UC-NRLF 
 
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 LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 
 
MONOGRAPHS 
 
 ON 
 
 APPLIED ELECTROCHEMISTRY 
 
 EDITED BY 
 
 VIKTOR ENGELHARDT, 
 
 Head Engineer and Chief Chemist of the Siemens & Halske A. G. , 
 
 Vienna. 
 
 WITH THE COOPERATION OF 
 Dr. E. Abel, Chemist for the Siemens & Halske A. G., Vienna. 
 
 E. G. Acheson, President of the International Acheson Graphite Co., 
 
 Niagara Falls, N. Y. 
 
 Dr. P. Askenasy, Superintendent of the Akkumulatorwerke, Liesing. 
 
 H. Becker, Publisher of "L'Industrie electro-chimique, " Paris. 
 
 Dr. W. Borchers, Professor at the Technical High School, Aachen. 
 
 Sh. Cowper-Coles, Publisher of "The Electrochemist and Metallur- 
 gist," London. 
 
 Dr. F. Dieffenbach, Professor at the Technical High School, Darm- 
 stadt. 
 
 Dr. G. Erlwein, Chief Chemist of the Siemens & Halske A. G., Berlin. 
 
 H. Friberg, Engineer of the Siemens & Halske, A. G., Berlin. 
 
 H. Gall, Director of the Socie"te d'Electrochimie, Paris. 
 
 F. E. Giinther, Mining Engineer, Aachen. 
 
 Dr. F. Haber, Professor at the Technical High School, Karlsruhe. 
 
 Dr. C. Ha'ussermann, Professor at the Technical High School, Stutt- 
 gart. 
 
 Dr. R. Hammerschmidt, Electrochemist, Charlottenburg. 
 
 Dr. G. Hausdorff, Registered Chemist, Essen. 
 
 Dr. K. Kellner, General Director, Vienna. 
 
 A. Krakau, Professor of the Electrochemical Institute, St. Petersburg. 
 
 Dr. H. Landolt, Director of the Society for Electrochemical Industry, 
 Turgi. 
 
 Dr. M. Le Blanc, Professor at the Technical High School, Karlsruhe. 
 
 C. Liebenow, Engineer, Berlin. 
 
 Dr. R. Lorenz, Professor at the Swiss Polytechnic, Zurich. 
 
 Dr. R. Lucion, Director of Solvay & Co., Brussels. 
 
 A. Minet, Publisher of " L'l^lectrochimie, " Paris. 
 
 A. Nettel, Engineer, Berlin. 
 
 H. Nissenson, Director of Akt.-Ges. of Stolberg & Westfalen, 
 Stolberg. 
 
 Dr. F. Peters, Instructor at the Royal Mining Academy, Berlin. 
 
 Dr. W. Pfanhauser, Manufacturer, Vienna. 
 
 Registered Chemist Dr. O. Prelinger, Chemist of the Siemens & 
 Halske A. G., Vienna. 
 
 Titus Ulke, M. E., Electrometallurgical and Mining Engineer of the 
 Lake Superior Power Co., Sault Ste. Marie, Ontario. 
 
 Dr. Th. Zettel, Chief Chemist of Brown-Boveri & Co,, Baden. 
 And other experts. 
 

 
 MONOGRAPHS ON APPLIED ELECTROCHEMISTRY. 
 
 VOL III. 
 
 THE PRODUCTION OF 
 
 Chromium and Its Compounds 
 
 BY THE AID OF THE 
 
 Electric Current 
 
 BY 
 
 DR. MAX LE BLANC. 
 
 PROFESSOR AND DIRECTOR OF THE PHYSICAL-CHEMICAL 
 
 (ELECTROCHEMICAL) INSTITUTE OF THE TECHNICAL 
 
 HIGH SCHOOL, KARLSRUHE. 
 
 AUTHORIZED ENGLISH TRANSLATION BY 
 
 JOSEPH W. RICHARDS, M.A., A.C., PH.D. 
 
 PAST-PRESIDENT OF THE AMERICAN ELECTROCHEMICAL, SOCIETY. 
 PROFESSOR OF METALLURGY AT LEHIGH UNIVERSITY. 
 
 [^ or THE 
 f UNIVERSITY 
 
 PUBLISHED BY THE CHEMICAL PUBLISHING COMPANY, 
 1904. 
 
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 7 " 
 
 Itni 
 
 COPYRIGHT, 1904, BY THE CHEMICAL PUBLISHING Co. 
 
AUTHOR'S PREFACE TO THE GERMAN EDITION. 
 
 It has been my endeavor to give in the present Monograph 
 a complete review of what has been published up to the end of 
 the year 1901, in relation to the manufacture of chromium and 
 its compounds with the assistance of the electric current. 
 To accomplish this I undertook a comprehensive study of the 
 literature of the subject, in particular reviewing the German, 
 English and American patent literature. I can scarcely hope 
 to attain the end I had in view, since to get together all the 
 observations which have been made concerning chromium, 
 part of which are in places where they would scarcely be ex- 
 pected, is indeed, at least for the single investigator, an almost 
 impossible task ; I may, however, remark that I have taken 
 special pains in this direction. I shall receive with thanks 
 any information concerning items which I have overlooked 
 and which are deserving of mention. 
 
 The original publications quoted have been extracted in 
 such manner that reference to the original for further par- 
 ticulars is in most cases unnecessary. Further remarks on 
 this subject are made on page 10. 
 
 It will be to me a satisfaction if this work proves itself of 
 service to my colleagues in the profession. 
 
 I thank heartily Dr. J. Erode for his friendly assistance in 
 reading the proof. M. LE BLANC. 
 
 Karlsruhe. 
 
 TRANSLATOR'S PREFACE. 
 
 The study of these attempts to produce chromium and its 
 compounds electrolytically will be profitable not only to the 
 electrochemist particularly interested in chromium, but also 
 to every active electrochemist whose work deals with difficult 
 problems in electrolysis. 
 
 I wish to acknowledge the assistance furnished by Walter 
 S. Landis, Met. Eng., in the preparation of the manuscript 
 and reading of proofs. JOSEPH W. RICHARDS. 
 
 Lehigh University. 
 
 .A O O 
 
CONTENTS. 
 
 I. OBTAINING OF METALLIC CHROMIUM .... i 
 
 A. By electrolysis of aqueous solutions . '. I 
 
 B. By the use of high temperatures 32 
 
 II. THE OBTAINING OF COMPOUNDS OF CHRO- 
 MIUM WITH METALS 53 
 
 A. By electrolysis of aqueous solutions 53 
 
 B. By the use of high temperatures 54 
 
 III. OBTAINING OF THE COMPOUNDS OF CHRO- 
 MIUM WITH THE NON-METALS 66 
 
 A. Carbon compounds 66 
 
 B. Silicon compounds 67 
 
 C. Phosphorus compounds 71 
 
 D. Sulphur compounds 72 
 
 E. Oxygen compounds 73 
 
 (1) Chromous oxide compounds 73 
 
 (2) Chromic oxide compounds 76 
 
 (fl) BY ELECTROLYSIS OF AQUEOUS SOLUTIONS 76 
 
 (b) BY THE USE OF HIGH TEMPERATURES . . 8 1 
 
 (3) Chromic acid compound 86 
 
 (a) CHROMATES OF THE HEAVY METALS ... 86 
 () CHROMATES OF THE ALKALI METALS AND 
 
 CHROMIC ACID 95 
 
 APPENDIX .... .120 
 
I. OBTAINING OF METALLIC CHROMIUM. 
 
 A. By Electrolysis of Aqueous Solutions. 
 
 Nearly fifty years ago Bunsen, in his ramblirigs in the field 
 electrochemistry, found a process for the manufacture of me- 
 tallic chromium. 1 At that time the cheap production of 
 chemical compounds on a large scale with the assistance of 
 the electric current was essentially impracticable, and it has 
 only been in the last fifteen years, in fact, that the previously 
 unanticipated development of electro-technology has rendered 
 it possible. I reproduce the most important principles of his 
 manipulation, mostly in his own words, which show an aston- 
 ishing clearness of view considering the time at which it was 
 written, concerning the importance of current density in elec- 
 trolytic operations. 
 
 " Most important for the chemical action of the current is 
 the density of the current, that is, the current strength divided 
 by the electrode surface at which the electrolysis takes place. 
 With this density increases the power of the current to over- 
 come the chemical affinities. If one conducts a current, for in- 
 stance, of constant strength through a cell of chromic chloride 
 in water, it depends upon the area of the reducing electrode 
 whether one gets hydrogen, chromic oxide, chromous oxide? 
 or metallic chromium. The relative amounts of the constit- 
 uents of the electrolyte through which the current passes 
 are of no less importance. If one increases gradually, for 
 instance, the amount of chromous chloride in solution, keep- 
 ing constant the current strength and the electrode surfaces, 
 a point is soon reached where the elimination of chromous 
 oxide is accompanied by a reduction of the metal and finally 
 is entirely replaced by it." 
 
 He then describes further on the decomposing cell, one pole 
 of which was the interior surface of a carbon crucible con- 
 tained inside a porcelain crucible and filled with hydrochloric 
 acid, and kept hot in a water-bath, while the other pole was 
 
 1 Poggendorff's Ann. 91, 619 (1854). 
 
2 CHROMIUM AND ITS COMPOUNDS 
 
 a narrow strip of platinum placed inside a clay cell in which 
 the fluid to be decomposed was placed, and the whole stood 
 inside the carbon crucible. This arrangement proved itself 
 as very suitable for the obtaining of high current densities at 
 one electrode, and he recommended it in general for the 
 electrolytic deposition of metals, especially for the reduction 
 of chromium from its aqueous solutions. 
 
 " Using in such a reduction experiment chromous chloride 
 solution containing some chromic chloride, metallic chromium 
 can be easily obtained in continuous sheets of 50 sq. mm. in 
 size, but quite brittle, the surface lying against the platinum 
 electrode being perfectly white and of metallic lustre. The 
 chromium, which can be obtained chemically pure only in 
 this way, resembles iron very much in its external appear- 
 ance, but it is more permanent in damp air and burns on being 
 heated in air to chromic oxide. Hydrochloric and sulphuric 
 acids dissolve it slowly to chromous salts with evolution of 
 hydrogen. It is scarcely attacked by nitric acid even when 
 boiling." 
 
 Bunsen gives further details of the experiments in the fol- 
 lowing sentences: "The reduction of the metal takes place 
 therefore out of concentrated chlorous solutions heated to 
 boiling, when each square millimeter of the reducing pole 
 surface receives a current of the absolute intensity 0.067. z 
 If the current density is gradually lowered a point is soon 
 reached where the reduction of metal disappears, and is re- 
 placed by a copious formation of anhydrous chromous-chromic 
 oxide. This oxide can be made only in this manner and can 
 be made in large quantities and is purified by long boiling 
 with aqua regia. It is a very black non-crystalline powder, 
 soluble in no acid, and burning in the air like pyrophoric 
 iron, with lively deflagration, to a green chromic oxide. The 
 composition of this chromous-chromic oxide varies between 
 
 Cr 2 Cr and Cr 3 Cr" (Cr 4 O 5 and Cr s O 6 . See further under 
 
 1 0.67 ampere per square centimeter. 
 r "^ sa*AAJA UA>V CA C/H* %V\l 
 
 *" 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 3 
 
 chromic oxide)." Bunsen remarks finally that it would cer- 
 tainly be of great interest to prove whether the metal reduced 
 out of the green and the blue salts of chromium is identical 
 in both cases, or u whether the allotropic conditions would 
 make themselves evident also in the deposited metal." At 
 present we recognize as the ground for the division between 
 the green and the blue chromium solutions, the presence in 
 them of different molecules or molecular complexes, and no 
 longer speak of the allotropic form of the metal in these two 
 solutions. 1 
 
 The data of Bunsen are on the one hand valuable for the 
 general point of view which they take, and for the conditions 
 which they impose for the separation of chromium, but one 
 misses on the other hand exact numercial data ; his work has 
 the appearance as if he had left over for a more comprehen- 
 sive work the determination of the exact details, as is indi- 
 cated by the following sentence: " I have so far determined 
 the influences on which the decomposing power of the current 
 depends, and have left over further investigations to my stu- 
 dents." However, nothing further on the subject was pub- 
 lished. 
 
 The next investigations on the obtaining of chromium were 
 a generation later ; they were directed towards the industrial 
 manufacture of chromium and are part of patent literature. 
 The names of Placet and Bonnet are in particular found at 
 the heads of such patents which were concerned principally 
 with the electrolysis of metallic compounds in general, and 
 partly in particular with the electrolytic production of chro- 
 mium. We will consider the contents of the first as far as it 
 refers to chromium. 
 
 The first patent of these two experimenters is concerned 
 with improvements in electrolysis in general, and in particular 
 with the electrolysis of metallic solutions. 2 It is characterized 
 like others of their patents by its comprehensiveness, by its very 
 
 1 R. Whitney : Zeitschr. f. physik. Cheuiie, 2O, 40 (1896). 
 
 2 English Patent No. 19, 344, November 27, 1890. 
 
4 CHROMIUM AND ITS COMPOUNDS. 
 
 general point of view and by its endeavor to extend the 
 limits of the patent as far as possible. 
 
 They ascribe the poor results in the electrolytic separation 
 of metals, up to their time, to the injurious formation of gas 
 bubbles on the negative electrode. In order to prevent this 
 they recommend keeping the bath under an increase or de- 
 crease of pressure ; if this is done, then can all metals chro- 
 mium is particularly named be obtained electrolytically 
 with the greatest ease, of high purity and of any desired size 
 and thickness, by simply using high current density ! Satis- 
 factory results are also said to be obtained by taking two 
 electrodes of different conductivity, for instance a copper wire 
 for leading in the electricity to the cell and an iron, zinc 
 or platinum electrode for the taking away of the current. 
 Or two electrodes may be used of the same material but of 
 different sizes. In place of the increasing of the external 
 pressure similar good results may be obtained in many 
 cases by increasing the density of the bath by dissolv- 
 ing in it salts of more electropositive metals. The following 
 salts are recommended for this purpose : i. Saturated solution 
 of a mixture of potassium, sodium and ammonium sulphates ; 
 2. Saturated solution of a mixture of potassium, sodium and 
 ammonium chlorides ; 3. Saturated solution of the sulphate 
 or chloride of the metal to be deposited. 
 
 A litre each of the three solutions is taken and mixed ; this 
 mixture is a remarkable bath from which the metal can be 
 precipitated pure in any desired thickness! 
 
 In place of the saturated solutions, normal concentrated 
 solutions may be taken, 120 to 150 grams of each of the three 
 alkaline salts and 150 to 200 grams of the metallic salt to 
 each litre of water. 
 
 For the refining of metals a mixture is recommended, made 
 by pouring together a litre of each of the saturated solutions 
 of the three alkaline chlorides and three alkaline sulphates as 
 well as water acidified with sulphuric or hydrochloric acids. 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 5 
 
 As electrodes, two plates of the metal to be refined are used. 
 
 The alkaline sulphates and chlorides may be replaced by 
 all other possible salts ; by alkaline nitrates and phosphates, 
 magnesium chloride and nitrate, etc. According to the nature 
 of the metal the baths should be alkaline, neutral or acid ; 
 especially with chromium they should be strongly acid. 
 
 For acidifying the baths all possible organic acids may be 
 used besides the inorganic. The addition of acid influences 
 favorably the purity of the deposited metal since any acci- 
 dental suboxide will be dissolved. Warming' of the solution 
 appears advantageous. 
 
 Either soluble or insoluble anodes may be used, and it is 
 recommended to use diaphragms in order to avoid polarizing 
 action by gas bubbles and the contamination of the bath in 
 consequence of insufficient purity of the anodes, the anodes 
 being immersed in fluids which will combine with the oxygen 
 set free there, for instance sulphuric acid, hydrochloric acid, 
 sodium chloride solution, sulphurous acid, etc. When using 
 insoluble anodes, polarization may be largely avoided by 
 roughening their surface. 
 
 The quality of the precipitate is improved by the addition 
 (i to 2 grams to 10 litres) of all possible organic compounds, 
 such as gelatine, gum, etc., or sulphur chloride, sodium sul- 
 phide, iodine, arsenic acid, etc. 
 
 To obtain alloys the following procedure is recommended : 
 After making the bath of great density, for instance, the 
 above-described mixture of the three alkaline sulphates or 
 chlorides, there is added the salt of the different metals which 
 one wishes to alloy, or soluble anodes of the metals concerned 
 are used. Then a feeble current is passed through the solu- 
 tion and gradually increased. Two cases are now possible. 
 If the bath is acid, that metal which is the most electronega- 
 tive is deposited first ; if the bath is alkaline, that metal sepa- 
 rates out first which is the most electropositive ! Later, it is 
 stated, that it is only necessary to increase the strength of 
 the current in order to obtain an alloy consisting of all of the 
 
6 CHROMIUM AND ITS COMPOUNDS. 
 
 metals contained in the bath. The relative quantities of metal 
 in the alloy may be varied by altering the relative concentra- 
 tions or the surfaces of the soluble metallic anodes. 
 
 Operating in this way very malleable alloys of zinc, tin or 
 copper with aluminium, chromium, tungsten, and molybdenum 
 have been obtained, also very hard and coherent deposits 
 of chromium with tungsten, iron and molybdenum, and very 
 light alloys of aluminium with a small quantity of chromium,, 
 tungsten, iron and molybdenum. 
 
 If the ores are sufficiently good conductors of electricity 
 they may be used directly as anodes. In other cases the valu- 
 able metals must be dissolved and can then be obtained in the 
 v pure condition from the impure salts by the methods de- 
 scribed. 
 
 We reproduce here only those patent claims which relate 
 directly or indirectly to chromium : 
 
 (1) A method of strengthening the action of the current in 
 electrolysis consisting in subjecting the hot or cold electrolyte 
 to a determined pressure, obtained either by physical means r 
 gas pressure or fluid pressure, or by a greater density of the 
 electrolyte obtained by dissolving therein indifferent material 
 not decomposed by the current, or by using conductors of 
 various cross-section or various conductivities, which hinder 
 the current in its passage and so produce an artifical pressure. 
 
 (2) An exerting of pressure upon the hot or cold electro- 
 lytic bath containing the compound of the metal to be depos- 
 ited, or in which the anode of the metal concerned is placed. 
 This pressure is obtained by physical means (gas or fluid 
 pressure), and at the same time currents of comparatively high 
 intensity are used for the production of the pure metal. 
 
 (3) The exerting of pressure upon the hot or cold electro- 
 lytic bath containing different compounds of two, three or 
 more metals or in which anodes formed of these metals are 
 dipped. This pressure is produced by physical means, and 
 such currents are utilized at the same time whose electromo- 
 tive force and intensity can be so regulated that the precipitate 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 7 
 
 of those metals is obtained of which the alloy should consist. 
 
 (4) The use of anodes of varying section and different con- 
 ductivity as the means for the production of the artificial cur- 
 rent pressure, using at the same time a current of relatively 
 high intensity, the electrolytic bath being either hot or cold 
 and containing the metal or metals to be deposited. 
 
 (5) The use of hot or cold electrolytic baths whose density 
 and consequently the pressure is increased by the solution of 
 indifferent salts as sulphates, sulphites, phosphates, or oxalates 
 of the alkalies or alkaline earths and, in fact, by all com- 
 pounds of all bases which are more electropositive or more 
 electronegative than the metal to be deposited according as to 
 whether the bath is acid or alkaline, and which contain the 
 compounds of the metal to be deposited, while pure or impure 
 soluble anodes of the metals contained in the bath are used, 
 using at the same time currents of relatively high intensity. 
 
 (6) The use of cold or hot electrolytic baths whose density 
 is increased by saturating them with (a) the three alkaline 
 sulphates, (ft) the three alkaline chlorides, (c) a sulphate or a 
 chloride or a soluble compound of the metal to be deposited, 
 using at the same time currents of relatively high intensity. 
 
 (7) The use of cold or warm electrolytic baths whose den- 
 sity may be increased by preparing them from saturated solu- 
 tions of (a) the three alkaline sulphates, (b) the three alkaline 
 chlorides, in which are placed soluble anodes of the metals to 
 be deposited, using at the same time currents of relatively 
 high intensity. 
 
 (8) The use of electrolytic baths whose density is increased 
 by making them from a saturated solution of the three alka- 
 line chlorides, or a saturated solution of the three alkaline 
 sulphates and to one of these solutions a saturated solution of 
 the chloride or sulphate of any other soluble salt of the metal 
 to be deposited is added, or by using smooth or rough anodes 
 of the metal concerned, using at the same time currents of rela- 
 tively high intensity. 
 
8 CHROMIUM AND ITS COMPOUNDS. 
 
 (9) The use of electrolytic baths whose density is increased 
 as described above and which contain insoluble anodes placed 
 in porous vessels, which latter contain for the avoidance of 
 polarization one of the following solutions : Sulphuric acid, 
 hydrochloric acid, sodium chloride, calcium chloride, sul- 
 phurous acid or sulphites, using at the same time currents of 
 relatively high intensity. 
 
 (10) The use of electrolytic baths whose density is increased 
 as before described and in which soluble, roughened anodes 
 are placed in porous vessels for the avoidance of polarization 
 and the arrangement of which is shown in the accompanying 
 plate, for the purpose of avoiding the contamination of the 
 bath by the impurities of these anodes, using at the same time 
 currents of relatively high intensity. 
 
 (n) The use of electrolytic baths whose density is increased 
 as above described in which roughened soluble or insoluble 
 anodes are contained in porous vessels whose arrangement is 
 shown by the accompanying plate and which contains a de- 
 polarizing fluid in case insoluble anodes are used. The de- 
 polarization fluid or the fluid to be decomposed or both should 
 be automatically renewed, using at the same time currents of 
 relatively high intensity. 
 
 (12) The use of electrolytic baths whose density is in- 
 creased as above described in which a soluble zinc anode is 
 placed in a porous vessel containing oxalic acid or an alkaline 
 oxalate in order to hinder the zinc salt formed from passing 
 into the bath which is being decomposed, using at the same 
 time currents of relatively high intensity. 
 
 (13) The use of electrolytic baths whose density is in- 
 creased as before described, into which a soluble or insoluble 
 anode dips and in which, for the improvement of the quality 
 of the metal, there is added per litre of bath i to 2 grams of 
 gelatine, gum, dextrin or similar material, using at the same 
 time currents of relatively high intensity. 
 
 (16) The use of electrolytic baths whose density is in- 
 creased as before described and into which dip soluble anodes 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 9 
 
 (ores when of sufficient conductivity may be used as anodes) 
 or in which compounds of the metals to be deposited as alloys 
 are dissolved (these compounds may be the ores of such 
 metals if sufficiently soluble). The surfaces of the anodes 
 and the relative quantities in which the compounds are dis- 
 solved vary according to the proportions in which the metals 
 are desired in the alloys, using at the same time a current 
 whose electromotive force and intensity may be so regulated 
 that a precipitate of the metals is obtained of which the alloy 
 .should consist. 
 
 (17) The alloys: (a) of aluminium, zinc, tin or copper, 
 of chromium, zinc, tin or copper, of tungsten, zinc, tin or copper, 
 of molybdenum, zinc, tin or copper, etc.; (d) of molybdenum and 
 silver, of uranium and silver ; (c) of chromium and tungsten, 
 of iron and chromium, of nickel and chromium, of nickel and 
 molybdenum, etc.; (d) of aluminium and chromium, of alu- 
 minium and tungsten, of aluminium and iron, of aluminium and 
 molybdenum, etc. These alloys can be alloyed with each 
 other. 
 
 (18) The use of electrolytic baths whose density is increased 
 as before described and in which good conducting ores are 
 used as soluble anodes, using at the same time currents of rel- 
 atively high intensity suitable for precipitating the metal. 
 
 (19) The use of electrolytic baths whose density is in- 
 creased as before described in which poorly conducting ores 
 are dissolved by being previously transformed into soluble 
 sulphates, chlorides, etc., using at the same time a current of 
 relatively high intensity suitable for precipitating the metal. 
 
 (20) The use of electrolytic baths whose density is in- 
 creased as before described, in which the compounds of valu- 
 able metals are dissolved, in case these are soluble or trans- 
 formable into soluble compounds, using at the same time 
 currents whose density may be progressively altered in order 
 to precipitate successively the single metals forming the alloys. 
 
 (21) The use of electrolytic baths whose density is in- 
 creased as before described and in which the alloys of valuable 
 
10 CHROMIUM AND ITS COMPOUNDS. 
 
 metals dip, if these alloys can serve as soluble anodes, using- 
 at the same time a current whose intensity may be progres- 
 sively altered in order to be able to precipitate successively the 
 single metals forming the alloy. 
 
 (22) The use of several electrolytic baths in series whose 
 density is increased, or which are subjected to an increased 
 pressure as before described, and in which one or more me- 
 tallic compounds are dissolved or in which one or more solu- 
 ble anodes are placed, according to whether a single metal or 
 alloy is to be produced, using at the same time currents of 
 relatively high intensity, whose intensity and electromotive 
 force may be altered in the case that alloys are to be manu- 
 factured. 
 
 It is superfluous to criticize the above patent claims since 
 every one, who has only a small knowledge of the subject, rec- 
 ognizes at once that these are not the outcome of actual ex- 
 periments, but are at least for the most part mere fantasies. 
 The further patents of Placet and Bonnet contain similar 
 fantasies, and they are to be found also in the patents of other 
 inventors. An explanation of this lies in the fact that the 
 patent specifications are often written out before the comple- 
 tion and at times even before the beginning of tedious investi- 
 gations, and on this account contain statements which have 
 in no way been controlled by experiment. On this account a 
 certain caution is to be recommended concerning statements 
 in patents. 
 
 The question may be quite prudently asked as to whether 
 it is worth while to reproduce the contents of such fantastic 
 patents in this monograph. I have answered the question in 
 the affirmative after considerable reflection and acted accord- 
 ingly, for on the one hand the limit separating works worth 
 quoting from others not worth quoting is not always easy to 
 draw and might be decided differently according to the person 
 making the decision, and as many times a small grain of gold 
 may be hidden under much rubbish, and yet in truth serve as a 
 crystallizing point for further investigations and also, however. 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. II 
 
 l>e highly detrimental to the claims of later investigators. 
 Any one who has had much to do with the taking out of pat- 
 ents has probably had the experience that the remarks of 
 many patentees are so general that they frequently cover more 
 particulars than was intended, and their generalities frequently 
 include in their terms facts which were completely unknown 
 to the patentee, but such generalities are frequently of 
 great hindrance and burdensome to applicants for new pat- 
 ents ; naturally in the second case an exact knowledge of 
 the literature would be of considerable use. 
 
 This monograph endeavors, in contrast with the yearly re- 
 ports, etc., to give a complete compilation of the subject of 
 such extensiveness as shall make superfluous the necessity of 
 referring to the frequently difficultly accessible original litera- 
 ture. We wish first to find our bearings in the mass of ma- 
 terial to be found in this field, valuable and valueless. On 
 these grounds I did not deem a selection admissible. 
 
 A second patent 1 of Placet and Bonnet is concerned directly 
 with the electrolytic production of chromium. The inventors 
 state that it is necessary in manufacturing chromium and 
 chromium alloys electrolytically to keep the content of chro- 
 mium in the bath constant during the whole duration of the 
 process. The electrical conductivity of the bath is increased 
 by adding sulphates or chlorides of the alkalies, or alkaline 
 earths; the addition of organic materials like gum and dex- 
 trin is also useful. 
 
 Regarding the concentration of the chromium salt solution 
 itself, they recommend to use only about one-fifth of the quan- 
 tity of salt necessary to make a completely saturated solution; 
 the solution is preferably to be warmed. 
 
 The nature of the metallic precipitate is favorably in- 
 fluenced by making the surface of the anode larger than that 
 of the cathode. As anodes, soluble and insoluble materials 
 may be used, but it is, however, always to be recommended 
 that in order to avoid the contamination of the baths and the 
 
 1 German Patent No. 66,099, December 5, 1890. 
 
12 CHROMIUM AND ITS COMPOUNDS. 
 
 polarization resulting from gas bubbles, diaphragms should 
 be used and to place in the anode compartment such fluids 
 as will combine with the oxygen there liberated ; for instance 
 sulphuric acid, hydrochloric acid, sodium chloride solution, 
 sulphurous acid, etc. 
 
 To keep the chromium content of the bath constant, solid 
 chromium salt is to be added from time to time. 
 
 A tension of 30 to 40 volts (!) is recommended as particu- 
 larly advantageous for operating the bath. 
 
 If alloys are to be directly precipitated the salt of the metal 
 to be alloyed is dissolved in the bath just described or the 
 metal to be alloyed is used as a soluble anode in a one-half or 
 three-quarter saturated solution of the alkalies or the alkaline 
 earths and the current used at that tension " which corresponds 
 to the composition of the alloy." 
 
 For example, if it is wished to alloy iron with chromium it 
 is well to add about one-quarter of the quantity of iron salt to 
 the solution that would be necessary to saturate it, and about 
 one-fifth of that quantity of chromium salt which would like- 
 wise saturate the liquid in the absence of any other salt. To 
 the solution thus formed is added as much alkali or alkaline 
 earth salt as it will take up. 
 
 " The alloy can either be directly extracted from such a 
 bath or the two metals may be deposited consecutively, but 
 one upon the other and subsequently melted together to the 
 alloy." In both cases the composition of the alloy may be 
 regulated, " in the first case by using a certain determined 
 tension, in the latter by the duration of the action of the 
 current on the bath. At 6 volts tension only iron separates 
 out, at 30 volts only chromium." By using intermediate ten- 
 sions, alloys of any composition desired may be obtained. 
 The latter can also be obtained by precipitating first the iron 
 with a tension of 6 volts, then the chromium at a tension of 
 30 and finally melting the precipitated metals together. 
 
 Patent Claim. 
 
 The electrolytic obtaining of chromium and its alloys, 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 13 
 
 characterized by adding to the solution of chromium salt in 
 about five times the volume of water necessary to dissolve it, 
 materials which will not chemically injure the metal to be 
 precipitated, for instance, alkali or alkaline earth sulphates, 
 chlorides, or similar salts alone or in combination with or- 
 ganic materials, gum, dextrin or similar materials, such ma- 
 terials being added to saturation and the mixture electrolyzed 
 hot or cold, keeping the chromium content of the bath as con- 
 stant as possible. 
 
