which are two retorts semi-circular in section, lying side by side horizontally across the furnace, with the circular part up. They are supported on refrac- tory pillars so that their open side is a small distance above the floor of the furnace. The aluminium compound being melted on the hearth, it stands to the same depth in both retorts, and if the electrodes are passed through the bottom of the hearth they may remain entirely submerged in molten salt and each under its own retort cover. The metal therefore collects in a liquid state under * German Patent (D. R. P.), No. 34728. REDUCTION BY THE USE* OF ELECTRICITY. 273 one retort and the chlorine under the other, both being preserved from contact or mixture with the furnace gases by the lock of molten salt. The chlorine can thus be led away by a pipe, and utilized, while the aluminium collects without loss, and is removed at convenient intervals. Henderson's Process (1887). A. C. Henderson, of Dublin,* patents the process of fluxing alumina with cryolite, the bath being put into a graphite crucible, which serves as the negative electrode, and which is put inside a larger crucible and the space between filled with graphite. The positive electrode is of carbon and dips into the fused material. A current of only 3 volts is used, and the dissolved alumina only is decomposed, the cryolite remaining unaltered. The aluminium collects in the bottom of the crucible, and as the operation pro- ceeds alumina is added to renew the bath. To prepare alloys, a negative electrode is made of the metal and used in a similar position to the positive electrode, and as the current passes the alloy is formed and falls melted to the bottom of the crucible. We must give Mr. Henderson credit for having introduced the idea of decomposing alumina held in solution in a fused bath, an idea which is, however, more fully developed by Hall (see p. 288) ; and also for hitting what Hampe designates as the best mode of procedure for obtaining alloys in such processes (see p. 286). It is to be regretted that, having such a good beginning, we have not heard more of Mr. Henderson's process in the three years since it was patented. Bernard Bros.' Process (1887). Messrs. M. and E. Bernard, of Paris, have patented a processf which consists in electrolyzing a mixture of sodium chloride with aluminium fluoride or with the separate or double fluorides of aluminium and sodium, melted in a non-metallic crucible or in a is * English Patent, No. 7426 (1887). f English Patent, No. 10057, July 18, 1887. 274 ALtJMINIUM. metallic one inclosed in a thin refractory jacket to avoid filtration. The details of the apparatus and bath are as follows : Disposition of the Apparatus. The pots or crucibles used may be of refractory earth, plumbago or of metal, and in cases where an alloy is required the crucible itself serves as an electrode. None of these, however, resist the corrosive power of the electro- lyte and would under ordinary conditions be quickly destroyed. To overcome this difficulty two special devices are employed. When alloys are to be made directly, the pot is cast of the metal with which the aluminium is to be combined. It is shaped with a sloping bottom and provided with a tap hole. The pot is en- cased in thin brickwork and is then made the negative electrode, the positive being two carbon rods dipping into the bath. As soon as the current is passed aluminium is deposited on the walls of the pot, forming a rich alloy with the metal of which the pot is made (iron or copper). When this coating becomes sufficiently rich in aluminium, the heat of the bath melts it and it trickles down and collects at the bottom. After a certain time, the alloy can be tapped out regularly at intervals without interrupting the electrolysis. The metal thus obtained is principally aluminium containing a few per cent, of the metal of the pot, which is of no consequence since the end to be finally attained is the production of an alloy with a smaller quantity of aluminium. When pure aluminium is to be obtained, an ingenious device is used to pro- tect the metal from contamination by the metal of the pot. Two carbon rods serve as anode and cathode, the cathode standing up- right in a small crucible placed upon a plate resting on the bottom of the pot. This crucible and plate are made from carbon blocks or from fused alumina or fluorspar moulded into the shape de- sired. As the metal is set free it trickles down the cathode and is caught in the crucible or cup, thus being prevented from spreading out over the bottom of the pot. To prevent the bath from corroding the pot, a wire is passed from the latter to the negative pole of the battery. The pot is thus made part of the negative electrode, but it is not intended that much of the current should pass through it, so a resistance coil is interposed between it and the battery or dynamo, so that the derived current passing through the sides of the pot is only 5 to 10 per cent, of the whole REDUCTION BY THE USE OF ELECTRICITY. 275 current. The effect of this is that a small amount of aluminium is deposited on and alloys with the sides of the vessel, which protects the latter from corrosion and is only feebly acted upon by the bath. The metal deposited in the crucible is thus kept nearly pure, while a small amount of alloy falls to the bottom of the pot and is poured out after the crucible has been removed. When it is wished to obtain the purest aluminium, the intensity of the derived current passing through the pot is increased by removing part of the resistance interposed between it and the negative wire, thus also decreasing the intensity of the principal current. The nature of the electrodes proper may be varied. For producing pure aluminium the anode is carbon, the cathode carbon and the pot either of copper or iron ; for producing copper alloys the anode may be either carbon or bright copper, and the cathode (pot) of carbon or copper ; for producing iron alloys the anode may be either carbon or iron, while the vessel used as cathode is either of cast-iron or plumbago. Composition of the bath. The proportions of the different salts used for the bath vary between 30 to 40 per cent, of fluorides of aluminium and of sodium and 60 to 70 per cent, of sodium chlor- ide. Very good results are reported with Aluminium fluoride ....... 40 Sodium chloride ........ 60 100 Pure cryolite may be used, mixed with varying quantities of sodium chloride. Moreover, the separate fluorides of aluminium and sodium can be used in different proportions to those in which they are found in cryolite ; for instance Aluminium fluoride ....... 35 Sodium fluoride ........ 10 " chloride 55 100 As aluminium is removed, the bath becomes poor in aluminium fluoride, and this salt must be added to keep up its strength. For each kilo of aluminium produced about 3 kilos of aluminium fluoride would need to be added, but only 1J kilos is added as 276 ALUMINIUM. such, the other 1 J kilos being regenerated by causing the fluorine vapors evolved to act on alumina or beauxite placed somewhere about the anode. The materials used, then, for producing 100 kilos of aluminium are estimated as Aluminium fluoride . . . . . 150 kilos. Commercial alumina ...... 200 " Sodium chloride . . . . .; . . 100 " Power required. M. Ad. Minet, who has written a sketch of Bernard's process as carried out at their works at Creil (Oise), maintains that aluminium fluoride is the principal electrolyte. The bath is very fluid and the temperature and composition kept constant during the operation, the laws of electrolysis can there- fore be applied easily to the discussion of the process. M. Minet states that the electro-motive force absorbed by the bath is from 4 to 5 volts, and that this is not much above the minimum poten- tial necessary to decompose aluminium fluoride, deduced from its heat of formation, which is 3J volts. I confess that I do not know of any determination of this heat of formation referred to ; we can probably draw the inference that it is greater than that of aluminium chloride, but I do not know that its exact value has been determined. Taking, however, Minet's figure of 3J volts, the current is certainly very economically applied if decomposition is produced with 4 volts. With 3J volts tension, a current of 1 horse-power should produce 72 grammes of aluminium per hour. It is stated that 25 grammes are produced per hour per indicated mechanical horse-power, which shows that the aluminium pro- duced represents a quantity of energy equal to 35 per cent, of the power of the engine. Assuming that 20 per cent, of the engine power is lost in being converted into electric energy, we have only 56 per cent, of the electric current not productive, including the loss by transfer resistance of the bath. Since 5 volts are absorbed by the bath altogether, the amount lost by resistance is to the amount utilized in decomposition as 1 J to 3J, which would show the former item to be (100 56) x f or 19 per cent, of the energy of the current. This loss is unavoidable, and as small as can be well expected, so that the real loss in working is 56 19 or 37 per cent. This is caused principally by re-solution of aluminium DEDUCTION BY THE USE OF ELECTRICITY. 277 in the bath. We might reach this conclusion by another way. One horse-power furnished by the engine would produce 0.8 electric horse-power, which at a tension of 5 volts would furnish 120 amperes. According to Faraday's law, 120 amperes would set free 40 grammes of aluminium per hour. As only 25 were obtained practically, it shows that 15 grammes have been pro- duced and re-dissolved by the bath, making this loss 37.5 per cent. From the figures furnished, we see that to produce 100 kilos of aluminium in 20 hours would require an engine of 200 horse-power, and since each pot produces 4 kilos of pure metal or 6 kilos of aluminium in alloys, per hour, a plant of this output would require 25 pots for making pure aluminium or 18 for working on alloys. Quality of metal. When working for pure aluminium, about three-fourths of the metal produced is taken from the crucible in which the cathode stands, and is 98 to 99 per cent, pure ; the other one-fourth has been deposited on the sides of the cast-iron pot, and contains 10 to 20 per cent, of iron. It is poured out and used for making ferro-aluminium. Reactions in the process. M. Minet claims that aluminium fluoride is the chief electrolyte, since the yield of aluminium in- creased with the proportion of this salt in the bath. However, on reviewing this gentleman's statements, we find that when the bath contains Aluminium fluoride ....... 40 Sodium chloride ........ 60 100 the best results are obtained. It is conceivable that the yield of aluminium increases with the proportion of aluminium fluoride up to this point, but there is no reason for saying that a further increase would give a better yield if this has been found the best mixture. Mr. Rogers found that when the proportion of alu- minium fluoride to sodium fluoride in an electrolytic bath was greater than 40 to 60 (the proportions in which they exist in cryolite) the resistance increased very materially, from which he concluded that pure aluminium fluoride is not an electrolyte (p. 283). Further, Mr. Hall has found that when making a bath of 278 ALUMINIUM. Aluminium fluoride ....... 67 Sodium fluoride . 33 100 it was hardly possible to pass a current through it, but on adding alumina the latter dissolved in the bath and was easily decora- posed by a current of low tension; however, as soon as the alumina was exhausted, the resistance rose quickly. It seems probable that sodium chloride, in Bernard's process, is the chief electrolyte, or else its combination with aluminium fluoride in certain proportions, but that the aluminium fluoride is the electro- lyte is hardly probable. Messrs. Bernard exhibited at the recent Paris Exposition a collection of articles made of their metal, such as round tubes, medals, keys, opera-glasses, ingots, etc., for which they received the same reward as the other exhibitors of aluminium a gold medal. Feldman's Method (1887). A. Feldman, of Linden, Hannover, patented the following electrolytic process : * A double fluoride of aluminium and an alkaline earth metal, mixed with an excess of a chloride of the latter group, is either electrolyzed or reduced by sodium. The proportions of these substances to be used are such as take place in the following reactions : 1. (Al 2 F 6 +2SrF 2 )+6SrCl 2 = 2Al+5SrF 2 -f3SrCl 2 +6Cl. 2. (Al 2 F-f 2SrF a )+6SrCl 2 -f6Na= 2Al+5SrF 2 +3SrCl 2 +6IS T aCl. The three equivalents of strontium chloride are found in practice to be most suitable. Potassium chloride may also be added to increase the fluidity, but in this case the strontium chloride must be in still greater excess. Even if the above reactions and transpositions do take place, the use of so much costly strontium salts would appear to render the process uneconomical. * English Patent, No. 12575, Sept. 16, 1887. REDUCTION BY THE USE OF ELECTRICITY. 279 Warren's Experiments (1887). Mr. H. Warren, of the Everton Research Labofatory, has outlined the following methods or suggestions, some of which had already been carried out, and probably others have since given useful ideas to workers in this line. The principle can hardly be called new, since suggestions almost identical with Mr. Warren's were made previously to his, but the latter's results are the first recorded in this particular direction :* " This method of preparing alloys differs only slightly from the manner in which amalgams of different metals are prepared, substituting for mercury the metals iron, copper, or zinc made liquid by heat. These metals are melted, connected with the negative pole of a battery, and the positive pole immersed in a bath of molten salt floating on top of the melted metal. The apparatus used is a deep, conical crucible, through the bottom of which is inserted a graphite rod, projecting about one inch within, the part outside being protected by an iron tube coated with borax. As an ex- ample of the method, to prepare silicon bronze-copper is melted in the crucible, a bath of potassium silico-fluoride is fused on top to a depth of about two inches. A thick platinum wire dips into this salt, and on passing the electric current an instantaneous action is seen, dense white vapors are evolved and all the silicon, as it is produced, unites with the copper, forming a brittle alloy. Cryo- lite may be decomposed in like manner if melted over zinc, form- ing an alloy of zinc and aluminium from which the zinc can be distilled leaving pure aluminium." Mr. Warren does not affirm that he has actually performed the decomposition of cryolite in the way recommended, but states that it may be done ; from which we would infer that he simply supposed it could. A well-recorded experiment, then, is needed to establish the truth of this statement. Neither does he propose to make aluminium bronze in this way; it may be that it was attempted and did not succeed, for Hampe states that an experi- ment thus conducted did not furnish him aluminium bronze (p. 283). * Chemical News, Oct. 7, 1887. 280 ALUMINIUM. BognsWs Patent. J. Bognski,* of Warsaw, Russia, appears to have patented the above principle in 1884, for in his patent he states that the metal to be alloyed with aluminium is melted in a crucible, covered with a fusible compound of aluminium for a flux (alumina and potassium carbonate may be used) and made the negative pole of an electric current, the positive pole being a carbon rod dipping in the flux. Grabau's Apparatus. Ludwig Grabau,f of Hanover, Germany, proposes to electro- lyze a molten bath of cryolite mixed with sodium chloride. The features of the apparatus used are an iron pot, in which the bath is melted, and water-cooled cylinders surrounding both electrodes, the jacket surrounding the negative one having a bottom, the other not. The object of these cylinders is, at the positive elec- trode, to keep the liberated fluorine from attacking the iron pot and so contaminating the bath, at the other pole the liberated aluminium is kept from dropping to the bottom of the pot, where it might take up iron, and can be removed from the bath by simply lifting out the water-cooled cylinders and carbon electrode. Mr. Grabau states that he has abandoned this process because the inseparable impurities in the cryolite produced impurities in the metal ; it may be that with the pure artificial cryolite, which he makes by his other processes (see p. 139), this electrolytic process may again be taken up. Rogers' Process (1887). In July, 1887, the American Aluminium Company, of Mil- waukee, was incorporated, with a capital stock of $1,000,000, for the purpose of extracting aluminium by methods devised by Prof. A. J. Rogers, a professor of chemistry in that city. This gentleman had been working at the subject for three or four * English Patent 3090, Feb. 11, 1884. f German Patent (D. R. P.), No. 45012. REDUCTION BY THE USE OF ELECTRICITY. 281 years previous to that time, but it has not been until quite recently that patents have been applied for, and they are still pending. The principle made use of has already been suggested in con- nection with the production of sodium (p. 183). It is briefly, that if molten sodium chloride is electrolyzed using a molten lead cathode, a lead-sodium alloy is produced. This alloy is capable of reacting on molten cryolite, setting free aluminium, which does not combine with the lead remaining because of its small affinity for that metal. If, then, cryolite is placed in the bath with the sodium chloride, the two reactions take place at once, and alu- minium is produced. In the early part of 1888, the company erected a small experimental plant, with a ten horse-power engine, with which the following experiments, among many others, were made : *1. A current of 60 to 80 amperes was passed for several hours through a bath of cryolite melted in a crucible lined with alu- mina, and using carbon rods 2J inches in diameter as electrodes, one dipping into the bath from above, the other passing through the bottom of the crucible into the bath. Only 1 or 2 grammes of aluminium were obtained, showing that the separated metal was almost all redissolved or reunited with fluorine. With the temperature very high, it was found that sodium passed away from the bath without reducing the cryolite. . 