HARRISON LABORATORY O F CHEMISTRY]. NEW RESULTS IN ELECTRO-ANALYSIS.'
[CONTRIBUTION FROM THE JOHN
BY THOMAS P. MCCUTCHEON,J R . Received August 15, 1507.
Previous workers in electro-chemical analysis have directed their efforts almost entirely to the determination and separation of metals. A year ago, J. H. Hildebrand', working in this Laboratory, showed that such anions as Br, I, PO,, Fe(CN),, CNS could be determined in the electrolytic way. H e employed the mercury cathode and an attackable silver anode in a cell especially devised for the purpose. Sodium and potassium can be determined simultaneously, so that a complete analysis of such salts as sodium chloride and potassium ferrocyanide can now be made with ease and accuracy. T h e purpose of the first part of this investigation was to extend this work to the estimation of other anions and to learn whether other metals than silver could be advantageously used as anodes. In the second part of the work, the same form of cell was used in the separation of certain metals.
Apparatus. T h e decomposition cell, devised by Hildebrand, consisted of a crystallizing dish, the bottom of which was covered with a layer of mercury. In-
side of this was placed a beaker of smaller diameter, without a bottom and supported so that its lower edge extended just below the surface of the mercury. T h e inner cup was held in position by means of three From author's thesis for P h , D. degree, 1907. This Journal, 29, 4,447.
3
‘446
T H O M A S 1’.
NCCUTCHEOX, J K .
corks placed radially. T h e mercury was connected with the cathode by means of a stout platinuiii wire enclosed in a glass tube. T h e inlier coinpartmeiit contained tlie solution to be atialyzed. Water m s placed in tlie outer coinpartmeiit, to wliich a few drops of sodium chloride solution were added to increase the conductivity and a nickel wire to aid in the decomposition of tlie amalgam. The aiiode consisted of two disks of platinuiii gauze, placed one above tlie other atid supported by a platinum rod. I t was plated with silver by making it the cathode in a bath of silver potassium cyanide. It was then wa.;hc-cl, dried and weighed. I t was rotated 2 jo-300 times per ininute by means of a siiiall motor. T h e anode was lowered into t h e inner compartiiient until the upper gauze was covered by the solutiori. T h e procedure for the analysis of such a salt as sodium chloride was as follows: t h e salt was placed in tlie iiiiier compartment and diluted to about 50 cc. atid the anode placed in position, Kliile in the outer cornparttnent, as stated above, purc water v a s placed and a little sodium chloride solution so that the curretit wou:d be conductecl more rapidly at first. On electrolyziiig the sodium cliloridc in the iiiner compartment, the sodiuiii p a s e d into the mercury ami formed an amalgam. I n a sliort time this anialgani found its way into tlie outer compartment, where it \vas decomposed nitli fornia’cioii of sodium I~!.tlroxidt.. A t t h e coiiclusion of the experiment the sodium liydroxicic \\as ebtiiiiated by titration witli standard acid, using nietliyl orange :is iiidicntor. Tiie chlorine appeared a< silver cliloritlti a t the aiiode and was perlectly adherent. As nothing reinained it1 tlie iiiner compartment but pure water, tlie needle of the aniiiieti-r gradually fell alniost to zero. This indicated the end of the experiiiient aud tlie anode was removed, dried and weiglied. T h e increase in weight represented tlie chlorine in the sodiuiii chloride. Experimental Part. experiinenting with other anions than those mentioned above, it appeai-ed that the silver anode was unsatisfactory. I n some cases, as witli borate aiid sulphide, the silver salt formed was not perfectly adherent; silver fluoride, on the other hand, was somewhat soluble in water. T h e following experitnetits were instituted, with tlirse facts in mind, in the hope that other anodes than silver might prove helpful. 011
Lead Anode. Tiie platinum gauzes were plated with lead in a bath of lead sulphocyanide dissolved in pota3siuni hydroxide. I u the experiments to be described 4 - j volt.; were used. T h i s ordinarily gave a current of about 0.5 aiiipere, falling to 0 . 0 2 - 0 . 0 1 ampere \vIicii the salt was completely reiiioved r.i-om tlie iniirr coinpartiiient. T h e anode was rotated 250 times per iiiiiiute.