 The next patent 1 of the same inventors is entitled : " Im- 
 provements concerning the electrolysis of metals." They 
 refer to their first English patent No. 19,344 of 1890 (page 3) 
 and now propose to avoid the formation of oxide at the cathode 
 by the use of acid salts (bisulphates and phosphates, acetates, 
 etc.) in place of acids. It is particularly difficult to find the 
 correct amounts of acid to add in depositing chromium from 
 the solutions containing 10-15 grams of chromium alum, 10- 
 15 grams of sodium, potassium or ammonium sulphates or a 
 mixture of these sulphates in 100 grams of water, whereas, on 
 the other hand, they obtain at once a particularly fine chro- 
 mium deposit by using bisulphates in place of the sulphates, 
 as for instance 10-15 grams of bisulphate to 10-15 grams of 
 chromium alum in 100 grams of water. In case the bisul- 
 phates contain free acid the corresponding quantity of normal 
 sulphate is to be mixed with it. Besides chromium, chromium 
 alloys as well as other metals may be precipitated from the 
 corresponding solutions. 
 
 The patent claim reads : The use of strong polybasic salts 
 alone or mixed with neutral salts in order to obtain electro- 
 lytic precipitates of chromium, aluminium, copper, iron, nickel, 
 cobalt, tungsten, molybdenum, antimony, tin, silver, etc., 
 and their alloys in the above-described way. 
 
 In two further patents taken out at the same time, Placet 
 and Bonnet protect several modifications of their process for 
 making chromium. 
 
 1 English Patent 22,854, Dec. 31, 1891. 
 
14 CHROMIUM AND ITS COMPOUNDS. 
 
 The first patent 1 bears the title: " A method for the precipi- 
 tation of chromium with the assistance of electrolytic baths 
 containing chromium salts. 
 
 The bath used is again given the composition of 10, 15, to 
 20 grams of chromium sulphate with 100 grams of water to 
 which besides is added so much sulphuric acid that no forma- 
 tion of oxide can take place at the negative electrode. In 
 place of chromium sulphate may also be used chrome alum, 
 in place of sulphuric acid, either nitric, hydrochloric or hydro- 
 fluoric and organic acids or a mixture of the same. First- 
 class precipitates are said to have been obtained for instance 
 by using a bath of 10 to 15 grams of chrome alum, 10 to 15 
 grams of sodium or potassium sulphate, 5 grams oxalic acid 
 or some other organic acid and 100 grams of water, heated 
 until the originally green solution has become violet and 
 then electrolyzed. 
 
 The solution of alkaline chromate or bichromate to which 
 some sulphate is added may also be used, and for the accelera- 
 tion of the reaction the addition of a little alcohol is recom- 
 mended. The chromium salt preferably used is the sulphate 
 or a chrome alum in about the following proportions : 10 to 
 
 15 grams of chromate or bichromate with 10 to 15 grams 
 of chrome alum and 100 grams of water. 
 
 In place of the chromate the more costly chromic acid may 
 be used and in place of the chrome alum other chromium 
 salts such as the nitrate. Alkaline chromium baths likewise 
 furnish chromium when electrolyzed, even if the chromium 
 solution gives a precipitate with alkali ; the same is true of 
 baths containing cyanides or sulphocyanides of the alkalies, 
 and finally chromium may be electrolytically precipitated 
 from solutions of the roseo-chrome salts or ammoniacal 
 chrome compounds. 
 
 For raising the conductivity there may be added to any of 
 these baths 10 to 15 per cent, of alkali sulphate or ammonium 
 sulphate or a mixture of both or alkali nitrates, phosphates, 
 
 1 English Patent 22,855, Dec. 31. 1891. U. S. Patent 526,114. 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 15 
 
 etc., so that the bath may consist of, foi instance, 10 to 15 
 grams of chrome alum or chromium fluoride, 10 to 15 
 grams of sodium, potassium or ammonium fluorides, 5 to 
 10 grams of hydrofluoric acid or another acid. 
 
 In case a heavy precipitate is desired in a short time the 
 bath must be heated to higher temperatures. " In many cases 
 we heat our baths so high that the salts are melted v (see later). 
 
 The composition of the solution is kept constant either by 
 using soluble anodes or by circulation. The addition of small 
 quantities of alcohol, sugar, glycerin or analogous organic 
 compounds exercise a favorable influence upon the qualities 
 of the precipitated metal. 
 
 Finally, alloys can be made by using the baths described 
 and adding the salt of the other metal. An alloy may also be 
 obtained by the alternate precipitation of chromium and the 
 other metal and subsequent melting down. 
 
 The patent claim reads : The use of an electrolytic bath 
 containing chromium salts in the manner and for the purpose 
 described. 
 
 The second patent 1 has the title : A method for the pre- 
 cipitating of chromium by the use of electrolytic baths con- 
 taining chromic acid salts. The baths described therein need 
 to contain only i to 2 grams of chromic acid in 100 grams of 
 water ; however, with increasing concentration the quantity of 
 deposit increases. The shade of the precipitated metal alters 
 if small quantities 5 to 10 grams per litre of the following 
 acids are added : Phosphoric, sulphuric, oxalic, benzoic, formic, 
 gallic, pyrogallic, picric, purpuric (?) (phenic), salicylic ; all 
 such solutions give white chromium deposits. 
 
 Acetic and hydrofluosilicic acids give shining but dark de- 
 posits, boric acid dead but very copious deposits, while by adding 
 sulphuric, nitric, hydrochloric, arsenic, tartaric, citric, lactic 
 or tannic acids the metal is more or less dark according to the 
 quantity added. It may be noticed also that the chromic acid 
 necessary for the baths may be manufactured by the electro- 
 
 1 English Patent 22,856, Dec. 31, 1901. 
 
1 6 CHROMIUM AND ITS COMPOUNDS. 
 
 lytic oxidation of chromic salts ; also that alloys of chromium 
 and other metals may be obtained from solutions containing 
 chromic acid and other metals. 
 
 The claim reads : The use of electrolytic baths containing 
 chromic acid in the manner and for the purpose described. 
 
 In an article 1 published in 1892, "The Manufacture of 
 Metallic Chromium by Electrolysis," E. Placet presents nothing 
 new. He only repeats that a beautiful lustrous deposit of 
 pure chromium was obtained by electrolyzing an aqueous so- 
 lution of chrome alum to which alkaline sulphates and a 
 small quantity of sulphuric or other acid has been added. 
 Also chromium coatings on bronze, brass, copper and even 
 iron of any desired thickness and resembling oxidized silver 
 can be obtained in this manner. There was shown at a 
 meeting of the Academy, when this article was read, a piece of 
 metallic chromium weighing more than a kilogram, chro- 
 mium alloys and brass accoutrements electrolytically coated 
 with chromium. 
 
 In reference to the qualities of the metal so obtained, which 
 was then being industrially produced, it was mentioned that 
 it was of a bluish white color, very hard and extraordinarily 
 resistant alike to atmospheric influences as also to concentrated 
 sulphuric acid, nitric acid and caustic potash solution. 
 
 If the baths are electrolyzed under certain conditions, groups 
 of chromium crystals are obtained which have the form of 
 pine tree branches. 
 
 The fruitfulness of the two inventors E. Placet and J. Bon- 
 net is not exhausted by the five patents already described ; 
 two years later we run across a new patent 2 worded thus " Im- 
 provements in the electrolytic manufacture of chromium and 
 chromium alloys." 
 
 They commence with one of the observations made in a 
 former patent (see page 15) according to which they heat the 
 baths in some cases so high that the salts are melted, and give 
 us the following additional information thereon : 
 
 1 Comptes rendus, 115, 945 (1892). 
 
 2 English Patent 6,751, March 30, 1893. 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 1 7 
 
 We take, they say, for instance 10 to 15 grams of potassium 
 bisulphate, 100 grams of chrome alum and 100 grams of water, 
 bring the salts into solution by heating and electrolyze ; 
 chromium precipitates at once upon the cathode. The con- 
 centration of the bath is kept up by the addition of chromium 
 alum or a concentrated solution of chromium alum and alkali 
 bisulphate ; by doing this the volume increases and on this ac- 
 count an overflow is provided to keep the level of the bath 
 constant. In case only chromium alum is added all the water 
 originally in the solution is soon used up and the bath con- 
 sists only of the salts " reduced either by water or by heat(?)." 
 
 According to that, water can be dispensed with for the for- 
 mation of the bath and the latter be formed by directly melt- 
 ing down the mixture of salts. If that is so when and where 
 could we add to the bath a little potassium chlorate, boric 
 acid, benzoic acid or analogous material(!) in order to facilitate 
 the precipitation of the metal. In place of the potassium bi- 
 sulphate there may be used as a flux either sodium or am- 
 monium sulphate or bisulphates or the phosphates, borates, 
 chlorates, silicates, chlorides, fluorides, etc., of the alkalies or 
 alkaline earths or mixtures of the same ; in place of the 
 chrome alum also chromic oxide and all other chromium 
 salts which melt easily when mixed with the alkaline earths. 
 On account of the high melting-point of chromium we usually 
 use an electric furnace and in place of pure carbon electrodes 
 we use electrodes made of a mixture of carbon, chromic oxide, 
 chromic salts or ores, a flux as borax, etc., and a reducing 
 agent (like zinc, magnesium, aluminium, etc.) so that the 
 metal is simultaneously reduced and melted. 
 
 If chromium alloys are to be immediately produced the 
 electrodes may be made of the alloying metal (copper, 
 aluminium, silver, nickel, zinc) or of their oxides. 
 
 It is finally recommended to introduce into the melting 
 crucible indifferent or reducing gases, as hydrogen, etc., and 
 as the simplest manner of introduction through hollow elec- 
 trodes. 
 
1 8 CHROMIUM AND ITS COMPOUNDS. 
 
 The patent claim reads : i. The above-described improve- 
 ments in the obtaining of metallic deposits of chromium of 
 any thickness and in considerable quantities for commercial 
 purposes. 2. The above-described improvements in chro- 
 mium coating various articles, among others of carbon fila- 
 ments and rods such as are used in electric lighting. 3. The 
 above-described improvements for the direct electrolytic pro- 
 duction of alloys of chromium and other metals. 
 
 My opinion of the contents of this patent of Placet and 
 Bonnet is a repetition of what I have said on page 10. In order 
 to give my judgment some experimental justification I have 
 had Mr. Shick produce and electrolyze in my laboratory some 
 of the baths recommended in the patent specifications. 
 
 I quote some extracts from the report of Mr. Shick : 
 
 A well-saturated solution of chromic sulphate at the tem- 
 perature of the room, was used and 100 cc. diluted to 600 cc. 
 with water and then sodium chloride added to saturation. A 
 platinum foil was used in each case as cathode. With 40 
 sq. cm. active cathode surface, using a current density of 
 0.2 ampere per sq. cm. there was obtained a quite small 
 black precipitate which from its behavior appeared to be chro- 
 mium. With a current density of 0.3 ampere per sq. cm. 
 no precipitate was obtained. A precipitate .did not appear 
 also when the above bath was saturated with sodium sulphate 
 instead of sodium chloride and electrolyzed at 30 and 80 
 with a current of 0.2 and 0.3 ampere per sq. cm. 
 
 Another bath was prepared with 15 grains of chromium 
 alum and 15 grams of potassium bisulphate dissolved in 100 
 grams of water. 
 
 Also in this case there was obtained with the above current 
 densities and varying temperatures only at the most traces of 
 chromium deposits. 
 
 Other baths gave no better results. It is sufficient therefore 
 to merely mention the baths used and to notice that in all 
 cases good circulation was obtained by active motion of the 
 cathode. 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 19 
 
 Bath III. Fifteen grams of chrome alum, 15 grams of am- 
 monium fluoride, 10 grams of concentrated hydrochloric acid 
 and 100 grams of water. 
 
 Bath IV. Fifteen grams of chrome alum., 15 grams of bi- 
 sulphate, 100 grams of water. 
 
 These statements agree entirely with the results of other 
 investigators who likewise could obtain no chromium deposits 
 in the manner described. 1 According to that there is no longer 
 any doubt that the kilogram of chromium (page 16) exhib- 
 ited at the French Academy by Placet could not have been 
 obtained in the manner stated or that at least conditions of 
 the highest importance for the obtaining of good chromium 
 deposits were not then stated by him. 
 
 While the processes so far described attempt to obtain me- 
 tallic chromium, and the accessory phenomena of the process 
 were only very slightly or not at all noticed, the patent of the 
 Electro-Metallurgical Company, Limited, 2 about to be de- 
 scribed, lays particular weight upon these phenomena. The 
 patentees start from the undotibtably correct point of view 
 that whoever wishes to reach an economical operation must 
 keep in view two other points besides the consumption of 
 electrical energy, points which have an important influence 
 upon the cost of the metal ; namely, the anodes to be used 
 and the nature and the quantity of the products resulting. 
 Since platinum electrodes are much too expensive to be used for 
 the production of chromium it is preferable to use chromium 
 sulphate solutions for the electrolysis, which permits of the use 
 of lead anodes. The latter are coated over with a layer of 
 peroxide which protects them for a long time from destruc- 
 tion, provided that the sulphuric acid is no more concentrated 
 than is usually employed in lead accumulators. Care must 
 be taken on this point, if a diaphragm is used and sulphuric 
 
 1 Cowper-Coles : Chemical News, 81, 16 (1900) ; J. Fe"re*e : Bull. Soc. 
 Chim., [3] 23 1 , 617 (1901). 
 
 2 German Patent 105,847, Sept. 7, 1898. The corresponding English 
 Patent No. 18,743, f r 1898, is under the name of Moller and Street. 
 
2O CHROMIUM AND ITS COMPOUNDS. 
 
 acid is the anode fluid, to bear in mind that the latter becomes 
 more concentrated during electrolysis and must therefore be 
 diluted in a suitable manner. If no diaphragms are used the 
 content in sulphuric acid must in that case be kept low in 
 order to get a precipitate of chromium at all, and therefore 
 there is no need of giving precautions for the preservation of 
 the electrode. 
 
 The second object, the obtaining of by-products which 
 will have a certain marketable value and at the same time to 
 keep their quantities down to the minimum is obtained by 
 the patentees in the following somewhat complicated manner. 
 
 Imagine, for instance, an electrolytic apparatus provided 
 with a diaphragm, the anode solution consisting of water 
 acidulated with 5 per cent, of its weight of concentrated sul- 
 phuric acid of 66 B., while the cathode fluid contains to 
 each 1.5 kilograms of water, 1.5 kilograms of sodium-chrome 
 alum and 1.5 kilograms of sodium sulphate. If this is heated to 
 about 90 and electroly zed with a current density of 0.4 ampere 
 per sq. cm. there is obtained 40 grams of chromium per ampere 
 hour. 1 As the electrolysis proceeds the sulphuric acid in the 
 anode compartment becomes more concentrated, as already de- 
 scribed, and also sodium sulphate and chromic sulphate pass into 
 it, the latter being oxidized at the anode to chromic acid. An 
 analysis showed that during the obtaining of 23.5 kilograms 
 of metallic chromium 0.562 kilogram of chromic acid and 
 0.936 kilogram of sodium sulphate passed into the anode 
 compartment. 
 
 Since, as may be seen from the formula of chromic sulphate, 
 294 grams of sulphuric acid are set free at the electrode for 104 
 grams of chromium precipitated, a works which manufactures 
 a ton of chromium in twenty-four hours would obtain nearly 
 three tons of sulphuric acid of 66 B., but in a diluted condi- 
 tion and mixed with the other by-products mentioned and 
 therefore in a form of little commercial value. In order to 
 
 1 Apparently this is a mistake ; in the English patent it is given as 0.2 
 gram, which Jwould be about 30 per cent, of the theoretical amount. 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 21 
 
 || 
 
 avoid this and other difficulties the process was operated as 
 follows : 
 
 The anode liquid after it has become somewhat rich in 
 chromic acid, etc., is treated with gaseous sulphur dioxide 
 whereby the chromic acid is reduced to chromic sulphate ; 
 the fluid is then concentrated to 30 B., by doing which the 
 excess of sulphur dioxide is driven off. Then sodium bi- 
 chromate is added in such quantities that independently of the 
 sodium sulphate formed 2CrO 3 is present for every two equiva- 
 lents of sulphuric acid, 1 and allows this mixture to flow in a 
 more or less thin stream into a lead vessel which contains 
 always an excess of melted sulphur kept at 130. The 
 chromic acid oxidizes the sulphur, and chromic sulphate is 
 formed by the two equivalents of free sulphuric acid alluded 
 to. This with the sodium sulphate formed regenerates the 
 alum. By treating with some water and filtering from the 
 excess of sulphur there is obtained a solution of chromic 
 alum (and sodium sulphate), which can be led into the elec. 
 trolyzing apparatus if necessary. 
 
 The first treatment with sulphurous acid can be omitted 
 by taking account of the chromic acid present when adding 
 the bichromate. 
 
 Considering the reactions in the cathode compartment there 
 is naturally a much greater depletion of the chromic sulphate, 
 while the content of sodium sulphate is only slightly altered. 
 It is clear that under such conditions with a cathode solution 
 saturated with sodium chrome alum the quantity of sodium 
 sulphate soon reaches such a point that the operation of the 
 apparatus is interrupted. 
 
 This interruption in fact occurs very easily as was empha- 
 sized since the content of free acid in the solution is carefully 
 regulated in order to obtain a good output and the quantity of 
 
 1 The explanation is not very clear ; the following formula according to 
 which the oxidation apparently proceeds gives the relations between the 
 chromic acid and the sulphuric acid : 
 
 Na 2 Cr 2 7 + 3H 2 SO 4 + S -= Cr. 2 (SO 4 ) 3 -f Na 2 SO 4 + sH 2 O. 
 
22 CHROMIUM AND ITS COMPOUNDS. 
 
 p 
 
 sodium chrome alum and the accessory salts (in the foregoing 
 case sodium sulphate) must stand to each other in the right 
 proportions. If this is not the case, the following occurrences 
 take place : 
 
 No precipitate of chromium comes down, the bath is too 
 acid. 
 
 It is then electrolyzed some time, whereby the content in 
 acid diminishes of itself or it is neutralized by means of chro- 
 mium hydroxide or any other base or a carbonate. 
 
 There results chromic acid at the cathode, a sign that the 
 addition of acid is necessary. 
 
 There occurs also the necessity of removing the sodium 
 sulphate in excess, which may be most simply done by cooling 
 the hot cathode liquor and crystallizing out the sodium sul- 
 phate. 
 
 It may be seen that continuous working with a utilization 
 of the by-products may be achieved in this way. If wished, 
 other changes may be introduced. Instead of supplying the 
 apparatus with chromium alum, chromic sulphate may be used 
 in which case the sodium sulphate is superfluous. Further, 
 the acid produced in the anode compartment can be neutral- 
 ized by chromic hydroxide and later the whole anode fluid, if 
 a sufficient migration of chromium has taken place, be brought 
 over to the cathode side. In that case it is previously neces- 
 sary to reduce the chromic acid formed by sulphurous acid 
 and neutralize further with chromic hydroxide. Or the whole 
 of the chromic hydroxide added may be supplied after the re- 
 duction of the chromic acid. 
 
 Finally it is remarked that the process may also be carried 
 out without diaphragms, but with more difficulty, and that al- 
 kali, earth alkali or chromic sulphides are proposed for the 
 reduction of the chromic acid. 
 
 The patent claims read : 
 
 i. Processes for the obtaining of chromium by electrolysis 
 of salts containing chromic sulphate, using lead anodes, and 
 characterized by the reduction of the fluid leaving the anode 
 
R /* 
 OF THt 
 
 UNIVERSITY 
 
 BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 23 
 
 compartment by sulphurous acid and further treatment with 
 melted sulphur, whereby chrome alum is formed when sodium 
 chromate is added, and the chrome alum being then conducted 
 to the cathode compartment, the cathode fluid being circulated 
 and its temperature kept low in order to avoid its enrichment 
 in sodium sulphate. 
 
 2. A method of carrying out the process of Claim i, char- 
 acterized by saturating the fluid coming from the anode com- 
 partment, after its reduction by sulphurous acid, with chromium 
 hydroxide, and thereupon using it for supplying the cathode 
 compartment. 
 
 After working one's way through this patent specification 
 one has not the feeling that it is a process proved through 
 practical investigations, and which has been found profitable. 
 
 At this place we may also mention the process of the same 
 company Electro-Metallurgical Company intended to ren- 
 der possible exact control of electrolytic metal depositions and 
 especially chromium deposition. 1 The company has found out 
 in their investigations (see also Bunsen, page i) that using 
 a chromium bath with sulphate salts of known composition 
 and keeping the current strength constant the alteration of 
 the amount of cathode surface changes the nature of the pre- 
 cipitate. " There is obtained, for instance, from the same bath 
 and with the same current strength a precipitate of oxide if a 
 rod 8 mm. diameter is used, but with a rod of 15 mm. diame- 
 ter a fine metallic precipitate which increases in thickness 
 with a good efficiency of deposition. With a rod 18 mm. in 
 diameter a precipitate is obtained which does not increase in 
 thickness, and finally with a rod of 20 mm. in diameter no 
 precipitate is obtained. These figures are only given by way 
 of example ; according to the composition of the bath and its 
 content of free acid, they are quite different." 
 
 For a given bath which with a certain current strength 
 gives a good precipitate on a rod 15 mm. thick, there may be, 
 therefore, easily found the diameter of a rod which will give 
 
 1 German Patent No. 104,793, Sept. 7, 1898. 
 
24 CHROMIUM AND ITS COMPOUNDS. 
 
 in the same bath a chromium precipitate which does not in- 
 crease in thickness. As long as the composition of the solu- 
 tion suffers no material change, the chromium precipitate upon 
 the first rod will increase in thickness as is desired, while the 
 weight of the second rod remains unchanged. The reverse is 
 true, that an alteration in the weight of the test rod would be 
 a sign that the solution had changed, and that a chromium 
 precipitate upon the first rod was not coming down in the 
 properly prescribed manner. 
 
 In order then that the test rod which should remain of con- 
 stant weight may act as an automatic signal of the current it 
 is hung from the arm of a balance whose other arm is fur- 
 nished with contacts which ring an electric bell as soon as the 
 test rod loses or gains in weight. To make the bell stop ring- 
 ing and bring the electrolyte again into proper condition the 
 bath must be neutralized if the weight of the rod has decreased, 
 or acidified if it has increased. 
 
 " The process permits of finding out with exactness the 
 condition of the electrolyte and thereby regulating properly 
 the operation of the apparatus." 
 
 The patent claim reads : 
 
 A process for the control of electrolytic depositions of metals 
 characterized by the use of a test rod which is connected in 
 parallel in the precipitating bath, the dimensions of the rod 
 being so chosen that with a proper current density and with 
 normal content of acid the test rod is covered with only a 
 light deposit as may be determined by removing it from the 
 bath or by hanging it from the arm of a balance. In the 
 latter case the other arm of the balance should be connected 
 with an electric bell whereby the increase of acid content of 
 the bath or the diminution of metal in the bath on the one 
 hand, or the decrease of the content in acid or the increase of 
 metal precipitated on the test rod on the other hand, causes a 
 movement of the arm of the balance and the closing of the 
 circuit through the electric bell. 
 
 The series of patents concerning the electrolytic precipita- 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 25 
 
 tion of chromium from aqueous solutions is herewith ex- 
 hausted. We have to add to them simply two scientific 
 articles on this subject. 
 
 J. Feree 1 states that he has obtained steel-gray chromium 
 99.82 per cent, pure by using a platinum cathode and electro- 
 lyzing a solution of 740 grams of water, 100 grams of hydro- 
 chloric acid and 160 grams of crystallized chromic chloride 
 (see also under chromium amalgam.) The current density 
 used is 0.15 ampere per sq. cm., tension 8 volts. 
 
 He obtained a silver-white precipitate of finer appearance 
 from a solution of chromium-potassium chloride; 266.5 
 grams CrCl 3 -f 6H 2 O (i molecule) and 223.5 grams KC1 
 (3 molecules) were dissolved in one litre of water and the cur- 
 rent density and tension used were as above. With 15 sq. 
 cm. cathode surface the weight of the precipitate was 3 grams 
 corresponding to an ampere-efficiency of 45 per cent. 
 
 The author complains that often processes for the electro- 
 lytic precipitation of chromium are described without exact 
 data being given (compare the foregoing chapter), and states 
 that he has tried in vain to get chromium from a solution of 
 chromium sulphate acidulated with sulphuric acid and satu- 
 rated with alkaline sulphates, as Placet claimed to have done 
 (see page 18). 
 
 The electrolytically obtained metal is very hard and un- 
 changeable at ordinary temperature. At a red heat, it covers 
 itself with a light layer of green chromic oxide. 
 
 It is unattacked by either concentrated sulphuric or nitric 
 acid, and is not acted upon by a concentrated solution of 
 caustic potash. 
 
 Some further data on electrolytically-precipitated chromium 
 has been given by Co wper- Coles. 2 According to this writer, 
 chromium precipitated upon copper can be scratched by the 
 diamond point only when it is weighted with 0.07 gram. 
 Electroplated nickel requires, for instance, o.oi gram, elec- 
 
 1 Bull. Soc. Chim. [3], 25, 617 (1901). 
 * Chem. News, 81, 16 (1900). 
 
26 CHROMIUM AND ITS COMPOUNDS. 
 
 troplated palladium 0.066 gram, a brilliant palladium precip- 
 itate 0.09 gram. Fused chromium is still harder. 
 
 The capability of reflecting light is soon diminished in the 
 case of chromium by tarnish, which accumulates under the 
 same conditions much stronger than with silver, platinum or 
 palladium. In the finely polished condition its capability of 
 reflection is equal to that of silver. 
 
 When making this communication Cowper-Coles stated 
 that he had made experiments on the production of chromium 
 alloys electrolytically and had taken out a patent for the same 
 in March, 1884, but I have not been able to discover the same. 
 He manufactured chromium alloys by heating chromium com- 
 pounds with charcoal in a closed crucible and pouring upon 
 the reduced mass 2 J^ parts of copper and then i to i J^ parts 
 of melted tin ; the whole was then granulated, again melted 
 and cast into the desired form. " The plates thus formed were 
 used as anodes in a solution which is made by dissolving i 
 pound of potassium cyanide and i pound of ammonium car- 
 bonate in a gallon of water at 53 C. until a good precipitate 
 was obtained on the cathode, using a low current density." It 
 must be granted that these data are somewhat hazy. 
 
 Later he reports on several new investigations. He ob- 
 tained a fine, lustrous precipitate of chromium from a solution 
 of 25 parts of chromic chloride in 75 parts of water electro- 
 lyzed at 75 C., with a current density of 40 to 50 amperes 
 per square foot (0.3 ampere per square meter). No metal is 
 obtained from a cold solution, but only a black non-adhering 
 precipitate ; the tension was 4 volts. An evolution of gas took 
 place at both electrodes. Good precipitates could be obtained 
 only by the use of an excess of hydrochloric acid, which 
 dissolving the precipitate of chromic oxide kept the bath clear; 
 according to this the chromium chloride solution before men- 
 tioned would have to be acid. 
 
 Chromium could not be obtained either in the cold or warm 
 solution containing 100 parts of water to 100 parts of chrome 
 alum and 12 parts of barium sulphate (potassium sulphate), 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 
 
 using current densities between 15 and 90 amperes per square 
 foot. The anodes used were carbon and platinum, and the 
 cathode copper. The tension was about 4 volts. 
 
 Finally, we mention a work of B. Neumann 1 appearing in 
 1901, in which the different conditions were determined which 
 are of importance for separating out chromium. His investi- 
 gation was very properly based upon determining singly the 
 influences of current strength, density, concentration and tem- 
 perature with different solutions. His data are, on this ac- 
 count, of importance and we will consider them in detail. 
 
 The experiments were carried out by G. Glaser with the 
 use of diaphragms ; the cathode space contained the chromium 
 solution, and the anode space mineral acid or salt solution. 
 The cathode was ordinary carbon, but the metal deposited 
 adheres also to metals such as platinum, brass or lead ; the 
 anode was, according to the solution, lead, platinum, or car- 
 bon. A strong circulation of the cathode fluid is important 
 for the obtaining of useful deposits because otherwise the 
 solution at the cathode becomes too much impoverished when 
 using high current densities and in that case no metal, but 
 only chromous-chromic oxide is precipitated. 
 
 Current den- 
 sity in amperes 
 per square 
 centimetre. 
 
 Product separated out. 
 
 Ampere 
 output in 
 percentage. 
 
 0.009 
 O.OlS 
 0.036 
 0.045 
 
 0.072 
 
 0.091 
 0.137 
 0.182 
 
 
 
 At first metal then chromous-chromic oxide .... 
 Metal mixed with chromous-chromic oxide 
 Thin layer of metal upon which later is depos- 
 
 5-4 
 
 23-4 
 
 38-4 
 38.0 
 38.6 
 
 Metal with a small amount of chromous-chromic 
 
 
 
 
 
 These results were obtained with a chromic chloride solu- 
 
 1 Zeitschr. f. Blektrochemie, 7, 656 (1901). A lecture given at the 
 general meeting of the German Electrochemical Society at Freiburg, Baden. 
 
28 
 
 CHROMIUM AND ITS COMPOUNDS. 
 
 tion containing 100 grams of metallic chromium per litre, 
 electrolyzed at the temperature of the room. 
 
 If the temperature is varied while the current density re- 
 mains constant it is found that the precipitate remains good 
 up to about 50 but over 50 the chromium deposits as a 
 black powder ; the output changes very little. 
 
 The alteration of the concentration of the solution gave the 
 following results : 
 
 Concentration 
 in grams of 
 chromium per 
 litre of solu- 
 tion. 
 
 The product separated out. 
 
 Ampere 
 output in 
 percentage. 
 
 210 
 184 
 158 
 135 
 105 
 79 
 53 
 26 
 
 Metallic powder mixed with chromous chloride- 
 Metallic powder mixed with chromous chloride- . - 
 
 56.6 
 49.0 
 38.4 
 
 
 
 At first metal, then chromous-chromic oxide 
 
 A trace of chromous-chromic oxide and a strong 
 
 
 
 The current density at which these tests were made is not 
 particularly given; probably it lay between 0.09 and 0.18 
 ampere per square centimetre. 
 
 There follows the incomprehensible remark that the ampere 
 output was increased from 51 per cent, up to 89.5 per cent, 
 by changing the anode solution. Or should this read "by 
 changing the cathode solution?" 
 
 All the preceding measurements were made on chromic 
 chloride solutions ; sulphate and acetate solutions gave simi- 
 lar results except that the values for the separation of metal 
 in the concentration and current density tables are changed. 
 The best proportion for sulphuric acid solutions with 65 to 
 85 grams of chromium to a liter was at 0.13 to 0.20 ampere 
 per square centimetre current density, using which the current 
 output of 84.6 per cent, was reached. The influence of tem- 
 perature was, as with the chloride, of slight importance ; in 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 29 
 
 the most favorable cases the current output rose to 86.2 per 
 cent. 
 