2. A current averaging 54 amperes and 10 volts was passed for five and a half hours through a mixture of 1 part cryolite and 5 parts sodium chloride placed in a crucible with 370 grammes of molten lead in the bottom as the cathode. After the experiment, 25 grammes of aluminium were found in globules on top of the lead-sodium alloy. This latter alloy contained some aluminium. The globules were about as pure as ordinary com- mercial aluminium and contained no lead or sodium. From another experiment it was determined that the lead-sodium alloy must first acquire a certain richness in sodium before it will part w r ith any of that metal to perform the reduction of the cryolite. It was also found that a certain temperature was necessary in order that aluminium be produced at all. * Proceedings of the Wisconsin Nat. Hist. Soc., April, 1889. 282 ALUMINIUM. 3. A current of 75 amperes and about 5 volts sufficed to de- compose the bath and to produce 105 grammes of aluminium in seven hours. This would be nearly 30 grammes per hour for each electric horse-power. 4. A current of 80 amperes and 24 volts was passed through four crucibles connected in series for six hours, using a bath of 1 part cryolite and 3 parts sodium chloride with 450 grammes of lead in each crucible. The crucibles were heated regularly to a moderate temperature. There were obtained altogether 250 grammes of quite pure aluminium. This would be equal to 16 grammes per electric horse-power-hour. A large number of similar experiments afforded a return of f to 1 J Ibs. of aluminium per electric horse-power per day. The experimental plant now in operation consists of a 40 volt 100 ampere dynamo, the current being sent through six pots connected in series. When the bath is completely electrolyzed the contents of the crucible are tapped off at the bottom and a fresh supply of melted salt poured in quickly. The lead-sodium alloy run off is put back into the crucibles, thus keeping approximately con- stant in composition and going the rounds continuously. With this apparatus, 3 to 4 Ibs. of aluminium are produced regularly per day of 12 hours. As soon as patents are obtained, it is the in- tention of the company to put up a plant of 50 Ibs. daily capacity which can be easily increased to any extent desired as the business expands. Professor Rogers observes in regard to the apparatus that he has tried various basic linings for his clay crucibles, but a paste of hydrated alumina, well fired, has succeeded best. Some " shrunk" magnesia lining, such as is used in basic steel furnaces, answered well but could not be used because of the amount of iron in it. Lime could not be used, as it fluxed readily. The carbon rods lasted 48 hours without much corrosion if protected from the air during electrolysis. Carbon plates and cylinders were tried, but the solid rods gave the best results. About 8 to 10 per cent of aluminium can be extracted from cryolite containing 12.85 per cent. The mineral used was obtained from the Penn- sylvania Salt Company, and was called pure, but it contained 2 per cent, of silica and 1 per cent, ot iron. These impurities pass KEDUCTION BY THE USE OF ELECTRICITY. 283 largely into the aluminium produced, but the company hope to be able to manufacture an artificial aluminium fluoride which will not only be purer but less costly than this commercial cryolite. Professor Rogers infers that pure aluminium fluoride would not be an electrolyte, since the resistance of the bath increases as the amount of other salts present decreases. It is useless to base any accurate estimation of the cost of alu- minium by this process on the data given above, since they are only for a small experimental plant. If, however, 75 per cent. of the aluminium in cryolite can be extracted at the rate of 1 Ib. of metal per day per electric horse-power, and the metal is free from lead and sodium, (a sample sent me recently is of very fair quality) it would seem that the process is in a fair way to com- pete on an equal footing with the other electrolytic processes which are coming into prominence. Dr. Hampe on the Electrolysis of Cryolite. Prof. W. Hampe, of Clausthal, whose name is a guarantee of careful and exact observations, has written the following valuable information on this subject, in presenting which we will also give the remarks of Dr. O. Schmidt, called forth by Hampe's first article. *"The electrolysis of a bath of cryolite mixed with sodium and potassium chlorides, using a layer of melted copper in the bottom of the crucible as cathode and a carbon rod as anode, gave balls of melted sodium which floated on the surface and. burnt, but scarcely a trace of aluminium. Yet here the conditions were most favorable to the production of the bronze. The battery used consisted of twelve large zinc-iron elements." fDr. O. Schmidt, referring to this statement of Hampers, quotes an opposite experience. He fused cryolite and sodium chloride together in a well-brasqued crucible in the proportions indicated by the reaction Al'F'.GNaF + 6NaCl = APC1 6 + 12NaF. At a clear red-heat the bath becomes perfectly fluid and trans- parent, and an anode of gas carbon and a cathode of sheet copper Chemiker Zeitung, xii. 391 (1888). f ^em, xii. 457 (1888). 284 ALUMINIUM. are introduced. On passing the current the copper did not melt but became covered with a film of deposited aluminium, which in part penetrated the electrode and in part adhered to the surface as a rich alloy which utimately fused off and sank to the bottom of the crucible. With a plate 1 to 1J millimetres thick, 10 per cent, of its weight of aluminium could thus be deposited ; with one 3 millimetres thick, about 5 per cent. The metal could be made perfectly homogeneous by subsequent fusion in a graphite crucible. Dr. Schmidt further remarks (evidently on the sup- position that the reaction he gives actually takes place) that on thermo-chemical grounds sodium would not here be reduced, be- cause while the molecule of sodium chloride requires 97.3 calories APC1 6 for its decomposition, that of aluminium chloride, , requires 2> only 80.4, and the current would attack first the most easily de- composed. He also states that the calculated difference of poten- tial for the dissociation of aluminium chloride, which is L- = 2i& 3.5 volts, was actually observed, and the tension of the current must have been increased to about 4.5 volts to bring about the decomposition of the sodium chloride.* Dr. Hampers statement occasioned several other communica- tions, which he considers and replies to in the following arti- cle : f * Aside from Hampe's subsequent remarks as to no aluminium chloride being formed, we would further point out the fact that the decomposition of a chemically equivalent quantity of aluminium chloride requires not -1~ = 2 00*1 f?O(\ 80.4 calories, but ! or 53.6 calories, and the calculated difference of 6 RO { potential is properly * 1_ or 2.3 volts. The fact that the observed tension 23 was 3.5 volts shows that the current was not strong enough to decompose the sodium chloride, as Schmidt observes, and the fact that this current deposited aluminium would show that the heat of formation of aluminium fluoride can- iiot be greater than 23 X,3.5 X 6 =483 (thousand) calories, while it is pro- bably much less than this, for the 3.5 volts, besides decomposing the alu- minium compound, were also partly expended in overcoming resistances, as explained on p. 248. f Chemiker Zeitung (Cothen) xiii. 29 and 49. REDUCTION BY THE USE OF ELECTRICITY. 285 " Dr. O (whose Dame I withhold at his own request) writes to me that by electrolyzing pure cryolite, using a negative pole of molten copper, he never obtained aluminium bronze ; but, on the other hand, always obtained it if he used the mixture of cryolite and sodium chloride mentioned by Dr. Schmidt, and in place of the molten copper a thick stick of the unfused metal. A letter from R. Gratzel, Hannover, contains a similar confirmation of the latter observation. By electrolyzing a mixture of 100 parts cryo- lite with 150 of sodium chloride in a graphite crucible holding 30 kilogrammes, aluminium bronze dripped down from the ring- shaped copper cathode used, while chlorine was freely disengaged at the carbon anode. But after a time, long before the complete decomposition of the cryolite, the formation of bronze stopped- even an attacking of that already formed sometimes taking place. Pellets of an alloy of sodium and aluminium appear on the sur- face and burn with a white light. " These comments excited me to further research in the matter. At first, it was necessary to consider or prove whether by melting sodium chloride with cryolite a true chemical decomposition took place, such as Dr. Schmidt supposed. If this were the case, the very volatile aluminium chloride must necessarily be mostly driven off on melting the mixture, and at a temperature of 700 to 1000 C. there could not be any left in it. But an experiment in a platinum retort showed that such a reaction positively does not occur ; for neither was any aluminium chloride volatilized nor did the residue contain any, for on treatment with water it gave up no trace of a soluble aluminium compound. During the melting of the mixture acid vapors proceeded from the retort, and a small quantity of cryolite was volatilized into the neck of the retort. Dr. Klochman has shown that cryolite always contains quartz, even colorless, transparent pieces which to the naked eye appear perfectly homogeneous showing it when examined in thin sections under the microscope, and on melting the mineral opportunity is given for the following reactions : SiO 2 4- 4NaF= SiF 4 + 2Na 2 O, 3Na 2 O + A1 2 F 6 = 6NaF + A1 2 O 3 , as is rendered probable by the appearance of delicate crystals of alumina on the inner surface of the retort just above the fusion. 286 ALUMINIUM. The silicon fluoride probably passes away as silico-fluoride ol sodium. " If cryolite is fused with such metallic chlorides that really do bring about a decomposition, there is never any aluminium chlor- ide formed in these cases, but the sodium of the cryolite is ex- changed for the other metal. Dr. O , to whom I owe this observation, fused cryolite with calcium chloride, hoping that aluminium chloride would distil, but obtained instead crystals of the calcium salt of alumino-fluoric acid ; thus, ISa'APF 12 + 3CaCl 2 = 6NaCl + Ca 3 Al 2 F 12 , and in like manner can be obtained the analogous strontium or barium compounds. " Just as erroneous as the supposed production of aluminium chloride are the other arguments advanced by Dr. Schmidt, re- garding the reasons why sodium could not be set free. The self- evident premises for the propositions are lacking, viz : that the two bodies compared are conductors. On the contrary, I have previously shown* that aluminium chloride and bromide and more certainly its fluoride belong to the non-conductors. It fol- lows, then, that there can remain no doubt that on electrolyzing pure cryolite, or a mixture of it with sodium chloride, only sodium will be set free at first, either from sodium fluoride or the more easily decomposable sodium chloride. The presence or absence of sodium chloride is consequently, chemically, without signifi- cance. " Since the experiments with solid cathodes gave aluminium, while those with molten copper did not, these results being inde- pendent of the presence or absence of sodium chloride, the next attempt made was to seek for the cause of the diiferent re- sults in the differences of temperature. It was found that when the electrolysis takes place at a temperature about the melting point of. copper, bubbles of sodium vapor rise and burn, and any aluminium set free is so finely divided that it is attacked and dis- solved by the cryolite. To explain this action of the cryolite it is necessary to admit the formation of a lower fluoride of aluminium * Chemiker Zeitung (Cothen) xi. p. 934 (1887). REDUCTION BY THE USE OF ELECTRICITY. 287 and sodium, such as I have recently proven the existence of.* The solution of the aluminium takes place according to the fol- lowing reaction APF 6 .6NaF -f Al= 3(AlF 2 .2NaF.) If the electrolysis takes place at a temperature so low that the sodium separates out as a liquid (its volatilizing point is about 900), large globules of aluminium will be produced on which the cryolite seems to exert no appreciable action. Nevertheless, the yield of aluminium is much below the theoretical quantity set free. Since pure copper melts at 1050, and aluminium bronze at 800, the copper electrodes can remain unfused in the bath while the bronze melts off as it forms, while the temperature can be low enough to keep the sodium in the liquid state. By mixing sodium or potassium chlorides with the cryolite, the melting point is lowered, or at a given temperature the bath is more fluid and so, easier to work. When there is not enough aluminium fluoride present in the bath to utilize all the sodium liberated, the excess of sodium may form an alloy with some aluminium, and rising to the surface, burn to waste. Since cryolite always contains silica, as previously explained, the bronze thus obtained is always ren- dered hard with silicon, and is not of much value commercially/ 7 Winkler's Patent. fAugust Winkler, of Gorlitz, proposes to electrolyze a fusible phosphate or borate of aluminium. This bath is made by melt- ing alumina or kaolin with phosphoric or boracic acid, the pro- portions being such that the acid is saturated ; the separation of aluminium will not be hindered if alumina is added continually to combine with the acid set free. Carbon electrodes are used. * Chem. Zeit. (Cothen) xiii. p. 1 (1889). Hampe melted together alumin- ium and sodium fluorides in the proportions of one molecule of the first to four of the second, and obtained what is apparently a lower fluoride than cryo- lite, in which aluminium cannot be otherwise than diatomic, since analysis gives it the formula AlF a .2NaP. This salt is similar in appearance and prop- erties to cryolite. As there are still some doubts, however, about this com- pound, the above explanation of the solution of aluminium by the cryolite need not be accepted as final. f- German Patent, 45824, May 15, 1888. 288 ALUMINIUM. Faure's Proposition. Camille A. Faure, whose process of making aluminium chlor- ide is described on p. 1 34, proposes to obtain the metal therefrom by electrolysis, using carbon electrodes. M. Faure states that if the process is carried out on a large scale the chlorine set free can be utilized to form bleaching powder, and will thus nearly repay the whole cost of manufacturing the aluminium. Patents have been applied for covering the details of the electrolytic apparatus, but have not yet been granted. The inventor states, however, that he has determined on a large scale that anhydrous, molten aluminium chloride can be practically decomposed at 300 by an electro-motive force of 5 volts, which comprises the force re- quired for actual decomposition and also that required to over- come the resistance of the bath. While, therefore, the reduction of 1 kilo of aluminium per hour theoretically requires a minimum expenditure of 9.2 electric horse-power, the actual resistance of 5 volts would increase this requirement to 20 horse-power or 9 horse-power per Ib. produced per hour. Therefore, if each bath could be decomposed by 5 volts, the production of 2000 Ibs. of aluminium in 20 hours would require the use of a 920 horse- power current, and could not be possibly achieved by a 400 horse- power dynamo, as calculated by M. Faure. Hairs Process (1889). Mr. Chas. M. Hall, a graduate of Oberlin College, has, since 1885, experimented with electrolytic aluminium processes, and has finally attained such success that a company has been formed to work by his methods. The Pittsburgh Reduction Company was organized about the middle of 1888, and since March, 1889, have had their metal on the market. They are located on Fifth Ave- nue, Pittsburgh, Pa. The plant is at present equal to a produc- tion of about 300 Ibs. of aluminium a week, and their metal is quoted at $2 per Ib. Contracts have recently been given out for the erection of a plant of 2500 Ibs. weekly capacity ; a plant of the same size is also being erected at Patricroft, Lane., England. *Mr. Hall claims the process of dissolving alumina in a fluid * U. S. Patents, 400664 to 400667, and 400766, April 2, 1889. REDUCTION BY THE USE OF ELECTRICITY. 289 bath composed of aluminium fluoride and potassium fluoride, or with also the addition of lithium fluoride, then electrolyzing this bath using an anode of non-carbonaceous material. The bath is formed by fusing a mixture of the required fluorides in certain proportions; thus, 169 parts of aluminium fluoride and 116 parts of potassium fluoride form proportions corresponding to the formula A1 2 F 6 .2KF. A slight variation from these proportions affects the process but little, but it is observed that a larger pro- portion of potassium fluoride increases the capacity of the bath for dissolving alumina, while a larger proportion of aluminium fluoride renders the bath more fusible but decreases the amount of alumina it can dissolve. However, the bath is rendered more fusible and its capacity for dissolving alumina increased also, if lithium fluoride is added to the above mixture or substituted for part of the potassium fluoride. Thus, the combinations in proportions represented by the formulae Al 2 F 6 .KF.LiF and 2Al 2 F 6 .3KF.3LiF are useful in both respects. These materials may be conveniently prepared by saturating aluminium hydrate and carbonates of potassium and lithium, mixed in the proportion required, with hydrofluoric acid. In electrolyzing the bath, the negative electrode is to be of carbon or a metal coated with carbon and the positive electrode of copper, platinum, or other suitable non-carbonaceous material. When of copper, it soon becomes coated with oxide of copper, which is a conductor at a red heat, and therefore does not affect the passage of the currenij, while it forms a protecting cover over all the surface of the anode and prevents further oxidation, the oxygen thereafter escaping at this electrode in a free state. The containing vessel is of metal pro- tected by a carbon lining, which is preferably made the negative electrode. A low red heat is sufficient for carrying on the opera- tion, and on account of the liability of reducing the solvent a current of low electro-motive force is used. In the second patent, Hall claims the use of a bath composed of alumina dissolved in compound fluorides of aluminium with alkaline-earth metals, such as in proportions varying from Al 2 - F 6 .CaF 2 to Al 2 F 6 .3CaF 2 . Since this bath is of higher specific gravity than aluminium, that metal would rise to the surface and there be subject to loss by oxidation ; to remedy which a quan- 19 290 ALUMINIUM. tity of the salt represented by A1 2 F 6 .2KF may be added suffi- cient to lower the specific gravity of the bath below that of alu- minium.