1.147
ELECTRO A N A L Y S I S
Pofassizint CJfa?ride.-\$T11ite lead cyanide formed readily, b u t did not adhere to the anode. Borax.--Xniperes 0.7-0.03. T h e lead borate was non-adherent. Pofassirint Ffr~u~~ide.--Xmpereso 7-0.01. After many trials it was again found inipossihle to obtain a satisfactory deposit. A considerable amount of lead peroxide formed on the anode. S O n " ? L m
[email protected] lead sulphate formed on the anode, but the formation of lead peroxide prevented the estimation of SO,. By titrating the caustic soda formed in the outer compartment, it was possible to determine t h e sodium in the salt with fair results. Grams
Sodium sulphate present 0 . 0 S j Z " o.ozj6 found 0 . 0 2 j 4 0 . 0 2 73 0.0276
Amperts
......
0.1-0.0 I
...... ......
......
yo:ts
..
Time. m i n .
..
3
~i '
..
..
.. ..
.. ..
Sodimt
[email protected] lead anode became black a s soon as placed in the solution of sodium sulphide. However, as the electrolysis proceeded, pieces of the lead sulphide became detached, making an exact estimation of the sulphur impossible. A curious phenomenon mas noticed during this experiment. T h e solution of sodium sulphide used was quite colorless. I n a few minutes t h e solution i n the inner compartment took on a very pronounced yellow color. T h e same color was noticed when cadmium and bismuth anodes were used with soluble sulphides. T h e cause of this color will shortly receive further investigation.
Cadmium Anode. T h e anode was plated in a bath of potassium cadmium cyanide. Sua'izinr
[email protected] formation of yeliow cadmium sulphide became apparent before t h e current was passed. T h e solution in the inner compartment became yellow, b u t after a few minutes became colorless again. T h e deposit of cadmium sulphide on t h e anode w a s adherent, if carefully handled. I t was dried in an oven a t I 15' and weighed. X low voltage should be used and care be taken not to rotate the anode too rapidly; otherwise small pieces of cadmium sulphide may become detached. Grams
Sodium sulphide present 0.0429 "
found
0.0252 O.ozj2 0.02 56 0.02 j I
Volts
..
3.5
.. .. ..
amperes
......
0.1-0.0;
...... ...... ......
Tinie. iniii,
..
15
..
.. ..
Sodiwt Chmmnte. -The cadmium chromate was gelatinous and nonadherent. Sodiznt Arsenate. -White cadmium arsenate formed ~ b u n d a n t l y , but did not adhere tp the anode.
I448
THOBIAS P . M C C C T C H E O S , J K .
Bismuth Anode. T h e anode was plated from a solution of bismuth nitrate contailling sulphuric acid. Sodl'zwz Chronzafe. -The color of the liqiiid in the inner conipartment altered from yellow to green and finally a green gelatinous precipitate separated, probably chromium hydroxide. S o bismuth chromate formed on the anode. Sodi?rn~Sulphide. -The liquid in the inner conipartinent again became yellow. \Lrhen a high pressure was used (14 volts) black bismuth sulphide separated from the liquid. Little bismuth sulphide formed on tlie anode. Sodiiim Arse/znfc.--No bismuth arsenate appeared, indicating that the bismuth iv3s not attacked by the arsenate anion. T h e liquid in the inner compartment became acid to litmus, probably due to the forniation of arseriic acid. Sodizrvz Iodzde---The solution in the inner compartment assumed a deep orange color a t first. On continuing tlie electrolysis the color became 1iluch paler. T h e bismuth anode did not change in appearance.