 The acetate solutions gave imperfect precipitates and very 
 deficient current output. 
 
 Concerning the properties of the electrolytically precipita- 
 ted chromium it was said that it showed the tendency like 
 nickel to spring off in thin sheets. In spite of that, white de- 
 posits were made on the cathode several mm. in thickness. If 
 the cathode itself is rapidly rotated branch-like deposits several 
 millimeters in length with crystalline projections are formed. 
 On breaking thick pieces, a laminated structure is plainly to 
 be seen, which in fact comes from thin formations of chromous- 
 chromic oxide lying between the laminae. The metal is bright 
 gray, frosted, and resembles white steel. In thin layers it is 
 silvery. Its purity is high, containing only o.i to 0.2 per 
 cent, of iron, while commercial chromium usually has a purity 
 of only 97 to 98 per cent, on an average, though purer kinds 
 may be produced. Electrolytic chromium is hard and brittle, 
 showing, like the Goldschmidt chromium, two different con- 
 ditions an active and a passive which may be artificially pro- 
 duced and destroyed. Taken fresh out of the bath it is active, 
 but by lying in the air becomes gradually passive and can 
 easily be made active again by the methods proposed by 
 Hittorf. 
 
 While being dissolved periodic phenomena, as far as has 
 been determined, do not take place during solution, which 
 may be explained by the assumption that the periodic phe- 
 nomena are really caused by a foreign element in the chro- 
 mium, and, therefore, do not appear with the very pure elec- 
 trolytic metal. 
 
 The value of the potential of electrolytic chromium in 
 absolute measure when dipped in normal chromium sulphate 
 solution was 0.258 volt, in normal chromic chloride solution 
 0.241 volt, while the corresponding values for zinc were 
 0.524 and 0.503 and the values of cadmium 0.162 and 0.174. 
 
3O CHROMIUM AND ITS COMPOUNDS. 
 
 Active chromium stands, therefore, in the tension series, as has 
 already been remarked by Hittorf, between zinc and cadmium. 
 
 The voltage required for decomposition was found for a five 
 times normal sulphate solution 1.90 volts, for an eight times 
 normal chromic chloride solution 1.69 volts. For practical 
 purposes at least double these tensions must be used. 
 
 In the discussion connected with this communication 
 H. Goldschmidt stated that he likewise had performed ex- 
 periments for the precipitation of chromium in similar appa- 
 ratus. Hydrochloric and also acetic acid solutions were used, 
 the latter with the worst results ; an iron tube was used as 
 cathode, rotated rapidly around its axis, the anode was retort 
 carbon in acidulated chromic chloride or in hydrochloric acid. 
 A small propeller was placed in the cathode fluid which was 
 contained in a porous cell, in order to increase the circulation. 
 With current densities of o.i to 0.4 ampere per square centi- 
 meter of cathode surface there was obtained peculiar ribbed 
 or furrowed layers of metallic chromium several millimeters 
 thick, but very brittle, easily detached, and never quite free 
 from oxygen ; it was particularly lustrous upon the tops of 
 the ribs. " Dr. Neumann has gone decidedly further in his 
 experiments than I, since he has made exact determinations 
 of favorable conditions ; moreover, I obtained much poorer 
 current output than Dr. Neumann. On that account I laid 
 these investigations completely to one side, because calcula- 
 tions showed that even if a higher current output can be ob- 
 tained, these methods would be too expensive for commercial 
 use, at least as far as concerns the manufacture of chromium it- 
 self, in consequence of the complicated apparatus, and the high 
 current consumption caused by the high tension in the bath." 
 
 A later remark of the same person is worthy of reproduc- 
 tion. " Chromium is, as is well-known, a somewhat noble 
 metal in certain relations since it is more resistant to air than 
 nickel and even better than cobalt. Unfortunately it has not 
 been possible so far to obtain a strongly adhering deposit of 
 
BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 31 
 
 electrolytic chromium. If it were only possible to plate 
 metallic articles with a thin sheet of chromium, as is so often 
 done with nickel (recently electrolytic zinc-platings have 
 also been successfully produced), it would be a great ser- 
 vice, I believe, to many branches of technology and also to 
 the artistic industries. It may be perhaps a small step in the 
 direction of reaching that goal to use soluble anodes of chro- 
 mium, with the aid of which a constant electrolytic chromium 
 bath may be produced. The investigations of Dr. Neumann, 
 which we have just listened to, go far in this direction, and 
 which may well form the foundation of a technically useful 
 method of chromium-plating, but will hardly, as before re- 
 marked, serve for manufacturing metallic chromium. Appar- 
 ently a chromium-plating upon iron ought to be just as good 
 as a zinc-plating." 
 
 In relation to the latter point Ostwald says that even if it 
 was possible to plate iron with chromium, the chromium 
 would scarcely be permanent since it would become active 
 again by contact with this metal. " Therefore the danger of 
 using chromium is that when rain falls upon it hydrogen 
 commences to evolve, and in that case we can carry the chro- 
 mium from our chromium-plated bicycles home in our hand- 
 kerchief." 
 
 If, however, this observation is worth noticing, the fear of 
 such calamitous results has no foundation. Chromium is even 
 in its active condition more passive than zinc. 
 
 As already remarked, Hittorf established the fact that chro- 
 mium occurs in two conditions, one active in which it lies be- 
 tween zinc and cadmium, and one passive in which it stands 
 near to silver ; he also gives the conditions under which 
 chromium becomes active or passive. I will content myself 
 in this work with referring to the original article 1 since it is 
 easily accessible and scarcely falls within the limits of our 
 subject, as also the work of Ostwald : " On the Periodic 
 
 1 Zeitschr. f. phys. Chem., 25, 729 (1898) ; 3O, 481 (1899) ; 34, 385 
 (1901). 
 
2 CHROMIUM AND ITS COMPOUNDS. 
 
 Phenomena when Chromium Is Dissolved in Acids ; m and the 
 communication of Brauer: 2 " On the Electrolytic Behavior of 
 Chromium during Solution in Acids." 
 
 B. By the Use of High Temperatures. 
 
 (See also pages 17 and 18.) 
 
 The obtaining of chromium at high temperatures by the 
 help of the electric current was mentioned in a patent speci- 
 fication 3 not much later than the first patent was taken out for 
 the electric precipitation of chromium from aqueous solutions. 
 The invention is concerned with the melting and the reduc- 
 tion of ores, heated by the assistance of the electric current 
 and used for the production of aluminium and its alloys as 
 well as other metals and their alloys of a more or less refrac- 
 tory character like boron, silicon, calcium, chromium, titanium, 
 etc., iron and steel. If the ores and ordinary oxides are 
 melted and heated by means of the electric current they are 
 decomposed and the oxygen set free violently attacks the 
 vessel and the electrodes, causing considerable expense. This 
 is avoided in Wilson's apparatus by the introduction of a re- 
 ducing gaseous agent into the apparatus in such manner that 
 the oxygen and the injurious constituents combine with the 
 reducing medium so that the electrodes are protected. 
 
 When treating oxides, hydrogen, hydrocarbons and in par- 
 ticular ordinary illuminating gas, for instance, may be used. 
 
 The manipulation when producing aluminium and alumin- 
 ium bronze, which were the probable productions to which 
 the invention was applied, was described at length and we 
 need not follow this branch further. It will suffice to repro- 
 produce the most important patent claims relating to our sub- 
 ject. 
 
 (i) The herein-described process of reducing metals or ores, 
 consisting in heating them to the melting-point by the elec- 
 tric arc passing from the metal or ore to an electrode and in- 
 
 1 Zeitschr. f. phys. Chem., 35, 33, 204 (1900). 
 
 2 Ibid., 38, 441 (1901). 
 
 3 English Patent No. 9,361, June 17, 1890, Thomas Leopold Wilson. 
 
BY THE USE OF HIGH TEMPERATURES. 33 
 
 troducing a reducing agent between the place at which the 
 oxygen or other corrosive agent is set free, and the incandes- 
 cent surface endangered by the corrosion, in order to protect 
 the latter from destruction, substantially as described. 
 
 (2) The herein-described process of reducing metals or 
 ores consisting in heating them to melting by an arc passed 
 between the metal or ore and an electrode above and the in- 
 troduction of a reducing agent downwards into the arc be- 
 tween the place at which the oxygen or any other destructive 
 agent is set free and the incandescent electrode surface which 
 is endangered, in order to protect the latter from destruction, 
 substantially as described. 
 
 (3) The herein-described reduction process for metals or 
 ores, consisting in heating them to melting by means of an 
 electric arc passed between the metal or ore and an electrode 
 above, and the introduction of a reducing agent downwards 
 into the arc by passing it through the electrode shown, 
 whereby the gas distributes itself uniformly around the incan- 
 descent end of the electrode and rising in a protecting stream, 
 surrounds the electrode on all sides, as described in the speci- 
 fications and for the purpose designated. 
 
 (4) The herein-described reduction process for metals or 
 ores consisting in subjecting them to the heat of the electric 
 arc passing from the positive electrode underneath the metal 
 or ore to the negative electrode above the same, introducing 
 a reducing gas into the arc through the said negative elec- 
 trode, whereby the gas is introduced into the center of the 
 current of gas which is projected from the positive electrode 
 beneath, against the negative electrode, and the gas so protects 
 the electrode from destruction, substantially as described. 
 
 (5) The herein-described process for the reduction of 
 aluminium and other metals from refractory ores and for the 
 production of alloys of these metals, consisting in the melting 
 of the ores by means of the electric arc in the presence of the 
 melted bath of the base metal to be alloyed and passing the 
 electric current through the said bath as anode to a carbon 
 
34 CHROMIUM AND ITS COMPOUNDS. 
 
 cathode placed above it, in the presence of a reducing agent 
 which can unite with the oxygen set free or any other corro- 
 sive elements resulting from the decomposition of the ore, 
 substantially as previously described. 
 
 (6) The improved electric furnace for the reduction of re- 
 fractory ores consisting of the melting crucible connected 
 with the current conductor which serves to conduct the cur- 
 rent to the interior of the crucible, a tube-formed electrode 
 projecting downwards into the said crucible and a source of 
 reducing gas in connection with the electrode through which 
 the gas enters the crucible, in order to surround the white-hot 
 end of the electrode and to protect it, substantially as de- 
 scribed. 
 
 The patent 1 taken out in the year 1893 y the nrm f 
 Friedrich Krupp, of Essen, has essentially for its principal 
 object the manufacture of chromium ; as the raw material for 
 the manufacture of pure chromium, there is used an anode of 
 impure, carbonaceous, crude metal in the ordinary commercial 
 form ; if an electric current is led through it, using, for in- 
 stance, molten sodium chloride as electrolyte, the anode is 
 changed into metallic chloride by the chlorine evolved, which 
 dissolves in the melt, while at the cathode metallic sodium is 
 evolved. The latter must be rendered harmless since it would 
 precipitate again the metal from the metallic chloride by 
 simple replacement ; to avoid this the patent provides various 
 devices. 
 
 The negative pole may be surrounded by a clay cell or an 
 unattackable diaphragm may be brought between the two 
 poles, or the electrolysis may be performed in a U-shaped 
 tube of refractory material. The sodium evolved may also be 
 vaporized by the use of a high enough temperature, or changed 
 back again to chloride by the use of a current of chlorine gas. 
 
 As soon as a sufficient amount of metal has been converted 
 into chloride at the anode any sodium or sodium oxide re- 
 maining at the cathode is removed in a suitable manner, and 
 1 German Patent 81,225, June i, 1893. 
 
BY THE USE OK HIGH TEMPERATURES. 35 
 
 by further electrolysis the pure metal or alloy is obtained, 
 while at the same time fresh metal is continually dissolved at 
 the anode and the composition of the bath remains constant. 
 By using impure ferro-chromium as an anode, pure ferro-chro- 
 mium is obtained at the cathode ; the same process may be 
 employed for other metals and alloys. 
 
 In place of sodium chloride other halogen salts melt- 
 ing at a red heat may be used, and in case they can be ob- 
 tained the halogen compounds of the metallurgical products 
 being electrolyzed. 
 
 The patent claim reads : An electrolytic process for the 
 manufacture of pure chromium and manganese and pure 
 alloys of the same by electrolyzing compounds rendered fluid 
 by heat characterized by using the carbonaceous metals and 
 alloys of the two named metals as anodes in an easily fusible 
 bath of halogen compounds, and precipitating out pure metals 
 and pure alloys at the cathode. 
 
 The manufacture of pure chromium does not succeed in the 
 manner described without further precautions, since the 
 metallic impurities of the crude metal will be found for the 
 most part in the metal precipitated at the cathode. 
 
 The idea of " purity" seems to be somewhat indistinct in 
 the patentee's mind, since the mere absence of carbon seems 
 to be regarded as sufficient warrant for calling the metal pre- 
 cipitated " pure." What has just been said regarding chro- 
 mium itself is true also of its alloys since besides the metals 
 to be alloyed, other metals were separated out of the electro- 
 lyte if present. 
 
 With constant use the bath would further become very im- 
 pure ; it is not clear that the solution of the anode would go 
 forward easily and without a considerable increase of voltage. 
 
 Much better results 'may be obtained by the manner de- 
 scribed by Moissan in two communications. 1 He heated a 
 
 1 Compt. rend., 116, 349 (1893) and 119, 185 (1894). See also Ann. 
 chim. phys., 78, 559 (,1896). A form of furnace which is described in 
 Compt. rend., 117, 679, in which the raw material is passed into the melt- 
 ing zone through a hollow, suitably inclined, carbon, tube terminating about 
 i cm. underneath the arc. 
 
36 CHROMIUM AND ITS COMPOUNDS. 
 
 mixture of calcined chromic oxide and carbon in the electric 
 furnace and obtained a shining and completely melted mate- 
 rial. Using 350 amperes and 50 volts, the operation was 
 imished in eight to ten minutes ; the charge had a weight of 
 100 to no grams. With 30 volts and 50 amperes he obtained 
 a button of TO grams in thirty to forty minutes. 
 
 These buttons stuck to the crucible and contained more or 
 less carbon according to the composition of the original mix- 
 ture. The carbon content of the pieces analyzed varied be- 
 tween 8.6 and 12.8 per cent. The mass was purified by a 
 further operation : It was broken into large pieces, put into a 
 carbon crucible carefully lined with chromic oxide, and covered 
 with chromic oxide. The mixture was then subjected to the 
 heat of the electric arc by which the oxide upon the surface and 
 also the metal melted and the latter gradually lost its carbon 
 content ; at least in heating in a current of chlorine no traces 
 of carbon remained behind. 
 
 The natural chrome iron ore, FeO.Cr 2 O , can be reduced 
 in the same manner as chromic oxide forming a chromium- 
 iron alloy ; the material is broken to a coarse powder, an ap- 
 propriate quantity of carbon added and the whole heated in 
 the electric furnace. Moissan operated with 2 kilograms 
 of ore and 1000 amperes of current, at 60 volts, and obtained 
 in a few minutes completely melted lumps of ferro-chrome of 
 the following composition : Chromium 60.9 per cent, iron 
 31.6 per cent., total carbon 6.1 per cent., silicon i.i per cent. 
 He proposed to use this product for the manufacture of alka- 
 line bichromates by bringing the coarsely pulverized material 
 into a bath of molten potassium or sodium nitrate; there would 
 result insoluble iron oxide and soluble alkaline chromates. 
 
 In his second communication, Moissan explains that the 
 chromium made in the way just described, " is saturated with 
 oxygen, and, therefore from the standpoint of the metallurgist 
 was burned" He attempted on this account another method 
 of purification, by melting the metal in quantities of one-half 
 to one kilogram with lime, this taking up the larger part of 
 
BY THE USE OF HIGH TEMPERATURES. 37 
 
 the carbon to form calcium carbide, but leaving in the chro- 
 mium the remainder of it, 1.5 to 1.9 per cent, as beautiful 
 cubical and octahedral crystals, which he could not remove. 
 " We observe, in fact, that the reverse reaction would take place 
 in the presence of the fluid lime and the furnace gases, if the 
 chromium was sufficiently pure. Thus the whole metal would 
 be transformed into the crystallized double oxide of chromium 
 and lime." 1 
 
 Finally this easily formed double oxide was used for puri- 
 fication ; a lime crucible was lined with it and the carbonized 
 metal melted in it. After cooling there was obtained a 
 brilliant metal which could be filed and polished easily and 
 showed on analysis no trace of carbon. 
 
 Borchers remarked .on this process : 2 " Moissan has solved 
 this question of the refining in a very skilful way by bring- 
 ing over for the purpose of refining chromium, the principle 
 of the basic Siemens-Martin furnace for making steel. By 
 heating lime with chromic oxide he has manufactured a basic 
 material which not only serves for oxidation but for the pur- 
 pose of slagging off the impurities. By lining the hearth of 
 the electric furnace with this calcium chromite and melting 
 thereupon the carbonaceous and siliceous metal the impurities 
 are entirely oxidized and removed by the chromic oxide just 
 as occurs to impurities in the Martin steel process by the action 
 of iron oxide. 
 
 No further data are known about the cost of this process. 
 The commercial practicability is scarcely to be doubted, but 
 the cost could be considerably reduced by producing the crude 
 chromium as a carbonaceous metallic powder either in cruci- 
 ble furnaces or in electrolytic resistance furnaces in order to 
 save the heat necessary for melting it. 
 
 At this point Moissan remarks that melted lime can 
 also be used for the refining of commercial ferro-chromium in 
 the electric furnace. He has for instance found that commer- 
 
 1 Moissan : " Der Elektrische Oefen," 1897, p. 196. 
 ' 2 "Elektrometallurgie," 2nd Ed., p. 347. 
 
38 CHROMIUM AND ITS COMPOUNDS. 
 
 cial ferro-chromium with 7.3 per cent, of carbon, contained 
 only 5 per cent., after having been melted once under a layer 
 of melted lime and after the second melting only o.i per cent.; 
 by using this commercial product a considerable amount of 
 chromium can be introduced into steel without raising its 
 carbon content. He is of the opinion that these experiments 
 might probably be utilized on an industrial scale. 
 
 Since the properties of pure chromium are of importance, 
 the following data of Moissan's are repeated, especially since 
 they contradict part of the information found in the text-books. 
 
 The density is 6.92 at 20 C. It burns quickly but with a 
 much more active discharge of sparks than iron when brought 
 into the blue point of the blowpipe flame ; the residue is a 
 round piece of melted chromic oxide. . It is worth while re- 
 membering, moreover, that the carbonaceous material burns 
 much more difficultly although it melts lower ; the melting- 
 point of pure chromium is above that of platinum. 
 
 Molten chromium in the electric furnace is a mobile shin- 
 ing fluid similar to mercury ; it can be cast into a mould. By 
 using 1000 amperes and 70 volts, 10 kilograms of (not quite 
 pure) chromium can be melted at one time, in a suitable fur- 
 nace. 
 
 Quite pure chromium containing no iron exerts no influ- 
 ence on the magnetic needle. It has great capacity for taking 
 a polish, and its hardness is less than that of quartz ; glass is 
 scratched by it with great difficulty. Carbonaceous chromium 
 is much harder. The carbide CCr 4 scratches quartz with 
 difficulty, the carbide C 2 Cr 3 scratches topaz, and the finely 
 granular metal, whose carbon content is between 1.5 and 3. 
 per cent., can only be worked by cutting stones charged with 
 diamond dust. 
 
 Carbonic acid and moisture have no appreciable influence 
 upon the crude chromium at ordinary temperatures, while 
 pure, well-polished chromium suffers a superficial light oxida- 
 tion. In general, it can be designated as unchangeable in the 
 air. Heated in oxygen to 2000 it burns with evolution of 
 
BY THE USE OF HIGH TEMPERATURES. 39 
 
 sparks. If filings are heated to 700 in sulphur vapor they 
 glow and are changed to chromic sulphide. 
 
 If a mixture of pure chromium and carbon is heated, crys- 
 talline needles of the carbide CCr are formed with a violent 
 deflagration, while at the temperature of the electric furnace 
 C 2 Cr s results. 
 
 Boron and silicon unite with chromium at the heat of the 
 electric furnace to finely crystalline compounds of great hard- 
 ness and resistance to chemical reagents. 
 
 Gaseous hydrochloric acid acts on it at a red heat, forming 
 chromous chloride. Aqueous hydrochloric acid attacks the 
 metal very slowly when cold, faster when warm ; used as an 
 anode it dissolves even in dilute acids which otherwise would 
 attack it only at boiling. Further data on the behavior of 
 chromium towards acids and its use as electrodes, about its 
 active and passive conditions, etc., were published a year later 
 by Hittorf (see page 29). 
 
 At 1200 chromium is attacked by a current of hydrogen 
 sulphide and converted entirely into a sulphide of crystalline 
 appearance ; in carbonic acid it covers itself at this tempera- 
 ture superficially with a layer of green chromic oxide mixed 
 with carbon ; carbon dioxide attacks it, forming superficially 
 a layer of Cr 2 O 3 while the metal absorbs carbon, a circum- 
 stance which explains the difficulties which are met with 
 when one tries to refine chromium in the lime crucible. 
 
 Chromium is not sensibly attacked by melted caustic potash; 
 on the other hand it burns with beautiful illumination in con- 
 tact with melted potassium nitrate or still better at a red heat 
 with potassium chlorate. 
 
 Finally, the interesting properties of some alloys are men- 
 tioned. Pure copper containing 0.5 per cent, chromium has 
 nearly double as much electrical resistance and is, when well 
 polished, more resistant to damp air than without this addi- 
 tion. 
 
 Two Russians, A. Koryscheff and S. Demmenie, together, 
 
40 CHROMIUM AND ITS COMPOUNDS. 
 
 in the year 1896, took out the English patent 1 for a very gen- 
 eral process for the direct manufacture of iron, chromium 
 and analogous metals from their oxygen, sulphur, arsenic, etc., 
 compounds, and since they use electrical energy we will re- 
 produce the more important part of it from their very com- 
 prehensive patent specifications which contain many draw- 
 ings. We need not go further, however, into the considera- 
 tion of their metallurgical furnace likewise protected by En- 
 glish patents. 
 
 The two authors emphasize that the study of "pyrochem- 
 ical solutions," that is, the solutions in which one body is dis- 
 solved in another rendered fluid by heat, leads to the convic- 
 tion that the dissolved bodies, be they of simple or of combined 
 chemical nature, have acquired a gas-like that is, a very 
 diluted condition. The degree of "dilution" (rarefaction) can 
 be increased in three ways : First, by raising the temperature ; 
 second, by the action of chemical agents ; and third, by the 
 help of electricity. Naturally, all three aids to this end may 
 be used alone or in combination with each other ; so may, for 
 instance, iron oxide dissolved in molten silicates be reduced 
 either by raising the temperature to the dissociation point or 
 at a lower temperature by the help of chemical reagents or by 
 electricity. 
 
 After this somewhat fantastic presentation they explain the 
 main idea of their invention, that of performing the decom- 
 position or the reduction of metallic compounds by bringing 
 them into the condition of pyrochemical solutions, in order 
 to then subject them to the action of heat, chemical and elec- 
 trical energy ; they then affirm that this pyrochemical pro- 
 cess is applicable to all metals and alloys. 
 
 Since a pyrochemical solution is aimed at, great care must 
 be taken that the ores, gangue and furnace lining are so chosen 
 that a fluid mass containing the metal will result. 
 
 Electrical energy can be called upon as explained, as sup- 
 plementary to the influence of heat and chemical action, but 
 
 1 English Patent 6,654 ; March 26, 1896. 
 
BY THE USE OF HIGH TEMPERATURES. 41 
 
 its office when so used is an entirely different one from elec- 
 trolysis ; it acts here upon materials which are already in the 
 condition of "tension," so that only the smallest assistance is 
 required from it in order to complete the dissociation. 
 
 The electric energy can be used either as dynamic or static. 
 In practice it is advantageous to use transformers for the ob- 
 taining of very high tensions, and to connect the anodes with 
 the slag and the cathodes with the hearth of the furnace 
 which in this case is made of a conductor such as graphite. 
 
 The current produced in the transformer is so regulated 
 that an "electric" discharge passes from one side of the elec- 
 trodes, and a dark discharge from the other. For this pur- 
 pose suitable resistances are put into the circuit as well as a 
 quick-working interrupter to avoid the development of the 
 small high-tension closing currents. 
 
 The above will do for characterizing this new invention ; 
 further criticism is not necessary. Of the patent claims, the 
 following concern us. They claim : 
 
 (i) A new process for the direct production of metals and 
 their alloys from their ores, characterized by the conversion 
 of the whole charge into the melted condition in such manner 
 that the metallic compounds are dissolved " pyrochemically " 
 in the rest of the mass. 
 
 (5) In the manufacture of metals from their ores according 
 to the methods described under (i), the use of chemical reagents 
 in the form of pyrochemical solutions as a supplement to the 
 thermic energy. 
 
 (6) For the manufacture or formation of pyrochemical so- 
 lutions (see 5) the introduction of carbon into the charges in 
 quantities of 1/5 to 1/40 of that necessary fof the conversion 
 of the oxygen present in the oxide into carbon dioxide. 
 
 (7) The combination of the process described under (i) with 
 the use of electrical currents as supplemental to thermic and 
 chemical energy as described. 
 
 (8) In the process as described the use of electrical energy 
 in the form of dark discharges of very high tension, which are 
 
42 CHROMIUM AND ITS COMPOUNDS. 
 
 rendered possible practically by the including in the circuit 
 of suitable resistances for the purposes of choking the contact 
 currents of the transformer or by means of the acoustic inter- 
 rupter which produces alternating current of very high tension 
 and extremely high frequency, as described. 
 
 The German patent of Aschermann 1 is concerned only with 
 the reduction of chromium. An air-tight electrical melting 
 apparatus of cast steel, containing an exactly-fitting graphite 
 crucible to receive the bath into which a movable non-porous 
 electrode passes, is used. It is charged with a mixture of 
 chromic oxide and antimony sulphide, in the proportion of 
 10:23 or also, not so strongly recommended, however, with a 
 mixture of chromic oxide, sulphur and pure antimony in the 
 proportions of i o : 10 : 23; the apparatus is thereupon closed air- 
 tight and a relatively gentle current of 20 to 2 5 amperes passes 
 through. This suffices to melt the mass and cause the reaction 
 in the crucible. The process proceeds with considerable de- 
 velopment of heat. On opening the apparatus there is found, 
 in the upper part, antimony oxide as an amorphous deposit, a 
 very small part of which may, however, be crystalline, also 
 antimony sulphide and traces of chromic oxide, but on the other 
 hand the crucible contains a molten mass of evidently crys- 
 talline structure consisting of metallic chromium in combina- 
 tion with the excess of antimony. The removal of the anti- 
 mony by repeated remeltings is difficult and costly ; it is much 
 simpler and cheaper to break up the mass and heat it over an 
 open fire. The antimony volatilizes at a white heat and me- 
 tallic chromium remains behind, since chromium itself only 
 volatilizes at temperatures above 2000. 
 
 It is worth remarking in connection with this process that 
 the electric current seems to be used only for starting the re- 
 action. A small part of the mass is heated by the help of the 
 heat developed by the current to the temperature of reaction 
 and the heat generated by the decomposition then suffices to 
 continue the reaction throughout the whole mass and to bring 
 
 1 German Patent 93,744, June 30, 1896. 
 
BY THE USE OF HIGH TEMPERATURES. 43 
 
 it to fusion. The cost of the electrical energy is, therefore, al. 
 most negligible. If the reaction takes place as is claimed, and 
 if the separation of the chromium from the antimony proceeds 
 in such a simple manner as the description would lead one to 
 believe, then this process must be described as comparatively 
 simple and applicable for the manufacture of large quantities 
 of chromium. 
 
 The patent claim reads : Obtaining of metallic chromium 
 from chromic oxide by the agency of antimony sulphide in 
 the electric furnace. 
 
 In a supplementary patent 1 the author extends his process 
 to other metals and to metallic alloys. He makes in this con- 
 nection the following remarks which are of interest, particu- 
 larly for the obtaining of pure chromium and part may be re- 
 garded as an explanation of the process described in the 
 principal patent. 
 
 " The manufacture of pure metals in electric melting fur- 
 naces from their oxides offers great difficulties if the metals 
 have a great capacity for dissolving carbon. There is then 
 -obtained either a carbide or a metal highly contaminated with 
 carbon. It is necessary to use an easily fusible metal as an 
 addition which will unite with the reduced metal in the nas- 
 cent state and prevent it thereby from taking up carbon. 
 But this alone is not sufficient. To obtain the metal as free 
 as possible from carbon it is further necessary that the reduc- 
 tion proceed quickly and that it be operated by the smallest 
 current possible. Quite aside from the cost of production, 
 this is an important requisite. It is not possible to obtain the 
 reduced metal pure if strong currents are used or by a lengthy 
 application of the arc. The fluxes volatilize and in their 
 place carbon is absorbed by the metal. Finally the metal 
 obtained will volatilize itself, and there will remain behind 
 only carbon in the form of graphite. The metal added has 
 
 1 D. R. P. No. 94,405 of 24th of November, 1896. Extreme life until 
 June 29, 1911. The English Patent No. 859, taken out by Aschermann, Jan- 
 uary 12, 1897, contains the substance of both the German patents cited. 
 
44 CHROMIUM AND ITS COMPOUNDS. 
 
 either none or only a very slight influence upon the course of 
 the reduction; it serves more as a means of protection against 
 the taking up of carbon. If a metallic sulphide is used as 
 the addition, the reaction takes place quickly and with a 
 much smaller expenditure of electrothermal energy. It is 
 therefore the sulphur which influences favorably the course of 
 the reduction." 
 
 The manufacture of metallic compounds in the way de- 
 scribed is stated to be of great importance. For instance, ac- 
 cording to this process, ferro-chrome can be made by the melt- 
 ing together of 10 parts of iron sulphide and 9 parts of chromic 
 oxide ; also for this reaction a comparatively small amount of 
 electrical energy suffices. 
 
 Patent Claim. 
 
 A process of obtaining metallic alloys and pure metals by 
 the electrical heating of a mixture consisting of the oxide of 
 one and the sulphide of another metal or the oxide of the 
 metal and the sulphide of a non-metal, or from one oxide of a 
 non-metal and the sulphide of the metal with the exclusion of 
 the process of manufacture of chromium described in patent 
 
 No. 93,744- 
 
 The foregoing compilation exhausts the processes which 
 endeavor to manufacture chromium by the direct application 
 of the electric current. I cannot, however, close this chapter 
 without thinking of the processes which manufacture these 
 metals by the indirect use of the electric current such as by 
 reducing chromium from its compounds by means of alumin- 
 ium, or magnesium or calcium carbide, which substances are 
 indeed to-day manufactured by electrolytic processes. Since, 
 moreover, these processes are likely to become important and 
 are already beginning to be so at present, it is advisable to 
 present the patent literature on this subject, which may not 
 be easily accessible to everybody. 
 