* If it is desired to produce alloys, the metal to be alloyed may be made the negative electrode, in which case the addition of A1 2 F 6 .2KF is unnecessary, because the alloy will be sufficiently heavy to sink. For making alloys the barium com- pound is especially recommended, for its high specific gravity is of no inconvenience, and it is more fusible than the compounds of calcium and strontium. These double fluorides are said not to be subject to a decrease in efficiency such as occurs with the double fluoride of potassium and aluminium when used alone. In a third patent, the use of a bath formed of fluorides of cal- cium, sodium and aluminium, in which alumina is dissolved, is claimed ; these materials being obtained by melting together cryolite, aluminium fluoride and fluorspar in the proportions represented by the formula Al 2 F 6 .61SraF + Al 2 F 6 .CaF 2 . This bath is said not to become so readily clogged as the previous ones ; but when it does become so it is cleared by the addition of three or four per cent, of calcium chloride, and this device is said to permit the use of a carbon anode without the bath being affected by its disintegration. The plant now being operated in Pittsburgh consists of a 50 horse-power engine drwing two dynamos connected in parallel, the current produced varying from 1 6 to 25 volts in tension and 1700 to 1800 amperes in quantity. TAVO reducing pots are used, coupled in series. Each pot is of cast-iron lined with car- bon, the lining forming the negative electrode, while a number (6 to 10) of three-inch carbon cylinders are suspended in the bath and form the positive electrode. Each pot holds 200 to 300 pounds of the electrolyte, its dimensions being 24 inches long, 16 inches wide and 20 inches deep. These vessels are not heated from outside, as was done in the early stages of the process when a current of only 4 to 6 volts tension was employed, but the dis- * A specimen of the salt represented by the formula A1 2 F 6 .2KF was sent the author, who found its specific gravity to be 2.35. I should infer from analogy that its specific gravity when molten would be much less, probably not much over 2, since solid cryolite has a specific gravity of 2.9, and yet, when molten, a piece of aluminium of gravity 2.6 will sink beneath it. REDUCTION BY THE USE OF ELECTRICITY. 291 tance between the electrodes is now increased until the electro- motive force absorbed in each bath is 8 to 12 volts, and enough heat is thus generated by this resistance to keep the bath at the necessary temperature. The bath at present employed for pro- ducing pure aluminium is the last one described, and the tempera- ture is continuously kept very near to the melting point of brass, sometimes it is hot enough to melt copper, but the high tempera- ture is not a disadvantage since the bath is more efficient i e., conducts better and collects the aluminium better the hotter it is, within certain limits. During the operation, alumina (obtained by calcining pure aluminium hydrate) is fed in small quantities of 5 to 10 pounds as required. The exhaustion of the alumina in the bath is immediately shown by a rise in the resistance, so that the current can hardly be made to pass at all. Mr. Hall has estimated that when the bath is saturated with alumina its conducting power is at least 200 times that of copper sulphate solution. In an experiment which he made, a copper anode of about 30 to 40 square inches area transmitted as high as 150 amperes with an electro-motive force less than 3J volts. Only the dissolved alumina is decomposed by the current, for the fluoride solvents waste only very slightly and require replenishing to the extent of a small fraction of the weight of metal made ; and as these materials cost only about 7 cents a pound, their waste forms a very small item of expense. An accurate account of the amount of calcined alumina used shows that a fraction over 50 per cent, of aluminium is extracted from it (theoretically pure alumina contains 52.94 per cent.). It is thus seen that the process is able to extract nearly all the aluminium from commercial alu- mina in one direct operation. When it is desired to form bronze, a bath of different composition is used, as before mentioned, and both electrodes are of copper. On working at a temperature just below that of melting copper, the anode remains undissolved and practically unattacked, while the bronze formed at the cathode drips down melted to the bottom of the vessel. In either case the metal is allowed to collect in the pots for one or two days, and is then ladled out with cast-iron ladles, taking the metal from the bottom as one might dip water out from under oil. The pro- duction is about one pound of aluminium an hour from each pot, 292 ALUMINIUM. and the operations are kept up without stopping for several weeks at a time. The metal produced has varied from 94 to over 98 per cent. pure. Three analyses by Mr. Hall have given i. ii. irr. Aluminium .... 94.16 95.93 98.34 Silicon 4.36 2.01 1.34 Iron 1.48 2.06 0.32 The metal being made at present averages over 97 per cent., and a specimen kindly sent the author compares favorably with other commercial brands. A specimen sent me at an early stage of the process contained copper, probably from the copper anodes, but this has since been avoided by discontinuing the use of copper anodes in making the pure aluminium. The essential features of Mr. HalFs process have been ante- dated ; the principle of dissolving alumina in a fluid bath, and electrolyzing it without decomposing the solvent, is the matter of Henderson's patent issued in 1887, and Bernard Bros, claim the use of a copper anode in their patent of the same year (pp. 273 and 274). It is only just to Mr. Hall, however, to observe that his patent applications were dated in 1886, and that the use of these principles is clearly original with him. If we seek to find the efficiency of the process, basing our calculations on the data given, we reach the following results : The current is said to average 1700 amperes and 20 volts, being 10 volts to each pot. A cur- rent of this size would represent or a little over 45 elec- tric horse-power, which would need about a fifty horse-power engine to drive the dynamos. If the energy of this current could be entirely utilized for dissociating alumina into aluminium and 1700 x 20 x 0.00024 oxygen, it would be able to produce - _ = 11 grammes per second, or 4 kilos per hour. Since the output is stated as 1 Ib. per hour for each pot, the production of aluminium 2 represents or nearly one-quarter of the energy of the current, 8.8 which it is almost needless to observe, is a high efficiency in this kind of work. Further, a current of 1700 amperes passing * REDUCTION BY THE USE OF ELECTKICITY. 293 through two pots will set free 0.00009135x1700x60x60x2 = 1008 grammes of aluminium per hour, or about 1 kilogramme. 2 This shows that - - or 91 per cent, of the aluminium set free is practically obtained and weighed, the other 9 per cent, being re- dissolved or otherwise lost. Since we have calculated that the decomposition of alumina requires an electro-motive force of 2.8 volts, the fact that something like 10 volts is required for each bath would show that about 7.2 volts, or 72 per cent, of the energy of the current is absorbed in other resistances, being prin- cipally converted into heat, and thus keeping the bath in fusion. As to the probable cost of aluminium by this process, I have no official figures to present, but an approximate idea can easily be estimated from the data given. Pure hydrated alumina should not cost over 3 cents per lb., and since it contains about one-third water, the alumina produced costs 4 J cents, with the cost of cal- cination to be added, which should not be over 1 J cents per lb. The bath wastes very little, let us suppose 15 per cent, of the weight of aluminium produced. The cost of power, number of men, etc., will have to be guessed at. We might then put down for twenty-four hours 7 work 100 Ibs. calcined alumina (a) 6 cts. fluorides for bath @ 7 cts. carbons .... 50 horse-power engine 2 engineers @ $3.00 per diem . 6 workmen (oj $2.00 " Superintendence, office expenses, etc. Interest on plant, rent, etc. Cost of about 50 Ibs. of aluminium . . . $50.00 "When the large plant now being erected is in operation, the cost of aluminium by this process will not exceed $0.50 per lb. Cowles Bros.' Process. Messrs. E. H. and A. H. Cowles patented in the United States and Europe* an electric furnace and its application for producing * U. S. Patents 324658, 324659, Aug. 18, 1885 ; English Patent 9781, same date ; German Patent, 33672. 294 ALUMINIUM. aluminium. Their patent claims " reducing an aluminium com- pound in company with a metal in presence of carbon in a fur- nace heated by electricity; the alloy of aluminium and the metal formed being further treated to separate out the aluminium." The history of the development of this process has already been sketched, we will proceed to describe the details of its operation. The first public description was given in two papers, one read before the American Association for the Advancement of Science* by Prof. Chas. F. Mabery, of the Case School of Applied Science, Cleveland, the other before the American Institute of Mining Engineersf by Dr. T. Sterry Hunt, of Montreal. Prof. Mabery said in his paper : " Some time since, the Messrs. Cowles conceived the idea of obtaining a continuous high tem- perature on an extended scale by introducing into the path of an electric current some material that would afford the requisite resistance, thereby producing a corresponding increase in the tem- perature. After numerous experiments, coarsely pulverized car- bon was selected as the best means for maintaining an invariable resistance, and at the same time as the most available substance for the reduction of oxides. When this material mixed with the oxide to be reduced was made a part of the electric circuit, in- closed in a fire-clay retort, and subjected to the action of a current from a powerful dynamo, not only was the oxide reduced, but the temperature increased to such an extent that the whole interior of the retort fused completely. In other experiments lumps of lime, sand, and corundum were fused, with a reduction of the corre- sponding metal ; on cooling, the lime formed large, well-defined crystals, the corundum beautiful red -green and blue octahedral crystals. Following up these results, it was soon found that tlie intense heat thus produced could be utilized for the reduction of oxides in large quantities, and experiments were next tried on a large scale with the current from a fifty horse-power dynamo. For the protection of the walls of the furnace, which were of fire-brick, a mixture of ore and coarsely pulverized gas-carbon was made a cen- tral core, and was surrounded on the side and bottom by fine char- * Ann Arbor Meeting, Aug. 28, 1885. f Halifax Meeting, Sept. 16, 1885. REDUCTION BY THE USE OF ELECTRICITY. 295 coal, the current following the lesser resistance of the core from carbon electrodes inserted in the ends of the furnace in contact with the core. The furnace was charged by first filling it with charcoal, making a trough in the centre, and filling this with the ore mixture, the whole being covered with a layer of coarse char- coal. The furnace was closed on top with fire-brick slabs con- taining two or three holes for the escape of the gaseous products of the reduction, and the whole furnace was made air tight by luting with fire-clay. Within a few minutes after starting the dynamo, a stream of carbonic oxide issued through the openings, burning usually with a flame eighteen inches high. The time required for complete reduction was ordinarily about an hour. Experience has already shown that aluminium, silicon, boron, manganese, sodium, and potassium can be reduced from their oxides with ease. In fact, there is no oxide that can withstand the temperature attainable in this furnace. Charcoal is changed to graphite ; does this indicate fusion ? As to what can be accom- plished by converting enormous electrical energy into heat within narrow limits, it can only be said that it opens the way into an extensive field of pure and applied chemistry. It is not difficult to conceive of temperature limited only by the power of carbon to resist fusion. " Since the motive power is the chief expense in accomplishing reductions by this method, its commercial success is closely con- nected with obtaining power cheaply. Realizing the importance of this point, Messrs. Cowles have purchased at Lockport, N. Y., a water power where they can utilize 1200 horse-power. An important feature in the use of these furnaces from a commercial standpoint is the slight technical skill required in their manipula- tion. The four furnaces operated in the experimental laboratory at Cleveland are in charge of two young men, who six months ago knew absolutely nothing of electricity. The products at present manufactured are the various grades of aluminium bronze, made from a rich furnace product obtained by adding copper to the charge of ore. Aluminium silver is also made ; and a boron bronze may be prepared by the reduction of boracic acid in con- tact with copper, while silicon bronze is made by reducing silica in contact with copper. As commercial results may be mentioned 296 ALUMINIUM. the production in the experimental laboratory, which averages 50 Ibs. of 10 per cent, aluminium bronze daily, which can be supplied to the trade in large quantities on the basis of $5 per Ib. for the aluminium contained, the lowest market quotation of alu- minium being now $15 per Ib." Dr. Hunt stated further that if the mixture consisted of alu- mina and carbon only, the reduced metal volatilized, part escaping into the air and burning to alumina, part condensing in the upper layer of charcoal, affording thus crystalline masses of nearly pure aluminium and yellow crystals supposed to be a compound of aluminium with carbon. Great loss was met in collecting this divided metal into an ingot, so that only small quantities were really obtained. To gather all the aluminium together, a metal such as copper was added, thus producing an alloy with 15 to 20 per cent, of aluminium ; on substituting this alloy for pure copper in another operation, an alloy with over 30 per cent, of alumin- ium was obtained. Dr. Hunt, in a later paper,* stated that pure aluminium has been obtained in this process by first producing in the furnace an alloy of aluminium and tin, then melting this with lead, when the latter takes up the tin and sinks with it beneath the aluminium. He also stated that in the early experiments a dynamo driven by a 30 horse-power engine yielded a daily output of 50 Ibs. of 10 per cent, aluminium bronze, but with a larger machine the output was proportionately much greater. In the latest practice, one-half cent per horse-power per hour is said to cover the expense of working, making the 10 per cent, bronze cost about 5 cents per Ib. over the copper used. Various shapes of furnaces have been used by the Cowles Bros., the first described being a rectangular box, lined with carbon, with the electrodes passing through the ends. Although two other forms have been patented, we understand that the kind now used, and which is described at length in Mr. Thompson's paper, is also of the oblong, horizontal style. Chas. S. Bradley and Francis B. Crocker, of New York, patented and assigned to the * National Academy of Science, Washington Meeting, April 30, ]886. REDUCTION BY THE USE OF ELECTRICITY. 297 Cowles Electric Smelting Company,* the use of a retort, composed of conducting material, surrounded by a substance which is a poor conductor of heat, and having inside a mixture of charcoal and the ore to be heated. Electric connection being made with the ends of the retort, the walls of the retort and the material in it are included in the circuit and constitute the greater part of the resistance. The retort may be stoppered at each end during the operation, and the heating thus performed in a reducing atmos- phere. Mr. A. H. Cowles devised a style of furnace adapted for continuous working and utilizing the full current of a dynamo of the largest size.f The electrodes are tube-shaped and placed vertically. The positive pole is above, and is surmounted by a funnel in which the mixture for reduction is placed. The regular delivery of the mixture is facilitated by a carbon rod, passing through the cover of the funnel, which is serrated on the end and can be worked up and down. The melted alloy pro- duced, with any slag, passes down through the negative electrode. The distance between the poles can be regulated by moving the upper one, and the whole is inclosed in a fire-brick chamber. The space between the electrodes and the walls is filled with an isolating material, which is compact around the lower electrode but coarse grained around the upper to facilitate the escape of the gases produced. The chamber is tightly closed excepting a small tube for the escape of gas. A very complete description of the Cowles process was given by Mr. W. P. Thompson (agent for the Cowles Co. in England) in a paper read before the Liverpool Section of the Society of Chemical Industry. J He describes the process as then carried on in Lockport; the dynamo used being a large Brush machine weighing 2J tons and consuming about 100 horse-power in being driven at 900 revolutions per minute. " Conduction of the current of the large dynamo to the furnace and back is accomplished by a complete metallic circuit, except where it is broken by the interposition of the carbon electrodes * U. S. Patent 335499, Feb. 2, 1886. f English Patent 4664 (1887). t Journal of the Society of Chemical Industry, April 29, 1886. 