Zinc Anode. T h e anode was plated from a solution of sodium zincate. Sodiuin Phos$4atee.--U'hite zinc phosphate formed, but did not adhere. Sodiuiiz Tziizgstatc.-When the anode was rotated slowly, the surface of t h e mercury in the inner compartment took on a blue iridescent tarnish. KO hydrogen was evolved in the outer conipartment and the current did not fall. Rapid rotation of the anode caused a slight evolution of hydrogen in the outer compartment and a non-adherent, white, flocculent precipitate, probably zinc tungstate, formed i n the inner compartment. I n the latter case the current fell from 0 . 1 - 0 . 0 1 ampere. Five volts were used in each case. Pofassium Cq'aizate.-A white, non-adherent precipitate formed. Further a copper anode was used with a solution of sodium arsenite. T h e green arsenite of copper was formed readily, but little of it adhered to t h e anode. When an iron anode was used with potassium ferrocyanide, t h e anode was not attacked and hydroferrocyanic acid seemed to form in t h e inlier compartment. It is clear, then, that t h e anodes, described above, behave in several ways toward the different anions. I n some cases a n insoluble precipitate is formed whicli may or may not adhere to tlie anode. In other cases, for example, t h e iron anode with a soluble ferrocyanide, the anode is not attacked, but t h e free acid is generated. These experiments, while not a t all exhaustive, seem to indicate that silver is the most suitable anode for receiving most a~iions. It is entirely
ELECTKO-ANALYSIS
I449
probable that further study will reveal conditions under which the other anodes will give good results. Electrolysis of Solutions of Metallic Chlorides with a Silver Anode. U p to this time only salts of sodium and potassium had been electrolyzed in this apparatus. Attention was next turned to other metals, using their chlorides with a silver anode, to learn whether they formed amalgams and whether the amalgams, if formed, decomposed in the outer compartment with formation of hydroxides. A solution of calcium chloride was placed in the inner compartment and electrolyzed in the usual manner. From the appearance of the surface of the mercury it was evident that an amalgam was formed at first, but in a short time i t decomposed in the inner compartment, giving rise to a large quantity of calcium hydroxide. H. S. Lukens, working in this laboratory at the same time, found that the amalgams of barium and strontium deported themselves like those of sodium and potassium and decomposed in the outer compartment with formation of hydroxide. He succeeded in making a complete analysis of barium chloride, weighing the chlorine collected at the anode and titrating the barium hydroxide formed in the outer compartment in the manner to be described later. These facts seemed so suggestive that solutions of a number of the metallic chlorides were made u p and electrolyzed with the following results : Amalgams of lithium, sodium, potassium, calcium (see below), strontium and barium decompose in t h e outer compartment with formation of the corresponding hydroxides. Amalgams of cadmium, tin, antimony, iron, aluminium, chroniium, manganese, zinc, nickel, cobalt, titanium, vanadium, zirconium, thorium, lanthanum, cerium, neodymium, praseodymium, magnesium and uranium decompose in the inner compartment with formation of hydroxides. Electrolysis of Cerium Chloride. A peculiar result was observed on electrolyzing a solution of cerous chloride. A t the beginning the appearance of the surface of the mercury indicated the formation of an amalgam. A subsequent examination proved conclusively that considerable cerium had passed into the mercury. Later t h e solution in t h e inner compartment took on a pink color, which finally resembled a somewhat dilute solution of potassium permanganate. T h i s color was observed by transmitted light, I t had a greenish, fluorescent appearance by reflected light. T h e solution was filtered without losing a n y of its properties. Addition of common salt produced a brownish red precipitate, which differed in appearance both from the hydrated dioxide of cerium, produced by conducting chlorine into an alkaline cerous salt and from the hydrated trioxide, produced by the action of ammonia and hydrogen peroxide on a cerous salt. T h e precipitate did not dissolve readily in hydrochloric acid, but dissolved in concentrated sulphuric acid with a yellow color
.
1450
THOJIrlS P . M C C U T C H E G S , J H .
I n this latter respect it resembled tlie dioxide. T h e saiiie precipitate formed on allowing the purple so1utio:i to stand several d:ij-s or 011 C O K tiiiui~igthe electrolysis for about an hour. *A prc.s,\ure of S volts seemed d . appeared to lie most favorable for the forinntioil of this c o i ~ i p o ~ i ~ i It to be 3 derivative of cerium i i i a colloidal condition. ;'r furtlier study of t 11 is co 11 I 1x1LI ti d \vi 11 be m ad e i iii III ed i at e 1 !, . E / L * C ~ ~ofV SC-(cZci2~iii IS ~ - h i o ~ . i d ~.i ~ .uiore careful study was next macle of the behavior of calcium cliloride i n tlie cell. T,ukens found that t h e salt with which we h a d beeii \vorkiiig was coiitainiiiateil with considerable aiiiouilts of magnesium. The calcium w a s purified by a number of precipitations as oxalate. On electrolyzing tlie pure chloride, he found that a part of the calcium appeared in the outer ccJrnpartinent lil-\e strolitiuiii and bariuin. I i e \vas never able to obtain a l l of it. !In inixitig iiingnesiuii~chloride with it agaiii, none of tlie calcitiin appeared outsitie. ITl'ith these facts i n initid, Lukeiis made :i mixture of liariuiii, calcium and magiiesiuiii chlorides aiid was able to completely separzte tlie bariain from the calcium and niagnesium. A determiiiation by the writer gave t h e follon.ing result : 'r,l., , Grains.