 The first to be mentioned is the proposition to obtain chrom- 
 ium in the already-mentioned manner, made by J. Vautin. 1 
 
 1 English Patent 8,306, April 26, 1894. 
 
BY THE USE OF HIGH TEMPERATURES. 45 
 
 His patent is dated April 26, 1894. He alludes to the great 
 affinity of the finely divided metallic aluminium for oxygen 
 and sulphur by means of which other metals may be reduced 
 from their oxides and sulphides and in every case from their 
 sulphates while the heat generated in the decomposition keeps 
 in fusion the difficultly fusible metals and brings the reduced 
 metal mostly into a compact molten condition. The metal 
 obtained is free from aluminium and naturally also from 
 carbon. 
 
 For the reduction there is used a vessel lined with refrac- 
 tory material like magnesia into which the substance to be 
 reduced mixed with very finely divided aluminium is placed. 
 Stress is laid upon the very fine division of the aluminium, 
 since on this depends the obtaining of the reduced metal con- 
 taining no admixture of aluminium: The resulting slag may 
 be in certain cases made more fusible by the addition of fluxes 
 like cryolite and fluorite ; potassium chloride and sodium 
 chloride may also be used. 
 
 The equation of the reduction is given as Cr a O -f A1 2 = 
 Cr 2 -f A1 2 O 3 , which makes it evident that the normal propor- 
 tions by weight were used for the mixture, but this is not 
 particularly specified. An excess of aluminum will not hurt, 
 since it is easily burned out or volatilized, and in this manner 
 does not get into the reduced metal. In general, an excess of 
 oxide or sulphide is to be recommended. The reaction is com- 
 plete " as soon as the temperature is reached at which the 
 aluminium unites with the oxygen or sulphur." 
 
 The patent claim reads : 
 
 (1) The manufacture of chromium, iron, tungsten, titanium, 
 molybdenum, nickel, cobalt, uranium, vanadium, and beryl- 
 lium by the treatment of their oxides and sulphides with 
 aluminium, in the finely divided or powdered condition at high 
 temperatures, as described. 
 
 (2) In the herein-described process of reducing metals from 
 their oxides and sulphides the use of metallic aluminium in 
 
46 CHROMIUM AND ITS COMPOUNDS. 
 
 finely divided or powdered condition as the reducing agent, as 
 described. 
 
 The German patent 1 of the firm of Th. Goldschmidt, of 
 Essen, has, in the main, the same contents except that it is 
 limited especially to the manufacture of chromium. It states 
 that the attempts to reduce the oxides of manganese by alumin- 
 ium have not been practically successful, because the result- 
 ing slag, A1 2 O , with an admixture of manganese oxides, is 
 extremely fluid and highly capable of dissolving the materials 
 of which crucibles are made. The case is not so difficult with 
 chromium, because the chromium-carrying alumina slag does 
 not attack the crucible walls and is so viscous that it will not 
 pass through cracks of considerable size, " but in fact makes 
 its own containing vessel by the formation of a solidified layer 
 or coating." " The process is carried out by mixing the 
 chromium oxide with a small excess above the theoretically 
 required quantity of finely divided aluminium, and this mix- 
 ture heated in a suitable furnace, as for instance a reverberatory 
 furnace or in crucibles, until the reaction begins, whereupon 
 there is formed a metallic mass and a layer of melted alumina 
 lying upon it." 
 
 Patent Claim. 
 
 A process for the manufacture of molten reguline metallic 
 chromium characterized by heating a mixture of aluminium 
 with chromic oxide in a crucible or furnace by external heat 
 until the reaction begins, whereby a metallic mass of molten 
 chromium is formed and upon it a layer of melted chro- 
 miferous alumina. 
 
 In both the patents alluded to, the commencement of the 
 reaction is brought about by heating the whole mixture ex- 
 ternally up to the temperature of reaction. Since the reac- 
 tion is, however, strongly exothermic (evolving heat) it is 
 therefore evidently sufficient to heat only a part of the mass 
 either by the blowpipe flame or an incandescent body heated 
 electrically, or in any other way, and so bring it locally to the 
 1 German Patent 112,586, Jan. 20, 1895. 
 
BY THE USE OF HIGH TEMPERATURES. 47 
 
 reaction temperature. The heat set free by the reaction will 
 suffice to propagate it throughout the whole mass. As I have 
 already mentioned, a similar manner of ignition appears in 
 Aschermann's process (page 42). 
 
 The same idea is again worked out by Goldschmidt and 
 Vautin in two new patents. 
 
 The first 1 begins with the following sentence : " The object 
 of the present patent is a process for the manufacture of pref- 
 erably difficultly fusible metals and their alloys with each 
 other and with metalloids. These metals or metalloids are 
 separated out of their oxygen and sulphur compoiinds by a 
 process of fusion, either alone or several simultaneously by 
 the action of aluminium or a mixture of aluminium and mag- 
 nesium." 
 
 It is seen that the process is not here limited to chromium 
 but rendered general, and that magnesium is added to alumin- 
 ium as a means of reduction. Further attention is drawn to 
 the fact that the reaction is exothermic and a new manner of 
 ignition is proposed. It is worth noticing that the external 
 heating of the mixture is now designated as particularly im- 
 practicable. " Since if the mixture is heated all at once to 
 the temperature of ignition it will react with explosive violence 
 and it has been found impossible to manufacture the metals 
 or alloys of the same commercially in this way." 
 
 It is not necessary to enter further into the details of these 
 patents ; they are clearly mentioned in the patent claims. We 
 may add, however, that continuous working is described, for 
 instance, by taking out the metal formed at the bottom of the 
 reaction vessel from a tap-hole, and allowing the slag to flow 
 from a corresponding opening higher up, and continuing the 
 process in this manner by the addition of new reaction ma- 
 terial. 
 
 If it is desired to obtain an alloy, one may take a mixture 
 of the oxides of the metals concerned or of their sulphides or 
 evidently adding a part in the metallic form to the mixture ; if 
 
 1 German Patent 96,317, March 13, 1895. 
 
48 CHROMIUM AND ITS COMPOUNDS. 
 
 it is wished that the alloy contain aluminium the latter is used 
 in excess, while by using an excess of the other metallic com- 
 pounds, metals are obtained free from aluminium. The fol- 
 lowing patent claims are reproduced : 
 
 (1) An apparatus for the manufacture of metals and metal- 
 loids or alloys of the same with each other by reducing their 
 oxygen or sulphur compounds by means of aluminium or 
 aluminium and magnesium, the process being characterized 
 by the fact that the whole mixture to be ignited is not ignited 
 at once but only a part, whereby the exothermic reaction 
 propagates itself from that part to the rest of the mixture 
 without the application of external heat. 
 
 (2) A method of operating the process described in claim i, 
 consisting in igniting in the melting vessel a small quantity 
 of the reduction mixture and continuing the reaction by the 
 addition of further quantities of the mixture, which may finally 
 be added in the briquetted condition. 
 
 (3) A method of operating the process described in claim i, 
 characterized by heating the reaction mixture placed in the 
 melting crucible, up to its reaction temperature at one point 
 only, whereby the exothermic reaction propagates itself from 
 this point. 
 
 (4) In the method of partial ignition described in claims i 
 to 3 the introductory process consisting in bringing into con- 
 tact with the principal mixture and igniting another mixture 
 acting upon the same principle, that is, consisting of alumin- 
 ium with a metallic compound (oxide or sulphide) which is 
 easily ignited and produces a high reaction temperature, 1 and 
 thus communicates the ignition to the principal mixture. 
 
 We may finally draw our attention to the fact that in the 
 patent specifications the manufacture of manganese is given as 
 an example, while this metal was not producible according to 
 the former patent (see page 45), evident!}' in consequence of 
 
 1 In the description a mixture of barium peroxide and aluminium 
 powder is given as an example. 
 
BY THE USE OF HIGH TEMPERATURES. 49 
 
 the extremely high temperatures obtained by the old method 
 of operation. 
 
 The second patent already referred to, 1 that of Vautin an- 
 nounced in the year 1896, agrees so exactly with the Gold- 
 schmidt patent that we can immediately pass to its patent 
 claims, which, leaving out unnecessary repetitions, are as fol- 
 lows: 
 
 (i) to (8) Process for the production of metals and alloys 
 from metallic oxides, sulphides or chlorides either alone or 
 mixed with each other, by the reducing action of aluminium, 
 consisting in heating to the reacting temperature a small 
 quantity of the mixture of aluminium or aluminium-magnes- 
 ium alloy with the metallic compounds, the latter in the 
 finely powdered condition. The temperature attained by the 
 reaction propagates itself successively and automatically to 
 the adjacent parts of the mixture and ignites the whole mass, 
 as above described. 
 
 (9) The process described for the production of metals or 
 alloys from metallic oxides, sulphides or chlorides alone or 
 mixed with each other, characterized by heating to the reac- 
 tion temperature a small quantity of the mixture of the finely 
 pulverized compound and finely pulverized aluminium or 
 aluminium-magnesium alloy in order to start the reaction, 
 and then adding the principal part of the mixture, so that in 
 consequence of the heat evolved by the reaction of the first 
 part the main reaction is propagated automatically through- 
 out the whole mass, as before described. 
 
 (10) The process described for the reduction of metals or 
 alloys from metallic oxides, sulphides or chlorides alone or 
 admixed with each other, characterized by covering a small 
 portion of the mixture of the finely pulverized compound with 
 finely pulverized aluminium or aluminium-magnesium alloy 
 with a small quantity of a similar mixture which is more easily 
 started in action, and heating the latter whereby the reaction 
 
 1 English Patent 16,685, July 28, 1896. 
 
50 CHROMIUM AND ITS COMPOUNDS. 
 
 is started and is then propagated to the principal mixture as 
 described. 
 
 Finally Dollner 1 has patented the use of carbides in place of 
 aluminiiim or magnesium. " The details of the process aside 
 from the replacement of aluminium and magnesium by the 
 carbide are exactly the same as set forth in the above patent 
 specifications Nos. 112,586 and 96,317." The reaction tem- 
 peratures are somewhat lower, and if it is wished to raise them 
 aluminium or magnesium may be mixed in ; if it is wished to 
 diminish them a ballast of negative material can be added, for 
 instance, an excess of the metallic compound to be reduced or 
 a flux, or finally an excess of calcium carbide if it is desired 
 to carbonize the metal produced or to introduce calcium into 
 it. 
 
 By using a sufficient excess of the oxide or the sulphide, the 
 metal can be obtained more or less free from carbon, at least 
 free from the metallic components of the carbide. It is not 
 possible to produce in this way completely carbonless metals 
 or alloys, and, moreover, the evolution of gas produced by the 
 formation of carbon monoxide may not be advantageous to 
 the process. 
 
 Patent Claim. 
 
 (1) A method of carrying out the process of patent No. 96,317, 
 for the manufacture of metals and alloys of the same with 
 each other or with metalloids, using a mixture of oxygen or 
 sulphur compounds of these metals or metalloids with pulver- 
 ized carbides of the earth or alkaline earth metals, with or 
 without the admixture of aluminium or magnesium, and 
 operating the process in such a manner that the mixture is 
 ignited at one point and thus the reaction started which is 
 concerned in the production of those metals or alloys. 
 
 (2) In the process described in claim i, the starting of the 
 reaction by using as igniting material a mixture of carbides 
 and oxides in composition analogous to the principal mix- 
 
 1 German Patent 113,037, Feb. 10, 1897. 
 
BY THE USE OF HIGH TEMPERATURES. 51 
 
 ture but reacting more violently, and thus transferring the 
 ignition to the principal reacting mass. 
 
 (3) A method of operating the process of claim i for the 
 manufacture of alloys, characterized by adding the compo- 
 nents in part in the metallic state to the reacting-mixture and 
 not in reducing both of the components of the alloy simul. 
 taneously from their oxygen or sulphur compounds. 1 
 
 Two lectures by Dr. Hans Goldschmidt given in iSgS 2 and 
 iQOi 3 contain some further additions concerning the alumino- 
 thermic operations. 
 
 It is stated that the mixture of aluminium with the oxide 
 to be reduced, called thermite, is theoretically made in quan- 
 tivalent proportions ; though in general an excess of oxide is 
 used since it is thereby possible to oxidize completely all the 
 aluminium so that metal free from aluminium is obtained, in 
 spite of the great alloying tendency of aluminium. 
 
 " Before all, such metals are to be considered whose produc- 
 tion in the pure state has not been possible by other processes, 
 or even in the electric furnace and whose production now in 
 the pure carbonless condition would offer particular advan- 
 tages to the metallurgist. Chromium and manganese are the 
 most important. The manufacture of these metals is carried 
 out on a large scale, since the consumption has become quite 
 large at several works. 
 
 The principal consumption is supplied by the Allgemeine 
 Thermit-Gesellschaft at Bssen ; besides them the French So- 
 ciete d'filectro-Chimie in St. Michael de Maurienne (Savoy) 
 has manufactured the metals named in particular chromium, 
 under a license since 1899. The manufacture is carried out 
 in large crucible-shaped vessels in which several hundred 
 weight of the metals are produced in one operation ; this 
 
 1 Another method of reduction by means of calcium carbide which shows 
 important variations from the above has so far been only incompletely de- 
 scribed. See Zeitschr. f. Elektrochemie, 7, 451 (1901). 
 
 2 Zeitschr. f. Elektrochemie, 4, 494 (1898). 
 
 3 Enlarged reprint from Stahl und Eisen, 1901, No. n. 
 
52 CHROMIUM AND ITS COMPOUNDS. 
 
 operation takes scarcely a half hour in consequence of the 
 rapidity of the reaction. 
 
 On top of the metallic mass there is found the resulting 
 alumina which, after removal, can be worked up again into 
 metallic aluminium in the most suitable manner. The metal 
 reduced from it, however, contains some chromium and is 
 therefore best used again for the manufacture of chromium, 
 so that we have here a complete cyclical process of technical 
 practicability. 
 
 The alumina can also be used as such, since it is quite free 
 from water and therefore possesses many advantages over 
 natural emery for use as an abrasive, since the emery on ac- 
 count of its small water content does not possess the great 
 hardness of the corundum made by fusion. 
 
 The slag is interesting from other considerations. It shows 
 small, red, transparent crystals mostly in small cavities, which 
 are to be regarded as true rubies. On account of their small- 
 ness they do not possess commercial value. 
 
 Concerning the pure carbonless chromium, in the manu- 
 facture of which pure aluminium must be used, it is principally 
 used in the production of steel. In doing so, it has confirmed 
 the old observation that metals very nearly pure possess other 
 qualities than those contaminated by additions and that by 
 their purity the properties of the alloys are influenced in the 
 foregoing cases quite favorably. 
 
 Some further communications concerning pure chromium 
 will be given in connection with the chromium alloys at the 
 conclusion of the next section. 
 
II. OBTAINING OF COMPOUNDS OF CHROM- 
 IUM WITH THE METALS. 
 
 A. By Electrolysis of Aqueous Solutions. 
 
 If a pure solution of chromic chloride is electrolyzed with- 
 out particular precautions, using mercury as the negative and 
 platinum as the positive electrodes, the mercury according to 
 J. Feree 1 takes up only traces of chromium, and there results 
 only a brownish black powder whose formula according to 
 Bunsen lies between Cr 4 O 5 and Cr s O 6 (see however later, under 
 chromium oxides). 
 
 In order to obtain large quantities of chromium amalgam a 
 solution must be chosen as electrolyte which contains 160 
 grams of crystallized chromic chloride, 100 grams of concen- 
 trated hydrochloric acid and 740 grams of water, and the cur- 
 rent density must be raised somewhat high. With a current 
 of 22 amperes and a mercury surface of 8.05 sq. cm. that is, 
 a current density of 2.73 amperes per square centimeter 1.5 
 kilograms of solid chromium amalgam was obtained in an 
 hour. A too feeble current density is to be avoided since with 
 a current density of 0.28 ampere per square centimeter the 
 formation of amalgam does not take place. 
 
 The amalgam formed is washed quickly with cold water 
 after pouring off the solution, and is then pressed out, after 
 being dried on filter-paper, in a piece of chamois leather. The 
 mercury pressed through the leather contains only traces of 
 chromium, scarcely 0.03 per cent. The amalgam remaining 
 in the leather has the composition Hg 3 Cr. 
 
 If this amalgam is further dried by laying it upon double 
 folded filter-paper and subjecting it to a pressure of 200 kilo- 
 grams per square centimeter for several minutes, it loses more 
 mercury and becomes a new amalgam having the formula 
 HgCr. 
 
 While the amalgam Hg 3 Cr is soft, lustrous, only slightly 
 alterable in the air, loses its mercury on heating without 
 melting and easily oxidizes, the amalgam HgCr is also lus- 
 
 1 Compt. rend., 121, 822 (1895). 
 
54 CHROMIUM AND ITS COMPOUNDS. 
 
 trous but harder and more easily alterable and small drops of 
 mercury soon form on its surface. Both amalgams leave a 
 residue of metallic chromium if heated in a vacuum ; the 
 metal is very crumbly, but retains the shape of the original 
 lump. If the amalgam is distilled in a vacuum at tempera- 
 tures below 300 it leaves (which amalgam is not stated) a 
 metallic chromium, the qualities of which are very different 
 from those of the chromium obtained by Deville and Fremy. 
 This chromium is pyrophoric even when cold ; it ignites 
 spontaneously in the air and absorbs at the same time, in a 
 remarkable manner, both nitrogen and oxygen. The heat 
 generated by the reaction brings the whole mass to a bright 
 incandescence. The chromium produced by Moissan by the 
 distillation of the amalgam below 350 ignited in the air only 
 when it was warmed slightly. 
 
 The pyrophoric chromium resembles in its behavior the 
 pyrophoric manganese obtained in a similar manner ; even 
 when cold it absorbs nitrogen dioxide with incandescence, 
 producing chromic oxide and chromic nitride. When heated 
 in an atmosphere of nitrogen it also glows, forming chromic 
 nitride. Even sulphur dioxide is absorbed in the cold with 
 incandescence, and a slight warming in an atmosphere of 
 carbon dioxide or carbonic acid will suffice to set the chro- 
 mium in active incandescence. 
 
 After heating, the pyrophoric chromium is less active and 
 almost unchangeable in air. 
 
 Some further communications on chromium alloys have 
 already been given on pages 5, 10, 14, 15 and 23. 
 
 B. By the Use of High Temperatures. 
 
 Besides the processes which have been mentioned in de- 
 scribing the methods for producing pure chromium (pages zfl, 3^ 
 ^et seq\ there are some others which are recommended for the 
 ^manufacture of chromium alloys ; according to Borchers 1 there 
 belongs here the process of Moissan patented in 
 
 1 Jahrbuch der Elektrochemie, 2, 183 (1895). 
 
 2 German Patent 82,624, Nov. 9, 1894. 
 
BY THE USE OF HIGH TEMPERATURES. 55 
 
 Borchers says: "The reason why chromium and similar 
 metals which it is desired to obtain free from carbon, cannot 
 be manufactured simply by processes analogous to the manu- 
 facture of aluminium lies in their high melting-point. Where 
 the presence of aluminium is not injurious the manufacture 
 of the more easily fusible aluminium alloys of these metals is 
 recommended after the general idea of the electrolysis of 
 alumina. It is a well-known knack of alloying to take one 
 metal which is not fusible easily or does not dissolve quickly 
 enough in a second metal with which it is to be alloyed, and 
 to dissolve it in a third, which forms a better solvent for it, in 
 order then to bring it in a dissolved form to the second metal. 
 This process has been patented in Germany by Moissan, with 
 his usual good fortune for getting patents for all known 
 things. His patent concerns the difficultly fusible metals and 
 metalloids such as molybdenum, tungsten, uranium, zirconium, 
 vanadium, cobalt, nickel, manganese, titanium, chromium, 
 silicon and boron which are to be dissolved in iron or other 
 metals. He gets these materials at first in solution in alumin- 
 ium or magnesium. 
 
 In fact Moissan does not say that his process is to be operated 
 electrolytically, but it is in fact operated in this way and has 
 been done so several years, as the author can especially verify. 
 Those metals which are not difficult to separate out electro- 
 lytically, yet are hard to melt, may be prepared in the fluid con- 
 dition from molten electrolytes, if they are received in more 
 easily fusible metals, which is done by making the latter the 
 cathode or by preparing the chromium simultaneously with 
 the other metal." 
 
 The patent specification describes the bringing the alumin- 
 ium or magnesium alloy in an iron bath, or other suitable 
 material whereby the difficultly fusible elements as chromium, 
 etc., are taken up at once by the latter. The elimination of 
 the aluminium is easy, in general it can be performed by 
 using the oxide of the metal with which one is working. 
 
56 CHROMIUM AND ITS COMPOUNDS. 
 
 "In order for instance to get chromium-copper alloy a 
 determined quantity of chromium-aluminium is added to 
 molten copper, according to the content of chromium which 
 is wished. The bath is well stirred and if the quantity of 
 aluminium present is too high and must be removed, the ex- 
 cess of aluminium is burned out by the addition of small 
 quantities of cupric oxide, and the aluminium passes into the 
 slag." 
 
 In other cases the aluminium in excess can be oxidized u by 
 the gaseous oxygen present in the solution," or by a current 
 of air. 
 
 An alloy of iron with tungsten, molybdenum, and chro- 
 mium is obtainable in the Siemens-Martin furnace or in the 
 Bessemer converter in an analogous manner. 
 
 Patent Claim. 
 
 Process for the manufacture of alloys, characterized by in- 
 troducing the difficultly fusible metals molybdenum, titanium, 
 chromium, etc., into metals and alloys in the form of alloys 
 with aluminium. 
 
 A process for the commercial manufacture of alloys of iron 
 with chromium, etc., in an electrolytic manner, by using a 
 flux consisting of lime, was patented by J. Heibling, of 
 Grenoble, in I895. 1 He uses a shaft furnace, the inner lining 
 being of carbon bricks and the outer of refractory bricks ; a 
 cast-iron plate lies upon the movable bottom of the shaft, 
 which is likewise lined with carbon bricks. Above the latter, 
 which together with the lining of the furnace acts as the 
 negative electrode, is the positive electrode in the form of a 
 carbon rod of suitable dimensions. 
 
 A carbon crucible is made " by placing in the closed cast- 
 iron form a suitable mixture of pulverized coke or graphite 
 and tar and baking." 
 
 A mixture of pulverized ore (oxide), carbon and pulverized 
 caustic lime is brought into the furnace, the lime being to the 
 carbon in the proportion of 3 molecules to i. If practicable 
 
 1 German Patent 86,503, July 12, 1895. 
 
BY THE USE OF HIGH TEMPERATURES. 57 
 
 there is added to this mixture a quantity of iron oxide neces- 
 sary to form an iron alloy of a certain proportion, with the 
 carbon necessary for the reduction, in which case the weight 
 of the cast-iron furnace bottom is to be taken into considera- 
 tion. To the whole mass is finally added a suitable quantity 
 of pulverized fluor-spar to combine with the silicon in excess. 
 
 The action of the electric current is described as follows : 
 The ore and finally the oxide of iron is reduced and forms an 
 iron alloy which dissolves the carbon. The latter unites, 
 however, immediately to form calcium carbide with the cal- 
 cium from the lime (carbonic oxide being formed). The car- 
 bide contains, dissolved, the remainder of the silicon as carbide 
 of silicon and with the latter forms the slag under which the 
 fluid regulus is found. By inclining the movable carbon 
 bottom to one side the alloy can be drawn off. 
 
 The silicious material serves as a protection for the calcium 
 compound which, without its presence, would be much more 
 easily subject to attack by damp air. An excess of silicon is 
 to be avoided. 
 
 The author predicts likewise the application of his process 
 in particular to ores poor in the heavy metals. 
 
 The patent claim reads : Preparation of alloys of iron with 
 manganese, chromium, aluminium, nickel from their ores, in 
 the electric furnace, characterized by the use of lime as a flux. 
 
 In contrast to the processes so far mentioned which work 
 with large amounts of carbon and afterwards treated by the 
 process of Moissan (see page^g^, furnishing alloys containing 
 carbon, stress is laid by La Societe Neo-Metallurgie Marbeau, 
 Chaplet & Co., 1 upon the obtaining of alloys as free as possible 
 from carbon. For this purpose they also use a "suitable 
 electric furnace" which is apparently lined with a material 
 containing no carbon, and heated with u horizontal arcs in 
 such a manner that contact of the carbon electrodes with the 
 metal and oxides in question, and the consequent carburiza- 
 tion of the final product is avoided." 
 
 1 English Patent, 7,847, April 19, 1895. 
 
58 CHROMIUM AND ITS COMPOUNDS. 
 
 The process is described in detail as follows : 
 
 A sufficient amount of a more or less easily fusible metal 
 which is to form the alloy either in the metallic form or as an 
 oxide mixed with the necessary amount of carbon for reduc- 
 tion is put in the furnace, heated and, after reduction, melted. 
 To the bath so made is added gradually the already prepared 
 oxide of the heavy metal to be alloyed mixed with the req- 
 uisite amount of carbon for reduction. 
 
 Another method of procedure can also be used in place of 
 the one already mentioned : "The same alloys can also be ob- 
 tained by mixing the oxide of the difficultly fusible metal 
 with the oxide of the easily fusible metal in sufficient quanti- 
 ties and in the right proportions to form the desired alloy. 
 
 " To this mixture of the various oxides there is added the 
 proper amount of carbon for reduction, and a suitable amount 
 is charged into the furnace. Under the influence of the elec- 
 tric arc, the oxide of the more easily fusible metal is first re- 
 duced and melted and forms the foundation of the metallic 
 bath by which is gradually accomplished the reduction and 
 fusion of the other oxide (the addition of the mixture of the 
 oxides is dependent on the output of the furnace)." 
 
 Finally there can be added to the bath of the easily fusible 
 metal, the difficultly fusible metal in the form of a fine powder, 
 which may have been produced by an electrolytic process. 
 
 The composition of the manufactured alloy can be easily 
 calculated, and the process is applicable for the manufacture 
 of alloys with a high content of the difficultly fusible metal 
 (70 to 80 per cent.) which then in this condition can find ap- 
 plication as additions to other metals. 
 
 It is quite possible with this process to obtain alloys quite 
 low in carbon, but with certainty not entirely free from 
 carbon. 
 
 The patent claim reads : 
 
 i. The preparation of improved alloys, as described, in a 
 suitable furnace heated by horizontal arcs, to avoid the contact 
 
BY THE USE OF HIGH TEMPERATURES. 59 
 
 of the carbon electrode with the oxides and metals in question 
 and thereby prevent the carburizing of the finished product, 
 as explained. 
 
 2. The herein-described improved methods for the prepara- 
 tion of improved alloys as performed in various cases ; as 
 alloys of a more or less difficultly fusible metal, as chromium, 
 tungsten, molybdenum, etc., with a more easily fusible metal, 
 as nickel, cobalt, manganese, iron, copper, aluminium, etc., 
 whereby the alloys named are obtained in the molten metallic 
 condition, with the desired content of each the single con- 
 stituents but particularly with a high content of the difficultly 
 fusible metal. Such alloys are more easily fusible than the 
 more difficultly fusible metal, as explained. 
 
 3. Various applications of the above-described method of 
 preparing alloys ; in particular it is possible to add a diffi- 
 cultly fusible metal when molten to another metal, or alloy, 
 and particularly to iron and steel to which they will com- 
 municate the characteristics of the difficultly fusible metal, as 
 explained. 
 
 A complete exclusion of carbon and other impurities is 
 possible in the process of the Electro-Metallurgical Company, 
 Limited, of London 1 , for the preparation of chromium alloys. 
 In the description the effect of the addition of chromium will 
 be discussed, although it is pointed out that the chromium is 
 to be added in the chemically pure condition, in particular free 
 from carbon, otherwise the property of the alloy will be in- 
 juriously influenced. 
 
 Further it is remarked that the addition of chemically pure 
 chromium, electrolytically prepared, will improve all metals ; 
 it makes them harder and more resistant to shocks, tension, 
 and friction, as well as the corrosive action of air, dampness, 
 acids, high temperatures, etc. 
 
 Such chromium alloys are formed only when the chromium 
 is added directly to the molten alloy. Likewise it is possible 
 
 1 German Patent 89,348, IJan. 16, 1896 ; English Patent of Placet, 202, 
 1896. 
 
60 CHROMIUM AND ITS COMPOUNDS. 
 
 to add one or more metals, which facilitate alloying on account 
 of their large capacity for dissolving chromium, as zinc, man- 
 ganese, magnesium, aluminium, antimony, bismuth, palla- 
 dium, etc. Surely this last can only find application on paper. 
 
 In order to avoid, in this process, the oxidation of the chrom- 
 ium, it is electrolytically or otherwise covered with a more 
 or less thick coat of a protecting metal, as copper, nickel, 
 gold, silver, zinc, aluminium, tin, platinum. 
 
 The addition of chromium in very small amounts exerts a 
 good influence ; a few tenths of a per cent, makes the noble 
 metals, gold, silver, copper, nickel, tin, as well as lead and 
 zinc, considerably harder and tougher. For the best results 
 the chromium should be added in the proportion of 0.5 up to 
 15 or 20 per cent. 
 
 The metal alloys with a larger content of chromium are so 
 extraordinary hard that they can only be worked with the 
 grindstone. Recapitulating, the great advantages of the addi- 
 tion of chromium consist as follows : 
 
 An addition of chromium from 0.5 to 20 per cent, in copper 
 or copper alloys, as bronze, brass, German silver, etc., im- 
 proves them so that their "fracture" approaches that of steel. 
 A small addition of chromium to the coinage metals makes 
 them noticeably more resistant to pressure and the necessary 
 washing. Finally chromium makes all metals as well as al- 
 loys more resistant against high temperatures, and is valuable 
 for the manufacture of hearth-plates and moulds, also more 
 resistant against acids, alkalies, and other chemical reagents, 
 which is to be provided against in the manufacture of chem- 
 ical apparatus and cooking utensils ; it increases the hardness 
 of metals and their ring, as of bells and trumpets ; it raises 
 the electric resistance of manganese, manganese-iron, nickel- 
 iron, and other metals, serving for the manufacture of resis- 
 tance wire; and raises the anti-magnetic properties of copper, 
 platinum, palladium, manganese, tungsten, and cadmium, a 
 circumstance made use of in the construction of clocks, etc. 
 