298 ALUMINIUM. and the mass of pulverized carbon in which the reduction takes place. The circuit is of 13 copper wires, each 0.3 inch in diame- ter. There is likewise in the circuit an ampere meter, or am- meter, through whose helix the whole current flows, indicating the total strength of the current being used. This is an impor- tant element in the management of the furnace, for, by the posi- tion of the finger on the dial, the furnace attendant can tell to a nicety what is being done by the current in the furnace. Be- tween the ammeter and the furnace is a resistance coil of German silver kept in water, throwing more or less resistance into the circuit as desired. This is a safety appliance used in changing the current from one furnace to another, or to choke off the cur- rent before breaking it by a switch. " The furnace (see Figs. 25, 26, 27) is simply a rectangular box, A, one foot wide, five feet long inside, and fifteen inches deep, made of firebrick. From the opposite ends through the pipes BB the two electrodes (7(7 pass. The electrodes are im- mense electric-light carbons three inches in diameter and thirty inches long. If larger electrodes are required, a series this size must be used instead, as so far all attempts to make larger car- bons that will not disintegrate on becoming incandescent have failed. The ends of the carbons are placed within a few inches of each other in the middle of the furnace, and the resistance coil and ammeter are placed in the circuit. The ammeter registers 50 to 2000 amperes. These connections made, the furnace is ready for charging. " The walls of the furnace must first be protected, or the in- tense heat would melt the fire brick. The question arose, what would be the best substance to line the walls ? Finely powdered charcoal is a poor conductor of electricity, is considered infusible and the best non-conductor of heat of all solids. From these properties it would seem the best material. As long as air is ex-? eluded it will not burn. But it is found that after using pure charcoal a few times it becomes valueless ; it retains its woody structure, as is shown in larger pieces, but is changed to graphite, a good conductor of electricity, and thereby tends to diffuse the current through the lining, heating it and the walls. The fine charcoal is therefore washed in a solution of lime-water, and after REDUCTION BY THE USE OF ELECTRICITY. 299 drying, each particle is insulated by a fine coating of lime. The bottom of the furnace is now filled with this lining about two or three inches deep. A sheet-iron gauge is then placed along the sides of the electrodes, leaving about two inches between them. Fig. 25. Longitudinal section.. Fig. 27. Transverse section. and the side walls, in which space more of the charcoal is placed. The charge E, consisting of about 25 pounds of alumina, in its native form as corundum, 12 pounds of charcoal and carbon, and 50 pounds of granulated copper, is now placed within the gauge and spread around the electrodes to within a foot of each end of 300 ALUMINIUM. the furnace. For making iron alloy, where silicon also is not harmful, beauxite or various clays containing iron and silica may be used instead of the pure alumina or corundum. In place of granulated copper, a series of short copper wires or bars can be placed parallel to each other and transverse to the furnace, among the alumina and carbon, it being found that where grains are used they sometimes fuse together in such a way as to short-cir- cuit the current. After this, a bed of charcoal, F, the granules of which vary in size from a chestnut to a hickory, is spread over all, and the gauge drawn out. This coarse bed of charcoal above the charge allows free escape of the carbonic oxide generated in the reduction. The charge being in place, an iron top, 6r, lined with fire brick, is placed over the whole furnace and the crevices luted to prevent access of air. The brick of the walls insulate the cover from the current. " Now that the furnace is charged and the cover luted down, it is started. The ends of the electrodes were in the beginning placed close together, as shown in the longitudinal section, and for this cause the internal resistance of the furnace may be too low for the dynamo, and cause a short circuit. The operator, therefore, puts sufficient resistance into the circuit, and by watch- ing the ammeter and now and then moving one of the electrodes out a trifle, he can prevent undue short circuiting in the begin- ning of the operation. In about ten minutes, the copper between the electrodes has been melted and the latter are moved far enough apart so that the current becomes steady. The current is now increased till 1300 amperes are going through, driven by 50 volts. Carbonic oxide has already commenced to escape through the two orifices in the top, where it burns with a white flame. By slight movements outward of the electrodes during the com- ing five hours, the internal resistance in the furnace is kept con- stant, and at the same time all the different parts of the charge are brought in turn into the zone of reduction. At the close of the run the electrodes are in the position shown in the plan, the furnace is shut down by placing a resistance in the circuit and then the current is switched into another furnace charged in a similar manner. It is found that the product is larger if the carbons are inclined at angles of 30 to the horizontal plane. EEDUCTION BY THE USE OF ELECTEICITY. 301 " This regulating of the furnace by hand is rather costly and unsatisfactory. Several experiments have therefore been tried to make it self-regulating, and on January 26, 1886, a British patent was applied for by Cowles Bros., covering an arrangement for operating the electrodes by means of a shunt circuit, electro- magnet, and vibrating armature. Moreover, if the electrodes were drawn back and exposed to the air in their highly heated state, they would be rapidly wasted away. To obviate this, Messrs. Cowles placed what may be called a stuffing-box around them, consisting of a copper box filled with copper shot. The wires are attached to the boxes instead of the electrodes. The hot electrodes as they emerge from the furnace first encounter the shot, which rapidly carry off the heat, and by the time they emerge from the box they are too cool to be oxidized by contact with the air. " Ninety horse-power have been pumped into the furnace for five hours. At the beginning of the operation the copper first melted in the centre of the furnace. There was no escape for the heat continually generated, and the temperature increased until the refractory corundum melted, and being surrounded on all sides by carbon gave up its oxygen. This oxygen, uniting with the carbon to form carbonic oxide, has generated heat which cer- tainly aids in the process. The copper has had nothing to do with the reaction, as it will take place in its absence. Whether the reaction is due to the intense heat or to electric action it is difficult to say. If it be electric, it is Messrs. Cowles 7 impres- sion that we have here a case where electrolysis can be accom- plished by an alternating current, although it has not been tried as yet. Were the copper absent, the aluminium set free would now absorb carbon and become a yellow, crystalline carbide of aluminium ; but, instead of that, the copper has become a boiling, seething mass, and the bubblings of its vapors may distinctly be heard. The vapors probably rise an inch or two, condense and fall back, carrying with them the freed aluminium. This con- tinues till the current is taken off the furnace, when we have the copper charged with 15 to 30 per cent., and in some cases as high as 40 per cent, of its weight of aluminium, and a little silicon. After cooling the furnace this rich alloy is removed. A valuable 302 ALUMINIUM. property of the fine charcoal is that the metal does not spread and run through its interstices, but remains as a liquid mass sur- rounded below and on the sides by fine charcoal, which sustains it just as flour or other fine dust will sustain drops of water for considerable periods, without allowing them to sink in. The alloy is white and brittle. This metal is then melted in an ordin- ary crucible furnace, poured into large ingots, the amount of aluminium in it determined by analysis, again melted, and the requisite amount of copper added to make the bronze desired. " Two runs produce in ten hours' average work 100 pounds of white metal, from which it is estimated that Cowles Bros., at Lockport, are producing aluminium in its alloys at a cost of about 40 cents per Ib. The Cowles Company will shortly have 1200 horse-power furnaces. With a larger furnace, there is no reason why it should not be made to run continuously like the ordinary blast furnace. " In place of the copper any non- volatile metal may be used as a condenser to unite with any metal it may be desired to reduce, provided, of course, that the two metals are of such a nature that they will unite at this high temperature. In this way aluminium may be alloyed with iron, nickel, silver, tin, or cobalt. Messrs. Cowles have made alloys containing 50 aluminium to 50 of iron, 30 aluminium to 70 of copper, and 25 aluminium to 75 of nickel. Silicon or boron or other rare metals may be combined in the same way, or tertiary alloys may be produced ; as, for instance, where fire-clay is reduced in presence of copper we obtain an alloy of aluminium, silicon, and .copper." Soon after Mr. Thompson's description, the plant at Lockport was increased by the addition of the largest dynamo yet con- structed, built by the Brush Electric Company, and dubbed the "Colossus." This machine weighs almost ten tons, and when driven at 423 revolutions per minute, with 68 volts resistance in the external circuit, it produced a useful current of 3400 amperes, or at 405 revolutions produced a current of 3200 amperes with 83 volts electro-motive force, indicating 249000 Watts or 334 electric horse-power. The steam engine was, in the latter case, developing nearly 400 horse-power, and could not supply more; it was judged that the dynamo could have been driven to 300,000 REDUCTION BY THE USE OF ELECTRICITY. 303 Watts with safety. The first run with this machine was made in September, 1886. The furnaces used for this current are of the same style as that described by Mr. Thompson, but are larger, the charge being 60 Ibs. of corundum, 60 Ibs. of granulated copper, 30 Ibs. of coarse charcoal besides the pulverized lime-coated char- coal used in packing. The operation of reducing this charge takes about two hours. As soon as the operation is finished the current is switched off into another furnace prepared and charged, so that the dynamo is kept working continuously. In 1888, the Cowles Company had two of these large dynamos in operation and eight furnaces in use. With two-hour runs a furnace is tapped every hour, producing about 80 Ibs. of bronze averaging 18 per cent, of aluminium. The capacity of the plant is, there- fore, about 1 J tons of 10 per cent, bronze per day. Their alloys are now sold on the basis of $2.50 per Ib. for the contained aluminium. The Cowles Syndicate Company, of England, located at Stoke- on-Trent, have set up a large plant at Milton, where, profiting by the experience of the parent concern in America, still larger elec- tric currents are used, these being found more economical. The dynamo in use at this works was built by Crompton, and sup- plies a current of 5000-6000 amperes at 50 to 60 volts. There are two furnace-rooms, each containing six furnaces, aluminium and silicon bronze being produced in one room and ferro-alu- niinium in the other. The furnaces used measure 60 by 20 by 36 inches, inside dimensions. The electrodes used are formed by bundling together 9 carbon rods, each 2 J inches in diameter, each electrode weighing 20 Ibs. More recently larger carbons have been obtained, 3 inches in diameter, and an electrode formed of five of these weighs 36 Ibs. The furnace is charged as pre- viously described. The current is started at 3000 amperes, gradually increasing to 5000 during the first half hour, and then keeping steady until the run is ended, which is about one and a half hours from start- ing. The product of each run is about 100 Ibs. of raw bronze containing 15 to 20 per cent, of aluminium. The return is said to average 1 Ib. of contained aluminium per 18 electric horse- power per hour, or 1 J Ibs. per electric horse-power per day. The 304 ALUMINIUM. works produce about 200 Ibs. of aluminium contained in alloys per day. The raw bronze is stacked until several runs have accumulated, then a large batch is melted at once in a reverbera- tory furnace, refined, and diluted to the proportion of aluminium required by adding pure copper. The Cowles Company, both in England and America, produce six standard grades of bronze as follows : " Special" A ..... 11 per cent, of aluminium. A . 10 B . . . . ... 7 C D ...,,. E Their ferro-alu minium is sold with usually 5 to 7 per cent, of aluminium, but 10, 13, and 15 per cent, is furnished if asked for. Products of the Cowles furnace. Dr. W. Hampe obtained the following results on analyzing a sample of Cowles Bros/ 10 per cent, bronze : Copper . . . . . Aluminium . . . . . Silicon . . . . . Carbon . ... . . Magnesium ..... Iron ... 100.013 A sample of 10 per cent, bronze, made in the early part of 1886, and analyzed in the laboratory of the Stevens Institute, showed Copper 88.0 Aluminium ......... 6.3 Silicon 6.5 but it is evident that the percentage of silicon has since then been lowered. The ferro-aluminium used by Mr. Keep in his tests on cast- iron was furnished by the Cowles Company, and analyzed Aluminium ......... 11.42 Silicon 3.86 REDUCTION BY THE USE OF ELECTRICITY. 305 A sample shipped to England in December, 1886, contained Iron 86.69 Combined carbon ...... 1.01 Graphitic " 1.91 Total 2.92 Silicon 2.40 Manganese ......... 0.31 Aluminium ......... 6.50 Copper . ./ 1.05 Sulphur . .'.'' 0.00 Phosphorus . ' . 0.13 100.00 The copper in this alloy was present by accident, the alloy regu- larly made containing none, but the rest of the analysis gives a correct idea of the constitution of the alloy. Prof. Mabery gives several analyses of Cowles' ferro-aluminium : * Iron Aluminium . Silicon Carbon The slags formed in the furnace in producing this alloy were analyzed as follows : Silica . . 0.78 4.10 Alumina (insoluble) . . , . . 0.20 Lime 28.50 14.00 Iron ; . . . 1.50 29.16 Alumina (soluble) + aluminium . . 38.00 48.70 Sulphur . . . ... . . 0.50 Graphite . . . . . . 5.00 2.60 Combined carbon ;..'. . , . 0.90 0.48 The slags formed when producing bronze vary in composition, and are usually crystalline, with a shining, vitreous lustre. Their analysis shows Alumina (insoluble) . . , . .55.30 66.84 Alumina (soluble) -f aluminium . 21.80 14.20 Lime 3.70 1.44 6.77 Copper .;. ' '< . . . ' . . 3.32 1.00 Carbon 0.65 85.17 85.46 86.04 86.00 84.00 8.02 8.65 9.00 9.25 10.50 2.36 2.20 2.52 2.35 2.40 3.77 2.41 2.50 * American Chemical Journal, 1887, p. 11. 20 26.70 35.00 20.00 66.20 53.30 74.32 15.23 5.00 12.30 2.86 20.5& 2.00 0.20 2.86 49.26 306 ALUMINIUM. The lime present probably existed as calcium aluminate. These slags contained only a small amount of aluminium, rarely any iron, and were usually free from silica. The same chemist analyzed a peculiar product sometimes formed in the furnace when smelting for bronze, in the shape of crystalline masses, steel-gray to bright yellow in color, semi-trans- parent and with a resinous lustre. These all contained alu- minium, copper, silicon and calcium in various proportions, and when exposed to the air fell to powder. Analyses gave Copper Aluminium . . , Silicon . ... Calcium . . . Tin .... 99.90 100.80 100.04 85.04 The latter product was formed in smelting for aluminium-tin. Prof. Mabery also found that the soot collecting at the orifices on top of the furnace contained 10 to 12 per cent, of aluminium ; also that when alumina and carbon alone were heated and silica was present, the aluminium formed dissolved up to 10 per cent, of silicon, which, on dissolving the aluminium in hydrochloric acid, was left as crystalline or graphitic silicon. Reactions in Cowles'' process. The inventors, themselves, claim " reduction in a furnace heated by electricity in presence of carbon and a metal." In their first pamphlet they say that " the Cowles process accomplishes the reduction of alumina by carbon and heat." Professor Mabery and Dr. Hunt, already quoted, and Dr. Kosman* look at the process in no other light than that the electric current is utilized simply by its conversion into heat by the resistance offered, and that pure electrolysis is either absent or occurs to so small an extent as to be inappreciable. Indeed, if we consider the arrangement of the parts in the Cowles furnace we see every effort made to oppose a uniform, high resistance to the passage of the current and so convert its energy into heat, and an entire absence of any of the usual arrangements for electrolysis. For instance, electroysis requires a fluid bath in * Stahl und Eisen, Jan. 1889. REDUCTION BY THE USE OF ELECTRICITY. 