Ikiriuiii cliloritle 0.1049 preheiit o.o691 ' I
found
0.0692
I:[\
,
......
,.
.i '5 I FROM C R A S I C X . Grams. VOltS .4mperes
...
Uranium chloride O.IOOO Potassium I' 0.146 j present 0.0768 found 0.0771
3-5
0.077'
... ... ...
0.0766
...
I '
......
0 . j-0.01
...... ...... ......
......
Time. hours
.. .. 3
.. .. .. Time. hours.
.. 2
.. .. ..
..
L i t k i z m from Uranizmz. As lithium chloride had not been previously analyzed in this cell, a solution was made up.and electrolyzed with t h e following results : (:rams.
Lithiiitii chloride o.oS16 '' present o.or4o ' ' found 0.0143 0.0143 o.ori4
I'Olt.5
Ani!>eres
..
.......
5
0.03-0.02
..
.. ..
.......
.......
.......
Time, hoiirs
.. 2
.. .. ..
T h e separation was made as for sodium and potassium from uranium. Grams.
Uranium chloride 0.1000 Lithium chloride 0.0846 " present 0.0140 (' fonnd 0.0143 0.0142
0.0141 0.014r 0.0142
0.0143
Volts
5
.. .. .. .. .. ..
..
..
Amperes 0.03-0.02
Time, hours 2
.......
..
......
..
.......
....... .......
..
..
I453
ELECTRO-ANALYSIS
Barium from Uranium. I n this separation t h e addition of a few drops of hydrochloric acid during the electrolysis was necessary to separate the last traces of barium from the uranium. As under calcium, a slight excess of standard acid was added to the solution in the outer Compartment at the beginning of the experiment to prevent the formation of insoluble barium hydroxide. T h e excess of acid was estimated with standard alkali. Grams.
Volts
Amperes
5
0.15-0.01
..
Uranium chloride 0.1000 Barium chloride 0.1040 " present 0.0685 ' I found 0.06Sj 0.06S8
.. .. ..
0.06S2 0.06S2
..
Strontium f ~ o mUranium
.......
....... .......
Time, hours
.. I
..
.......
.. ..
.......
..
I n this separation strontium bromide was
used. Grams.
Uranium chloride 0.1000 Strontium bromide 0.1456 ' I present 0.0513 " found o.oj13 0.0513 0.0516 O.OjI0
Volts
..
5
.. .. ..
..
...
Amperes
...... ......
Time. hours
...... ......
..
0.4-0.02
......
......
.. 2
.. ..
.. ..
Separation of Barium from Thorium, Cerium, Lanthanum and Neodymium. T h e following separations were macle to further test the applicability of the method. As before, traces of barium were apt to remain with the hydroxide in the inner compartment unless a few drops of hydrochloric acid were added during the electrolysis. BARIUM Grams. 0.1300
Thorium chloride Barium chloride 0.1049 'I present 0.0691 " found 0.0689 0.0691 0.0689
FRON THORIUM. Volts Amperes
..
5
.. ..
..
*.
......
O.J-o.02
...... ......
...... ......
Time, hours
.. 2
.. . I
..
..
BARIUM FROM CERIUM. Grams.
Cerium chloride 0.1000 Barium chloride 0.1040 " present 0.0685 " found 0.0685 0.0684 0.0686
Volts
.. 5 .. .. .. ..
Amperes
...... 0.4-0.02 ...... ......
...... ......
Time, hours
.. 2
.. ..
..
...
T H O M A S P. NCCUTCHEON, J R .
I454
13 .IK I D b l i:KO SI L .ISTHA XUM. YOl!, .ktii;jcre Grains
Lxtithanuni chloride 0 . 0 j O o Barium chloricie 0.1~49 " preseiit 0.069 I '. f0Ulltl 0.069; 0.06S9
.. >
......
I 1,
j4 1 . 0 I
..
......
..
......
..
..
IlARIrlI FROM ~ P : O I > Y X I U X Grniiis Volts A :11 pe 1-e4
Seodytiiiuni chloride 0 . I joo Barium chloride 0 . io49 present 0.069 I " fout1d 0.069; 0.0690 I '
0.~69;
... >
...