 The patent claim reads : 
 
BY THE USE OF HIGH TEMPERATURES. 6l 
 
 Process for the preparation of alloys of pure chromium, 
 characterized by the fact that the chromium added to the 
 bath is coated previously in an electrolytic or other manner, 
 with a coating of a metal (copper, nickel, aluminium, gold, 
 silver, etc.), which prevents the oxidation of it at the moment 
 of contact with the bath. 
 
 A modification of this process of the same company is de- 
 scribed in a Russian patent of September 13, 1897, from 
 which the Chemiker-Zeitung 1 gives an extract. According to 
 it the oxidation of the chromium will be prevented by being 
 first brought into contact with a sufficient amount of molten 
 cryolite, borax, or other easily fusible flux sufficient to cover 
 it and then the metal to be alloyed added. In this way alu- 
 minium will readily alloy with chromium, although otherwise 
 even on long heating with molten aluminium a piece of chrom- 
 ium will not dissolve because it has coated itself with oxide. 
 
 It is remarkable that at these high temperatures the coating 
 of oxide will not easily be reduced by aluminium, although 
 the whole process of Vautin-Goldschmidt (see page ^efand 
 following), rests on this fact ; if anything, the temperatures 
 are still higher. 
 
 The process can also be worked in this manner : Sufficient 
 borax, cryolite, etc., can be added to form a complete cover- 
 ing to the molten bath and then pieces of the hard metal, or 
 it may be the alloy, thrown into the bath. While passing 
 through the fluid coating the metal will be prevented from 
 oxidizing and any coatings of oxide will be dissolved by the 
 flux. To avoid contamination, the crucible used in melting 
 must be lined with alumina or chromic oxide. 
 
 For completeness we have an American patent 2 , as well 
 as that of the Societe* Generate de Aciers Fins 3 , both patents 
 concerning the manufacture of chromium-iron alloys. 
 
 1 Chemiker-Zeitg., p. 1068(1897). 
 
 2 American Patent 567,757, Electrometallurgical Company, Limited, 
 July 8, 1896 ; the Official Gazette of the U. S. Patent Office, 76, 1642, 
 1896, nearly corresponding to the German Patent 90,746, of the I4th of June, 
 1896. 
 
 3 German Patent 120,310, April 6, 1899. 
 
62 CHROMIUM AND ITS COMPOUNDS. 
 
 The first patent claim reads : 
 
 The described improvements in the treatment of iron and 
 steel with pure chromium or similar metals, as molybdenum 
 or tungsten, for the preparation of alloys of these metals, con- 
 sisting therein, that by the addition of a proper amount of 
 aluminium to the molten mass of iron or steel, it is nearly 
 completely deoxidized, the deoxidation, however, by the alu- 
 minium being first only completed after a small part of the 
 chromium or similar metal has been oxidized, the rest alloy- 
 ing with the mass of iron or steel. 
 
 The other patent claim has the following wording : 
 
 Process for the manufacture of chrome-steel, characterized 
 by allowing a stream of open-hearth steel to flow over a mix- 
 ture of aluminium powder and chromium-iron alloy in the 
 casting ladle. 
 
 The ignition of the aluminium by the outflowing stream 
 evolves sufficient heat to bring the surrounding chromium- 
 iron alloy to a quick and complete fusion, so that the chrom- 
 ium can at once combine intimately with the stream of steel, 
 and the cast-steel block which is characterized by great den- 
 sity and freedom from blow-holes also shows a uniform distri- 
 bution of chromium throughout. 
 
 In concluding the processes for the preparation of chromium 
 alloys the process of Heroult 1 for the preparation of very rich 
 ferro-chrome must be considered. In the reference cited it is 
 stated that chromite is heated in an electric furnace with the 
 addition of a sufficient amount of carbon for reduction and 38 
 to 30 per cent, of fluxing material (lime, kaolin, or fluorspar). 
 The ferro-chrome formed will, on account of the greater vola- 
 tility of the iron, become richer in chromium the quicker the 
 operation is completed ; the fluxing material permits the 
 regulation of the operation. 
 
 Quite identical with the previous patent is an American 
 patent 2 , under the name of Vielhomme, whose claim only 
 was accessible to me. It reads : 
 
 1 French Patent 284,525, Dec. 30, 1898 ; Chemiker-Zeitg., 694 (1899). 
 
 2 U. S. Patent 648,119, July 25, 1899; the Official Gazette of the U. S. 
 Patent Office, 91, 717 (1900). 
 
BY THE USE OF HIGH TEMPERATURES. 63 
 
 Process for the manufacture of rich ferro-chrome, consisting 
 therein, by the heating of chromite in an electric furnace in 
 the presence of a sufficient amount of fluxing material and 
 powdered coke, to a temperature sufficient for reduction and 
 melting of the ore and the volatilization of the larger amount 
 of iron. The remaining iron then forms with the chromium 
 a rich ferro-chrome alloy. 1 
 
 At this place also, use will be made of a very kind letter of 
 Dr. H. Goldschmidt, and reference made also to page^&flmd 
 the literature quoted there, and some general remarks on the 
 preparation of chromium and its alloys will be added. 
 
 As much as is known chromium and its alloys are produced 
 technically in four ways : 
 
 i. As ferro-chrome in the blast-furnace ; 2, as ferro-chrome 
 in crucibles ; 3, as ferro-chrome in the electric furnace ; 4, 
 as pure chromium by means of aluminium. 
 
 The blast-furnace process furnishes no particularly rich 
 chromium product, but only one of 30 to 40 per cent, and 
 may get into a difficult position because at this day higher 
 percentage alloys are preferred. 
 
 Processes 2 and 3 furnish alloys containing 60 to 63 per 
 cent, of chromium and 8 to 12 per cent, of carbon, calculated 
 on the chromium content. Large quantities are produced in 
 this way in France and Germany. The process of manufac- 
 ture in crucibles in which, as is said, only a single kilogram 
 can be made at one time, is not cheap. The composition of 
 the chromium mixtures are held secret. 
 
 Finally this process has been somewhat superseded by the 
 electrical process, so that to-day the larger amount of ferro- 
 chrome is produced in the electric furnace, and particular 
 preference for this method is shown in France. In particular 
 the early calcium carbide manufacturers, who had to give up 
 
 1 In the Russian Privileg., 351, Sept. 30, 1897 (referred to in Chemiker- 
 Zeitg., 1897, 1068), E. Placet protects a process for the manufacture of 
 chrome-iron or -steel, Tubes or bars on which chromium has been electro- 
 lytically precipitated were melted together or welded or drawn into wires or 
 cemented ; in the last case the outer surface becomes very hard. See also 
 page ii. 
 
64 CHROMIUM AND ITS COMPOUNDS. 
 
 their production because the patents of Bullier under which 
 they worked were declared legal by the French Court, in 
 opposition to the German Imperial Court, turned to this new 
 opportunity with avidity. The foundation of this process is 
 indeed that given by Moissan (page^j^T 35~ 
 
 The disadvantage of the ferro-chromium, particularly that 
 made in the electric furnace, which probably contains a few 
 more per cent, of chromium than that made in the crucible, 
 lies in its high and irregular content of carbon, so that for the 
 best qualities of steel alloys, especially if several per cent, of 
 chromium is to be added, it cannot always be used. 
 
 For instance if it is a question of increasing the content of 
 chromium relatively to the carbon which is added to Martin 
 steel in the prepared condition at the end of the operation so 
 as to provide a charge, for instance, which along with 2.5 per 
 cent, of chromium shall contain 0.2 or scarcely only 0.15 per 
 cent, of carbon, this cannot be obtained without the assistance 
 of carbon-free chromium ; since when using ferro-chromium at 
 least 0.25 to 0.3 per cent, of carbon is carried in, which with 
 the carbon already in the fluid metal raises the percentage to 
 at least 0.3 or 0.35 per cent, in the finished metal. Also in 
 crucible casting even where small additions of chromium are 
 concerned, i to 2 per cent., and where therefore a particularly 
 small carbon content of the alloy added is not of importance, 
 carbon-free chromium is preferred. 
 
 Further, carbon-free chromium is used for the manufacture 
 of high chromium tool steel containing 6 to 10 per cent, or 
 even more chromium. 
 
 It is worth mentioning that the addition can be made in the 
 form of chrome-thermite (as the mixture of aluminium and 
 chromium oxide is called). It is used in the manner that the 
 highly heated steel is allowed to flow upon the mixture men- 
 tioned and immediately ignites it. The chromium dissolves 
 in the metal bath, while the slag floats on the top (see page 
 
 56). 
 
BY THE USE OF HIGH TEMPERATURES. 65 
 
 On the grounds before mentioned, in spite of the fact that 
 the ferro-chromium prepared in the electric furnace is much 
 cheaper, pure chromium prepared from chromium-thermite is 
 often preferred. The last ignites itself only at very high tem- 
 peratures as has been stated, and yields a good output only 
 when used in large amounts. 
 
 The market price of 60 per cent, ferro-chrome, according to 
 the quotations of December 15, 1901, was $350 per metric 
 ton ; it may upon large demands become much lower. It was 
 much higher a short time ago before the introduction of the 
 electrical process. 
 
 The price of commercially pure chromium is $2 per kilo. 
 In spite of that the product is used by many firms by the car- 
 load. 
 
 Besides ferro-chromium there is still another rich chromium 
 alloy which finds many applications, the chrome-manganese 
 containing 70 per cent, of manganese and 30 per cent, of 
 chromium. It is used in the manufacture of copper alloys, 
 the so-called chrome-manganin. Chromium alloys directly 
 with copper with great difficulty, it liquating out quite easily 
 so that the chromium-copper with 10 per cent, of chromium 
 made by the alumino-thermite process and used in the manu- 
 facture of chromium-treated copper is very seldom chosen, 
 while the chrome-manganese alloys easily with copper like 
 pure manganese itself and has just recently come into frequent 
 use. 
 
 In contrast to iron, chromium seems to raise the ductility of 
 copper. A chrome-copper with 10 per cent, of chromium has 
 almost completely the color of pure copper, but is, however, 
 considerably harder. 
 
III. OBTAINING OF THE COMPOUNDS OF 
 
 CHROMIUM WITH THE NON-METALS. 
 
 A. Carbon Compounds. 
 
 It has often been stated in the description of the methods 
 serving for the manufacture of chromium, that the chromium 
 often contains carbon. We shall now give information re- 
 garding the obtaining of well-characterized compounds of 
 chromium with carbon, which has appeared in the work of 
 Moissan 1 already referred to (see page 3$, et seq.\ 
 
 If a crucible containing chromium and a large excess of 
 carbon be heated in an electric furnace using 350 amperes at 
 70 volts for from ten to fifteen minutes, there is obtained an inco- 
 herent mass in the bottom of the crucible filled with crystals 
 of chromium carbide of the formula C 2 Cr (according to two 
 analyses). This carbide forms in lamellae of very high, 
 somewhat greasy lustre, and is only slowly attacked by dilute 
 hydrochloric acid on long standing, not by concentrated hy- 
 drochloric acid, fuming or dilute nitric acid, or aqua regia. 
 It is slightly attacked by molten caustic potash, but on the 
 contrary molten saltpeter attacks it with ease. Its specific 
 gravity is 5.62. Hot water is not decomposed by it. 
 
 The formation of another carbide has been observed in a 
 number of preparations of metallic chromium. The surface 
 of the metallic pieces are seen to be covered with brownish 
 red needles, which often reach a length of i to 2 cm, and show 
 the composition CCr 4 (after three analyses). Sometimes this 
 carbide takes the form of shining needles lining the cavities 
 which form in the molten chromium. Its density is 6.75. 
 
 Both compounds dissolve, on a further raising of the tem- 
 perature, large quantities of carbon, which they then again give 
 up in the form of small shining folia of well crystallized 
 graphite. 
 
 P. Williams 2 obtained a double carbide of iron and chrom- 
 ium, on heating a mixture of 200 grams of pure calcined 
 chromic oxide, 200 grams of iron and 70 grams of petroleum 
 coke in a carbon crucible for five minutes, using 900 amperes 
 
 1 Compt. rend., 119, 185 (1894). 
 
 2 Ibid., 127,483(1898). 
 
SILICON COMPOUNDS. 67 
 
 and 45 volts. The resulting metallic mass had a crystalline 
 appearance and resembled commercial ferro-chromium. On 
 treating from two to three hours on the water-bath with aqua 
 regia it was gradually disintegrated, and the crystals which sepa- 
 rated were retreated anew to separate from them the last traces 
 of iron. They were separated from the remaining impurity, 
 a small amount of graphite, by means of bromoform. 
 
 The crystals had a metallic appearance, somewhat the color 
 of nickel, and consisted of a conglomeration of tough needles; 
 they scratched glass but not quartz, were not magnetic and 
 had a density of 7.22 at 19. They oxidized at about 500 
 in a stream of air or steam. Gaseous or liquid acids attack 
 them slowly, nitric acid and aqua regia being without appre- 
 ciable effect. The analysis gave the composition of 3Fe 3 C. 
 2Cr s C 2 . It was also noticed that an excess of iron carbide 
 easily changed the results of analysis. 
 
 B. Silicon Compounds. 
 
 In connection with the description of the manufacture of 
 the hardest possible materials, which will scratch chromium 
 steel, the ruby and even the diamond, such as the silicide and 
 boride of titanium, carbon, etc.; it was mentioned by F. Chap- 
 let 1 that in the same manner also the silicides of the metals, 
 zirconium, chromium, iron, nickel, cobalt, manganese, molyb- 
 denum, tungsten, uranium and vanadium may be pre- 
 pared containing various amounts of nitrogen and carbon. 
 This patent demands more attention on this account. 
 
 For preparing the silicide of titanium, for instance, the fol- 
 lowing process was proposed : 82 parts of pulverized rutile, 
 60 parts of sand and 48 parts of pulverized carbon are mixed 
 together. The dry mixture is pressed into a carbon crucible, 
 placed in an electric furnace, built somewhat like Moissan's 
 with movable electrodes, which is closed up and heated for a 
 longer or shorter time according to the strength of the current. 
 
 There is obtained a gray, fused mass which, after cooling, has 
 a shiny fracture, is of great hardness and has a density of 
 about 4.8 and which can contain according to the duration of 
 
 1 English Patent 15,453, August 14, 1893. 
 
68 CHROMIUM AND ITS COMPOUNDS. 
 
 heating, besides the titanium and silicon, 20 to 25 per cent, 
 of carbon and a varying amount of nitrogen. This compound 
 can also be obtained in a crystalline state if a metal in the 
 molten state is employed as a solvent and is afterwards re- 
 moved by a suitable acid. 
 
 For further particulars of the process a reproduction of the 
 detailed patent claim will suffice : 
 
 (1) The manufacture or production of hard materials, which 
 are able to scratch chrome steel, and scratch or cut rubies or 
 diamonds, characterized by subjecting a mixture of the neces- 
 sary materials with or without reducing agents, as desired, in 
 a crucible to the heat of the electric arc, whereby there is ob- 
 tained the desired substances in pure crystallized, amorphous 
 or melted condition, or in the last case dissolved in a suitable 
 metal as solution medium from which it crystallizes out, and 
 then after the solution of the metal in an acid can be obtained 
 in the form of hard crystals. 
 
 The process can be carried out as follows: i. By a simple 
 direct combination of the mixed materials ; 2. By the direct 
 combination of the mixed materials in the presence of an excess 
 of a metal which can be later removed by the aid of an acid ; 
 3. By preparation of the material from an oxide or a salt of 
 one of its constituents, by reduction and solution in a metal 
 from which it can be afterwards obtained by removal of the 
 metal essentially as carried out above. 
 
 (2) The various new hard compounds which have been pre- 
 pared by the above process, as the silicide and boride of 
 titanium, as well as other silicides and borides, the silico- 
 carbide and silico-boride of titanium, and the silicides, boro- 
 silicides and silico-carbides of other metals and metalloids, are 
 able to scratch chromium steel and to scratch or cut rubies or 
 diamonds, and in the pulverized form as abrasive material, 
 glued to paper or cloth, for cutting, polishing or grinding. 
 
 Moissan 1 gives more exact information regarding the com- 
 mercial methods used in the preparation of chromium silicide. 
 After mentioning briefly that chromium and silicon will com- 
 1 Compt. rend., 121, 624 (1895). 
 
SILICON COMPOUNDS. 69 
 
 bine in a reverberatory furnace in a current of hydrogen at a 
 temperature of 1200, he turned his investigations to the elec- 
 tric furnace. 
 
 If 100 parts of chromium, free from carbon, and 15 parts of 
 silicon are brought together in a carbon crucible, and subjected 
 to a current of 900 amperes at 50 volts for nine minutes, there 
 will be found a silicide with a crystalline fracture embedded 
 in the surplus metal. 
 
 Or if 60 parts of silica, 200 parts of chromium oxide and 
 70 parts of sugar carbon be heated together with a current of 
 950 amperes at 70 volts for ten minutes, there is found a well- 
 fused, brittle and crystalline metallic mass. In the interior are 
 found spaces filled with needles of chromium silicide. This 
 metallic mass is coarsely pulverized and treated for a short 
 time with cold concentrated hydrofluoric acid, until the acid 
 attacks actively, then moderating the action by the addition 
 of water, in order to avoid raising of the temperature and de- 
 composition of the silicide. It must now be washed alternately 
 with water and cold hydrofluoric acid until all action has 
 ceased ; the residue consists of single or coherent small prisms 
 of silicide, which often are contaminated by small amounts of 
 silicon carbide. 
 
 The chemical properties of the chromium silicide remind 
 one of iron silicide, especially in its behavior towards acids ; 
 if finely pulverized it is attacked by hot strong hydrochloric 
 acid. Nitric acid has but slight effect, while aqua regia de- 
 composes it with the formation of silica. The gaseous hy- 
 drogen acids attack it only at temperatures lying between 
 dark and bright red heats. At 700 gaseous hydrochloric 
 acid transposes both the chromium and silicon into chlorine 
 compounds. 
 
 Chlorine alone acts at a red heat causing the silicide to 
 glow brightly. Molten potassium nitrate quickly forms chrom- 
 ate and silicate, while caustic potash acts only slowly. 
 
 The silicide scratches quartz and even corundum with 
 greatest ease; it appears that the majority of the silicides 
 
70 CHROMIUM AND ITS COMPOUNDS. 
 
 possess a much greater hardness than the corresponding car- 
 bides. 
 
 For performing the difficult analysis the silicide is fused 
 with a mixture of 2 parts of potassium carbonate and 8 
 parts of potassium nitrate, and afterwards treated with hydro- 
 chloric acid. The separation of the silica, which was made 
 insoluble by two treatments on the sand-bath, was tedious. 
 The presence of carbo-silicides complicated the analysis. The 
 results found corresponded closely to the formula SiCr 2 . 
 
 SiCr 2 . 
 
 Chromium 80.22 79.83 80.36 78.79 
 
 Silicon 19.60 21.08 19.92 21.21 
 
 Another much softer, but with the exception of hydrofluoric 
 acid also resistant to acids, crystallized chromium silicide of 
 the formula SiCr s was prepared by Zettel 1 by heating in a 
 Perrot furnace and utilizing the heat set free by the reduction 
 of chromium oxide by aluminium, in which he melted 140 
 grams of copper and 140 grams of aluminium in a refractory 
 crucible and gradually added 200 grams of previously ignited 
 chromic oxide. The mixture was vigorously stirred, and to- 
 wards the end some aluminium filings were added ; the silicon 
 came from the crucible and from the stirrer of like material. 
 
 In experiments to produce these silicides in the electric fur- 
 nace, mixtures of many chromium silicides were obtained but 
 could not be separated from each other because of their similar 
 chemical behavior. 
 
 Moissan and Zettel in their investigations used chromium 
 in excess and likewise obtained compounds containing chrom- 
 ium in excess. De Chalmot 2 carried on his researches in 
 quite a different direction ; he heated chromium oxide with 
 wood charcoal and an excess of silica in the electric arc, and 
 obtained large needles of a gray color and brilliant metallic 
 lustre, which were embedded in free silicon and could only be 
 separated from it mechanically with difficulty. Cold hydro- 
 
 1 Compt. rend., 126, 833. 
 
 ' 2 Am. Chem.- Journal, 19, 69 (1897). 
 
PHOSPHORUS COMPOUNDS. 7 1 
 
 chloric acid and aqua regia had no effect on it, hydrofluoric 
 acid dissolved it, which fact was made use of for separating out 
 free silicon. Two analyses showed a composition correspond- 
 ing to the formula Si 2 Cr, in one of which was found 13. 84 per 
 cent, of free silicon and in the other 4.71 per cent.; the last 
 one had a density of 4.393. The chromium silicide is charac- 
 terized by great tendency to crystallize even in the presence 
 of much free silicon. 
 
 In a later publication 1 the same author makes a statement 
 regarding the behavior of the above-described chromium-sili- 
 cide towards sulphur. Under 300 almost no reaction took 
 place, while at a higher temperature some silicon disulphide 
 and not free silicon (as with copper silicide, Cu 2 Si) could be 
 detected. The affinity of chromium for silicon is therefore 
 under these conditions somewhat greater than that of copper. 
 
 C. Phosphorus Compounds. 
 
 Th. Parker made the observation that in the electrolysis of 
 chloride solutions, if chromium phosphide is used as anode, it 
 was in general not seriously attacked by the chlorine set free, 
 and in 1892* protected the application of chromium phosphide 
 as anode material in the following patent claim : 
 
 An anode, in cells for the electrolysis of solutions contain- 
 ing chlorides, consisting of or containing chromium phos- 
 phide, essentially as previously described. 
 
 The patent literature gives several details regarding the 
 preparation of the chromium phosphide ; chromium phosphate 
 is mixed with carbon and if necessary a fluxing material, and 
 decomposed in any furnace at a high temperature, whereby 
 chromium phosphide is formed. Or chromium phosphate or 
 chromium oxide and other phosphates like calcium or alumin- 
 ium phosphate can be heated to the necessary temperature 
 in an electric furnace. 
 
 The chromium phosphate used as crude material need 
 in no way be pure. 
 
 1 Amer. Chem. Journal, 19, 871 (1897). 
 
 2 English Patent 6,007, March 28, 1892. 
 
72 CHROMIUM AND ITS COMPOUNDS. 
 
 Should the chromium phosphide anode be attacked at very 
 high current densities, the chromium which has gone into- 
 solution can be very easily removed. 
 
 Another process for the preparation of chromium phosphide 
 has been proposed by S. Maronneau 1 . He had found that by 
 the reduction of copper phosphate with carbon in the electric 
 furnace a copper phosphide could be obtained, which was- 
 stable at the temperature of boiling copper. This led him to 
 believe that by the help of copper phosphide, the phosphides 
 of the other metals and also that of chromium could be pro- 
 duced. He used for this purpose a commercial copper phos- 
 phide containing 90 per cent, of copper and 10 per cent, of 
 phosphorus. He mixed 100 parts of this copper compound 
 with 10 parts of chromium filings, which had been made by 
 the process of Moissan. After four minutes heating with a 
 current of 900 amperes at 45 volts, he found a somewhat 
 crumbly metallic material with a crystalline structure from 
 which could be isolated, by the use of concentrated nitric 
 acid, a chromium phosphide of the formula CrP. It occurs 
 as dull gray crystals, is insoluble in all acids with the excep- 
 tion of a mixture of nitric and hydrofluoric acids, and at 15" 
 has a density of 5.71. 
 
 D. Sulphur Compounds. 
 
 Mourlot 2 also used the electric furnace in his investigations 
 on the production of the sulphur compounds of chromium. He 
 first heated 100 grams of metallic chromium for from six to 
 eight hours in a reverberatory furnace heated by coke, leading 
 dry hydrogen sulphide over it. The metallic mass so ob- 
 tained showed a crystalline fracture, could be easily ground to 
 a black powder, and from appearances corresponded to the 
 protosulphide CrS. If heated three to four minutes in an elec- 
 tric furnace with a current of 900 amperes at 50 volts, it melted 
 completely and on cooling formed a regulus with a beautiful 
 crystalline fracture, and with cavities containing prismatic 
 
 1 Compt. rend., ISO, 656 (1900). 
 * Ibid., 121, 943(1895). 
 
OXYGEN COMPOUNDS. 73 
 
 needles. Long heating in contact with carbon causes decom- 
 position. This crystalline sulphide has a density of 4.08, and 
 scratches quartz somewhat easily. Fluorine attacks it strongly 
 at a low red heat ; chlorine at 340 with the formation of 
 chromic chloride and sulphurous chloride. Bromine reacts 
 only at higher temperatures, and iodine not at all. 
 
 Oxygen acts violently at a low red heat with the formation 
 of chromic oxide and sulphur dioxide, assuredly also SCK 
 Also gaseous hydrochloric and hydrofluoric acids act on it, 
 the latter even at low temperatures. Sulphuric acid reacts 
 only when heated ; there results sulphur, sulphurous acid and 
 chromic sulphate. Nitric acid and aqua regia decompose the 
 chromium sulphide at ordinary temperatures. Hydrogen sul- 
 phide is evolved by the action of steam at a red heat, and non- 
 crystallized chromic oxide remains behind. It is easily 
 oxidized by energetic oxidizing agents, also by molten potash. 
 Reducing materials react only with difficulty ; hydrogen not 
 even at 1200. On heating with carbon in the electric fur- 
 nace there is obtained according to the time more or less 
 molten metallic chromium containing more or less sulphur. 
 
 E. Oxygen Compounds. 
 
 (1) Chromous Oxide Compounds. 
 
 The chromous oxide compounds have up to recently not 
 been easily obtainable and at no time have played any im- 
 portant part in chemical technology. They are important 
 because of the great power of reduction they possess, so 
 it would appear desirable to discover a convenient method of 
 preparation in order, if opportunity offered, to be able to make 
 use of them in technical processes. 
 
 From an American patent of Villon 1 , from which we extract 
 the following from the patent claim, it is seen that active 
 search is being made to make practical this method of reduc- 
 tion, but chromium is too expensive after utilizing its power 
 of reduction for the proposed purpose, to throw aside the use- 
 
 1 Gazette U. S. Patent Office, 84, 846 (1898) ; U. S. Patent 608,652, 
 March n, 1897. 
 
74 CHROMIUM AND ITS COMPOUNDS. 
 
 less chromic salt, so it is desired at the same time to make 
 the chromium, by the help of the electric current, a means of 
 continuously transferring hydrogen. The chromic oxide salt 
 formed by the process of reduction should be reduced back in 
 a simple manner at the cathode. The heretofore-mentioned 
 extract of the patent claim which is concerned with the manu- 
 facture of ethyl alcohol reads : 
 
 " The herein-described process for the manufacture of ethyl 
 alcohol, consisting in the decomposition of calcium carbide by 
 water, by which acetylene is formed, and in the treatment of 
 the acetylene by chromium-ammonium double sulphate, thus 
 producing ethylene, in the absorption of the ethylene . . 
 and finally subjecting the reducing agent to the action of the 
 electric current either unbrokenly or in subdivided spaces. " 
 I have found no further information. 
 
 The preparation of chromous oxide salts in the solid form 
 has been protected within a few years by Boehringer and 
 Sons. 1 According to the patent specifications the process is 
 carried out in the following manner : The anode space of a de- 
 composition cell, provided with a diaphragm, is filled with a 
 30 per cent, sulphuric acid solution. In the cathode space is 
 poured a mixture of 500 parts by weight of chromium sul- 
 phate in 500 parts by volume of water and 250 parts by 
 volume of Concentrated sulphuric acid. This is reduced by 
 the use of lead for electrodes and a high current density of 
 1000 to 1500 amperes per square metre = from o. 10 to o. 1 5 am- 
 pere per square centimetre. 
 
 The chromous sulphate falls as a bluish-green, fine-grained 
 crystalline powder, which can be separated from the adhering 
 mother-liquor by filtration and washing with alcohol. It 
 contains one molecule of water of crystallization, does not 
 change in the air, and appears to be identical with the recog- 
 nized salt 2 CrSO 4 .H 2 O which is obtained by treating CrSCK 
 7H 2 O with concentrated sulphuric acid and which also changes 
 but little in the air. 
 
 1 German Patent 115,463, May 5, 1899. 
 * Dammer, Anorgan. Chemie, 3, 546. 
 
OXYGEN COMPOUNDS. 75 
 
 It dissolves slowly in water to a pale bluish-green solution. 
 
 If in place of chromic sulphate and sulphuric acid, chromic 
 chloride and hydrochloric acid is used as cathode-electrolyte, 
 and treated as before, chromous chloride is obtained as a 
 green, granular crystalline mass. 
 
 The patent claim reads : 
 
 Process for the preparation by electrolysis of chromous 
 oxide salts in the solid form from chromic oxide salts, charac- 
 terized by subjecting concentrated acid chromic oxide salt so- 
 lutions in the cathode compartment of an electrolytic cell to 
 the electric current. 
 
 In an experiment, to prepare chromous sulphate according 
 to the directions given in the patent claim, Dr. F. Glaser ob- 
 tained the following results in my laboratory: On electrolyz- 
 ing a cathode solution consisting of 200 grams of Cr a (SO 4 ) 3 
 (calculated on anhydrous salt), 200 cc. of water and 100 cc. of 
 concentrated H 2 SO 4 , for some time, with a current density of 
 o. 10 to 0.15 ampere per square centimetre, there separated out 
 solid chromous sulphate in bluish-green, thread-like crystals. 
 They were quickly filtered and the adhering mother-liquor 
 washed from them with a small amount of sulphuric acid 
 (i : i) and then washed with alcohol and dried between filter- 
 paper. If the mother-liquor in the cathode space was electro- 
 lyzed still further, only a very small amount of fresh chromous 
 salt was formed, although the remaining solution was still 
 quite rich in chromic salt. It appeared meanwhile as if the 
 migrating SO ions increased the solubility of the chromous 
 sulphate ; the addition of concentrated sulphuric acid removed 
 the difficulty. For the further continuance of the process, 
 fresh chromic oxide salt was added from time to time. 
 
 The chromous salt was not obtained pure at any time, but 
 always mixed with the chromic salt, since it is very easily 
 oxidized, and at ordinary temperatures slowly decomposes 
 water with an evolution of hydrogen. Also during the filtra- 
 tion and sucking dry a continual oxidation took place, raising 
 the temperature somewhat high. In consequence the output 
 was disappointing. 
 
76 CHROMIUM AND ITS COMPOUNDS. 
 
 In contrast to the extract from the patent literature, the salt 
 obtained was easily oxidizable. The content of water was not 
 investigated. Also the reference as given in Dammer, 1 is that 
 the salt changes slightly in the air (as the salt with 7H 2 O) not 
 that it is unaltered. 
 