307 circulation, so that each element of the electrolyte may be con- tinuously liberated at one of the poles and the presence of any foreign material, as bits of carbon, between the poles is to be avoided if possible, since they short-circuit the current and hinder electrolysis proper. I think the arrangement of the furnace shows no attempt to fulfil any of the usual conditions for electrol- ysis, and one of the best arrangements for converting the energy of the current entirely into heat. Dr. Hampe, however, in spite of these evident facts, draws the conclusion that because he was unable to reduce alumina by carbon in presence of copper at the temperature of a Deville lime-furnace that it was therefore to be assumed that even the somewhat higher temperature of the electric furnace alone would be insufficient to accomplish the de- sired reaction, and hence the effect of the electric arc must be not only electro-thermic in supplying heat, but afterwards electro- lytic, in decomposing the fused alumina. If we figure out the useful effect of the current, i. e., the pro- portion of its energy utilized for the purpose of reducing alumina, we find a low figure, but it is well to note that although the power required is one of the main features of this way of reduction yet this item is so cheap at the firm's works that it becomes a secondary consideration in the economy of the process. A 300 horse-power current is equivalent to an expenditure of - = 191000 calories of heat per hour. Theo- 191000 retically, this amount of heat would produce = 26 J kilos 7.250 or 58 pounds of aluminium. However, about 7 pounds are ob- tained in an hour's working, which would show a useful effect of 12 per cent. This should even be diminished, since no account has been taken of the combustion of carbon in the furnace to car- bonic oxide. The remainder of the heat account, probably 90 per cent, of the whole, is partly accounted for by the heat con- tained in the gases escaping and the materials withdrawn from the furnace (of which no reasonable estimate can be made, since the question of temperatures is so uncertain) and the large re- mainder must be put down as lost by radiation and conduction. As before remarked, water power is obtained by this company 308 ALUMINIUM. very cheaply, and even this large loss does not make much show in the cost of the alloy, yet the figures show that a much larger useful effect should be possible, and it is not at all improbable that the prospect of getting double or triple the present output from the same plant is at present inciting the managers to fresh exertions in utilizing the power to better advantage. Since writing the above, I have seen Mr. H. T. Dagger's paper* on the Cowles process in England, in which the product at their Milton works is said to be 1 Ib. of aluminium to 18 electric horse-power per hour, which would show that the dissociation of the alumina represented nearly 30 per cent, of the energy of the current, but the data given in the body of this gentleman's paper (p. 303) do not seem to indicate so large a return as is stated above. Mr. Dagger, moreover, maintains the purely elec- tro-thermic action of the current, denying that any electrolysis takes place at all. In the discussion of Heroult's process (p. 314) it will be shown that in both it and Cowles' process the largest part of the reduc- tion must necessarily be performed by chemical and not by elec- trolytic action. I do not introduce this discussion here, since the two processes resemble each other so closely in the reaction in- volved that they can best be considered together. Manges' Patent. fThis inventor proposes to produce aluminium or aluminium bronze by mixing aluminous material with suitable conducting material, such as coal, and a cohesive material, then pressing into cylinders and baking hard. These strong, compact bars conduct electricity, and are to be used like the carbon electrodes of electric lamps in a suitably inclosed space. Farmer's Patent. M. G. Farmer! mixes aluminous material with molasses or pitch, making a paste which is moulded into sticks, burned, and * Read before the British Association for Adv. Science, Newcastle, 1889. f German Patent, 40354 (18S7). J English Patent, 10815, Aug. 6, 1887. REDUCTION BY THE USE OF ELECTRICITY. 309 used as electrodes, inclosed in a furnace. Aluminium is produced by the arc, and drops into a crucible placed immediately beneath. It appears that Messrs. Menges and Farmer hit upon the same idea at about the same time, but the practicability of the process as outlined has still to be demonstrated, and appears to be very improbable of attainment. The Heroult Process (1887). This is the invention of P. L. C. Heroult, of Paris, and has been patented in the United States, England, and most European countries.* As has already been outlined in Chapter I., the process was first put in operation at the works of the Societe Mettallurgique Suisse, at Neuhausen on the Rhine, where large water power is obtained from the Rhine-Falls. The English patent is headed "an improved process for the production of aluminium, aluminium bronze, and other alloys of aluminium by electrolysis." It specifies that for producing pure aluminium a mixture of cryolite and alumina is fused in a carbon crucible contained within one of plumbago, and set in a wind fur- nace. The inner crucible serves as the cathode of an electric current, while it is provided with a lid having two holes through one of which connection is made by a carbon rod with the cruci- ble, through the other another carbon rod dips into the middle of the bath. The cover is banked up with loam and garden mould ; the two carbon rods being protected from oxidation by passing through earthen tubes which pass through the arch of the furnace above. By using a current of 3 volts electro-motive force the alumina is electrolyzed, aluminium being deposited on the walls of the crucible and a corresponding amount of oxygen set free at the carbon anode, which is gradually consumed, thereby producing carbonic oxide. The bath must be replenished with alumina and the anode renewed from time to time. To form alloys, as of copper, the metal is melted in a carbon crucible by a voltaic arc, the positive pole being a movable carbon rod above * U. S. Patent, 387876, August 14, 1888 ; English Patent, 7426, June 21, 1887 ; French Patent, 170003, April 15, 1887. 310 ALUMINIUM. and the copper serving as the negative pole, connection being made with the crucible. When the copper is melted, alumina is introduced by degrees, without any flux. The intense heat fuses the alumina, and it is electrolyzed between the copper and the carbon anode above. The electrolyte is then liquid alumina, and it, as well as the copper cathode, is kept melted solely by the heat developed by the electric current. The alloy is tapped out and fresh materials added at suitable intervals without interruption to the process. A convenient strength of current for a crucible 20 centimetres deep by 14 centimetres in diameter inside, with a carbon anode 5 centimetres in diameter, is found to be 400 am- peres, with an electro-motive force of 20 to 25 volts. An ampere- meter introduced into the circuit indicates the progress of the operation and the necessity for tapping or adding new material. Of the two processes described in the above specification the first is very similar to that of Henderson, and to Hall's process (pp. 273 and 288), and has not been exploited as the second one has been. For some time the province of the " Heroult process" has generally been considered to be in producing aluminium alloys, which is the second part of the English patent and the whole sub- ject of the United States patent referred to. We must therefore conclude that the process for producing pure aluminium has been abandoned, and our subsequent remarks will be concerned solely with the process for producing the alloys. The Societe Metallurgique Suisse, which owned the patents, put up a plant on a commercial scale in July, 1888. It is said that this firm experimented some time with Dr. Kleiner's process, but abandoned it, about the middle of 1887, to try Heroult's pro- cess, and with such successful results that the plant about to be described was decided on. The instalment consisted of two large dynamos constructed especially for this work by the Oerliken Engineering Company, and directly coupled to a 300 horse-power Jonval turbine situated between them and mounted on a horizon- tal shaft. A separate dynamo of 300 amperes and 65 volts, driven by a belt from a pullej 7 upon the main shaft, is used to excite the field magnets of the two large machines. These large dynamos were originally intended to give each a current of 6000 amperes at 20 volts electro-motive force when running at 180 REDUCTION BY THE USE OF ELECTRICITY. 311 revolutions per minute, but sufficient margin was allowed in the strength of the field to be able to work to 30 volts. They have even worked up to 35 volts on unusual occasions without any undue heating. It happens sometimes that the end of the anode touches the molten cathode, producing a short circuit, when the current will suddenly rise to from 20,000 to 25,000 amperes without, however, damaging the machine. The main conductors are naked copper cables, about 10 cen- timetres diameter, and no special precautions are taken to insulate them, since the current is of comparatively low potential, and a leakage of 100 amperes more or less in such a large current is too insignificant to take the trouble to avoid. An amperemeter is placed in the main circuit, its dial being traversed by an index about 1 metre long, which is closely watched by the workman controlling the furnace. The furnace or crucible first used consisted of an iron box cast around a carbon block, the iron, on contracting by cooling, securely gripping the surface of the carbon on all sides, and thus insuring perfect contact and conduction of the current from the cathode inside. This method was found only suitable for small crucibles, and the next furnace was built up of carbon slabs held together by a strong wrought-iron casing. The interior depth of the crucible was 60 centimetres, length 50 and breadth 35 centimetres, which would permit the introduction of the carbon anode and leave a clear space of 4 centimetres all around it horizontally. At the botton of the cavity is a passage to a tap-hole, D (Fig. 28), closed by the plug E, which is withdrawn from time to time to run off the alloy. The carbon anode, F, is suspended vertically above the crucible by pulleys and chains, which permit it to be raised and lowered easily and quickly. This anode is built up of large carbon slabs laid so as to break joints, and securely fastened together by carbon pins. The whole bar is 250 centimetres long with a section of 43 by 25 centimetres, and weighs complete 255 kilos. The conductor is clamped to the anode by means of the copper plates, G. The crucible is covered on top by carbon slabs, Hj Hj 5 centimetres thick, leaving an opening just large enough for the anode to pass through. The openings, J, J, closed by the lids, K, K, serve for introducing fresh copper and alumina. 312 ALUMINIUM. The materials used have just been mentioned. Electrolytic or Lake Superior copper is used, the former being perhaps preferred if from a good manufacturer. The alumina is bought as commer- cial hydrated alumina, costing in Europe 22 francs per 100 kilos (2 cents per lb.). This is, of course, calcined before using, each 100 kilos furnishing about 65 kilos of alumina. Corundum can be substituted for the artificial alumina ; some from North Caro- lina was tried, and is said to have given even more satisfactory results. Commercial beauxite has been used, but since it con- tains more or less iron its use is confined to the manufacture of ferro-aluminium. It is very cheap in Europe, and requires no other preparation than simple calcining. The operation is begun by placing copper, broken into rather small pieces, in the crucible. The carbon anode is then approached to the copper, which is quickly melted by the current. The bath of fluid copper then becomes the negative pole, and ore is imme- diately fed into the crucible. It also is soon melted and floats on top of the copper. The electrolysis now proceeds, care being taken that while the anode dips into the molten ore, it does not REDUCTION BY THE USE OF ELECTRICITY. 313 touch the molten cathode. Particular stress is laid on the econ- omy of keeping the distance between the electrodes small, the reason given being that " the space between, being filled with a layer of badly-conducting molten ore, offers a resistance which increases with the distance ; and although resistance is necessary, in order that the current should produce heat, it is not economical to have more heat than is necessary to melt the ore the work of separating the metal from the oxygen being. chiefly done by the electrolytic action of the current, and not by the high temperature." In practice, this intervening space is not over 3 millimetres (one- tenth of an inch). The workman in charge, by watching the indications of the amperemeter, is enabled to maintain the anode at its proper distance without any difficulty ; it is proposed to do this regulating automatically by means of an easily-constructed electrical device. The oxygen liberated gradually burns away the anode, it being found that about 1 kilo of the anode is con- sumed for every kilo of aluminium produced. After the operation commences, the alumina and metal are introduced alternately in small quantities at frequent and regular intervals, and the alloy is tapped out about every twelve hours. The only wear to which the crucible is subjected is from the accidental admission of small quantities of air ; this waste is scarcely appreciable. All oxygen evolved from the bath is evolved in contact with the anode and burns it. When the anode has worn down until too short for further use, it is replaced by another, the pieces of carbon left being utilized for repairing, covering or building up the crucible. The operation is kept up night and day, and it is generally more than a day after start- ing before the crucible is thoroughly up to its maximum heat and work. Two reliefs of five men each operate the plant, one to superintend, one to prepare and dry the alumina, a third to control the working of the crucible by working the anode, a fourth to feed ore and metal into the crucible, and the fifth to take care of the machinery, prepare anodes, crucibles, etc. All five work together to replace an anode or tap the crucible. A part of each tapping is analyzed, to determine its percentage of aluminium. It is the aim to produce as rich a bronze as possible at the first operation (over 42 per cent, of aluminium has been 314 ALUMINIUM. reached) and its subsequent dilution to any percentage desired is done in any ordinary smelting furnace. The average current supplied the crucible is 8000 amperes and 28 volts, requiring an expenditure of a little over 300 horse- power in the turbine. Starting cold it required, in one instance, 36 hours to produce 670 kilos of aluminium bronze containing 18.3 per cent, or 122.67 kilos of aluminium. Taking the cur- rent as 300 electric horse-power, this would be a return of 11 grammes per hour or 0.264 kilos (0.6 Ibs.) per day for each electric horse-power. It is claimed by Mr. Heroult that the furnace takes several days to attain its full efficiency, and that when it does so the above charge can be worked in 12 hours, which would triple the above production per horse-power. This claim is backed by figures as to 271 hours of actual operation, during which time the crucible cooled several times, but the average over the whole period was 22| grammes per hour or 0.544 kilos (1.2 Ibs.) per day for each horse-power (163 kilos of aluminium per day, total production). During actual operation at full efficiency, Mr. Heroult claims to get 35 to 40 grammes of aluminium per horse-power-hour, which would mean 11 to 15 horse-power-honrs per pound of aluminium, or 1.75 to 2.1 Ibs. of aluminium per horse-power per day. An idea of the percentage of useful effect derived from the cur- rent may be had very easily by considering that 1 electric horse- power = 750 Watts = 644.4 calories of heat per hour. (See p. 247.) As each gramme of aluminium evolves 7.25 calories in forming alumina, the production of 1 electric horse-power in 1 hour (if its energy were utilized solely for separating aluminium from oxygen) would be 88.88 grammes. Therefore the heat energy of the current is amply sufficient to account for all the alumina decomposed, leaving over the heat produced in the crucible by the union of oxygen with the carbon anode. Looking at the other side of the question, the electrolytic action, we can easily calculate from the strength of the current what it could per- form. A current of 8000 amperes can liberate 2.68 kilos of alu- minium per hour,* according to the fundamental law of electro- * N. B. Only one furnace is used on the circuit. REDUCTION BY THE USE OF ELECTRICITY. 