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
I456
H I R A M S. L U K E N S A N D EDGAR F. SIIITH
T h e current was of the same strength a s given under barium cliloride. T h e time required was also practically the same. I t was perfectly natural to wish to learn how calcium chloride would conduct itself, although it seemed that it could not fail to behave like its analogues. T o our great surprise the amalgam formed in the inrier compartment did riot diffuse into the outer, larger dish, arid there clecompose, but contrariwise, it decomposed i n tlie inner vessel forrniiig there a mass of hydroxide. Calcium could not be detected in the outer vessel where the alkalies and barium arid strontium appeared as amalganis. decomposed and were determined. Instead of seeliiiig to solve tile mystery of this behavior of tlie calcium amalgatii, a t that tiioment, we decided to study t h e electrolysis of pure iiiagiicsium chloride. Upoil doing this, large quantities of magiiesiuni hydroxide fornied in t h e inner compartment, while not a trace of magnesium could lie detected iii the outer vessel. Perhaps then the presence of niagnesium chloride iii tlii. calcium chloride, wliicli had been electrolyzctl with tlie uiiexpected result of formation of calcium hydroxide in the iiirier clianiber, was iii a measure responsible for this undesired behavior ? Accordingly the calcium chloride, employed in the electrolysis, was examined for, magnesium. I t showed it in abundance. When calciuiii chloride, free from every trace of niagiiesium, was subjected to electrolysis, it behaved like the halides of the alkali metals, aiid like those of barium and strontium, i. c'. , its aiiialgani passed into the outer compartiiient of tlie cell aiid was there decomposed and the calcium hydroxide determined. T h e next step consisted in bringing together knowii amouiits of pure calcium chloride and pure niagnesiuni chloride, aiid subjecting the niixtures to electrolysis. T h e proportions of magiiesinni varied i n amount from one-half to equal that of tlie calcium. The dilution of the solutions was tlie same a s in all previous experiinents. I t never exceeded 30 cc. T h e pressure varied from j.j to 4 volts, while tlie time period did not exteiid beyond an hour. I n all such trials the results were identical. T h e inner cup mas filled with insoluble hydroxide and in t h e outer compartment Iiot a trace of calcium or niagiiesiuiii was detectible. I t seemed possible the]], to restrain t h e calcium by merely adding magnesium chloride to its salt solution uudergoing electrolysis. Could not calcium be separated in this electrolytic way from magnesium ? Evidently not, under the conditions previously outlined. It remained, however, for McCutcheon to show how t h a t separation could be successfully performed. T h a t , however, came later. A t this period of our experimentation the retention of tlie calcium by the niagiiesium suggested very promptly t h e separation of certain other metals froin calcium and magnesium. T h e subjoined records disclose our line of thought.
ELECTROLYSIS OF HALIDES OF ALKALINE METALS
I457
Scparafion of Sodium and Potassium from CaZcium and A4agnesium.A solution containing as chlorides : gram of calcium, " " magnesium, and 0.0474 I ' ' ( sodium, 0.0222
0.0210
was electrolyzed for a period of fifty minutes with a current of 0.25 anipere and 3.5 volts. T h e calcium and magnesium amalgams decomposed in the inner cup with the formation of their hydroxides, while the sodium amalgam sustained a like decomposition in the outer Compartment, where the sodium hydroxide formed was determined by titration with N / I Ohydrochloric acid : Sodium found in grams.
0.0471 0.0474 0.0472
0.0474 0.0476 0.0474
On substituting potassium chloride for sodium chloride in the mixture with calcium and magnesium chlorides, and exposing the same to electrolysis under conditions similar to those just given, the amount of potassium separated and determined was : Potassium present i n gram
Potassium found in gram. 0.0582
0.0580
0.0583
0.0580
O.Oj80
0.0579
o.og80 0.0580
0.0580 0.0580
0.0580 0.0580
T h e alkali metals may, therefore, be readily and accurately separated from calcium and niagnesiutn in the electrolytic wa.y. Se$aration of Barium and Strontizim from Calcium and Magnesium. I n attempting the separation of barium from calcium and magnesium the solution contained the following quantities of the three metals as chlorides : gram of calcium ' ' magnesium 0.045g " barium. 0.0222
0.0210
('
A drop of dilute hydrochloric acid was added to the solution in the inner compartment, and the mixture was then electrolyzed with a current of 0.3 ampere and 3.5 to 4 volts. T h e halogen attached itself firmly to the rotating silver-plated anode, calcium and magnesium amalgams were formed but speedily decomposed in the inner compartment, while the barium amalgam passed to the outer vessel, where it decomposed to hydroxide, which upon titration showed the presence of
E I I K . 1 3 1 S. L U K E X S ANI1 E D G A R 1:.
. . O.UJ.j6
2 . .
graiii of 1)ariuni
. . . . . . . . . . . . ...".04j
