THE PROPERTIES AND ELECTRODE BEHAVIOR OF MANGANESE AMALGAM BY WARREN COBINE BRUCE THESIS FOR THE DEGR E E O E BACHELOR O F S C I E N G E IN CHEMICAL ENGINEERING COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS ]!)22 Digitized by the Internet Archive in 2016 https://archive.org/details/propertieselectrOObruc /922 Be 3 UNIVERSITY OF ILLINOIS i 9 i THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Warren Cobine Eruce ENTITLED.. .. Amalgam IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Lachelor_cf .. Science .T.n .Che^caT.^ ACKNOWLEDGMENT The author wishes to express his apprecia- tion of the guidance and help given by Dr, John H. Reedy, under whose supervision this v/ork was car- ried on. I. II. III. IV. TABLE OP CONTENTS Page 1 1 4 4 6 8 ACKNOWLEDGMENT INTRODUCTION HISTORICAL EXPERIMENTAL A. Preparation of Manganese Amalgam B. Properties of Manganese Amalgam Table I. Rate of Oxidation of Manganese in Manganese Amalgam C. Electrode Potential of Manganese Amalgam 9 and the Manganese Amalgam-Manganese Di- oxide Electrode 1. Theoretical 9 2. Experimental 10 Table II. Electrode Potential Measure- 11 ments of Manganese Amalgam Graph I. Electrode Potentials oP Man- 12 ganese Amalgams in Contact with Vari- ous Concentrations of Manganous Sul- phate Graph II. Electrode Potentials of Man- 15 ganese Amalgams in Contact with 0.500 Molal Manganous Sulphate SUMMARY 14 17 BIBLIOGRAPHY 1 I INTRODUCTION The purpose of this work is to investigate the properties and electrode behavior of manganese arid manganese amalgam with regard to their use in the development of a manganese amalgam-manganese dioxide electrode for the measurement of oxidizing potentials of solutions* II HISTORICAL The earliest article on manganese amalgam was by Bftttger 1 . Bun- sen 2 obtained metallic manganese by electrolyzing a saturated solutior o of manganous chloride at 100 C. using platinum electrodes. If the current is less than 0.067 amperes mangano -manganic oxide is obtained instead of metallic manganese. The metal comes down in shining leaves which oxidize in air as fast as potassium. Moissan 3 obtained a needle-like, crystalline amalgam of manganese by electrolyzing a concentrated solution of manganous chloride using a mercury cathode, Moore" found that a very large proportion of the manganese in a solu- tion may be deposited as the metal, at the cathode, by employing a neutral solution containing a large excess of ammonium thiocyanate. A. powerful current is necessary. Smith and Frankel 5 using an excess of potassium sulphocyanide in a solution of manganous sulphate or citrate, upon electrolysis, obtained a grayish- white, compact deposit of metallic manganese upon the cathode, no manganese dioxide separa- ting at the anode. Warwick 6 has suggested the use of acetate in this . • ‘ ' . . 2 connection and Neumann 7 says that the same deposit can be obtained from neutral salt solutions or solutions containing a small excess of nitric acid, the acid in the latter being converted into ammonia by the action of the current. The deposit of metallic manganese decom- poses water. Guntz 8 obtained an amalgam rich in manganese when he electrolyzed a concentrated solution of manganous chloride at 15-20 amperes using 400-500 grams of mercury as the cathode. After strong pressing in chamois leather he obtained a solid amalgam which in air remained unchanged even for a month. It is slate-gray, begins to give o ip mercury at 130 C. and decomposes water at ordinary temperature. Prelinger 9 prepared manganese amalgam by electrolyzing a saturated solution of manganous chloride at 11 volts, the temperature rising to o 70 C. After filtration thru linen and subjection to a. pressure of 2000 kilos per sq. cm. for several hours, an analysis of the amalgam o gave 9.9 /o manganese, which indicates the formation of the compound VTn 2 Hg 5 . This compound is slate-gray in color, assumes a metallic lus- ter when rubbed or cut, and oxidizes slowly in air at ordinary tem- o peratures, metallic mercury being liberated. At 100-110 G. it decom- poses into its elements. The specific gravity 12.828, is a greater cumber than that of 12.532 calculated from the specific gravity