315 deposition. If, then, from the figures given, there was actually produced 3.3 kilos and 6.8 kilos per hour, and 10.5 to 12 kilos are claimed when up to full efficiency, it is impossible that more than a fraction of the aluminium is produced by electrolytic decom- position of alumina, and the claim that the process is essentially electrolytic is without foundation. Similar calculations with the data given with regard to Cowles' process will lead to exactly similar conclusions, viz : that the absolute energy of the current, if converted into its heat equivalent, is many times more than sufficient to account for the decomposition of the alumina on thermal grounds, but the amount of current used will not suffice to explain the decomposition of the alumina as being electrolytic. Therefore, in both these processes the oxygen is abstracted from alumina by carbon, the condition allowing this to take place being primarily the extremely high temperature and secondarily the fluidity of the alumina. The presence of copper is immaterial, as is clearly shown in the Cowles process. The Heroult process has been rapidly extended. In November, 1888, a syndicate was formed in Berlin, with a capital of $2,500,- 000, which purchased the Heroult continental patents and has united with the former Swiss owners in forming the Aluminium Industrie Actien Gesellschaft, which has commenced to erect a very large plant in place of the former one, at Neuhausen. Dr. Kiliani has been made manager of the works, which are being rapidly completed, and will include, when finished, foundries and machine shops for casting and utilizing their product. The new plant will consist of 8 crucibles, capable of producing at least 10 tons of ten per cent, bronze in 24 hours. In the beginning of 1889, the Societe Electro-Metallurgique of France, located at Froges (Isere), commenced to manufacture alloys by the Heroult process. Their plant consists of two tur- bines of 300 horse-power each, with two dynamos of 7000 amperes and 20 volts each. The output is estimated at 3000 kilos of alloys per day, which probably means 200 to 300 kilos of aluminium. An experimental plant, under the direction of Mr. Heroult, was started in July, 1889, at Bridgeport, Conn., but the dynamo 316 ALUMINIUM. proved inadequate to the work required and was burnt out, stop- ping operations temporarily. A dynamo was then ordered from the Oerliken Works, at Zurich, which arrived the following November, and another plant has been started at Boonton, N. J. The American company has not yet been incorporated. CHAPTER XII. REDUCTION OF ALUMINIUM COMPOUNDS BY OTHER MEANS THAN SODIUM OR ELECTRICITY. No very exact classification of these numerous propositions can be made, since often many reducing agents are claimed in one general process. Where such general statements are made, the method will be found under the most prominent reducing agent named, with cross references under the other headings. REDUCTION BY CARBON WITHOUT THE PRESENCE OF OTHER METALS. About the first attempt of this nature we can find record of, is the following article by M. Chapelle : * " When I heard of the experiments of Deville, I desired to repeat them, but having neither aluminium chloride nor sodium to use, I operated as follows : I put natural clay, pulverized and mixed with ground sodium chloride and charcoal, into an ordinary earthen crucible and heated it in a reverberatory furnace, with coke for fuel. I was not able to get a white heat. After cooling, the crucible was broken, and gave a dry pulverulent scoria in which were disseminated a considerable quantity of small globules about one-half a millimetre in diameter, and as white as silver. They were malleable, insoluble in nitric or cold hydrochloric acids, but at 60 dissolved rapidly in the latter with evolution * Compt. Rendus, 1854, vol. xxxviii. p. 358. REDUCTION BY MISCELLANEOUS AGENTS. 317 of hydrogen ; the solution was colorless and gave with ammonia a gelatinous precipitate of hydrated alumina. My numerous occupations did not permit me to assure myself of the purity of the metal. Moreover, the experiment was made under conditions which leave much to be desired, but my intention is to continue my experiments and especially to operate at a higher temperature. In addressing this note to the Academy I but desire to call the attention of chemists to a process which is very simple and sus- ceptible of being improved. I hope before many days to be able to exhibit larger globules than those which my first experiment furnished." M. Chapelle never did address any further communications to the Academy on this subject, and we must presume that further experiments did not confirm these first ones. The author was once called upon to examine a slag full of small, white, metallic globules, the result of fusing slate-dust in a similar manner to M. Chapelle's treatment of clay. They proved to be globules of siliceous iron reduced from the iron oxide present in the slate. It is not impossible that Chapelle's metallic globules were something similar in composition to these. G. W. Reinar* states that the pyrophorous mass, which results from igniting potash or soda alum with carbon, contains a car- boniferous alloy of aluminium with potassium or sodium, from which the alkaline metal can be removed by weak nitric acid. The manager of an aluminium company in Kentucky claims to produce pure aluminium by a process which the newspapers state consists in smelting down clay and cryolite in a water- jacketed cupola reducing furnace, it being also stated that the aluminium is reduced so freely, and gathers under the slag so well, that it is tapped from the furnace by means of an ordinary syphon-tap. These are all the particulars which have been made public. As to whether this company really does make alumin- ium by any such process, I am unable to assert ; about all that can be said further is that it has advertised its metal extensively at $2 to $3 per lb., and a sample of it sent to a friend of mine upon application was truly aluminium of fair quality. * Wagner's Jahresb., 1859, p. 4. 318 ALUMINIUM. O. M. Thowless,* of Newark, N. J., proposes to prepare a solu- tion, of aluminium chloride by dissolving precipitated aluminium hydrate in hydrochloric acid. The solution is concentrated and mixed with chalk, coal, soda, and cryolite, and the mass resulting heated in closed vessels to a strong, red heat. It is also stated that aluminium fluoride may be used instead of the chloride. The resulting fused mass is powdered and washed, when it is said that aluminium is obtained in the residue. According to a patent granted to Messrs. Pearson, Liddon, and Pratt, of Birmingham, f an intimate mixture is made by grinding together 100 parts cryolite. 50 " beauxite, kaolin or aluminium hydrate. 50 " calcium chloride, oxide or carbonate. 50 " coke or anthracite. These are heated to incipient fusion in a carbon-lined furnace or crucible for two hours, when the aluminium is said to be pro- duced and to exist finely disseminated through the mass. A mix- ture of 25 parts each of potassium and sodium chlorides is then to be added and the heat raised to bright redness, when the alu- minium collects in the bottom of the crucible. A better utiliza- tion of the fine powder is effected by washing it, drying, and then pouring fused zinc upon it, which alloys with the aluminium and can be afterwards removed by distillation. If melted copper is used, a bronze is obtained. REDUCTION BY CARBON AND CARBON DIOXIDE. J. Morris,J of Uddington, claims to obtain aluminium by treat- ing an intimate mixture of alumina and charcoal with carbon di- oxide. For this purpose, a solution of aluminium chloride is mixed with powdered wood-charcoal or lampblack, then evaporated till it forms a viscous mass which is shaped into balls. During the evaporation hydrochloric acid is given off. The residue consists * U. S. Patent, 370220, Sept. 20, 1887 ; English Patent, 14407 (1886). f English Patent, 5316, April 10, 1888. t Dingier, 1883, vol. 259, p. 86. German Pat., No. 22150, Aug. 30, 1882. REDUCTION BY MISCELLANEOUS AGENTS. 319 of alumina intimately mixed with carbon. The balls are dried, then treated with steam in appropriate vessels for the purpose of driving off all the chlorine, care being taken to keep the tempera- ture so high that' the steam is not condensed. The temperature is then raised so that the tubes are at a low red heat, and dry carbon dioxide, CO 2 , is then passed through. This gas is reduced by the carbon to carbonic oxide, CO, which now, as affirmed by Mr. Morris, reduces the alumina. Although the quantity of carbonic oxide escaping is in general a good indication of the pro- gress of the reduction, it is, nevertheless, not advisable to continue heating the tubes or vessels until the evolution of this gas has ceased, as in consequence of slight differences in the consistency of the balls some of them give up all their carbon sooner than others. The treatment with carbon dioxide lasts about thirty hours when the substances are mixed in the proportion of five parts carbon to four parts alumina. Morris states further that the metal appears as a porous spongy mass, and is freed from the residual alumina and particles of charcoal either by smelting it, technically u burning it out/' with cryolite as a flux or by mechani- cal treatment. KEDUCTION BY HYDROGEN. F. W. Gerhard* decomposes aluminium fluoride or cryolite by subjecting them to hydrogen at a red heat. The aluminium com- pound is placed in a number of shallow dishes of glazed earthen- ware, each of which is surrounded by a number of other dishes containing iron filings. These dishes are placed in an oven pre- viously heated to redness, hydrogen gas is then admitted, and the heat increased. Aluminium then separates, hydrofluoric acid, HF, being formed, but immediately taken up by the iron filings and thereby prevented from reacting on the aluminium. To prevent the pressure of the gas from becoming too great, an exit tube is provided, which may be opened or closed at pleasure. This process, patented in England in 1856, No. 2920, is ingenious and * Watts' Dictionary, article "Aluminium." 320 ALUMINIUM. was said to yield good results. The inventor has, however, re- turned to the use of the more costly reducing agent, sodium, which would seem to imply that the hydrogen method has not yet quite fulfilled his expectations. (See also Comenge's processes.) .REDUCTION BY CARBURETTED HYDROGEN. Mr. A. L. Fleury,* of Boston, mixes pure alumina with gas- tar, resin, petroleum, or some such substance, making it into a stiff paste which may be divided into pellets and dried in an oven. They are then placed in a strong retort or tube which is lined with a coating of plumbago. In this they are exposed to a cherry-red heat. The retort must be sufficiently strong to stand a pressure of from 25 to 30 Ibs. per square inch, and be so arranged that by means of a safety valve the necessary amount of some hydrocarbon may be introduced into the retort among the heated mixture, and a pressure of 20 to 30 Ibs. must be main- tained. The gas is forced in by a force pump. By this process the alumina is reduced, the metal remaining as a spongy mass mixed with carbon. This mixture is remelted with metallic zinc, and when the latter has collected the aluminium it is driven off by heat. The hydrocarbon gas under pressure is the reducing agent. The time required for reducing 100 Ibs. of alumina, earth, cryolite, or other compound of aluminium, should not be more than four hours. When the gas can be applied in a previously heated condition as well as being strongly compressed, the reduc- tion takes place in a still shorter period. Nothing is now heard of this process, and it has been presum- ably a failure. It is said that several thousand dollars were expended by Mr. Fleury and his associates without making a practical success of it. We should be glad to hear in the future that their sacrifices have not been in vain, and that the process still has possibilities in it which will some time be realized. Petitjeanf states that aluminium sulphide, or the double sul- * Chemical News, June, 1869, p. 332. f Polytechnisches Central Blatt., 1858, p. 888. REDUCTION BY MISCELLANEOUS AGENTS. 321 phide of aluminium and sodium (see p. 144), may be reduced by putting them into a crucible or retort, through the bottom of which is passed a stream of carburetted hydrogen. Some solid or liquid hydrocarbon may be placed in the bottom of the cru- cible. The aluminium is said to be thus separated from its com- bination with sulphur. The powder must be mixed with metallic filings, as iron, and melted, in order to collect the aluminium. Or, metallic vapor may be passed into the retort in place of carburetted hydrogen. Messrs. Reillon, Montague, and Bourgerel* patent the pro- duction of aluminium sulphide (see p. 143) and its reduction by carburetted hydrogen exactly as above. REDUCTION BY CYANOGEN. According to Knowles' patent,t aluminium chloride is reduced by means of potassium or sodium cyanide, the former, either fused or in the form of vapor, being brought in contact with either the melted cyanide or its vapor. The patent further states that pure alumina may be added to increase the product. The proportions necessary are in general 3 equivalents of aluminium chloride. 3-9 " potassium or sodium cyanide. 4-9 " alumina. Corbelli, of Florence,! patented the following method in Eng- land : Common clay is freed from all foreign particles by wash- ing, then well dried. One hundred grammes of it are mixed with six times its weight of concentrated sulphuric or hydro- chloric acid ; then the mixture is put in a crucible and heated to 400 or 500. The mass resulting is mixed with 200 grammes of dry yellow prussiate of potash and 150 grammes of common salt, and this mixture heated in a crucible to whiteness. After cooling, the reduced aluminium is found in the bottom of the crucible as a button. * English Patent 4576, March 28, 1887. f Sir Francis C. Knowles, English Patent, 1857, No. 1742. J English Patent, 1858, No. 142. 21 322 ALUMINIUM. According to Deville's experiments, this process will not give any results. Watts remarks that any metal thus obtained must be very impure, consisting chiefly of iron. Lowthian Bell* attempted to obtain aluminium in his labora- tory by exposing to a high heat in a graphite crucible mixtures of alumina and potassium cyanide, with and without carbon. In no case was there a trace of the metal discovered. REDUCTION BY DOUBLE REACTION. M. Comenge,f of Paris, produces aluminium sulphide (see p. 143) and reduces it by heating it with alumina or aluminium sulphate in such proportions that sulphurous acid gas and alu- minium may be the sole products. The mixture is heated to redness on the bed of a reverberatory furnace, in an unoxidizing atmosphere, the reaction being furthered by agitation. It is stated that the resulting mass may be treated in the way com- monly used in puddling spongy iron and afterwards pressed or rolled together. The reactions involved would be, if they oc- curred, A1 2 S 3 + 2A1 2 3 = 6A1 + 3S0 2 . A1 2 S 3 + A1 2 (S0 4 ) 3 - 4A1 + 6S0 2 . It is also claimed that metallic alloys may be prepared by the action of metallic sulphides on aluminium sulphate ; as, for in- stance A1 2 (SO 4 ) 3 + 3FeS= Al 2 Fe 3 + 6SO 2 . The sulphide is also reduced by hydrogen, iron, copper or zinc, the reactions being APS 3 In the case of reduction by a metal, alloys are formed. Mr. Niewerth'sJ process may be operated in his newly invented furnace, but it may also be carried on in a crucible or other form * Chemical Reactions in Iron Smelting, p. 230. f English Patent, 1858, No. 461, under name of J. H. Johnson. J Sci. Am. Snppl., Nov. 17, 1885. REDUCTION BY MISCELLANEOUS AGENTS. 323 of furnace. The furnace alluded to consists of three shaft fur- naces, the outer ones well closed on top by iron covers, and con- nected beneath by tubes with the bottom of the middle one: the tubes being provided with closing valves. These side shafts are simply water-gas furnaces, delivering hot water-gas to the central shaft, and by working the two alternately supplying it with a continuous blast. The two producers are first blown very hot by running a blast of air through them with their tops open, then the cover of one is closed, the blast shut off,, steam turned on just under the cover, and water-gas immediately passes from the tube at the bottom of the furnace into the central shaft. The middle shaft has meanwhile been filled with these three mixtures in their proper order : First. A mixture of sodium carbonate, carbon, sulphur and alumina. Second. Aluminium sulphate. Third. A flux, preferably a mixture of sodium and potassium chlorides. This central shaft must be already strongly heated to commence the operation, it is best to fill it with coke before charging, and as soon as that is hot to put the charges in on the coke. Coke may also be mixed with the charges, but it is not necessary. The process then continues as follows- : The water-gas enters the bottom of the shaft at a very high temperature. These highly heated gases, carbonic oxide and hydrogen, act upon the charges so that the first breaks up into a combination of sodium sulphide and aluminium sulphide, from which, by double reaction with the second charge of aluminium sulphate, free aluminium is produced. As the latter passes down the shaft, it is melted and the flux assists in collecting it, but is not absolutely necessary. Instead of producing this double sulphide, pure aluminium sulphide might be used for the first charge, or a mixture which would gen- erate it ; or again pure sulphide of sodium, potassium, copper, or any other metallic sulphide which will produce the effect alone, in which case aluminium is obtained alloyed with the metal of the sulphide. Instead of the first charge, a mixture of alumina, sul- phur and carbon might be introduced. Or the aluminium sul- phate of the second charge might be replaced by alumina. So 324 ALUMINIUM. one charge may be sulphide of sodium, potassium or any other metallic sulphide, and the second charge may be either alumina or aluminium sulphate. Messrs. Pearson, Turner, and Andrews* claim to produce alu- minium by heating silicate of alumina or compound silicates of alumina and other bases with calcium fluoride and sodium or potassium carbonate or hydrate, or all of these together. If other metals are added, alloys are obtained. REDUCTION IN PRESENCE OF on BY COPPER. Calvert and Johnson f obtained copper alloyed with aluminium by recourse to a similar chemical reaction to that employed to get their iron-aluminium alloy. Their mixture was composed of 20 equivalents of copper .,.,'. , * . 640 parts. 8 (24) " aluminium chloride . . . 1076 " 10 " lime . . V . . ' ; 280 " "We mixed these substances intimately together, and after having subjected them to a high heat for one hour we found at the bottom of the crucible a melted mass covered with cuprous chloride, Cu 2 CP, and in this mass small globules, which on analysis contained 8.47 per cent, aluminium, corresponding to the formula 5 equivalents of copper . . . 160 91.96 per cent. 1 " aluminium . . 14 8.04 100.00 " We made another mixture of aluminium chloride and copper in the same proportions as above, but left out the lime. We ob- tained an alloy in this case also, which contained 12.82 per cent, aluminium, corresponding to the formula 3 equivalents of copper ... 96 87.27 per cent. 1 " aluminium . . 14 12.73 100.00 * English Patent, 12332, Sept. 12, 1887. f Phil. Mag. 1855, x. 242. REDUCTION BY MISCELLANEOUS AGENTS. 