..
..
..
..
0. Lj-o. 0I
...... ......
Time, Ilours
..
.. .. .. Time. hours
.. 2
..
.. ..
..
Thallium. T h e similarity of thallium to the alkalies in inally of its behaviors raised the hope that its amalgam would decompose in the outer compartment of the cell. Owing to the itisolubility of thallous chloridc, the sulphate was used iri connection with a lead anode. T h e platinum gauze was plated with lead in a very satisfactory iiianner b y making it the cathode in a bath of hydrofluosilicic acid. T h e anode was a strip of pure lead. When thallous sulphate was electrolyzed in the cell, t h e solution in the outer compartment soon gave a very distinct test for thallium with potassium iodide. While no quantitative results can he given as yet, it is hoped that thallium can be estimated in this way and its separatiori from other metals accomplished. Ammonium Chloride. h solution of ammonium chloride was electrolyzed with a silver anode. A n amalgam was formed in the inner compartment, which swelled up enormously. It was interesting t o note that the surface of t h e mercury in the outer compartment became covered with bubbles aiid the solution showed a strong alkaline reaction, indicating that the nriimonium ;inialgam had passed to the outer compartment like the amalgaiiis of sodium and potassium. Electrolysis of a Mixture of Sodium and Potassium Chlorides. T h e following experirneiits were made to ascertain whether larger amounts of chlorine than formerly used could be estimated with t h e present form of anode. Hildebrarid used a solution of sodium chloride coritaiiiing 0.0708 granis of chlorine. I n these determinations double the amount was estimated with an error of less than 0,OoOjgram. T h e method might be used in the estimation of a mixture of sodium and potassium a s chlorides. T h e mixed chlorides could be weighed, dissoloed in water and electrolyzed. T h e chlorine could be weighed and
1455
ELECTROLYSIS O F HALIDES O F ALKALINE METALS
the combined sodium and potassium titrated in the outer compartment. T h e sodium and potassiutn could be readily calculated from these data, Grams.
Sodium chloride 0. I 166 Potassium chloride 0.1478 Chlorine present 0.1416 ‘I found 0.1420 0.1420 0.141S
0.1420
0.1414
Volts
Amperes
...... ......
.... 3.5-5 .... .... ....
Time, min.
..
45
c.5-0.02
.. ..
...... ......
..
...... ...... ......
.... .... ....
..
..
..
U N I V E R S I T Y OF P E N N S Y L V A N I A .
[COXTRIBUTIOS FROM T H E JOHS
HARRISON LABORATORY O F CHEMISTRY].
THE ELECTROLYSIS OF THE HALIDES OF THE ALKALINE EARTH METALS. BY
HIRAMS. LUKENSA S D E D G A R F. Received August 15, 1907.
SMITIf.
T h e studies made by Hildebrand and more recently by McCutcheon with the form of cell pictured and described’ and in which the rotating silver anode and mercury cathode are employed, led lis to try out certain lines of thought in the same way. For example, it seemed worth the while to learn just what quantities of barium chloride, let us say, could be electrolyzed in the Hildebrand cell and the analyst be sure of the accuracy of the results both with respect to the barium and the associated halogen. I t was very soon found that quantities of barium chloride exceeding 0 . 2 gram could be electrolyzed with satisfaction in the course of from forty to sixty minutes with a current of 0.3 ampere and from 3.5 to 4 volts. T h e anode made 300 revolutions per minute. T h e appended results appear in the order in which they were obtained. Barjuni present in gram.
Barium found 111 g r a m .
0.2277 0.2177 0.2277 0.2277 0.2277 0.2277
0.2276 0.2274 0.2277 0.2278 0.2277 0.2277
Chlorine present i n gram. 0. I IS0 0. I IS0 0.I rso
Chlorine found in gram
0.1180 0.I I 8 0 0.I IS0
0.1177 0.1178 0.1 181 0.I IS0 0. I rso 0.IISI
In t h e electrolysis of strontium bromide, the determination of the bromine was omitted. This halogen adhered firmly to the rotating silver anode to which it attached itself. I t was, however, not weighed. T h e determination of metal alone was made. Strontium present in gram.
Strqntium found i n gram.
0.0727 0.072j 0.0727 0.0727 0.0727
0.0725 0.0727
This Journal,
29, 447.
0.0727 0.0726
0.0726