of its constituents, so that contraction takes place in the formation of the compound Mn 2 Hg 5 . Mn 2 Hg 6 is electropositive to mercury. Consequently leat is probably absorbed in its formation. A solution of the com- pound in mercury is not attacked by dry air but is quickly oxidized by moist air to manganic oxide, Mn 2 0 3 , which forms a fine dust on the surface of the liquid. Erdman noted that manganese amalgam crystallizes in needles. He obtained a semisolid amalgam by the ac- 3 tion of sodium amalgam upon a concentrated solution of manganous chloride, as did many other workers. Foerster 11 states it is possi- ble to deposit metallic manganese at the cathode provided high cur- rent densities and strong, nearly neutral, solutions are used. Ram- say 12 says that manganese amalgam rapidly turns black in air but may be preserved some time under water, in a closed vessel, on which it has little or no action. Under alcohol in an open vessel it rapidly becomes oxidized owing to absorption of oxygen from the air. Laden- burg 13 finds that manganese amalgam slowly decomposes water with the evolution of hydrogen. Shaking the amalgam v/ith water in contact with air gives ozone. Abegg 1 - in 1913 states that very little is known about the electromotive behavior of manganese. Manganese is one of the more reactive metals and possesses a great affinity to form all of the metalloids, and has a rather high electrolytic solution pres- sure. Neumann 15 found that metallic manganese gives unsteady poten- tial values. He obtained better results with electrolytically pre- pared semisolid manganese amalgam. The values for the amalgam are nore positive than those of the pure metal. His results are given later. According to Ramsay 12 , manganese is one of the metals which gives a normal lowering of the vapor pressure of mercury. Van Ars- lale and Maier 16 found that metallic manganese can be deposited at the o iathode from neutral sulfate solutions v/ith 80-90 / 0 efficiency at 3 volts or more, but the deposit is powdery and a concentration of o .35 /o free sulphuric acid prevents deposition. Lorenz and Hostelet 17 md Muthmann and Fraunbergens gi ve some potential measurements of netallic manganese. 4 III EXPERIMENTAL A. PREPARATION OP MANGANESE AMALGAM Attempts to amalgamate manganese, prepared by the thermit process, by direct contact with mercury, failed* A piece of this kind of man- ganese was washed with ether, dried, weighed, and placed in contact with mercury at room temperature for three days. It failed to show any signs of amalgamation, its weight still being 1.7549 grams. Mer- cury does not wet the surface of this kind of manganese. On leaving it in contact with mercury at the temperature of the steam bath for 24 hours the manganese showed no signs of amalgamation, but lost its luster and gained .0005 grams in weight due to superficial oxidation to MnO ( OH ) 2 • The amalgams used in the experimental work were prepared by elec- trolyzing concentrated solutions of manganous sulphate. The appara- tus consisted of a 500 cc. beaker, a small crucible to hold the mer- cury cathode, a platinum foil anode, and an ordinary extraction cell of filter paper to cover the anode to prevent dispersion of manganese dioxide thru the solution. Connection to the mercury cathode was made by means of a platinum wire fused in the end of a piece of glass tubing filled with mercury. The voltages used ranged from the theo- retical amount up to 110 volts. At 110 volts a solid amalgam is ob- tained in several minutes. The electrolysis goes better in hot solu- tions, but the solution need not be heated externally as it soon be- comes heated by the current. The electrolysis goes faster if the solution is stirred but stirring was not necessary in this work. No 5 reagents to prevent the deposition of manganese dioxide at the anode or the solution building up in acid, were used, for fear of contami- nating the amalgam. In this connection ammonium acetate and arrmonium sulphate were tried, as they seemed to be the least objectionable. It /ms found, however, that when ammonium salts are present, ammonium amalgam readily forms. Ammonium amalgam is apparently easily