325 M. Evrard,* in order to make aluminium bronze, makes use of an aluminous pig-iron. (It is not stated how this aluminous pig-iron is made.) This is slowly heated to fusion, and copper is added to the melted mass. Aluminium, having more affinity for copper than for iron, abandons the latter and combines with the copper. After the entire mass has been well stirred, it is allowed to cool slowly so as to permit the bronze, which is heavier than iron, to find its way to the bottom of the crucible. M. Evrard makes silicon bronze in the same way by using siliceous iron. Benzonf has patented the reduction of aluminium with copper, forming an aluminium-copper alloy. He mixes copper, or oxi- dized copper, or cupric oxide, in the finest possible state, with fine, powdered, pure alumina and charcoal, preferably animal char- coal. The alumina and copper or copper oxide are mixed in equivalent proportions, but an excess of charcoal is used. The mixture is put in a crucible such as is used for melting cast-steel, which is lined inside with charcoal. The charge is covered with charcoal, and the crucible subjected first to a temperature near the melting point of copper, until the alumina is reduced, and then the heat is raised high enough to melt down the alloy. In this way can be obtained a succession of alloys, whose hardness and other qualities depend on the percentage of aluminium in them. In order to obtain alloys of a certain composition, it is best to produce first an alloy of the highest attainable content of alu- minium, to analyze it, and then melt it with the required quantity of copper. The same process can be used for the reduction of alumina with iron or ferric oxide, only the carbon must in this case be in greater excess, and a stronger heat kept up longer must be used than when producing the copper-aluminium alloy. In con- tact with ferric oxide the alumina is more easily reduced than with metallic iron. Benzon further remarks that some of these alloys, as the ferro- aluminium, may be subsequently treated so as to separate out the metallic aluminium ; also that the iron alloy may be mixed with steel in the melting pot, or suitable proportions of alumina and carbon may be put into the melting pot. The iron alloy may be * Annales du Genie Civil, Mars, 1867, p. 189. t Eng. Pat. 1858, No. 2753. 326 ALUMINIUM. useful for many purposes, especially in the manufacture of cast- steel. The question opened up by Benzon's statements is whether car- bon reduces alumina in presence of copper. This has been the subject of many careful experiments, and the verdict of the most reliable observers is that at ordinary furnace temperatures it does not. This principle has been the subject of numerous patents, and before presenting the negative evidence on this point we will review the claims made in these patents. G. A. Faurie* states that he has succeeded in obtaining alu- minium bronze by taking two parts of pure, finely-powdered alu- mina, making it into a paste with one part of petroleum and then adding one part of sulphuric acid. When the yellow color is uni- form and the mass homogeneous, sulphur dioxide begins to escape. The paste is then wrapped up in paper and thrown into a crucible heated to full redness, where the petroleum is decomposed. The calcined product is cooled, powdered and mixed with an equal weight of a metal in powder, e. g., copper. This mixture is put into a graphite crucible and heated to whiteness in a furnace sup- plied with blast. Amidst the black, metallic powder are found buttons of aluminium alloy. In an English patent, f by Mr. Faurie, it is further claimed that by making bricks out of the calcined alumina mixture and alloying metal, and using similar bricks of lixiviated soda ashes mixed with tar for flux, the re- duction can be affected in a cupola. Bolley,J at his laboratory in Zurich, and List, at the royal foundry at Augsburg, have shown that by following the process claimed by Benzon the resulting copper contained either no alu- minium, or at most a trace. In an experiment made by the author to test this point 40 grammes of copper oxide and copper, 5 " alumina, 5 " charcoal, * Comptes Rendue, 105, 494, Sept. 19, 1887. t English Patent, 10043, Aug. 18, 1887. J Schweizer Polytechnisches Zeitschrift, 1860, p. 16. Wagner's Jahresbericht, 1865, p. 23. KEDUCTION BY MISCELLANEOUS AGENTS. 327 were intimately mixed and finely powdered, put in a white-clay crucible and covered with cryolite. The whole was slowly heated to bright redness, and kept there for two hours. A bright button was found at the bottom of the crucible. This button was of the same specific gravity as pure copper, and a qualitative test showed no trace of aluminium in it. A friend of mine, Dr. Lisle, has repeated this experiment, taking the metal produced and return- ing it to another operation and repeating this four times, but the resulting button scarcely showed a trace of aluminium. Dr. W. Hampe has lately made an exhaustive test of this sub- ject with the following conclusions : * " The reduction of alumina by carbon, although often patented, is on thermo-chemical grounds highly improbable, but since alu- minium in alloying with copper, especially in the proportions 9.7 parts of the former to 90.3 parts of the latter (AlCu 4 ), evolves much heat, it might be possible that the reaction APO 3 + 3C -f 8Cu = 2 AlCu 4 -f SCO is exothermic. I therefore mixed alumina with the necessary quantity of lamp-black and copper, in other cases evaporated together to dryness solutions of aluminium and copper nitrates, afterwards igniting them to oxides and adding the necessary amount of carbon. These mixtures were put into gas-carbon crucibles contained within plumbago pots with well-luted covers, and heated in a Deville blast-furnace to a temperature sufficient to frit together the quartz sand with which the space between the two crucibles had been filled. In no case was there a trace of aluminium produced, nor did the addition of any flux for the alumina affect the result in any way." The possibility of reducing aluminium sulphide by copper has been generally decided affirmatively. M. Comenge claimed that it was possible (see p. 322), Reichelf also stated unreservedly that copper filings performed the reduction at a high temperature. In an experiment by the author, copper foil was used instead of copper filings, the latter not being immediately at hand, and the * Chemiker Zeitung (Cothen), xii. p. 391 (1888). f Journal fiir Pr. Chemie, xi. p. 55. 328 ALUMINIUM. result was negative. As a similar test with iron filings gave a good result, it seems quite probable that copper would have performed the reduction under proper conditions. Andrew Mann,* of Twickenham, patents a process which may be stated briefly as follows : Aluminium sulphate is mixed with sodium chloride and heated until a reaction begins to take place. The mass is mixed intimately with lime, and to this mixture alu- minium sulphate and ground coke added. This is calcined, the powder mixed with a metal, as copper, and melted down. In this case the slags are calcium sulphide and copper chloride, while aluminium bronze is obtained. L. Q. Brin,f of Paris, claims to produce aluminium bronze by the following process : Sheet copper is cleaned by pickling, and then covered with a mixture of 2 parts borax, 2 parts common salt, and 1 part sodium carbonate, made into a paste with water. The metal is then put into a reverberatory furnace, heated to bright redness and vapors of aluminium chloride led over it, car- ried in by a current of inert gas. (It is stated that the vapors of aluminium chloride are produced by heating in a retort a mix- ture of clay, salt, and fluorspar.) The aluminium compound is said to be decomposed, and the nascent aluminium to combine with the copper forming 1J to 2 per cent, bronze at one opera- tion, and by using this over it may be enriched to any extent desired. In a modification of this method, the coating put on the metal contains clay or other earth rich in alumina. It is also stated that the metal thus coated can be put into a cupola with alternate layers of fuel and run down to an alloy. REDUCTION BY OR IN PRESENCE OF IRON. M. Comenge claims that aluminium sulphide is reduced by iron (see p. 322) ; the statement is repeated by a writer in the " Chemical News," 1860 ; F. LauterbornJ states that the reduc- tion takes place at a red heat ; Reichel also records his success * English Patent, 9313, June 30, 1887 ; German Patent, 45755, Dec. 20, 1887. f English Patents, 3547-8-9, March 7, 1888 ; U. S. Patent, 410574, Sept. 10, 1889. J Dingier, 242, 70. Jrul. fiir Pr. Chemie, xi. 55. REDUCTION BY MISCELLANEOUS AGENTS. 329 in this reaction ; finally, the author has obtained encouraging results. I used a product containing 32.3 per cent, of aluminium sulphide. On mixing this intimately with fine iron filings, and subjecting to a high heat for one and a half hours, the product was a loose powder in which were small buttons of metal. They were bright, yellower than iron, and contained by analysis 9.66 per cent, of aluminium. H. Xiewerth* has patented the following process : " Ferro- silicum is mixed with aluminium fluoride in proper proportions and the mixture submitted to a suitable red or melting heat by which the charge is decomposed into volatile silicon fluoride (SiF 4 ), iron and aluminium, the two latter forming an alloy. In order to obtain the valuable alloy of aluminium and copper from this iron-aluminium alloy, the latter is melted with metallic cop- per, which will then by reason of greater affinity unite with the aluminium, while the iron will retain but an insignificant amount of it. On cooling the bath, the bronze and iron separate in such a manner that they can readily be kept apart. In place of pure aluminium fluoride, cryolite may advantageously be employed, or aluminium chloride may also be used, in which case silicon chloride volatilizes instead of the fluoride. Or, again, pure silicon may be used with aluminium fluoride, cryolite, or aluminium chloride, in which case pure aluminium is obtained." Mr. W. P. Thompsonf has taken out a patent in England^ for the manufacture of aluminium and similar metals, which is car- ried out as follows : The inventor employs as a reducing agent iron, either alone or conjointly with carbon or hydrogen. The operation is effected in an apparatus similar to a Bessemer con- verter, divided into two compartments. In one of these com- partments is placed melted iron, or an alloy of iron, which is made to run into the second by turning the converter. This last compartment has two tuyeres, one of which serves to introduce hydrogen, while by the other is introduced either aluminium chloride, fluoride, double chloride or double fluoride with sodium, in liquid or gaseous state. In presence of the hydrogen, the iron * Sci. Am. Suppl., Nov. 17, 1883. f Bull, de la Soc. Chem. de Paris, 1880, xxiv. 719. J March 27, 1879, No. 2101. 330 ALUMINIUM. takes up chlorine or fluorine, chloride or fluoride of iron is dis- engaged, and aluminium mixed with carbon remains as a residue. Then this mixture of iron, aluminium and carbon is returned to the other compartment where the carbon is burnt out by means of a current of air. The mass being then returned to the cham- ber of reduction, the operation described is repeated. When almost all the iron has been consumed, the reduction is termi- nated by hydrogen alone. There is thus obtained an alloy of iron and aluminium. (The preparation of sodium does not re- quire the intervention of hydrogen. A mixture of iron with an excess of carbon and caustic soda (NaOH) is heated in the con- verter, when the sodium distils off. When all the carbon has been burnt, the iron remaining as a residue may be converted into Bessemer steel. As iron forms an alloy with potassium, the method would scarcely serve for the production of that metal.) To obtain the pure aluminium, sodium is first prepared by the process indicated, the chloride or fluoride of aluminium is intro- duced into the apparatus in the other chamber, when the metal is reduced by the vapor of sodium. The chambers ought to be slightly inclined, and an agitator favors the reaction. The inventor intends to apply his process to the manufacture of mag- nesium, strontium, calcium and barium. Calvert and Johnson* made experiments on the reduction of aluminium by iron, and the production thereby of iron-aluminium alloys. We give the report in their own words : " We shall not describe all the fruitless efforts we made, but confine ourselves only to those which gave satisfactory results. The first alloy we obtained was by heating to a white heat for two hours the following mixture : 8 equivalents of aluminium chloride . . . 1076 parts. 40 " iron filings .... 1120 " 8 " lime 224 " " The lime was added to the mixture with the view of remov- ing the chlorine from the aluminium chloride, so as to liberate the metal and form fusible calcium chloride, CaCl 2 . Subtracting the lime from the above proportion, we ought to have obtained an * Phil. Mag., 1855, x. 240. REDUCTION BY MISCELLANEOUS AGENTS. 331 alloy having the composition of 1 equivalent of aluminium to 5 equivalents of iron, or with 9.09 per cent, of aluminium. The alloy we obtained contained 12 per cent., which leads to the for- mula AlFe 4 . This alloy, it will be noticed, has an analogous composition to the one we made of iron and potassium, and like it was extremely hard, and rusted when exposed to a damp atmos- phere. Still it could be forged and welded. We obtained a similar alloy by adding to the above mixture some very finely pulverized charcoal and subjecting it to a high heat in a forge furnace for two hours. This alloy gave on analysis 12.09 per cent.* But, in the mass of calcium chloride and carbon remain- ing in the crucible there was a large amount of globules varying in size from a pin-head to a pea, as white as silver and extremely hard, which did not rust in the air or in hyponitric fumes. Its analysis gave 24.55 per cent, aluminium ; the formula APFe 3 would give 25 per cent. Therefore this alloy has an analogous composition to alumina, iron replacing oxygen. We treated these globules with Aveak sulphuric acid, which removed the iron and left the aluminium, the globules retaining their form, and the metal thus obtained had all the properties of the pure aluminium. " We have made trials with the following mixture, but although they have yielded results, still they are not sufficiently satisfactory to describe in this paper, which is the first of a series we intend publishing on alloys. This mixture was : Kaolin 1750 parts. Sodium chloride 1200 " Iron 875 " " From this we obtained a metallic mass and a few globules which we have not yet analyzed." (See also Benzon's process, p. 325.) M. Chenot,t on the occasion of Deville's first paper on alumin- ium being read to the French Academy, Feb. 6, 1854, announced that in 1847, by reducing earthy oxides by means of metallic * In the original paper it is given as 12.09 per cent. iron. The inference is unavoidable that this was a misprint, but it is not corrected in the Errata at the end of the volume. f Comptes Rendue, xxxviii. 415. 332 ALUMINIUM. sponges, he had obtained a series of alloys containing up to 40 per cent, of the earth metals. He cited from a memoir presented by him to the " Societe d' Encouragement" in 1849, in which he had said, " on taking precipitates of the earths, they are all reduced by the metallic sponge (e. g., that formed by reducing iron oxide in a current of carbonic oxide gas). In this manner I have made barides, silicides, aluminides, etc., all of which are beautiful silver- white, very hard and unoxidizable in air or in contact with acid vapors. They are fusible, can be cast and work perfectly under the hammer." Faraday and Stodart* made an exhaustive investigation on the preparation of iron-aluminium alloys, being started on this line by finding that Bombay " wootz" steel contained 0.0128 to 0.0695 per cent, of aluminium, while no metals of the earths were to be found in the best English steels. This led to the conclusion that the peculiar properties of the former, especially the " damasceen- ing," were due to the small amount of aluminium. These scientists commenced by taking pure steel or sometimes good soft iron and intensely heating it for a long time imbedded in charcoal powder. Carbides were thus formed, having a very dark gray color, and highly crystalline. Average analysis of this product gave 5.64 per cent, carbon. This was broken and powdered in a mortar, mixed intimately with pure alumina and heated in a closed cru- cible for a long time at a high temperature. An alloy was ob- tained of a white color, close granular texture and very brittle, containing 3.41 per cent, of aluminium, with some carbon. When 40 parts of this alloy were melted with 700 parts of good steel (introducing 0.184 per cent, of aluminium) a malleable but- ton was obtained which gave a beautiful damask on treatment with acids ; while 67 parts of the alloy with 500 of steel (intro- ducing 0.4 per cent, of aluminium) gave a product which forged well, gave the damask and " had all the appreciable characters of the best Bombay wootz." This appears to be very strong syn- thetic evidence that alumina is reduced to a small extent even in the rude hearths in which the Indian steel is manufactured. Karsten, however, could not find weighable quantities of alu- * Quarterly Journal, ix. 320. REDUCTION BY MISCELLANEOUS AGENTS. 