 For continuous electrolysis it must be observed that from 
 time to time concentrated sulphuric acid must be added to the 
 cathode fluid, and the anode fluid moreover diluted, or it 
 may be partially replaced by water, or the conductivity will 
 reach a very low value. 
 
 (2) Chromic Oxide Compounds. 
 
 O) BY ELECTROLYSIS OF AQUEOUS SOLUTIONS. 
 
 Bunsen says that by the electrolysis of chromic salt solu- 
 tions under certain conditions, not metallic chromium but a 
 chromous oxide compound appears at the cathode (see page 2). 
 
 Lately, however, J. Feree 2 has proven that there must be 
 some error here. The important results of his investigation 
 are as follows : 
 
 The oxide of Bunsen is not formed when a mercury cathode 
 is used in an acid solution of chromic chloride, no matter what 
 current density is used. With weak current densities only 
 hydrogen is evolved at the cathode ; again with a current 
 density of 0.025 ampere per square centimetre of mercury sur- 
 face no precipitate appears. 
 
 If a neutral solution of chromic chloride is electrolyzed,. 
 even at high current densities, there appears no precipitate of 
 chromium, so that the earlier published investigations on the 
 preparation of chromium amalgam electrolytically, from neu- 
 tral solutions, evidently must have been in error. On the 
 contrary there is formed in the electrolyte a black powder 
 with the qualities which Bunsen ascribed to his chromous- 
 chromic oxide. It can be easily obtained in large quantities 
 if a platinum cathode is used, by the electrolysis of a solution 
 containing 160 grams of crystallized chromic chloride per 
 liter. 
 
 1 Loc. cit. 
 
 2 Bulletin Soc. Chim. de Paris [3], 25, 620 (1901). 
 
OXYGEN COMPOUNDS. 77 
 
 Returning to the opinion of Bunsen, it has been shown 
 qualitatively that the material was pure chromium hydroxide ; 
 a certain amount which had lain for some time in a vacuum 
 over sulphuric acid was put in a tube, which was exhausted 
 and sealed. When the lower part of the tube was heated in 
 an oil-bath, it was observed that at 80 water vapor was 
 evolved which condensed in the colder part of the tube ; at 
 400 the black contents of the tube glowed strongly and be- 
 came green. The vacuum was not changed, for on heating 
 one place to redness it flattened out; the change had also 
 taken place without the admission of oxygen. 
 
 From the experiment it may be concluded that no evolu- 
 tion of oxygen had taken place during the change, yet the 
 latter fact was proved by a separate investigation. 
 
 The analysis of the material gives the formula Cr 2 O 3 .H 2 O, 
 and the transformation consisted only in the change of the 
 black modification of the material into the green oxide. 
 
 The brownish black powder is formed also by the electrol- 
 ysis of a neutral chrome alum solution. It is insoluble in 
 acids but is easily attacked by nitric acid and potassium 
 chlorate (mixture of both ?). On being heated in the air it 
 changes to the green modification. 
 
 In the above-described preparation of chromic oxide the 
 current exerts neither an oxidizing nor a reducing influence ; 
 it acts by forming on the cathode an excess of OH ions, that 
 is to say,f produced alkali, which in turn reacts on the dis- 
 solved chromium salt and forms the insoluble oxide. It is 
 therefore clear that the electrolysis of an acid solution would 
 be without result, and also that the material of the cathode 
 was without influence at least as far as the description, accord- 
 ing to which mercury or platinum cathode may be used in- 
 differently^allows us to infer. 
 
 Chromic oxide can also be prepared by using the reducing 
 effect of the^current on an alkaline chromate solution ; this is 
 the reaction which occurs in the spontaneous working of the 
 chromic acid element, by which reaction electrical energy is 
 
78 CHROMIUM AND ITS COMPOUNDS 
 
 obtained. The achievement of a high current output in the 
 technical operation of this process lies in keeping within cer- 
 tain working conditions which G. Street has made the object 
 of several patents. 1 
 
 If a cold alkali chromate solution is electrolyzed between 
 platinum electrodes only a very moderate amount of oxide is 
 obtained, the amount being.only slightly increased on heating 
 the electrolyte up to 75. 
 
 If a mercury cathode is substituted for the platinum cathode^ 
 and the temperature of the electrolyte is kept between 70 
 and 80, chromic oxide is formed at once which remains sus- 
 pended in the electrolyte. The process is carried out as fol- 
 lows : An aqueous 10 per cent, (weight) solution of chromate 
 is electrolyzed between a temperature of 70 and 80, pref- 
 erably without the use of a diaphragm. An electromotive 
 force of 4 volts and a current density of 0.05 ampere per square 
 centimetre of cathode surface and 4 amperes per square centi- 
 metre of anode surface should be used. 
 
 It is known that the sodium amalgam formed effects the re- 
 duction of the chromic acid to chromic oxide, though doubt- 
 less some part of the chromic acid is transformed primarily into 
 chromic oxide ; the advantage which the mercury shows over 
 the platinum lies in the large overvoltage which is required 
 to set free hydrogen from mercury cathodes. The chromic 
 oxide separated out no longer dissolves in the soda solution at 
 the increased temperature. A circulation of the electrolyte 
 increases the efficiency of the reaction ; this circulation may 
 be accomplished by heating as well as by the rising column of 
 gas on the electrodes. 
 
 The chromium content can be quantitatively separated out 
 as chromic oxide, at the same time the whole of the sodium 
 being obtained in the form of caustic soda solution. Bichrom- 
 ates can be used in the place of chromates. If one starts 
 with chromate, then bichromate can be added to the bath in 
 such measure as the oxide is separated out ; by combination 
 
 1 German Patent 109,824, June n, 1899. 
 
OXYGEN COMPOUNDS. 79 
 
 with a corresponding amount of alkali the bichromate is 
 changed to chromate. These additions of bichromate are 
 limited only by the concentration of soda which is to be at- 
 tained in the valuable soda solution by-product. Instead of 
 using only one cell the electrolyte can be circulated through 
 a battery of cells. 
 
 The chromic oxide can be separated from the solution by 
 simple decantation. 
 
 The remark that the platinum anode could be replaced by 
 mercury ought not to be taken in earnest. Since in this case, 
 as was remarked, there is formed an insoluble mercury chrom- 
 ate, which would entail a high electromotive force were it 
 also, as remarked, possible to decompose it into mercury and 
 chromic oxide by a mere reversal of current, but which as we 
 will soon see is not at all the case. 
 
 Patent Claim. 
 
 Process for the electrolytic preparation of chromic oxide 
 from alkali chromates, characterized by the application of 
 mercury as cathode material. 
 
 In a note Strameo 1 mentions that he has tested and con- 
 firmed Street's remarks relative to the better working of mer- 
 cury electrodes ; on the contrary he found that by the use of 
 two mercury electrodes the change of mercury chromate to 
 mercury and chromic oxide did not take place ; there ap- 
 peared only mercury, and the simultaneous formation of 
 chromic oxide first began after the complete disappearance of 
 the mercury chromate. 
 
 It is also to be noticed further on in the remarks, that 
 along with the usual product, the hexahydrate, also the tetra- 
 hydrate Cr 2 O(OH) 4 , the so-called Guignet's green is formed, 
 which is insoluble in acids and extraordinarily valuable as 
 pigment, but the amount of it if the directions of Street are 
 followed is only i to 2 per cent. It is formed more abun- 
 dantly if the solution is kept rich in alkali and poor in 
 chromate. 
 
 1 L'Electricita 2O, 627 (1901). 
 
80 CHROMIUM AND ITS COMPOUNDS. 
 
 Finally the possibility is referred to of preparing all chrom- 
 ium salts by adding the desired acid in the manner of the 
 above method. For instance if a nitric acid solution of so- 
 dium chromate is electrolyzed, the chromium will be com- 
 pletely changed to chromium nitrate, along with which there 
 is present in the solution only sodium nitrate. But it should 
 be here noted that this " possibility" is not well founded, be- 
 cause the greater part of the oxide will be again oxidized to 
 chromic acid at the anode. Only so long as one, like Street, 
 works with an alkaline solution in which the chromic oxide 
 is insoluble, can the regeneration to chromate practically be 
 neglected, in case the aid of a diaphragm is not employed. 
 Regarding the many theoretical phantasies to be found in 
 this article we need not pay them further attention. 
 
 On the above subject there are still several interesting ob- 
 servations made by Reese 1 on the reducing action of electro- 
 lytically generated hydrogen on chromic acid. He arranged 
 the two platinum electrodes one above the other, the cathode 
 on the bottom of a burette, and the anode at the point, so that 
 the hydrogen had to pass through the whole length of the solu- 
 tion, while the oxygen could escape directly. Using perfectly 
 pure chromic acid as electrolyte, and electrolyzing for twenty- 
 four hours, with a strong evolution of hydrogen, no trace of 
 reduction was noticeable, but on the addition of a small 
 amount of a sulphate or sulphuric acid, reduction began in a 
 short time, but only up to a certain amount, which was in one 
 case 2.85 per cent, (reckoned on the whole solution). A like 
 behavior was noticed on the addition of sulphuric acid, potas- 
 sium sulphate and chromium sulphate. 
 
 A solution of pure potassium bichromate acted exactly like 
 the solution of chromic acid ; reduction first began on the 
 addition of sulphuric acid or sulphates. 
 
 The author thinks the fact that chromic acid may be 
 reduced to a varying degree according to its content of sul- 
 phuric acid or sulphates, may perhaps serve to determine the 
 1 Amer. Chetn. Journal, 22, 162 (1899). 
 
OXYGEN COMPOUNDS. 8 1 
 
 amounts of those substances present or the relative strength 
 of the acids (?). 
 
 It has almost the appearance as if there is here a catalytic 
 acceleration, and it may be of interest to know that work will 
 begin in my laboratory on a closer study of these facts. (See 
 also the remarks of Buff further on.) 
 
 () BY THE USE OF HIGH TEMPERATURES. 
 
 In order to investigate the behavior of chromic oxide at 
 high temperatures, Moissan 1 put ordinary, pure, anhydrous, 
 pulverized chromic oxide under the electrodes of an electric 
 furnace and sprung an arc over it. The carbon electrodes 
 were previously heated to a high temperature in a current of 
 nitrogen. 
 
 By the use of 30 amperes at 55 volts he obtained a black, 
 shiny wart-shaped mass, studded with groups of small dark 
 crystals, which when treated with potassium nitrate and pre- 
 cipitated with mercuric nitrate showed an average content 
 of 51.9 per cent, of chromium, corresponding closely to the 
 formula Cr a O . These crystals were very hard and left a green 
 streak on porcelain. 
 
 Molten chromic oxide combines very easily with calcium 
 oxide, and Moissan has obtained many of these double oxides 
 by heating a mixture of quicklime and chromic oxide in vari- 
 ous proportions in a limestone furnace, using the purest pos- 
 sible carbon electrodes and a current of 1000 amperes at 50 
 volts. Along with dark green, needle-like crystals, often sev- 
 eral millimeters long, and which were not investigated fur- 
 ther, were found towards the termination of the experiment, in 
 hollows in the molten cake, small, yellow, lamellar, trans- 
 parent crystals, which were slowly decomposed by water. 
 The result of an analysis corresponded very nearly to the 
 formula Cr 2 O 3 .4CaO. (See also page 3$) 
 
 An experiment of Moissan is also worth mentioning, in 
 which he added a little chromium oxide to aluminium oxide, 
 and melted the mixture in a carbon crucible with 25 to 30 
 
 1 Ann. de Chimie et de Physique [7], 4, 136 (1895). 
 
82 CHROMIUM AND ITS COMPOUNDS. 
 
 amperes at 50 volts. By this treatment small red crystals of 
 ruby separated from the mass, which, however, were very 
 much less beautiful than those of Fremy and Verneuil. The 
 operation lasted only ten to fifteen minutes, and furthermore, 
 since at this temperature the aluminium is easily volatilized, 
 so it appears quite possible to obtain beautiful ruby crystals 
 in this way without much trouble. In connection with this 
 work, Dufau 1 has later made a thorough investigation on the 
 formation of double oxides of chromium. 
 
 Moissan, in his work, made use of a " furnace of calcium 
 carbonate for crucibles," in the interior of which he put the 
 mixture of pure anhydrous oxide, which had just before been 
 calcined in a Pernot furnace. In order to avoid the influence 
 of the furnace material, the lime, the bottom of the cavity 
 was covered with a layer of the oxide, mixed with chromic 
 oxide, on which the mixture was poured, and which was then 
 surrounded with a wall of those oxides. 
 
 According to the investigations of Le Chatelier 2 , it was 
 noticed that at about 900 chromic oxide changed into another 
 form with a noticeable evolution of heat, this new form being 
 insoluble in acids and at 440 was attacked by neither sul- 
 phur, hydrogen sulphide, chlorine, or oxygen. This change 
 in the ordinary chromium oxide took place in the whole of 
 subsequent investigations. 
 
 For the preparation of a double oxide of chromium-magne- 
 sium a mixture of 150 grams of Cr a O 3 and 40 grains of MgO 
 was put in the furnace and heated for ten minutes with a cur- 
 rent of 30x3 amperes at 45 volts. After cooling there was 
 found a greenish brown, crystalline, partly melted mass, 
 which was attacked slowly by warm, concentrated hydro- 
 chloric acid with an evolution of chlorine, which denoted the 
 presence of chromate, which fact was also easily established 
 by treating the broken-up mass with boiling water. If this 
 mass is treated with nitric acid until no more dissolves, then 
 
 1 Ann. de Chimie et de Physique, [7], 12, 257 (1897). 
 
 2 Bulletin Soc. Chim. [2], 47, 303. 
 
OXYGEN COMPOUNDS. 83 
 
 the crystallized residue forms a double oxide, contaminated 
 by lamellar chromic oxide, the whole remaining stable at 
 the highest temperatures used. By repeated trituration (levi- 
 gation) separation can be obtained with a fair degree of ease. 
 There remains a dark green, nearly black, crystalline powder, 
 which under the microscope appears to consist of small octa- 
 hedral crystals, the thinnest being of a beautiful green color 
 by transmitted light and without action on polarized light. 
 Their density was 4.6 at 20, their hardness higher than that 
 of quartz, streak bright green ; their analysis agreed closely 
 to the formula Cr 2 O 3 .MgO. 
 
 A second experiment, using 50 volts and 1000 amperes, fur- 
 nished a brown, well-fused, very hard mass, which was only 
 attacked by acids with difficulty ; the carefully separated 
 crystals were also octahedral, and showed the above-described 
 characteristics. Before analysis the finely ground powder was 
 dried in a vacuum over sulphuric acid ; then 200 to 400 mm. 
 of the material were placed in a platinum crucible with ten 
 times the amount of a mixture consisting of 4 parts of potas- 
 sium nitrate and i part of potassium carbonate, and fused. 
 The decomposition took place very regularly in more or less 
 time, according to the nature of the oxides. When the de- 
 composition was thought complete the crucible was heated to 
 redness and allowed to cool. By treating the contents with 
 water the chromate went into solution, while the other oxide 
 remained behind as a carbonate. 
 
 With magnesium chromite especially, the decomposition 
 was somewhat long, over half an hour. The estimation of 
 the dissolved chromate and the precipitated magnesium oxide 
 was performed in the usual manner. The magnesium chrom- 
 ite showed characteristic reactions. Boiling sulphuric acid 
 dissolved simultaneously both the chromium and the magne- 
 sium ; likewise hydrofluoric and hydrochloric acids acted in 
 the same way, but more slowly; on the contrary boiling nitric 
 acid was without action, as also chlorine, bromine, and iodine. 
 As already seen in the analysis, oxidizing agents acted only 
 
84 CHROMIUM AND ITS COMPOUNDS. 
 
 slowly ; even oxygen at redness ; on the contrary, there is 
 always formed in the preparation of these double oxides in 
 the electric furnace a considerable amount of magnesium 
 chrornate. Other like combinations could not be obtained in 
 the electric furnace in spite of variation of the current 
 strength. 
 
 For the preparation of a double oxide of chromium and 
 calcium, a mixture of 115 grams of calcined chromic oxide 
 and 45 grams of unslaked lime was heated in an electric fur- 
 nace by 700 amperes at 50 volts. The crystalline product 
 showed, besides yellow laminae, resembling those described 
 by Moissan (see preceding), needles several millimeters long, 
 of a dark color, and occurring in radiating groups. With 300 
 amperes at 45 voks only the needles and not the yellow 
 laminae were obtained. 
 
 In order to isolate the needles, the crystallized parts lying 
 loose in the furnace were treated with concentrated hydro- 
 chloric acid. A strong reaction took place with a simultaneous 
 brown then green coloration of the solution and an evolution 
 of chlorine. After this had stopped the treatment was con- 
 tinued with boiling hydrochloric acid until no more would 
 dissolve. Finally the adhering crystallized chromium oxide 
 was separated by repeated trituration (levigation). The resi- 
 due consisted of dark green, prismatic needles, with metallic 
 luster, transparent thin sections appearing under the micro- 
 scope a beautiful green. Their density was 4.8 at 18, their 
 hardness close to 6, their powder bright green. The analysis 
 gave results corresponding closely to the formula Cr z O .CaO. 
 This double oxide is somewhat resistant to chemical reagents; 
 fluorine will not attack it when cold ; however it will with a 
 slight rise of temperature with a strong glowing and the evo- 
 lution of a thick yellow smoke. The action of chlorine at a 
 bright red heat slowly forms calcium chloride, while the 
 chromium oxide does not appear to be affected. Bromine and 
 iodine do not react. The calcium chromite is easily suscepti- 
 ble to oxidation ; a part is changed to chrornate when it is 
 
OXYGEN COMPOUNDS. 85 
 
 powdered and heated to 100 in air. In oxygen it burns 
 quickly at the temperature at which glass softens. It is unaf- 
 fected by solutions of hydrofluoric and hydrochloric acids and 
 by concentrated nitric and sulphuric acids. Anhydrous hy- 
 drofluoric acid forms calcium fluoride and amorphous chromic 
 oxide at a red heat, hydrochloric acid gas performing a simi- 
 lar reaction with glowing. Of oxidizing agents potassium 
 chlorate is the most effective. 
 
 Collectively, the earlier investigations of Moissan can be 
 stated thus : With the application of 300 amperes at 45 volts 
 the chromite, Cr a O 3 .CaO, is formed; with 700 amperes at 50 
 volts, and so at a higher temperature a second compound is 
 also formed, Cr a O .zj-CaO, which predominates when 1000 am- 
 peres at 50 volts is used. 
 
 Strontium chromite is not stable at high temperatures ; it 
 appears to be more easily oxidized than calcium chromite. 
 If an intimate mixture of strontium oxide and chromic oxide 
 is subjected to the heating action of an arc of 50 amperes at 50 
 volts or one of 300 amperes at 55 volts, a green crystalline mass is 
 obtained, which appears to consist of only chromate and crys- 
 tallized chromium oxide. Stronger electric currents have 
 the same effect. 
 
 The following, on the contrary, were the results with 
 barium oxide, in which a very high chromium-content 
 double compound was formed. On a ten-minute treatment of 
 a mixture consisting of equal parts of both oxides, with a cur- 
 rent of 300 amperes at 50 volts, there was found in the fur- 
 nace a fused green mass with a crystalline fracture, and which 
 was, as before, treated with hydrochloric acid; a lively reaction 
 also took place here, coloring the solution brown and then 
 green, with an evolution of chlorine. After treating until no 
 more would dissolve, there remained a mass of crystals. If 
 the solution is shaken up, dark shining crystals of the double 
 oxide first settled down and on them the green laminae of 
 crystallized chromic oxide; by repeated trituration they could 
 be separated. This double oxide formed small, black, shining 
 
86 CHROMIUM AND ITS COMPOUNDS. 
 
 crystals, which made a brown powder of a slightly greenish 
 shade ; under the microscope they appeared transparent and 
 hexagonal. They were somewhat harder than quartz; at 15 
 their density was 5.4. They were unattacked by hydrofluoric 
 hydrochloric, nitric, or sulphuric acids. 
 
 Chlorine and bromine acted slowly at red heat with the 
 formation of the corresponding barium haloid, while the 
 chromium oxide did not appear to have been affected ; iodine 
 had no effect. In oxygen barium chromate was formed below 
 a fed heat with a bright incandescence; it was on the whole 
 easily oxidizable like calcium chromite. Water and sulphur 
 vapors were without effect even at a bright red heat ; anhy- 
 drous, gaseous hydrofluoric and hydrochloric acids reacted very 
 slowly at redness with the formation of the respective barium 
 compounds. 
 
 The results of an analysis showed the compound to agree 
 very closely with the formula 4Cr 2 O 3 .BaO. 
 
 (3). Chromic Acid Compounds. 
 
 O) CHROMATES OF THE HEAVY METALS. 
 
 An American patent 1 has been granted to Arthur B. Browne, 
 in which the electric current is used in so far as concerns the 
 preparation of the necessary alkaline chromate. The patent 
 itself was not accessible to me, so a reproduction of the patent 
 claims must suffice. 2 
 
 Patent Claim. 
 
 (i) The process of manufacturing chromate of lead which 
 consists in first producing a solution of a soluble salt of lead, 
 as the nitrate, acetate, or chloride, simultaneously preparing 
 a solution of chrome alum, precipitating chrome hydrate 
 therefrom, mixing said chrome hydrate with an excess of 
 caustic alkali to redissolve it, mixing the resulting strongly 
 alkaline solution with a solution of common salt, passing an 
 electric current through combined solutions to produce a mix- 
 ture of bichromate and chromate of potash, mixing said com- 
 
 1 U. S. Patent 538,998, April 18, 1894. 
 
 * Official Gazette of the U. S. Patent Office, 71, 871 (1895). 
 
OF THE 
 
 UNIVERSITY 
 
 ^k OF 
 
 OXYGEN COMPOUNDS. *| 87 
 
 bined bichromate and chromate of potash with said solution 
 of a soluble salt of lead to precipitate lead chromate and wash- 
 ing it with water, refiltering it to remove the water, and 
 finally drying the resulting product. 
 
 (2) The process of manufacturing chromate of lead which 
 consists in first producing a solution of a soluble salt of lead, as 
 the nitrate, acetate or chloride, simultaneously preparing a solu- 
 tion of chrome alum, precipitating chrome hydrate therefrom, 
 filtering said chrome hydrate and washing it, then mixing said 
 filtered chrome hydrate with an excess of caustic alkali to re- 
 dissolve it, mixing the resulting strongly alkaline solution 
 with a solution of common salt, passing an electric current 
 through said combined solutions to produce a mixture of 
 bichromate and chromate of potash, mixing said combined 
 bichromate and chromate of potash with said solution of a 
 soluble salt of lead to precipitate lead chromate, filtering said 
 lead chromate and washing it with water, refiltering it to re- 
 move the water and finally drying the resulting product. 
 
 (3) The process of manufacturing chromate of lead, which 
 consists in first producing a solution of a soluble salt of lead, 
 as the nitrate, acetate or chloride ; simultaneously producing 
 a solution of a mixture of bichromate and chromate of 
 potash, by passing an electric current through an alkaline 
 solution of chrome hydrate ; mixing said solution of a mix- 
 ture of bichromate and chromate of potash with said solution 
 of a. soluble salt of lead, to precipitate lead chromate ; filter- 
 ing said lead chromate and washing it in water, refiltering it 
 to remove the water, and finally drying the resulting product. 
 
 In the patent specifications of one English and two German 
 patents of C. Luckow, which are concerned with the electro- 
 lytical production of difficultly soluble salts and oxides, we 
 find special data upon the manufacture of neutral and basic 
 lead chromates. We will examine the patents chronologically, 
 and take out of them what would interest the electrochemist. 
 
 In the first patent 1 Luckow will practically utilize u the 
 theory of electrolytic and hydrolytic dissociation " in the 
 1 German Patent 91,707, Dec. 4, 1894. 
 
88 CHROMIUM AND ITS COMPOUNDS. 
 
 manufacture of difficultly soluble salts or oxides, from solu- 
 ble metallic anodes ; he employs for this purpose only electro- 
 lytes, which, as he says, may be considered as dissociated 
 either electrolytically or hydrolytically or electrolytically and 
 hydrolytically. The maximum of dissociation appears to be 
 different for different salts, fluctuating, however, for the in- 
 vention concerned somewhere between 0.3 and 3 per cent, of 
 dissolved salt (calculated on anhydrous salt); the use of 1.5 
 per cent, of dissolved salt usually suffices. Better results 
 were obtained in this way with the use of considerably less 
 current consumption than was possible with the electrolytic 
 processes hitherto proposed for the same or similar purposes. 
 Luckow apparently only slightly understood this new theory 
 at that time ; the maximum of dissociation of the salts in 
 question (sodium chlorate, sodium carbonate, etc.), is at in- 
 finite dilution, while the maximum of conductivity in the 
 same case, if one chooses them for the maximum economy of 
 energy, lies with the much higher concentration. 
 
 Further Luckow says that the desired reactions take place 
 much better if a mixture of salts is used, and mixtures of 
 about 80 to 99.5 of the one to 20 to 0.5 of the other by 
 weight are the most suitable. For the preparation of salts in 
 general, a salt which forms an easily soluble compound with 
 the anode, composes 80 per cent, of the mixture, and the re- 
 maining 20 per cent, of such acids which will form a diffi- 
 cultly soluble combination with the anode material. 
 
 In most cases salts of the alkalies (ammonia included) and 
 the alkaline earths are suitable. The electrolyte should be 
 "as far as possible neutral, that is, slightly acid, slightly alka- 
 line, or neutral," and its composition should be kept as nearly 
 constant as possible ; also the dissolving anode should be re- 
 newed when the consumption has reduced it to 1.5 milli- 
 metres thickness. 
 
 " For electrodes there are used for each square metre of 
 anode surface eight positive and nine negative electrodes, 
 which are hung 15 mm. apart in a space 200 mm. high and 
 
OXYGEN COMPOUNDS. 89 
 
 300 mm. wide, and whose method of suspension allows a sur- 
 face contact of 4 square metres with the electrolyte. The 
 material of the anode varies according to the desired product; 
 the material of the cathode is preferably the same as the 
 anode, but it can, however, be different from it. It is advis- 
 able to hang the cathode in a bag of thin woven material. 
 
 " The electromotive force required depends on the mix- 
 ture of salts ; for weak acid electrolytes it is between 1.3 and 
 1.5 volts, for neutral about 1.8 volts, and for feebly alkaline 
 about 2 volts." 
 
 About 0.005 ampere per square centimetre is recommended 
 as the current density. The temperature should not rise 
 above 50. To avoid interruptions in running, the purest 
 possible materials should be used. The following special 
 directions are given for the manufacture of lead chromate : 
 
 Neutral Lead Chromate. 
 
 For electrolyte use a i y 2 per cent, aqueous solution of a 
 mixture of 80 parts by weight of sodium chlorate with 20 
 parts by weight of sodium chromate. 
 
 The anode is made of soft lead, the cathode of hard lead. 
 The electrolyte is neutral. The tension is 1.8 volts. The 
 current density is 0.5 ampere per square decimeter. During 
 electrolysis the electrolyte is kept neutral, and water and 
 chromic acid must be carefully introduced. 
 
 Acid Lead Chromate. 
 
 The electrolyte consists of a i y 2 per cent, aqueous solution 
 consisting of a mixture of 80 parts by weight of sodium chlo- 
 rate and 20 parts by weight of sodium bichromate. 
 
 The electrolyte is slightly acid. The electromotive force 
 is 1.5 volts. The current density is 0.5 ampere per square 
 decimeter. During electrolysis the electrolyte is kept feebly 
 acid and water and chromic acid must be carefully added. 
 
 The patent claims in question read : 
 
 (i) Process for the production of salts and oxides, which 
 are insoluble or soluble with difficulty in water or dilute, 
 
90 CHROMIUM AND ITS COMPOUNDS. 
 
 neutral or slightly acid or slightly alkaline salt solutions, by 
 means of electrolysis from a suitable metallic anode, charac- 
 terized by the use of electrolytes, which have been brought 
 into the condition of electrolytic or hydrolytic, or hydrolytic 
 and electrolytic dissociation near the neutralization point, and 
 by supplying the materials separated out in the electrolysis to 
 keep the composition of the bath as near as possible constant, 
 for the purpose of exerting a good influence on the consump- 
 tion of current and course of the reactions. 
 
 (4) The process characterized by claim i applied to the 
 production of neutral lead chromate as follows : A neutral 
 solution of a mixture of sodium chlorate and sodium chromate 
 is subjected to electrolysis between lead electrodes, with a cur- 
 rent density of 0.5 ampere per square decimeter, with addi- 
 tions of water and chromic acid. 
 
 (5) The process characterized by claim i applied to the 
 production of acid lead chromate as follows : A slightly acid 
 solution of a mixture of sodium chlorate and sodium bichrom- 
 ate is subjected to electrolysis between lead electrodes, with 
 a current density of 0.5 ampere per square decimeter, with 
 additions of water and chromic acid. 
 
 In the second patent 1 the process in question is elaborated. 
 In the previously patented process, the electrodes, particularly 
 the anode, was made of massive material, and the insoluble 
 or slightly soluble compounds formed did not stick on the 
 anode during the operation, as they were formed, but they 
 rolled off the surface of the anode in dense clouds into the 
 depths of the bath, where they collected together on the bot- 
 tom in the form of an extremely fine powder ; concerning the 
 obtaining of chemical compounds, it is just the opposite of 
 that which is desired in the operation of the manufacture of 
 the electrodes for electrical accumulators. In the improved 
 process metallic conducting frames were prepared in such a 
 manner as to hold on them insoluble or slightly soluble 
 oxides, salts, metals or ores, in a finely divided state as the 
 
 1 German Patent 105,143, Sept. 4, 1895 (compare also the supplemen- 
 tary German Patent 99,121, May 13, 1897). 
 
OXYGEN COMPOUNDS. 91 
 
 soluble material, so that the insoluble or slightly soluble end- 
 products would remain upon or in these electrode frames dur- 
 ing the operation. The preparation of the electrodes and the 
 operation of the process is the same as in the preparation of 
 electrodes for storage cells whose ribs and grating frames are 
 filled with metallic dust, or coated with insoluble or difficultly 
 soluble oxides or salts as the effective (active) material. 
 
 For electrodes a special woven wire net with the narrowest 
 possible meshes was employed ; meanwhile the accumulator 
 industry has invented a number of new practicable forms of 
 electrodes which can be used for this purpose. To protect 
 the metallic ribs in case they are made of a metal easily 
 alterable, it is possible to polish them with graphite or to 
 platinize them. 
 