decom- posed by triturating with water. It is not sure, hov/ever, whether the last trace of ammonia can be readily removed, especially since there is a possibility of c cmpound formation in the system manganese, ammonia, mercury. Therefore, ammonium acetate or ammonium sulphate were not used. The solution, of course, soon builds up in acid dur- ing the electrolysis but this has no deleterious effect. Manganous chloride solution is not as satisfactory as manganous sulphate be- cause the evolved chlorine corrodes the anode. The amount of manga- nese in 'the amalgams v/as obtained by weighing the mercury cathode be- fore and after electrolysis. After electrolysis the cathode vessel with the amalgam w as washed v/ith water, heated on the steam bath for five to ten minutes , cooled in a desiccator and v/eighed. Several blank runs proved that mercury heated on the steam bath for ten min- utes or less could be v/eighed to the fourth decimal place v/ithout showing any loss. The amalgam cannot be washed with alcohol v/ithout causing a slight oxidation of the manganese. Ether forms black com- pounds with the mercury because ether contains sulphur derivatives which are difficult to remove completely. The mercury used in the experimental v/ork was washed three times v/ith nitric acid by passing it three times thru a Meyer column, dried and distilled in a pyrex glass still en vacuo. The manganous sul- . * ' ‘ " . . . ■ ■ 6 phate was prepared recrystallizing twice from C. P. manganous sul- phate. The other reagents used were the ordinary C. P. materials. B. PROPERTIES OF MANGANESE AMALGAM The amalgam prepared in the manner described is always hetero- geneous. It is composed of liquid amalgam, semi so lid amalgam, and rather compact lumps of solid amalgam which apparently have a crys- talline structure interspersed with liquid amalgam. Liquid amalgam can easily be forced from the pores of the solid amalgam by merely squeezing a piece of the latter between the fingers. Even after standing three days the lumpy amalgams did not become homogeneous. If the amalgams were merely liquid amalgams in equilibriun with excess manganese they probably would have been entirely semisolid rather thar lumpy. The formation of these lumps is probably due to the crystal- lizing out of some compound of manganese and mercury, some liquid amalgam being brought down with the crystals of the compound. This compound, according to Prelinger 9 ' is probably Mn 2 Hg 5 . During the electrolysis bright needle or leaf-like crystals of am&lgam form, on the surface of the mercury cathode and upon long electrolysis these crystals tree up and creep over the edge of the crucible. This again seems to verify Prelinger’s conclusion that a compound is formed be- tween manganese and mercury. The lowest amount of manganese found in the semi sol id amalgams o was 0.465 /° , and it is concluded that the solubility of manganese in nercury at room temperature is not greater than this amount. . J • . 7 Trie approximate melting point of a dilute amalgam (one volume saturated amalgam plus fifty volumes mercury) was determined as being o about -35 C., by freezing the amalgam with liquid air and allowing it to melt. This is over three degrees higher than that of mercury o (-38.85 C.) and indicates that manganese and mercury form a compound. This is another proof of Pre linger ! s conclusion that manganese and mercury form a compound. Manganese amalgams of different concentration did not all appear to have the same reactivity towards oxygen so the following ex- periments were carried cut. The saturated amalgam was obtained by filtering semisolid amalgam thru a filter paper containing pinholes. It probably contained a small amount of the solid phase. The experi- mental method and results are given in the following table* Table I_. Relative Rates of Oxidati on of Mang a nese Amal gams of Various Concentrations . A. Exposed to laboratory air. Amalgam dry. Dilute Liquid Amalgam oat. Amalgam plus 53- Volumes Eg Sat. Amalgam plus 1 Volume Eg Saturated Acnalgam Semi solid Amalgam Solid Amalgam Instantly . Instantly . Fast . Very slow. Brown layer of oxide which turns black Brown layer of oxide ’which