333 minium in specimens of wootz, nor could Henry, a very expert analyst.. The latter suggested that Faraday was misled by the alumina contained in intermingled slag, yet the latter obtained alumina without silica in his analyses. In the light of more re- cent developments we would accept Faraday's results as being very near the truth in the matter. Ledebuhr* quotes an analysis made by Griiner in which 0.50 per cent, of aluminium was found in cast-iron containing besides 2.30 per cent, of carbon and 2.26 per cent, of silicon. This would tend to show that under certain conditions iron takes up aluminium in the blast-furnace. Karsten, however, in his many analyses of malleable iron, steel and cast-iron only found alu- minium in unweighable quantities. Griiner and Lauf stated that aluminium is reduced in small quantities in the blast furnace if the temperature is high and the slag basic ; a large addition of lime thus increases the reduction of alumina and hinders that of silica. Most pig irons contain very small amounts of aluminium, but some English varieties contain 0.5 to 1.0 per cent, and several Swedish pig irons 0.75 per cent. SchafhautlJ found as much as 1.01 per cent, of aluminium in a grey iron, and was led to con- sider silicide of iron and aluminide of iron as characteristic com- ponents of grey iron. Lohage states that adding alumina in the manufacture of cast-steel has a great influence on the grain and lustre of the steel, the effect being doubtless due to a minute quantity of aluminium taken up. Silicates of magnesium and aluminium are formed at the same time and separating out float on the surface of the molten steel. Corbin|| reports 2.38 per cent, of aluminium in chrome steel, but Blair, 1" of Philadelphia, found no more aluminium in chrome than in other steels. This chemist has examined many irons and steels particularly for alu- minium, and reports that nearly always it exists as such in steel, but never more than a few thousandths of a per cent., say 0.032 * Handbuch der Eisenhiittenkunde, p. 265. f Berg u. Hiittenmannische Zeitung, 1862, p. 254. J Erdman's Journal fr. Pr. Chemie, Ixvii. 257. Berg u. Hutteninannisclie Zeitung, 1861, p. 160. || Silliman's Journal, 1869, p. 348. If H. M. Howe, E. and M. J. Oct. 29, 1887. 334 ALUMINIUM. per cent, as a maximum. He has further been unable to connect its presence with any peculiarity in the properties of the metal or its mode of manufacture. G. H. Billings,* of the Norway Iron Works, Boston, made the following experiment on reducing alumina in contact with iron : A soft iron was used containing a trace of sulphur and phos- phorus, no manganese and only 0.08 per cent, of carbon. The mixture was made of 12 parts emery. 18 " alumina. 1 " pulverized charcoal. 36 " fine iron turnings. These were mixed thoroughly, and heated to whiteness for 48 hours. The metal resulting showed a solid, homogeneous fracture with a fine crystalline structure resembling steel with 1 per cent, of carbon, and contained on analysis 0.20 per cent, of carbon. 0.50 " aluminium. It was also found that if this quantity of aluminium was added to a pot of molten iron the product obtained exhibited the same characteristics as the above. Another attempt to produce iron-aluminium alloys directly is stated in E. Cleaver's patent specifications as follows :f Four parts of aluminium sulphate in solution are mixed with one part of lamp-black, the mixture dried and heated to the highest tempera- ture attainable by using coal-gas and oxygen in a lime-lined fur- nace similar to those used for melting platinum. Excess of reducing gas is maintained. The charge is cooled in the furnace, removed, mixed with twenty times its weight of finely-divided cast-iron, and fused in a steel melting furnace. If copper is used, a bronze results. The alloying metal may be added in the gas furnace, but this is not recommended as economical. This in- ventor also claims that aluminium ferrocyanide, either alone or with carbon, can be decomposed in the above-described gas fur- nace, yielding a rich iron-aluminium alloy. As a higher heat * Transactions American Inst. Mining Engineers, 1877, p. 452. f English Patent, 1276, Jan. 26, 1887. REDUCTION BY MISCELLANEOUS AGENTS. 335 than before is needed, it is recommended that the oxygen be pre- viously heated. The principal difficulty in this latter process would apparently be to procure the aluminium ferrocyanide to operate on. Mr. Ostberg,* connected with the Mitis process for making wrought-iron castings, stated that the ferro-aluminium used in that process in Sweden was made by adding clays to iron in process of smelting, that it contained 7 to 8 per cent, of alu- minium, and could be made very cheaply. Inquiries made for further particulars about this process have received no satisfac- tory reply, and there is no outside confirmation of the above statement to be found. Brin Bros, claim that they can alloy aluminium in small quan- tities with iron (see p. 328). Besides the processes described as most suitable for producing bronze, they also state that if soft strap-iron is coated with the flux composed of clay and salt and heated to over 1000 C. in a muffle or a blowpipe flame/ the iron absorbs aluminium and becomes tough and springy, having many of the properties of steel. They also claim that by simply charg- ing broken lumps of cast-iron into a cupola with alternate layers of common clay and a flux, the metal run down contains as much as 1.75 per cent, of aluminium, yielding a very fluid, strong iron, which runs into the thinnest castings. The London papers state that the alloys thus produced assuredly contain aluminium, and that the contained aluminium does not cost over 25 cents per Ib. A newspaper report speaks of exactly similar processes being operated by an aluminium company in Kentucky. (See also p. 317.) It is said that they charge a cupola with scrap-iron, pig-iron, coke, clay, and a flux, and that on melting the charge down and pouring, the castings produced are similar to the best steel, the fracture of the metal being white, slightly fibrous and free from blow-holes. It it stated, further, that the castings, on analysis, contained 1.7 per cent, of aluminium. Scrap-iron is also treated in the same way as reported by Brin Bros., being simply coated with a pasty mixture of clay and a flux and heated almost white-hot, when the iron absorbs aluminium. * Eng. and Mining Journal, May 15, 1886. 336 ALUMINIUM. The Aluminium Process Company, of Washington, D. C., own several patents granted to W. A. Baldwin, of Chicago, 111. In one of these,* a bath is formed by fusing together 4 parts of ground clay, 12 parts of common salt and 1 part of charcoal powder. The metal to be alloyed, e. aluminium. kilos per sq. mm. Ibs. per sq. in. 10 58.36 83,000 10 55.35 78,720 8 33.18 47,190 5 ...... 32.20 45,800 5 . , 31.43 44,700 French wrought-iron . . . 35.00 49,780 Deville determined the strength of aluminium bronze drawn into wire, compared with that of iron and steel wire of the same size (1 mm. diameter = No. 19 B. W. G.), as Aluminium bronze . Kilos per sq. mm. 85 60 Ibs. per sq. in. 120,900 85,340 Steel .... / 90 / 128,000 ' 1100 1 142,000 Experiments made in 1861,* on the relative strengths of alu- minium bronze and the common metals gave * Chemical News, v. p. 318. ALUMINIUM-COPPER ALLOYS. 425 Aluminium bronze ....... 19 Gun metal (copper 89, tin 11) 10 Drawn brass wire 8 Drawn copper wire 7 Tin bronze (copper 96, tin 4) ..... 4 Same, with 1 per cent, aluminium .... 10 Same, with 2 " " .... 16 In 1862, Anderson tested the strength of aluminium bronze at the Woolwich Arsenal; testing pieces 3J inches long and 0.6 inch diameter, with the following results : Lbs. per sq. iu. Aluminium bronze . ... . . 73,185 Gun metal '. 35,000 Hardest steel . . 118,000 Medium cast-steel 82,850 Steel from a Krupp cannon 74,670 The Cowles bronzes have been tested officially at the Water- town Arsenal and at the Washington Navy Yard, with especial reference to their comparison with the government bronzes. The Cowles alloys contain small variable quantities of silicon and the following content of aluminium : Grade. Special " A" 11 per cent. A 10 " B 7 " C 5-5 " D 2^ " E 1 " Three tests of the " special A" grade, made on the Watertown testing machine, gave the following results : 1. Cast in sand. Test piece 2 inches long, 0.2 sq. inch area. 2. Forged hot (some flaws). " 10 " 0.5 " " 3. Rolled hot " 2 " 0.2 " " 1. 2. 3. Tensile strength (Ibs. per sq. in.) 109,800 87,600 111,400 Elastic limit " " 79,900 41,000 84,000 Total elongation (per cent.) 0. 2. 6.5 Modulus of elasticity 17,240,000 15,625,000 The curve of number 3 is given on the diagram (Fig. 29) as A. Two tests of the " A" grade, on the same machine, gave 42() ALUMINIUM. 5. Cast in sand. Test piece 1 inch long, 0.08 sq. inch area. 6. Forged hot " 10 inches " 0.25 " " 5. 6. Tensile strength (Ibs. per sq. in.) 87,510 89,680 Elastic limit " " 50,000 Total elongation (per cent.) 17. 29.7 Modulus of elasticity 15,741,000 The curve of number 6 is given on the diagram (Fig. 29) as B. Ibs. per sq. in. 44 00 Kilos per Fig. 2$. sq. mm. II _| 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 | 1 1 1 I] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 . i ::::::: T ijjjijjjIiEjjjIjjijijEEijjEJE I i_:::_ ::: ":---"s'E53ZE^ 2" iZ5'u!!EZE2:: . 843(J + ^ J :e -- 4.1-- i ~9 * f ::::,? 100.000 1)1 ti: I ib ^::::: ::_::: :: ::: :::_~:: 90000 4- T. ;::: = = = = 63.27 ;;;;::::::!!"":::: ::"::: ao ooo I 1 = 1 : ' 3 _ : *-*_ 4. If J ,-._, , f < '. .. 1_ . ____. 49 21 \\ / If ' w.ooo CM 4|i C5 ?^--:;;:: : = ; = := = = "*"~^ eoooo-HkUne*'--- 35 ,5 40000 .Ul-l-l^ .. > - - Pi 14--- 4^j-j- - t:::::::::::::::::::::::::::: 10.000 4J4- - - g Elongation per cent. The test of a specimen of Cowles' bronzes of " A 3" grade, con- taining 8J per cent, of aluminium made by Professor Unwin, F. K. S., gave ALUMINIUM-COPPER ALLOYS. 427 Tensile strength 82,389 Ibs. per sq. in. Elastic limit . . . . .39,738 " " Elongation 33.26 per cent. Test piece 10 inches long and 0.2 sq. inch area. The B, C, D, and E grades decrease in tensile, transverse, tor- sional and compressive strength and in elastic limit in the order in which they are named, but the extensibility increases as the other properties decrease. Samples of Cowles' B and C grades, tested by Mr. Edw. D. Self, at the Stevens Institute, Hoboken, N. J., gave B. c. Tensile strength (Ibs. per sq. in.) . . 51,680 40,845 Elongation (per cent.) 4.1 11.2 A sample of the D grade, tested on the manufacturer's machine, gave a strength of 42,770 Ibs., with 53 per cent, elongation. The bronzes made at Neuhausen by the Heroult process have been tested in Zurich with the following results : TENSILE STRENGTH. i Per cent. Grade. aluminium A 7 B 7 a 10 H 10$ Professor Tetmayer, under whose supervision the above tests were made, made a series of bronzes from the pure metals, for the express purpose of testing, and obtained the following results : kilos per Ibs. per Elongation, sq. win. sq. in. per cent. (35.9 138.7 49,200 55,060 25.4 27.3 (38.4 140.7 54,600 58,320 27.4 25.5 (36.4 j 45.0 (46.3 51.760 64,000 65,950 34.3 45.7 48.4 48.0 68,270 37.5 f 50.6 151.6 72,250 73,380 32.9 39.2 (52.2 156.0 74,240 79,650 23.5 16.1 J55.3 U2.1 78,620 88,325 18.5 10.5 ( 59.0 164.0 83,915 91,000 12.0 6.3 kilos per sq. mm. Ibs. per sq. in. UlUUgOiLlV/Uj per cent. 44 62,580 64.0 50 71,115 52.5 57.5 81,780 32. 62. 88,180 19. 64. 91,000 11. 68. 96,720 1. 80. 113,780 0.5 428 ALUMINIUM. TENSILE STRENGTH. Per cent, of aluminium. 10 11 The annexed diagram (Fig. 30) shows by its curves the varia- tion of tensile strength and elongation of the aluminium bronzes with the increasing percentage of aluminium, the curves C and C r being taken from Cowles' advertised guarantee (1889), the elonga- tion being the minimum and the strength the average values guar- anteed in castings ; H and H f represent the average values given by Professor Tetmayer for bronzes made by the Heroult process ; T and T f represent Tetmayer's determinations with bronzes made from the pure metals. Cowles Bros, tested the effect of temperature on the strength of aluminium bronze. A bar was tested, and showed a tensile strength of 109,120 Ibs. per square inch with 5 per cent, elonga- tion. A duplicate bar was then put in the machine and 100,000 Ibs. per square inch put on it. It was then heated (still under stress) by a blowpipe flame to about 400 F., and the strain in- creased to 107,000 Ibs. The bar was then cooled down to the temperature of the room, and afterwards stood 110,160 Ibs. per square inch without breaking. It thus appears that aluminium bronze does not seem to lose any strength up to a heat of about 400 F. Annealing and hardening. Aluminium bronze acts like ordi- nary brass in these respects. It is softened by chilling ; the best procedure is said to be to heat the articles to bright redness for some time, to destroy all crystalline structure, then cool in still air to full redness and plunge into cold water. The metal becomes very hard and stiff when worked for some time without anneal- ing. To get the bronze to its maximum elasticity and hardness it must be cooled very slowly. Articles of bronze can be heated red-hot in charcoal powder and allowed to cool embedded in it. It is said that the bronze can be thus made elastic enough for the hair-springs of watches. ALUMINIUM-COPPER ALLOYS. 429 Tensile strength, Ibs. per sq. in. Fig- 3( 130.000 5 i 100.000 80.000 .. it - i. n:":~:~~::::":"::~:::::"::z::: ::::::::::::::::::::: CAJBINET MAKER'S ALBUM OF FURNITURE: Comprising a Collection of Designs for various Styles of Furniture. Illustrated by Forty-eight Large and Beautifully Engraved Plates. Oblong, 8vo $3.50 CALLINGHAM. Sign Writing and Glass Embossing: A Complete Practical Illustrated Manual of the Art. By JAMES CALLINGHAM. i2mo $1.50 CAMPIN. A Practical Treatise on Mechanical Engineering: Comprising Metallurgy, Moulding, Casting, Forging, Tools, Work, shop Machinery, Mechanical Manipulation, Manufacture of Steam- Engines, etc. With an Appendix on the Analysis of Iron and Iron Ores. By FRANCIS CAMPIN, C. E. To which are added, Observations on the Construction of Steam Boilers, and Remarks upon Furnaces used for Smoke Prevention ; with a Chapter on Explosions. By R. ARMSTRONG, C. E., and JOHN BOURNE. Rules for Calculating ths Change Wheels for Screws on a Turning Lathe, and for a Wheel* cutting Machine. By J. LA NICCA. Management of Steel, Includ- ing Forging, Hardening, Tempering, Annealing, Shrinking anl Expansion ; and the Case-hardening of Iron. By G. EDF. 8vo. Hlusfcrahtd with twenty-nine plates and 100 wood engraving* $5.00 HENRY CAREY BAIRD & CO.'S CATALOGUE. CAREY. A Memoir of Henry C. Carey. By DR. WM. ELDER, With a portrait. 8vo., cloth . . f5 CAREY. The Works of Henry C. Carey : Harmony of Interests : Agricultural, Manufacturing and Commer* cial. 8vo. ...'.. $1.50 Manual of Social Science. Condensed from Carey's " Principles of Social Science." By KATE McKEAN. I vol. I2mo. . 2.25 Miscellaneous Works. With a Portrait. 2 vols. 8vo. $10.00 Past, Present and Future. 8vo $3.50 Principles of Social Science. 3 volumes, 8vo. . . $10.00 The Slave-Trade, Domestic and Foreign; Why it Exists, and How it may be Extinguished (1853). 8vo. . . , $2.00 The Unity of Law : As Exhibited in the Relations of Physical, Social, Mental and Moral Science (1872). 8vo. . . $3.50 CLARK. Tramways, their Construction and Working : Embracing a Comprehensive History of the System. With an ex' haustive analysis of the various modes of traction, including horse- power, steam, heated water and compressed air; a description of the varieties of Rolling stock, and ample details of cost and working ex- penses. By D. KINNEAR CLARK. Illustrated by over 200 wood engravings, and thirteen folding plates. 2 vols. 8vo. . $12.50 COLBURN. The Locomotive Engine : Including a Description of its Structure, Rules for Estimating its Capabilities, and Practical Observations on its Construction and Man- agement. By ZERAH COLBURN. 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The Goldsmith's Handbook : Containing full instructions for the Alloying and Working of Gold, including the Art of Alloying, Melting, Reducing, Coloring, Col- lecting, and Refining; the Processes of Manipulation, Recovery of Waste; Chemical and Physical Properties of Gold; with a New System of Mixing its Alloys ; Solders, Enamels, and other Useful Rules and Recipes. By GEORGE E. GEE. I2mo. . . $1.75 GEE. The Silversmith's Handbook : Containing full instructions for the Alloying and Working of Silver, including the different modes of Refining and Melting the Metal; its Solders ; the Preparation of Imitation Alloys ; Methods of Manipula- tion ; Prevention of Waste ; Instructions for Improving and Finishing the Surface of the Work ; together with other Useful Information and Memoranda. By GEORGE E. GEE. Illustrated. I2mo. $1-75 GOTHIC ALBUM FOR CABINET-MAKERS: Designs for Gothic Furniture. Twenty-three plates. Oblong $2.00 GRANT. 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S. 8vo. . . . $2.50 Hand-Book of Useful Tables for the Lumberman, Farmer and Mechanic: Containing Accurate Tables of Logs Reduced to Inch Board Meas^ ure, Plank, Scantling and Timber Measure; Wages and Rent, by Week or Month ; Capacity of Granaries, Bins and Cisterns ; Land Measure, Interest Tables, with Directions for Finding the Interest on any sum at 4, 5, 6, 7 and 8 per cent., and many other Useful Tables. 32 mo., boards. 186 pages .25 HASERICK. The Secrets of the Art of Dyeing Wool, Cotton, and Linen, Including Bleaching and Coloring Wool and Cotton Hosiery and Random Yarns. A Treatise based on Economy and Practice. By E. C. HASERICK. Illustrated by 323 Dyed Patterns of the Yarni or Fabrics. 8vo $7-5<3 HATS AND FELTING: A Practical Treatise on their Manufacture. By a Practical Hatter. Illustrated by Drawings of Machinery, etc. 8vo. . . $r.2 H OFFER. 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The Practical Brass and Iron Founder's Guide: A Concise Treatise on Brass Founding, Moulding, the Metals and their Alloys, etc. ; to which are added Recent Improvements in the Manufacture of Iron, Steel by the Bessemer Process, etc., etc. By JAMES LARKIN, late Conductor of the Brass Foundry Department a; Reany, Neafie & Co.'s Penn Works, Philadelphia. Fifth edition, revised, with extensive additions. I2mo. . . . $2.25 LEROUX. A Practical Treatise on the Manufacture of Worsteds and Carded Yarns : Comprising Practical Mechanics, with Rules and Calculations applied to Spinning; Sorting, Cleaning, and Scouring Wools; the English and French Methods of Combing, Drawing, and Spinning Worsteds, and Manufacturing Carded Yarns. Translated from the French of CHARLES LEROUX, Mechanical Engineer and Superintendent of a Spinning-Mill, by HORATIO PAINE, M. D., and A. A. FESQUET, Chemist and Engineer. Illustrated by twelve large Plates. 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