 After the pasty mass has been kneaded or pasted into the 
 grooves, it is surrounded with a tightly stretched bag of filter 
 cloth or like material. The electrodes should be spaced 20 
 millimeters apart. 
 
 Concerning the electrolyte, according to patent No. 91,707, 
 one anion causes the solution of the massive anode, forming 
 an easily soluble salt of the anode metal, the other transforms 
 the anode metal into the desired insoluble or difficultly solu- 
 ble compound ; " it is self-evident that the first anion performs 
 the function of preventing the precipitated insoluble or 
 slightly soluble compound formed on the anode from adher- 
 ing to it. Which constituent must have predominating in- 
 fluence is determined by the nature of the product to be ob- 
 tained." 
 
 This remarkable fact deserves explanation. How is it for 
 instance that by the electrolysis of a mixture of sodium 
 chromate and chlorate between lead electrodes a beautiful 
 precipitate of lead chromate is formed in the electrolyte, and 
 the anode dissolves easily, while the solubility of the anode 
 weakens and it is finally covered over with an adhering coat 
 when the pure sodium chromate solution alone is used? 
 
92 CHROMIUM AND ITS COMPOUNDS. 
 
 Perhaps this action depends on the increase of solubility 
 which lead chromate would certainly show in a solution con- 
 taining a large excess of sodium chlorate. It is accomplished 
 by the formation of a non-dissociated lead chlorate. This in- 
 creased solubility allows a somewhat relatively increased super- 
 saturation of chromate of lead, and so prevents the formation 
 of a dense adhering coat of lead chromate directly on the 
 anode. 
 
 With these explanations, advanced reservedly, agrees the 
 fact that the current density is normally low ; the formation 
 of an adhering coat on the anode is to be feared using a high 
 density. An exhaustive experiment which meanwhile has 
 been worked in my laboratory, has furnished another explana- 
 tion for the above phenomena. The results may be found in 
 Zeitschr. f. Elektrochemie, p. 255 (1902). 
 
 In the more generalized process the salt forming the 
 easily soluble compound does not predominate so strongly, 
 it only composes one-half to two-thirds of the mix- 
 ture of salts. The temperature is usually kept below 50, 
 without, however, excluding higher temperatures. 
 
 The current density is, as in the older process, preferably 
 about 0.005 ampere per square centimetre, but the electro- 
 motive force is higher, lying between 2 and 4 volts. 
 
 Finally there remains several words to be said on the gen- 
 eral method of operation, etc., in so far as they were not 
 stated in the first patent specification. 
 
 During the electrolysis and the separation of the ingre- 
 dients out of the solution to form the desired product, water, 
 chromic acid, etc., must be added in such a manner that the 
 concentration and the neutrality of the solution is not ap- 
 preciably changed. On the other hand, the accumulation of 
 impurities and deleterious substances is to be avoided. 
 
 The introduction of a current of air or steam in fine 
 division producing a good stirring without bringing the elec- 
 trolyte into too strong agitation has a good effect. 
 
 Basic lead chromate (and lead) may be prepared in the fol- 
 lowing manner : 
 
OXYGEN COMPOUNDS. 93 
 
 " The electrolyte used is a i */ to 2 per cent, aqueous 
 solution of a mixture, consisting of two-thirds sodium 
 chlorate and one-third sodium chromate. The electrolyte 
 is made slightly alkaline with sodium hydroxide. The 
 anode frame consists of platinized hard lead and the cathode 
 frame of either hard or soft lead. The filling for the anode 
 frame is composed of lead dust or litharge, that of the cathode 
 frame of red lead or Phcenicochroite (basic lead chromate). 
 Should the cathode charge not liberate during the electrolysis 
 a sufficient amount of chromic acid (which may be expected) 
 this must be added to the electrolyte." 
 
 The difficulty with this process plainly lies in converting 
 the lead powder or litharge completely to chromate ; small 
 pieces are completely surrounded by chromate and insulated 
 from further action. At least to convert this final portion a 
 disproportionate current consumption is necessary, if a pure 
 material is desired. Also many difficulties are introduced in 
 the same process in making a product of a certain sized par- 
 ticle, as demanded by the trade, upon which depends the 
 shade or the facility of reaction, as with lead peroxide ; this 
 condition is considered in patent No. 91,707. 
 
 Patent Claim. 
 
 The extension of the process protected in patent No. 91,707 
 to the manufacture from finely divided metals and ores of insol- 
 uble or slightly soluble oxides or salts at both poles, thereby 
 characterized by the filling or spreading out of these materials 
 in or on electrode frames of metallic conducting material and 
 subjecting them to the action of the electric current in a 
 highly dilute electrolyte conformable to patent No. 91,707. 
 
 The English patent 1 corresponds to the two German patents 
 in contents. Some special data is given on the preparation 
 of lead and copper chromates. 
 
 The color of the lead chromate depends on the bath ; a neu- 
 tral electrolyte, consisting of a solution of alkaline nitrate, 
 acetate, or chlorate with alkaline chromate or chromic acid 
 
 1 English Patent 14,801, Aug. 6, 1895. 
 
94 CHROMIUM AND ITS COMPOUNDS. 
 
 yields with lead anodes a beautiful chrome yellow, which be- 
 comes brighter if the solution begins to become acid, and 
 redder if it becomes alkaline. Slightly acid solutions yield, 
 therefore, a fiery citron yellow, and slightly alkaline solutions, 
 a beautiful chrome orange, which changes to a chrome red 
 with increasing alkalinity. 
 
 For the production of the bright chrome yellow, care must 
 be taken that the solution at the anode does not become too 
 acid, or this may become covered with an insoluble coat of 
 oxide or peroxide ; the gradual addition of the necessary 
 amount of chromic acid or chromate is to be recommended. 
 
 For the production of chrome orange a mixture of potassium 
 perchlorate and chromate is used. Chrome red is obtained 
 by the addition of more alkali. 
 
 The cost of manufacture of 100 kilograms of pure chrome 
 yellow is $17.50 to $20*00, and of 100 kilograms of pure 
 chrome orange about $12.50. Copper chromate can be pro- 
 duced in the same manner by using copper anodes. The 
 electrolyte consists of a mixture of either an alkaline nitrate^ 
 sulphate, chloride, or chlorate with chromic acid or a soluble 
 chromate. If the solution is neutral or slightly acid a brownish 
 red chromate is precipitated, if feebly alkaline, a green. By 
 increasing the acidity of the solution, the brownish red will 
 become brighter, until finally with too much acid the copper 
 no longer precipitates. With increasing alkalinity the green 
 color becomes deeper but much duller. 
 
 A very dilute solution of a mixture of six parts of sodium 
 chlorate with one part of sodium bichromate is suitable for 
 the preparation of the red chromate, while for the preparation 
 of the green chromate a dilute solution of a mixture of 4 
 parts of sodium or potassium chloride with i part of sodium 
 chromate, to which before the beginning of the electrolysis a 
 little alkali is added, can be recommended. The necessary 
 chromic acid for the operation of the process must be con- 
 tinually supplied. 
 
OXYGEN COMPOUNDS. 95 
 
 The current density must be so regulated that no free oxy- 
 gen is evolved on the anode ; with too high current densities 
 the desired product is not precipitated fine enough. 
 
 The amount of free alkali or free acid should not be above 
 i y? per cent, by volume of the solution, and the concentra- 
 tion of the salt should remain between 0.3 and 3 per cent, by 
 weight. Great stress is laid on these conditions. 
 
 A greater dilution is not advisable because of the smaller 
 conductivity of the solution ; a lesser is likewise not, because 
 in those kinds of solutions, particularly if they contain too 
 much alkali or acid, the anodes are oxidized " with quickly 
 decreasing rapidity and more superficially and irregularly ; " 
 moreover, the product suffers and tends to become crystalline. 
 The product is obtained as a pure, amorphous and finely 
 divided powder only when the solution is made up within the 
 above given limits. 
 
 Patent Claim. 
 
 (1) The herein-described process for the production of in- 
 soluble or practically insoluble oxides and salts from very 
 dilute neutral, slightly acid or alkaline solutions essentially as 
 described. 
 
 (2) In the electrolytic production of insoluble or practically 
 insoluble salts or oxides, the simultaneous use of an anode of 
 the desired metal or containing it, and very dilute neutral, or 
 slightly acid or alkaline electrolyte, essentially as described. 
 
 As far as I know, in the attempts to manufacture chrome 
 colors on a large scale by these methods, serious technical 
 difficulties have arisen. Whether their solution has been un- 
 successful or if finally the processes have proven unprofitable, 
 I know nothing of there lately having appeared on the market 
 large quantities of electrolytically prepared chromium colors. 
 
 (b) CHROMATES OF THE ALKALI METALS AND CHROMIC ACID. 
 
 Already in the year 1886, F. Fitzgerald attempted to solve 
 the problem of transforming chromic oxide compounds into 
 chromic acid compounds by the aid of the electric current, in 
 
96 CHROMIUM AND ITS COMPOUNDS. 
 
 a cheaper way than formerly. Evidently he had in view the 
 treatment of the chromic oxide solutions found in chromic 
 acid cells after their exhaustion, in that he wished to produce 
 simultaneously at the cathode metallic zinc from a part of the 
 zinc sulphate occurring in the solutions. In the patent spec- 
 ifications 1 is given several detailed statements. 
 
 A solution containing zinc and chromic sulphate (or chromic 
 chloride) is electrolyzed preferably by the use of lead anodes, 
 although all other less attackable conductors as platinum and 
 carbon (? !) are not excluded. Lead, zinc, or the like can be 
 used as cathodes, and are usually suspended in an acid zinc 
 sulphate solution or a solution of ammonium alum in which 
 zinc oxide is dissolved. A diaphragm separates the anode and 
 cathode solutions. The electrolysis is continued until the 
 dark-colored anode solution has become bright red. The 
 metallic zinc precipitated on the cathode can be melted and 
 in this way separated from the chromic oxide precipitated 
 there at the same time. 
 
 The proposed separation of zinc in this manner must have 
 been attended with considerable difficulty and expense. 
 
 In order to avoid the inconvenient transportation of large 
 quantities of fluid, the solutions were, after exhaustion, run 
 into a large reservoir, precipitating therein chromium and 
 zinc oxides by lime, magnesia, or the like, the supernatant 
 liquid run off, and the solid residue taken to the chromic acid 
 regeneration plant. There the oxides were mixed together 
 and either dissolved together by a dilute mineral acid, or first 
 treated with ammonia or a boiling solution of fixed alkali, to 
 bring the zinc into solution, and then to dissolve the chrom- 
 ium, a weak acid or the cold solution of a fixed alkali was 
 poured over. The solutions were then respectively oxidized 
 and reduced in the following manner. 
 
 The patent claim reads : 
 
 ( i ) The herein-described process for the electrolytic regenera- 
 tion or production of dissolved chromic acid from chromic 
 
 1 English Patent 5, 542, April 21, 1886. 
 
OXYGEN COMPOUNDS. 97 
 
 salts, which result by the reduction of this acid when it has 
 been used for the production of oxygen for galvanic elements, 
 or chlorine for bleaching or other purposes. 
 
 (2). The herein described process for the electrolytical re- 
 generation or production of dissolved chromic acid from the 
 exhausted or reduced solutions of this acid produced in the 
 manufacture of chlorine or oxygen, consisting in treating the 
 solution with a base which precipitates the chromic oxide 
 and also zinc oxide, redissolving the precipitated oxide and 
 converting it into chromic acid by electrolysis. 
 
 A note of K. F. Smith 1 shows the preparation of alkali 
 chromates directly from chromite, in which the chromite is 
 intimately mixed with molten potash and the mixture elec- 
 trolyzed (see also page 36). Although he has used this 
 method only for the analytical determination of chromium in 
 chromite, the method is of great practical interest and serves 
 as an intimation of the production of chromates by the aid of 
 the electric current on a large scale. 
 
 In the first experiments a current of one ampere was used. 
 After fifteen minutes the oxidation of the mineral appeared 
 complete. A stronger current worked poorly: "Among 
 other things, a stronger current acted principally on the iron 
 oxide in the ore and affected the potash, so that a larger or 
 smaller amount of the metal concerned was precipitated. 
 The above-mentioned phenomena appeared after a partial de- 
 composition of the mineral so that some chromite always re- 
 mained undecomposed." 
 
 Finally good results were obtained with the following 
 method of operation : 30 to 40 grams of caustic potash 
 were melted in a nickel crucible i T/Q inches high and 2 inches 
 in diameter, and heated until the excess water was driven 
 off. The crucible was then placed on a heavy copper ring, 
 which was connected to the anode of a battery, the finely 
 ground mineral (o.i to 0.5 gram) was placed upon the 
 fluid potash and a platinum rod was put in for cathode. The 
 
 1 Berlin, Ber., 24, 2182 (1891). 
 
9$ CHROMIUM AND ITS COMPOUNDS. 
 
 crucible was kept covered during the analysis, and warmed 
 gently. Before stopping the determination the current should 
 be reversed, because metallic iron is precipitated on the 
 cathode and surrounds small particles of the ore, protecting 
 them from being attacked. By reversing the current the lat- 
 ter were set free and exposed to oxidation. 
 
 We have already shown that it is not possible to use more 
 than one ampere for the above quantity of ore ; after thirty 
 to forty minutes the ore is decomposed, even when it is very 
 resistant. When decomposition is complete hydrochloric acid 
 will dissolve the contents of the crucible completely. Other- 
 wise the decomposition is not complete. The chromate can 
 be determined in the aqueous alkaline filtrate by the usual 
 methods. 
 
 A treatise by C. Haussermann 1 is concerned with the 
 electrolytic oxidation of alkaline chromic oxide solutions. 
 Haussermann puts a solution of chromic oxide in an excess of 
 concentrated caustic soda solution, in a porous clay vessel, 
 forming an anode compartment, and then puts the latter in a 
 glass vessel filled with water, which forms the cathode space. 
 The anode is a platinum sheet, the cathode an iron sheet 
 each 7 X 12 square centimeters effective surface. With a 
 current strength of 2 amperes the electromotive force finally 
 dropped to 5 volts. Sodium chromate and some oxygen were 
 formed at the anode, while at the cathode caustic soda and 
 hydrogen. The investigation was performed without external 
 heating and was interrupted before the complete oxidation of 
 the chromite and showed a yield of 0.563 grams of the 
 original sodium compound transformed into the higher oxide 
 form per ampere hour, corresponding to a current output of 
 42 per cent. 
 
 Further, this method of procedure was applied to the pre- 
 paration of bichromates from neutral chromates, in which 
 the anode space was charged with a solution of 58 grams 
 of Na 2 CrO 4 in 0.5 liter of water. With a current strength of 
 1 Dingler's Polytechnisches Journal, 288, 161 (1893). 
 
OXYGEN COMPOUNDS. 99 
 
 between 2 and 3.5 amperes the electromotive force dropped 
 finally to 6 volts ; after eight and one-half hours the experi- 
 ment was interrupted. An evolution of oxygen and an odor 
 of ozone was noticed at the anode, and at the cathode a strong 
 evolution of hydrogen ; the cell was not warmed. The solu- 
 tion in the anode space after some time became red, that in 
 the cathode space yellow ; this last appearance was "ascribed 
 to a wandering or diffusion of the neutral chromate." To 
 prevent misunderstanding it was remarked that the chromate 
 ion, CrO 4 , which is negatively charged travels toward the 
 anode under the influence of the current. Only by diffusion 
 can a small amount of chromate get into the cathode space. 
 An analysis showed at the end of the electrolysis in the cathode 
 solution 14 grams of caustic soda and only 0.4 gram of neu- 
 tral chromate ; the anode liquor after evaporation left 40 
 grams of crystallized Na 2 Cr 2 O 7 .2H 2 O. In case the soda liquor 
 is returned to the circuit of manufacture to lixiviate the 
 roasted material the chromate admixture does no injury. 
 Excess of caustic soda which was formed in the previously used 
 lixiviation of the roasted material containing calcium chro- 
 mate by aqueous soda solution, does not act injuriously, and 
 therefore the solution obtained by lixiviation of the roasted 
 mass and containing sodium chromate along with caustic soda, 
 can after concentration without further preparation be sub- 
 jected to electrolysis and worked over into bichromate. 
 
 To be quite clear, let the old process for the preparation of 
 bichromate be briefly compared with the electrolytic process 
 of Haussermann. It should be first noticed that Hausser- 
 mann left undecided the practical utilization of the transfor- 
 mation of sodium chromite into chromate in the electrolytic 
 manner, and was concerned only with the conversion of 
 chromate into bichromate. 
 
 According to the old methods of Haussermann as we have 
 recently described, the roasted material containing the calcium 
 chromate is treated with an aqueous solution of sodium car- 
 bonate. 1 Often sodium sulphate solution is used, thus pre- 
 
 4 may have been employed. 
 
100 CHROMIUM AND ITS COMPOUNDS. 
 
 cipitating insoluble calcium carbonate and forming soluble 
 sodium chromate, along with some free caustic soda. The 
 solution is concentrated after nitration, and just enough sul- 
 phuric acid is added to neutralize the caustic soda, and trans- 
 form the neutral chromate into bichromate. With the proper 
 concentration conditions the greater part of the sulphates are 
 precipitated in the anhydrous form while the bichromate re- 
 mains in solution. 
 
 According to the new process the alkaline chromate liquor 
 is placed in the anode compartment of a cell, and the cathode 
 space is filled with pure water. 1 By electrolysis bichromate 
 is formed, and on the cathode side caustic soda solution, of 
 which not an inconsiderable part gets over to the anode side 
 on account of the large velocity of migration of the OH ions. 
 After the completion of the electrolysis the cathode solu- 
 tion or at least a part of it shall find application in the leach- 
 ing of the roasted material in place of a part of the soda so- 
 lution, where it then transforms the calcium chromate into 
 calcium hydrate and dissolved sodium chromate, which latter 
 is again placed in the anode compartment of the electrolytic 
 cell for further oxidation. 
 
 The bichromate solution in the anode compartment, com- 
 pletely free from sulphates, may be used directly for oxidation 
 or worked up into solid bichromate. 
 
 It is perhaps advisable to explain just what part the electric 
 current plays in the transformation of chromates into bichro- 
 mates in the anode compartment. Aside from some acces- 
 sory processes we do not find an oxidation taking place, but 
 oxygen is evolved quantitatively. Thereby the electrolyte 
 would become acid, and we know that acid hinders the re- 
 action. The current decomposes, therefore, in this view, neu- 
 tral salt only into base and acid. Incidentally it may be re- 
 marked that according to the investigations of Ostwald 2 
 chromic acid has the formula H 2 Cr a O 7 . 
 
 1 Naturally not to be recommended in practice ; it is customary to use a 
 not too concentrated solution of sodium carbonate. 
 
 2 Zeitschr. f. Physikalische Chemie, 2, 78 (i! 
 
OXYGEN COMPOUNDS. IOI 
 
 Haussermann has claimed a great deal when he said : 
 41 After the preceding, there can be no doubt that the applica- 
 tion of electrolysis to the manufacture of alkali bichromates 
 involves an important step forward, and that the process de- 
 scribed, which is protected by patents, will become an im- 
 portant factor in the commercial world." 
 
 Nothing has been done with the patent, and there is noth- 
 ing known of a practicable application of the process. 
 
 The electrolysis of the alkali chromates and the like is, as 
 mentioned before, not new, for Buff J decomposed dissolved 
 neutral potassium chromate in 1856. He was influenced to 
 take up these experiments because of a statement of Geuther, 
 who claimed to have found that by the electrolysis of aqueous 
 solutions of pure chromic acid, hydrogen and chromium were 
 precipitated at the cathode, and oxygen at the anode to the 
 extent of a third or more greater than should be expected 
 from the amount of electricity passing. Buff could not sub- 
 stantiate these claims ; the oxygen evolved always corre- 
 sponded to Faraday's law and also the hydrogen when using 
 a ten per cent, solution of chromic acid. By the electrolysis 
 of a five per cent, solution of pure chromic acid reduction in- 
 versely proportional to the current density was observed. The 
 addition of sulphuric acid increased the reduction. By the 
 electrolysis of acid potassium chromate, the same phenomena 
 was observed as with chromic acid. These results agreed in 
 part with the much later ones of Reese (see page 80). 
 
 The formation of bichromate at the anode by the electroly- 
 sis of a neutral chromate was not established ; it can only be 
 supposed to have taken place from the remark : 2 " the solution 
 in the region of the positive pole gradually became red and 
 gave an acid reaction." 
 
 1 Ann, derChemie und Pharmacie, 1O1,-I (1857). 
 
 2 In an article by Merges [Cotnpt. rend. 87, 15 (1878)] the remark is 
 found that by the electrolysis of potassium chromate, bichromate is formed 
 at the anode ; and it was also noticed that chromic acid in a dilute solution 
 was partly reduced by the electric current to chromic chromate. 
 
 
 
102 CHROMIUM AND ITS COMPOUNDS. 
 
 Potassium bichromate, according to the method of R. 
 Lorenz, 1 can be made directly from ferrochrome, by the help 
 of the electric current. He made the ferrochrome the anode 
 in a caustic potash solution, and for cathode used a porous 
 copper oxide plate. On the application of two volts terminal 
 tension, dense red streams ran down off the anode and oxygen 
 was not evolved, even with a considerable rise of tension. 
 
 Since the ferrochrome consisted of about equal parts of 
 iron and chromium, it might be expected that along with the 
 red chromate potassium ferrate would be formed. This was 
 not the case. The clear red color proved that ; the iron col- 
 lected as hydroxide on the bottom of the vessel and was 
 scarcely "detectable in the solution. 
 
 Two years later, Heibling obtained a patent in England, 
 for in the main the same idea as Lorenz had. 2 He used as 
 anode an alloy of iron and 'chromium containing at least 55 
 per cent, of chromium, and a carbon or iron cathode in an 
 electrolyte consisting of alkali salts, preferably an alkaline 
 chloride. He surrounded the electrodes with bells for the 
 separate collection of the hydrogen and chlorine, which later 
 formed the materials for the manufacture of pure hydrochloric 
 acid. The amount of chlorine set free at the anode corre- 
 sponded to the loss of current occurring in the manufacture of 
 chromate. The iron of the anode was changed to oxide. 
 
 The electromotive force required for the electrolysis is 1.5 
 volts, and to produce i kilogram of crystallized sodium bi- 
 chromate (Na 2 Cr 2 O 7 -f 2H 2 O) required an energy expenditure 
 of two kilowatt hours. For the preparation of i kilogram of 
 crystallized sodium bichromate there was consumed about 
 1 100 ampere hours, corresponding to a current output of 80 
 per cent. 
 
 It is also worth noticing that in case the anode contains 
 less than 55 per cent, chromium, both iron and chromium 
 will be simultaneously oxidized without the formation of 
 
 1 Zeitschr. f. anorgan. Chem., 12, 396 (1896). 
 
 2 English Patent 4,624, Feb. 24, 1898. 
 
OXYGEN COMPOUNDS. 103 
 
 chromate. If the alloy contains crystals (of nearly pure 
 chromium ?) in its interior, at the end of the operation these 
 can be fused together with the use of graphite into a valuable 
 by-product ; in this way chromium practically free from iron 
 can be obtained. 
 
 The patent claim following will furnish the remaining in- 
 formation. 
 
 1. Apparatus for the electrolytic production of alkali 
 bichromates, consisting of electrolytic cells, containing the 
 solution of an alkaline salt, as a chloride, nitrate or caustic 
 alkali, and anodes of chromium or a chromium-iron alloy with 
 a content of over 55 per cent, of chromium and any suitable 
 cathodes. The cells are arranged in a descending series so 
 that the electrolyte can flow from one cell to the other, be- 
 cause of this difference of level, essentially as described. 
 
 2. Apparatus for the electrolytic production of alkaline 
 bichromates, consisting of electrolytic cells, containing a 
 solution of an alkali salt as a chloride, nitrate or caustic 
 alkali, and anodes of chromium or a chromium-iron alloy con- 
 taining over 55 per cent, of chromium and any suitable 
 cathodes. The individual electrodes are surrounded by sepa 
 rate collecting bells, which are intended for the collection of 
 the gases chlorine and hydrogen at the two poles to utilize 
 them for the production of pure hydrochloric acid, essentially 
 as described. 
 
 3. In the apparatus described for the production of alkaline 
 bichromates electrolytically, the arranging of a number of 
 carbon anodes either in each cell or in each division of many 
 cells for the purpose of facilitating the separation of chlorine 
 from the electrolytes. 
 
 With the exception of Fitz-Gerald (page 95) all inventors 
 have attempted the production or regeneration of chromates 
 in alkaline solutions. Since at the present time large amounts 
 of sodium chromate in sulphuric acid solution are used for 
 oxidation, the preference for performing the regeneration in 
 alkaline solution would add the loss of sulphuric acid to that 
 of the soda. 
 
 
104 CHROMIUM AND ITS COMPOUNDS. 
 
 These and other disadvantages (high tension) were as stated 
 in the patent claim 1 of the Hochst Color Works " to be avoided 
 by a rational process which in a large plant has already been 
 proved to be of high commercial importance. Starting with 
 a solution of the chromium salt in the desired acid, as chrom- 
 ium sulphate in sulphuric acid, and always with the solu- 
 tion of the highest electrical conductivity, 100 grams of Cr o O 3 
 and 350 grams of H 2 SO can be diluted to a liter. Both the 
 anode and cathode spaces of the lead : lined vessel, provided 
 with a diaphragm, are filled with the solution (lead plates 
 serve for electrodes). By the action of the current chromic 
 acid is formed on ?he anode side, and hydrogen is evolved on 
 the cathode side. A change takes place in the concentration 
 of the sulphuric acid on both sides, decreasing on the cath.or 
 side and increasing on the anode side. The oxidized so* ,^10^ 
 can be used in manufacturing without further treatment, 
 going back again to chromium oxide, when it comes back to 
 the cathode side, the old cathode liquor being now placed in 
 the anode compartment. The cathode solution has by this 
 second operation become richer in sulphuric acid than the 
 anode solution, but on the passage of the current this excess is 
 transferred from the first to the second. NQ f. umulation of 
 sulphuric acid, etc., takes place in this cyeir operation in 
 which the solutions are brought alternately jn the anode and 
 cathode compartments, and these solutions can be, used for a 
 long time as an excellent carrier of r^vgen, with practically 
 no loss or change in composition. The electronic? ve force 
 with a current density of 0.03 ampere per square Centimeter 
 is not quite 3^ volts at 50." '--., 
 
 The patent claim reads : 
 
 Process for the regenejff- e ^i of chromic acid fro pi solutions 
 of oxidized chromium --jo ccmy an elects 1 y tic methoc 1 ")iar- 
 acterized by the use of I, o gra on of a c 2 O 3 <iiic c :ide sa ts 
 corresponding acid, as ci ' ; ed. ..ulplr nnot* sulphuric aciu, as 
 1 German Patent 103,860, June 12, 1898; identic?- 1 With the American 
 Patent 630,612, which bears the lames of Le Blanc a tfReisenegger. 
 
OXYGEN COMPOUNDS. IO5 
 
 both anode and cathode solutions, but alternated in this way, 
 that the solution containing the chromic acid after passing 
 through its stage of usefulness and having been converted to 
 chromic oxide again, is returned to the cathode side, the 
 previous cathode solution being placed in the anode compart- 
 ment. 
 
 An interesting article by Regelsberger, on the regeneration 
 of chromic acid from materials containing chromic oxide, ap- 
 peared in 1899 in the Zeitschrift fur angewandte Chemie* 
 After a short review of all the previously proposed processes 
 for the manufacture of chromic acid, Regelsberger described 
 some investigations he himself had made on the electrolytic 
 regeneration of chromic acid. 
 
 ^e first thought to oxidize solid residues containing chromic 
 oxiuc in an alkaline solution, by the oxidizing influence of 
 chloride of calcium, similarly to what Dercum 2 had done for 
 the chromium solutions. The results were unfavorable, and it 
 appeared advisable to combine the. formation of the oxidation 
 reagents (of the chloride of lime) and the regeneration of the 
 chromic acid in one process, so a solution of chloride was 
 electrolyzed ? an auxiliary electrolyte, and in this solution 
 chromium h oxide was slowly introduced. With a suffi- 
 ciently lon^ sSage of the current he found that a complete 
 transformation into chromate of the added chromic oxide had 
 taken place, while a corresponding oxidation was not to be 
 detected when using --. 1 kaline sulphates ; the reaction only 
 began c >r the addition of a certain amount of chloride. 
 
 By the-'addition of chromic" chloride alone only chlorine and 
 metallic Chromium resulted ; but on the addition of a larger 
 amount of chloride oxid^tlfvn^tQ chromic acid began. 
 
 From this was crutful, unless l^Lrin the best current out- 
 put^ .;* much clrsually present a sim, continuously dissolved 
 i almost .- , it might be used in s .ine chlorides in amount 
 equal to th/e chromium resi^nes a' given time interval, in 
 
 1 Page i:r the purpose o r 
 
 2 Engli: ou t of the S0- b - T 5, 1898. 
 
106 CHROMIUM AND ITS COMPOUNDS. 
 
 doing which naturally the chromic oxide must be well dis- 
 tributed." 
 
 The oxidation product was principally bichromate and may 
 be allowed to accumulate in the solution without decreasing 
 greatly the current output, although doing so perceptibly. 
 By the use of KC1 as the auxiliary electrolyte, potassium bi- 
 chromate can be finally crystallized out in the purest form 
 from the hot solution, while in the case of the sodium bichro- 
 mate solution the largest part of sodium chloride must be pre- 
 viously removed by evaporation. 
 
 By not quite clear theoretical considerations, Regelsberger 
 attempts then to prove "that with equal returns in formation 
 of chromate the highest current consumption (in ampere 
 hours) takes place when using a chromic salt, a considerably 
 smaller (4/7 of the first) by the use of chromium hydroxide, 
 and the smallest (3/7 of the first) by the presence of a quan- 
 tity of base equivalent to the bichromate solution." 
 