turns black brown layer of oxide in 5 minutes Thin brown layer after 94 hours No signs of oxidation ev en after 7)2 days a. Under water exposed to laboratory air. Fast • Fast . Slow . Slow . Very slow. Brown precipi tate after several minutes . Brown precipi tate after several minutes Black layer after 24 hours Well developed black layer after 24 hours Thi n brown layer after 24 hours C. Under boiled water in a glass-stoppered bottle sealed with sealing wax. Bottle filled as full as possible with water while boiling hot. ho immediate action was noticed in any case Small Small Brown amount amount splotches LnO (OH ) o MnO (OH ) r> after after 72 after 72 59 days days days D. A piece of solid amalgam was partly exposed to water and partly to laboratory air. The part above water showed no signs of oxidation, even after 24 hours. The part below water developed a brownish tinge after an hour and a well- developed brown layer after 24 hours. In all cases in the experiments with with amalgams exposed to the air the film of oxide appeared to prevent further oxidation. In no case was any evolution of gas noted. 9 Some semis olid amalgam, in a crucible heated very gently over a bunsen flame for 48 hours still retained its silver-bright surface and showed no signs of oxidation. Attempts to preserve manganese amalgam under benzene and toluene failed. In both cases a film of brown oxide formed and also a black precipitate due to the action of impurities such as sulfur deriva- tives o Attempts to preserve manganese amalgam under manganous sulphate and chloride solutions failed. The oxidation is not as rapid as in the case of water, probably because oxygen is not as soluble in these solutions or because the manganese in the solution reacts with the oxygen. C. THE ELECTRODE POTENTIAL OP MANGANESE AMALGAM, AND THE MANGANESE AMALGAM - MAN GANE SE DIOXIDE ELECTRODE 1 , The ory of the Manganese Amalgam - Manganese Dioxide Electrode . It would appear that in the various forms in which this electrode might be developed, might be found a suitable combination for measur- ing the ©xidi zing potential of a number of solutions. This electrode should be reversible with respect to manganous ions. The half cell is of. the type Mn In the case of the half cell Mn | MnO a | MnO^“ the reaction should be Mn + © + MnO*" ^ MnO a 0 2 Mn 0 2 10 2 o Experimental . E. M. F. measurements of the following combinations were made with a Leeds andNorthrup student’s potentiometer, a standard cadmium cell, a tenth normal calomel half cell, and a three normal potassium chloride intermediate solution. . . . . Table II 11 Elec trode Potential Measurements of Manganese Amalfi ms « Referred to the 0.1 N calomel electrode as +.613 volts. The last figure in each case is doubtful. Room temperature = 23.5 - 1° G. Saturated Saturated Saturated Amalgam Semi solid Hg Amalgam Amalgam Amalgam + 51 vol s + 9 vols .4645$ Mn Kg Hg vol ts volts volts volts volts .0004-5 MnS0 4 + .765 - .717 -.857 - . 777 « o M ivuibu^ + .7o4 -.739 -.302 -.800 - .800 1.0 M MnS0 4 M ilO p — I • 0 M + .669 -.859 -.313 -.808 -.839 MnC 1 2 -.374 MnO p—1.0 M MnS 04 .00045 M -.895 KMn 0 4 -.617 -.957 MnOp- .00045 M Kiin 0 4 . M nG p— 0.4 M -.397 -1.047 KMn0 4 ,000325 M -.931 1.116 Klin 0 4 in .005 it KCE -.857 .000335 M KMn 0 4 in .05 M H o S0 4 -.743 MnOp- .000335 M Kl£n 04 in .005 M K0H -.937 - *980 MnO p- .000235 M KMn0 4 in .05 JS H p S0 4 -.817 MnO 0 - . 2M KMnC 4 in .005 M KGH .939 .863 MnO p- . 2 M KMn 0 4 in .05 N Hp J 4 1.435 .973 In the half cell, semi solid amalgam -MnO g- 1.0 M MnCl 0 , a volume of mercury, equal to that of the amalgam, was added and the cell shaken, without causing any change in th e electrode potential. Comparison Wi th Neumann 1 s Values for Semi soli d Amalgam . Neumann Bruce G.5 M MnS04 -.315 volts -.300 volts Rrnrn ig| m Sli or iimt tSSBSffl U -mh. ■ Bg S id; Co loo \M r m £C>4- IN MOLES PER LITER #^ra .p O.J 0.4- OS 0.6 0.7 0.8 (T9 Q ±55 m i m 4 - or <4 1 1 ° K gg mm o E nw IfejF r™” n t# fpp [tm mtlpM ■ -~^-o i , o 1 M 99 o gg <^> m 3 T iti Si M PS 1 1 A// Q pp is if m S il 3 & 1VI ±N3±0d 300tfd0313 'J- m rs| W CO Q Wm o o o' i m i m ft I m S- m < m § 1 m I o U m o QO d CS