 In relation to the method of procedure, a diaphragm is not 
 necessary. For larger experiments (40 amperes and over) a 
 rectangular metal box was used, whose under part was roof- 
 shaped and fastened with a flange to the upper part, which 
 is lined inside with vulcanized rubber. The lower part 
 serves as a cathode, opposite to which a roof-shaped anode of 
 platinum netting hangs. Air is blown in to increase the cir- 
 culation. For small experiments the following apparatus 
 serves : two vertical platinum electrodes in a glass vessel. No 
 other suitable anode material than platinum has been found ; 
 PbO 2 has too low a conductivity, and carbon is too strongly 
 attacked. The results of the experiments are given as fol- 
 lows : 
 
 (i). 400 ccm. of saturate. ri of chromilution -f- 100 grams of 
 NaCl was diluted to 450 ccmy an elect-- -Jyi. of chrome alum 
 solution containing 4.20 gra on of a c 2 O 3 iiic s slowly added. 
 12.84 ampere-hours applied. >n.lplr )mot* sulphce 3.55 volts 
 at 49 to 66, and electrodes 15 U3; identic?-* With -.'rent density 
 at the anode, which had 24 square lanc a> t^ eisen ^face, 0.178 
 
OXYGEN COMPOUNDS. 107 
 
 ampere per square centimeter, on the cathode with 94 square 
 centimeters surface, 0.0454 ampere. The current output of 
 K 2 Cr 2 O 7 was 34.2 per cent. Almost all the Cr z O 3 was used up. 
 
 2. 200 cc. of a 25 per cent, solution of KC1 with a gradual 
 addition of 62.6 cc. of neutral chrome alum solution, con- 
 taining 1.9 grams of Cr 2 O 3 . 5.6 ampere-hours applied. A 
 dark brown flocculent precipitate came down first, and all ex- 
 cept a few flakes disappeared ; there was no Cr 2 O 3 present at 
 the end. The current output of K 2 Cr 2 O ? corresponded to 36 
 per cent. 
 
 3. 25 per cent. KC1 solution gradual addition of chromic 
 chloride solution (from 100 grams of chromic hydroxide = 
 50 grams Cr 2 O 3 dissolved in HC1 and neutralized as far as 
 possible by repeated evaporations). 32.5 ampere-hours. 4 
 volts at 60. The current output of K 2 Cr 2 O 7 represented 35 
 per cent. ; nearly half had crystallized out. 
 
 4. 25 per cent, solution of KC1, to which was gradually 
 added 50 grams of chromic hydroxide which had been pre- 
 cipitated with 21 grams of caustic lime. 29.5 ampere-hours. 
 Anode current density 0.754 ampere per square centimeter, 
 4.45 volts at 48. Current output of K 2 Cr a O 7 61.9 per cent. 
 A part had crystallized out. 
 
 5. Saturated NaCl solution to which was added a solu- 
 tion of 50 grams of chromium hydroxide and 12. 75 grams of 
 NaOH. 36 ampere-hours. Anode current density 0.692 
 ampere per square centimeter, 5.2 volts at 78. 63 per cent, 
 output. In the last two cases, the formation of a dark brown 
 precipitate consisting of Cr 2 O 3 and CrO 3 was particularly 
 noticeable. 
 
 In reference to the practical application of the method, I 
 will say that it is doubtful, unless the oxidation in an acid 
 solution does not usually present a simpler method of proce- 
 dure. However, it might be used in some special cases, for 
 instance, if the chromium residues are available in the solid 
 form or if for the purpose' of purifying, a precipitation of the 
 chromium out of the solution as chromic oxide is to be 
 
108 CHROMIUM AND ITS COMPOUNDS. 
 
 recommended. The case may also be imagined where the 
 oxidation of the alkaline electrolyte would follow advan- 
 tageously the ignition of chromic oxide with lime as an 
 auxiliary operation. 
 
 On the whole it can be said that the outlook for the prac- 
 tical application of the alkaline oxidation, even with cheap 
 electrical energy is at present, very limited. 
 
 For performing the oxidation in acid solution, Regelsberger 
 first used only platinum anodes and even had little success 
 with the use of a diaphragm. He first obtained satisfactory 
 results in a sulphuric acid solution by the use of lead anodes. 
 According to Elbs 1 a 70 per cent, current efficiency could be 
 obtained by the use of freshly ignited platinum anodes and a 
 low current density. The application of electrolysis, relative 
 to economy of voltage, should occur in warm solutions ; also 
 raising of the temperature seems to have a good influence on 
 the current output itself. The alternation of the cathode and 
 anode solutions as in the patent of Hochst Color Works (see 
 page 104) is emphasized as practical. An addition of iron to 
 the solution must be avoided, as it causes a loss of current, 
 which at least would not be the case if the iron possessed an 
 oxidizing effect in the application of the oxidized solution. 
 
 The output with the application of a pure chrome alum 
 solution with or without free sulphuric acid for the electro- 
 lyte, went up to 92.5 per cent., 70 per cent, of the added 
 amount being oxidized, and with 80 to 86 per cent, efficiency 
 of oxidation. The chrome alum solution used carried about 
 30 grams of Cr 2 O 3 per liter. 
 
 As soon as the larger part of the chromium was oxidized, 
 there occurred a strong evolution of oxygen, this serving as a 
 sign for the renewal of the solution or a more active circu- 
 lation. 
 
 With each electrolysis there formed a small amount of a 
 yellowish white slime, composed of. lead sulphate and lead 
 chromate, and a brownish coat on the anode, which scarcely 
 
 1 Zeitschr. f. Elektrochemie, 6, 388 (1900). 
 
OXYGEN COMPOUNDS. 1 09 
 
 influenced the electromotive force, since it was easily shaken 
 off. 
 
 With an anode current density of 0.065 to o.ojo ampere per 
 square centimeter, a somewhat higher cathode density, and a 
 total current of 42 amperes, three volts tension was used, tem- 
 perature 75 ; to use this voltage at 30 temperature, not over 
 0.03 ampere per square centimeter could be exceeded. The 
 apparatus consisted of a lead box. In the box is found the 
 diaphragms, and the cathodes of any suitable conducting mate- 
 rial. The anode may be either the lead box, or may consist of 
 perforated lead plates surrounding the diaphragms. 
 
 The power consumption may be reckoned as 8 to n kilo- 
 watts for each 100 kilograms of Na 2 Cr 2 O y produced per 24 
 hours. To this must be added the cost of the simple appara- 
 tus, the diaphragms being the chief consideration according to 
 Regelsberger, but which is not the case at present, and finally 
 the regulation of the apparatus, which may be assumed for 
 the most part simple and automatic. "It is therefore 
 very apparent that the cost of the regeneration of 100 kilo- 
 grams of Na 2 Cr 2 CT should not be over $5.00. Of course cheap 
 electrical energy is assumed. Regelsberger compares this 
 cost of $5.00 with the commercial value of 100 kilograms of 
 bichromate, worth at present $13.50, not counting in the last 
 the required amount of sulphuric acid to start the oxidizing 
 action which up to the present was always lost.'' 
 
 The comparison would have been more exact if made with 
 the former regeneration cost, which did not amount in toto to 
 more than $5.00. 
 
 Regelsberger closes with the words : 
 
 " The process for the 'oxidation in acid solutions' will 
 doubtless be of great importance, as soon as the question of 
 diaphragms, which to-day is a serious problem in the electro- 
 chemical industry, has been satisfactorily solved," etc. 
 
 A little later there came into general notice, a patent 1 of 
 
 1 German Patent 109,012. January 13, 1897. Identical with the Austrian 
 patent 5658, of v. Erggelet, dated April 19, 1901. 
 
110 CHROMIUM AND ITS COMPOUNDS. 
 
 Darmstadter's, which apparently solves the problem of the re- 
 generation of chromic acid in a highly simple and elegant 
 manner. Darmstadter puts the substance to be oxidized into a 
 solution, for instance, of chromium sulphate in sulphuric acid, 
 and electrolyzes. " In case there is sufficient circulation 
 every trace of chromic acid formed must immediately be oxi- 
 dized ; an accumulation of it is not possible, and therefore 
 any too strong action impossible," which in the usual oxida- 
 tion methods leads easily to a combustion of the substance 
 being oxidized. 
 
 In this way chinon can easily be prepared from aniline ; 
 this latter compound is brought directly into the cold bath, 
 consisting of chromium sulphate and sulphuric acid, and 
 electrolyzed with continual stirring. The change takes place 
 without noticeable loss. 
 
 In an analogous manner acetic aldehyde may be prepared 
 from ethyl alcohol. 
 
 Also the process is said to be particularly advantageous for 
 the oxidation of anthracene or naphthaline .; these materials 
 are put without further precautions into the chromium solu- 
 tion acidified with sulphuric acid, and electrolyzed with good 
 circulation. " There results a good output of phthalic acid 
 or anthrachinone." 
 
 In the same manner the most varied other soluble or insolu- 
 ble organic compounds may be oxidized. 
 
 The high current output of this process is a further advan- 
 tage. If chromic sulphate is oxidized in acid solutions with- 
 out simultaneously introducing reducing substances, the cur- 
 rent output decreases the more chromic acid there is formed. It 
 is quite otherwise with the process in question ; an almost quan- 
 titative current output is here obtained. " Since in this case 
 every trace of chromic acid is changed instantly back into 
 chromic sulphate there is always a large excess of the latter 
 present whereby the electrolytically produced oxygen is very 
 completely utilized." 
 
OXYGEN COMPOUNDS. Ill 
 
 Diaphragms are according to the patent specification 
 not necessary, because the chromic acid is utilized immedi- 
 ately after its production for oxidation and no trace reaches 
 the cathode. A. diaphragm is used only in such cases where 
 the organic oxidation product is decomposed by the cathodic 
 hydrogen. 
 
 It is at times used when producing insoluble materials in 
 order to hinder a deposition upon the electrodes, being placed 
 in a particular part of the electrolytic bath which itself is 
 separated from the electrode space by a filter cloth or the 
 like. 
 
 The substance to be oxidized can be put in a separate ves- 
 sel, which must be in direct and continual communication 
 with the electrolytic bath, between which as above a piece 
 of filter cloth is interposed. 
 
 In relation to the details of operation, is appended : " When 
 the oxidation of the organic material and the regeneration of 
 the chromium solution takes place in separate vessels, the 
 solutions employed should be as concentrated in chromic 
 oxide as possible, containing 10 to 12 per cent, or more 
 thereof, so that it will be seldom necessary to transfer the 
 heavy solution from the electrolytic bath to the oxidation ves- 
 sel, and to perform other heavy operations as infrequently as 
 possible. With the process in question this is for evident 
 reasons not necessary, and it suffices completely if the solu- 
 tion contains 4 to 5 per cent, of chromic oxide or less. The 
 content of sulphuric acid is made high 20 to 25 per cent. 
 in order to increase the conductivity of the electrolyte." 
 
 u The current density may vary within wide limits for an 
 equally good output is obtained with currents from 0.005 to 
 0.05 and even higher ampere per square centimeter." The 
 electromotive force varies between 2.5 and 4 volts. 
 
 Patent Claim. 
 
 i. Process for the oxidation of organic substances by means 
 of chromic acid, characterized by the reactions taking place 
 
112 CHROMIUM AND ITS COMPOUNDS. 
 
 in the electrolytic bath, in such manner that the reduction 
 pioduct of the chromic acid is continually re-transformed into 
 chromic acid by the action of the electric current. 
 
 2. A manner of carrying out the process of oxidation pro- 
 tected by claim i, consisting in treating the organic substance 
 to be oxidized, in a part of the cell separated from the elec- 
 trode compartment by a sieve or filter cloth. 
 
 3. A manner of carrying out the oxidation process pro- 
 tected in claims i and 2, consisting in bringing the substance 
 to be oxidized in a separate vessel whose contents are in 
 direct communication with the contents of the bath, instead 
 of in a part of the bath partitioned off. 
 
 I have already given a criticism of the preceding process in 
 a lecture entitled : u The Electrolytic Regeneration of Chromic 
 Acid and the Production of Acid Resisting Diaphragms." * 
 I said therein: "He (Darmstadter) takes the point of view, 
 that the chromic acid yields its oxygen up immediately to the 
 substance to be oxidized, so that the reducing action of the 
 cathode does not enter into the question, and the oxidized 
 substance itself is little or not changed by the cathode. Aside 
 from the latter assumption we must on the grounds of ex- 
 perience also regard this process as very little hopeful, since 
 the action of the oxidizing agent on organic substances is in 
 general not instantaneous, and from previous investigations 
 (see further on) on the great facility of reduction of the 
 chromic acid. On reading the patent specification, it might 
 be believed, that the problem is simply solved when he 
 speaks of the obtaining of a practicable output of phtalic 
 acid or anthrachinone, from the oxidation of respectively 
 napthaline and anthracene. According to our investigations 
 the process is not applicable for the direct production of just 
 these materials; we have not once been able to prove the 
 formation of phtalic acid qualitatively, with assurance. 
 
 The following experiments had for their object the settling 
 of the question as to whether it was promising to work with- 
 1 Zeitschr. f. Elektrochemie, 7, 290 (1900). 
 
OXYGEN COMPOUNDS. 1 13 
 
 out diaphragms. If the chromium sulphate solution acidified 
 with sulphuric acid is electrolyzed without 'diaphragms, an 
 oxidizing action of the current is noticed, Li out the output is 
 very unsatisfactory. There was obtained in" an investigation 
 with a sulphuric acid solution containing 100 grams of 
 chromic oxide per liter and using 0.03 amjjere per square cen- 
 timeter and lead electrodes, at ordinary temperatures, a cur- 
 rent output of less than 10 per cent, for the solution contained 
 at the end of the investigation about 6 grams of chromic 
 acid per liter, and this large loss in spite of the small concen- 
 tration of the chromic acid formed. If the current density at 
 the cathode is raised, a larger output is obtained with a 
 simultaneous increase of voltage ; but a practical application 
 of the process is not to be thought of. Changing the mate- 
 rial of the cathode had no beneficial effect. 
 
 In reference to the process 1 6f FitzGerald (page 95) for the 
 simultaneous separation of 2ihc and chromic acid, I should 
 say: Theoretically such 'a 'combination of double working 
 appears pretty, and it pefhaps 1 directs the attention to making 
 such combinations in m&hy electrolytic processes; we have 
 it also in the decomposition of the 1 alkaline chlorides, but here 
 it lies in the nature of the operation. In practice such an 
 artificial combination cannot often be arranged, since for 
 practical use there is always the danger that in obtaining one 
 material the other must always be' produced, even when its 
 production is unprofitable. In such changeable combinations 
 great precautions must be taken in their installation. 
 
 The proposition of FitzGerald is naturally unusable in the 
 electrolytic regeneration of chromium on a large scale ; since 
 where would the large quantity of zinc sulphate come from? 
 It is not a long step, however, to replace the zinc sulphate 
 solution by sulphuric acid. If we 'do this we quickly observe 
 an enrichment in sulphuric acid at the anode side 'and an im- 
 poverishment at the cathode side. It would therefore 'be 
 necessary in this process to precipitate the excess^of sulphuric 
 acid out of the chromium solution- from time to time 'by lime 
 
114 CHROMIUM AND ITS COMPOUNDS. 
 
 and to replace by fresh concentrated acid the dilute sulphuric 
 acid on the cathode side, which is contaminated by the chro- 
 mium which has diffused over. 
 
 I spoke further in the lecture quoted of the German patent 
 103,860 (see page 104) invented by me and belonging to the 
 Hochst Color Works ; and will make some further remarks : 
 The current output is principally dependent upon the per- 
 centage of chromic oxide in solution and how far it is to be 
 oxidized, as well as on the quantity of organic substances in 
 the solution and how far it must be burned by the oxidizing 
 action of the current, and finally on the properties of the 
 electrodes and the temperature. In general 70 to 90 per cent, 
 output can be counted on, on a large scale. The tension 
 changes with the conductivity of the solution used, the cur- 
 rent density, the distance of the electrodes apart, the temper- 
 ature of the solution and the thickness of the diaphragms 
 used. If one has, for instance, cheap electrical power no par- 
 ticular value would attach to the least possible working ten- 
 sion, but other considerations would be of first importance in 
 obtaining the best commercial result. Usually the tension is 
 held between 2.7 and 4 volts. 
 
 Only lead anodes are used, which quickly, cover themselves 
 with a layer of peroxide. According to Regelsberger (see 
 page 106) the output is considerably larger with lead electrodes 
 than with platinum, which is to be ascribed to the over- 
 voltage, which must be used to evolve hydrogen on the per- 
 oxidized plates and which thus allows of the conversion of 
 trivalent chromium ions into the hexavalent, without free 
 oxygen escaping in considerable amount. 
 
 Another way is perhaps worth mentioning by which chro- 
 mium solutions are oxidized, although it has not proven itself 
 of practical value. Lead peroxide oxidizes chromic oxide to 
 chromate, and a charged accumulator plate placed in chromic 
 sulphate solution discharges itself spontaneously, oxidizing 
 the solution. The discharged plate can now be put into 
 storage-battery sulphuric acid, and charged, using a lead plate 
 
OXYGEN COMPOUNDS. 115 
 
 as cathode. By allowing the plate to alternately discharge in 
 the chromic solution and be recharged in sulphuric acid, the 
 putting in of a diaphragm is unnecessary, and the oxidation 
 may be done with a low tension. Unfortunately the plate 
 gives out quickly. 
 
 Summing up, I remarked that a rational process for the elec- 
 trolytic regeneration of chromic acid without a diaphragm did 
 not exist. We are therefore restricted to them and will con- 
 sider finally the attempts which led me to the production of a 
 good and cheap diaphragm. 
 
 Lastly concerning the cost, an average of 350 kilowatt-hours 
 will produce 100 kilograms of CrO 3 in solution from chromic 
 oxide, according to the data given. In conclusion I refer to 
 the data of Regelsberger (page 109), in which it perhaps might 
 be remarked that the hope is entertained that the partial ac- 
 cumulation of a sinking fund would materially reduce the 
 cost. 
 
 A short time after this lecture, Darmstadter published a 
 second process 1 for the regeneration of chromic acid. He 
 mentions the process protected by the German Patent 
 103,860 (page 104), and believes that the difficulties there 
 avoided by the changing of the anode and cathode solutions 
 could be avoided by taking into consideration ordinary hydro- 
 diffusion. 
 
 The sulphuric acid formed in the cathode space by the elec- 
 trolysis as well as that formed by the oxidation of the chromic 
 sulphate tends to distribute itself equally in both compart- 
 ments, and therefore to act against the accumulation of the 
 acid in the cathode compartment. Likewise the chromic 
 sulphate, which, for like reasons, accumulates in the cathode 
 space and decreases in the anode space, tends by diffusion to 
 become of equal concentration in both spaces. If now the 
 current density is so regulated that the transference of the 
 sulphuric acid as well as the chromic sulphate in the one 
 direction is compensated by the transference in the other 
 
 1 German Patent 117,947, Nov. 3, 1899. 
 
1 1 6 CHROMIUM AND ITS COMPOUNDS. 
 
 direction, one has a simple means at hand for overcoming the 
 aforesaid difficulties without it being necessary to frequently 
 renew the solution in the cathode compartment. 
 
 As the velocity of hydro-diffusion is dependent on the 
 difference of concentration, and on the surface and penetra- 
 bility of the diaphragm, so is (I remark further according 
 to the specifications) the current density regulated to these 
 conditions, that is it may be so much the greater, the greater 
 the diaphragm surface and the greater the differences of con- 
 centration of the sulphuric acid and chromic sulphate in the 
 two compartments. The current strength corresponds to the 
 changes in the latter during the electrolysis. 
 
 If changes in concentration occur during the electrolysis, 
 that do not injure anything, they must after ending be 
 equalized. 
 
 Under certain conditions it is practicable to so operate the 
 process that one constituent maintains its concentration con- 
 stant, while that of the other changes. 
 
 If the highest allowable current densities are to be em- 
 ployed then care must be taken to keep the difference in con- 
 centration very large, that is the content of sulphuric acid in 
 the anode compartment very high, the content of chromium 
 sulphate as low as possible. To attain this with continuous 
 driving, one must resort to the addition of fresh solution 
 mixed with a large amount of solution which has been al- 
 ready oxidized, so that the solution in the anode compartment 
 is always to a great extent oxidized and contains a relatively 
 large quantity of free sulphuric acid and a small amount of 
 chromic sulphate. 
 
 If the solution to be oxidized is passed through the anode 
 compartments of a number of baths, using the apparatus in 
 series, then it is recommended that a smaller current density 
 calculated on the diaphragm surface should be used in the 
 first than in the last. 
 
 Patent Claims. 
 
 i. Process for the oxidation of acid chromium salt solutions 
 
OXYGEN COMPOUNDS. 117 
 
 in electrolytic baths with diaphragms, characterized by the 
 regulation of the current density, so that the content of free 
 acid or chromium salt or both in the cathode space during 
 the course of the electrolysis, is not appreciably altered. 
 
 2. A method of operating the process of claim i, wherein 
 for the furtherance of the therein expressed purpose, the addi- 
 tion of fresh and the abstraction of oxidized solution is so reg- 
 ulated that in the anode compartment there is always found 
 a solution which for the most part is oxidized, so that it con- 
 tains proportionately a large quantity of free acid and a pro- 
 portionately small quantity of unoxidized chromium salt. 
 
 3. A method of operating the process of claim i, whereby 
 when passing the solution to be oxidized through a series of 
 several baths, varying current densities calculated on the 
 diaphragm surface are used in the single baths for the at- 
 taining of the desired object. 
 
 The carrying out of the general idea mentioned in the pre- 
 ceding patent, to make the concentration changes through 
 diffusion occasioned by the action of the current retrogressive, 
 appears hopeless in practice because the velocity of diffusion 
 is so small. Above all things it must be mentioned that the 
 application of this idea in the above case, seems to be wholly 
 out of place. For if there is a noticeable diffusion of sulphuric 
 acid from the anode into the cathode compartment, and of 
 chromic sulphate in the opposite direction chromic acid 
 formed on the anode side will wander over to the cathode 
 side where its concentration is almost zero, and so correspond- 
 ingly diminish the output. If the chromic acid concentra- 
 tion on the anode side is kept as high as possible right from 
 the beginning, as is especially recommended, the loss will 
 naturally be so much the greater, until it happens that the 
 chromic acid formed at the anode becomes so much smaller 
 in comparison with the quantity of current sent through, the 
 more chromic acid is already present. On the whole the 
 process must be characterized as impracticable. 
 
 An English patent 1 of Schneider, of a later date concerns 
 
 1 English Patent 19,029, Oct. 24, 1900. 
 
Il8 CHROMIUM AND ITS COMPOUNDS. 
 
 itself very closely with the contents just described of the Ger- 
 man patent of Darmstadter. Schneider also uses the aid of 
 diffusion in order to make the diffusion changes, which dur- 
 ing the electrolysis of chromium solution take place on both 
 sides of the diaphragm, again retrogressive, to which he adds 
 at least that in general only small current densities may be 
 employed. He also mentions that using a solution contain- 
 ing 100 grams of chromic sulphate and 100 grams of sulphuric 
 acid per liter, and a current density of 0.0025 to 0.0050 am- 
 pere per square centimeter (according to the nature of the 
 diaphragm) no change of concentration of sulphate or acid 
 took place in the cathode space before or after the electrolysis ; 
 also working with 0.03 ampere current density, it made itself 
 noticeable and it could therefore, in this case if the vessel 
 stood long enough without current, be made retrogressive. 
 
 As a means of increasing this back diffusion it is recom- 
 mended as in the German Patent 117,949, to use only such 
 solutions as anode electrolytes which are already in the greater 
 part oxidized, and according to that regulate the addition of 
 new solution and the abstraction of old in the anode compart- 
 ment, or better still to mix the anode and cathode solutions. 
 The latter could be done in this manner, by allowing fresh 
 solution to run into the electrolyzing vessel until the level of 
 the fluid stood above the edge of the diaphragm, which is 
 usually lower than the edge of the vessel, thus allowing un- 
 hindered diffusion of both fluids, which finally is also facili- 
 tated by stirring. 
 
 The practical application was carried out in the following 
 manner. By using a solution containing 100 grams of 
 chromic sulphate and 50 grams of sulphuric acid per liter, 
 and a current density of 0.02 to 0.03 ampere per square centi. 
 meter, it is found that after about half of the chromic sulphate 
 had been oxidized at the anode, the acid concentration at the 
 anode had risen to 100 to 150 grams per liter, and a corre- 
 sponding fall had taken place at the cathode. At this time 
 enough fresh chromic solution was put into the vessel 
 
OXYGEN COMPOUNDS. 119 
 
 until the edge of the diaphragm was covered, when a mixture 
 of the anode and cathode fluids will take place in several 
 hours, or in a shorter time by the aid of stirring, and the dif- 
 ference of concentration will be equalized, upon which the 
 electrolysis may be continued after the removal of the upper 
 layer of solution. 
 
 If the solution contains 100, 150 or more grams of sulphuric 
 acid per liter, then such a mixing will be required only at 
 longer intervals, because the content of sulphuric acid in the 
 cathode solution will not be reduced to such a small value in 
 so short a time. 
 
 The electrolysis of sulphate solutions is also recommended 
 because of the possibility of using lead electrodes. 
 
 The patent claim reads : 
 
 1. A method for the equalization of the concentration 
 changes occurring in the electrolysis of chromium oxide solu- 
 tions acidified by sulphuric acid, when a diaphragm is used, 
 consisting in mixing the anode and cathode fluids, either by 
 increasing the diffusion through the diaphragm in relation to 
 the action of the electrolytic migration or by free diffusion or 
 by the aid of artificial means. 
 
 2. A method of equalization (as above), consisting in mix- 
 ing the solutions, by the aid of diffusion through the dia- 
 phragms, and increasing this diffusion velocity in relation to 
 the transfer velocity of the sulphuric acid by a regulation of 
 the current density, essentially as described. 
 
 3. A method for the equalization (as above), consisting in 
 mixing the solutions by the help of diffusion through the 
 diaphragm, and admitting a continuous or intermittent stream 
 of new solution in the anode compartment, drawing off a 
 corresponding amount of old solution, essentially as described. 
 
 4. A method for the equalization (as above), consisting in 
 mixing the solutions by the aid of diffusion through a dia- 
 phragm, and from time to time interrupting the electric cur- 
 rent. 
 
120 CHROMIUM AND ITS COMPOUNDS. 
 
 5. A method for the equalization (as above), consisting in 
 the direct mixture of the solutions of both compartments. 
 
 6. A method for the equalization (as above), consisting in 
 directly mixing the solutions, by allowing fresh solution to 
 flow in until the edge of the diaphragm is covered, allowing 
 the whole to stand for some time, and then drawing off a 
 sufficient amount of solution, essentially as described. 
 
 7. A method for the equalization (as above), consisting in 
 a direct mixing of the solution, while stirring, essentially as 
 described. 
 
 In passing judgment upon this last process the following 
 with reference to page 105 is added : If there occurs a mixing 
 of the anode and cathode fluids in any way, either by free or 
 limited diffusion, or diffusion facilitated by stirring, there re- 
 sults under all conditions under the assumption that an in- 
 fringement of patent 103,860 (page 104) is to be avoided a 
 certain amount of the chromic acid formed at the anode going 
 to the cathode, where according to the investigations men- 
 tioned on page 101, it is again reduced. This process is less 
 valuable than that of patent 103,860. 
 
 APPENDIX. 
 
 1. The chromium carbide C 2 Cr , described on page 66, can 
 also be made according to a contribution of Moissan 1 by heat- 
 ing a mixture of equal parts of chromic oxide and calcium 
 carbide (200 grams was taken) in an electric furnace for five 
 minutes, using 900 amperes at 45 volts. Moissan found as 
 the products of the reaction, a metallic regulus covered with 
 crystalline needles, underneath a covering of melted calcium 
 carbide, and by analysis corresponding to the above formula, 
 and containing traces of iron and calcium. 
 
 2. On the preparation of acid lead chromate according to 
 the process of Luckow (page 89), J. Rontschewsky remarks 
 in a paper, 2 that the production of the lead chromate may be 
 combined with the electrolytic obtaining of zinc in one process, 
 if a diaphragm is employed. 
 
 1 Compt. rend., 125, 841 (1897). 
 
 ' 2 Zeitschr. f. Elektrochemie, 7, 29 ( 1900). 
 
INDEX OF AUTHORS. 
 
 Aschermann 42, 43, 47 
 
 Boehringer & Sons 74 
 
 Bonnet 3, TO, u, 13, 16, 18 
 
 Borchers 37, 54 
 
 Browne 86 
 
 Buff 81, 101 
 
 Bullier 64 
 
 Bunsen i, 2, 3, 23, 53, 76, 77 
 
 Chaplet 67 
 
 Cowper-Coles 19, 25 
 
 Darmstadter t no. 112, 115, 118 
 
 De Chalmot 70 
 
 Demmenie 39 
 
 Dercum 105 
 
 Deville 54 
 
 Dollner ' ;" '. 50 
 
 Dufau 82 
 
 Elbs i 108 
 
 Electro-Metallurgical Co 19, 23, 59 
 
 Erggelet, von 109 
 
 Fe*re*e 19, 25, 53, 76 
 
 FitzGerald 95, 103, 113 
 
 Fremy 54, 82 
 
 Geuther 101 
 
 Glaser, F 75 
 
 Glaser, G 27 
 
 Goldschmidt, H 30, 51, 63 
 
 Goldschmidt, Th 46, 47, 49, 6 1 
 
 Haussermann 98, 99, 101 
 
 Heibling 56, 102 
 
 Heroult . 62 
 
 Hittorf 29, 31, 39 
 
 Hochst Color Works 104, 108, 114 
 
 KoryschefF 39 
 
 Krupp 34 
 
 L,e Blanc 104, 112 
 
 Le Chatelier 82 
 
 Lorenz 102 
 
 I/uckow 87, 88, 120 
 
 Maronneau 72 
 
122 INDEX. 
 
 M oiler 19 
 
 Moissan 35, 36, 37, 38, 54, 55, 57, 64, 66, 68, 70, 81, 82, 85, 120 
 
 Merges lor 
 
 Mourlot 72 
 
 Neumann ..'.... 27, 30 
 
 Ostwald . ' 31, 100 
 
 Parker 71 
 
 Placet 3, 10, u, 13, 16, 19, 25, 59, 63 
 
 Reese . . . 80, 101 
 
 Regelsberger . , . , . '. . '. 105, 106, 108, 109, 115 
 
 Reisenegger 104 
 
 Rontschewsky 120 
 
 Schneider 117 
 
 Smith '. 97 
 
 Societe" d'lectro-Chimie . '..'.' 51 
 
 Socie'te Ge'ne'rale de Aciers Fins 61 
 
 Socie'te Neo-Metallurgie Marbeau, Chaplet & Co . 57 
 
 Strameo 79 
 
 Street . . . . . . .... . ' ! ! 19, 78, 80 
 
 Vautin 44, 47, 49, 61 
 
 Verneuil 82 
 
 Vielhomme , 62 
 
 Villon 73 
 
 Williams 66 
 
 Wilson 32 
 
 Zettel 70 
 
 UNIVERSITY