ELECTROLYTIC DETERMINATIONS AND SEPARATIONS
459
nionia, electrolyzed with concordant percentage results. Platinum was constantly sought for but not found. T h e anodes were regularly weighed before and after their use, but showed no loss. Copper was successfully separated from iron-the quantity of the former being twice that of the latter. T h e same occurred when the quantity of iron greatly exceeded that of the copper. U N I V E R S I P Y O F PENNSYLVANIA.
[CONTRIBUTION FROM T H E JOHN
HARRISON LABORATORY O F CHEMISTRY.]
ELECTROLYTIC DETERMINATIONS AND SEPARATIONS WITH THE USE OF A ROTATING ANODE’. BYJULIA LANGNESS. Received January 25, 1907.
T h e following paragraphs contain data obtained by the use of a rotating dish anode in the electrolysis of several metallic salt solutions. Curves accompany the various experiments to show more clearly the progressive deposition of metal. The remarkably short period in which copper, silver, nickel and zinc are precipitated by the use of the dish anode leaves no doubt as to the superiority and advantage of electrolytic methods over ordinary gravimetric procedures. The separations of metals, using the rotating anode, make the rapid methods even more useful. There seems little doubt but that in a short time many of the electrolytic separations now quite satisfactory with stationary electrodes will be further improved by the addition of conditions under which they can be executed with rotating anodes, using increased current and pressure, thereby decreasing the time factor to a minimum. The spiral anode used and described by Exner has been employed in nearly all the work done in this laboratory on the rapid precipitation of metals in the electrolytic way. It was with a view of still further reducing the time element that a new form of anode was devised, following a brief description of which, will be recorded a series of experiments illustrating its advantage over the older forms.
The new anode is a platinum dish of the same genera1 form as the cathode (see Figure I ) . It is about 7 cm. in diameter and 3 cm. deep. Its sides are provided with ten slits perpendicular to the edge, each slit about 1.8 cm. long, and 0.5 cm. wide. These openings, together with a circular opening 1.3 cm. in diameter in the bottom of the dish, insure free circulation of the liquid. ‘From the author’s Ph. D. thesis, 1906.
460
JULIA LANGNESS
It is held in positioii by a stout platinum rod, and is so adjusted that it is equidistant from the sides of the cathode. During the rotation of the anode the liquid is all contained within the space bounded by the cathode and the outer surface of the anode, no liquid remaining within the inner dish. It is, therefore, evident that the dilT.ttion in this case must be inuch less than when the spiral anode is employed. The volunie of the electrolyte shoiild not exceed 6; cubic centimeters.
When properly adjusted there is no splashing of the liquid and consequent loss of the electrolyte, as one might at first suppose there would be, nor is there any danger of incomplete precipitation due to liquid adhering to the inside of the anode, the decanted liquid showing no trace of the metal when subjected to tests.
Determinations of Metals. Copper. A solution of copper sulphate was prepared containing about 0.5035 gram of copper in 25 cc., and a series of determinations were made with the spiral anode (as described by Exner). The most satisfactory conditions for rapid precipitation were found to be as follows :
To 2j cc. of the copper sulphate solution add I cc. of sulphuric acid (dil. I : I O ) , roo cc. of boiling ibater, and electrolyze:
461
ELECTROLYTIC D E T E R M I N A T I O K S A N D SEPARATIOXS
No. I
Volts.
2
3
IO IO
4
IO
10
Amperes.
6-13 5-13 6-13 5-13
Time, mins.
7 7 7 7
w t . of cu. 111 grams.
0.5038
0.5037 0.5034 0.5035
2. 4. 6 . Fr/linutes. T h e perfectly adherent deposits were dark red in color, with a beautiful velvety appearance.
Observing the above conditions the following time curve, ( Curr,c,, I ) was deterniined : ?Vt. of cu ,~. T'olts.
Anipere.;.
10
j.6 5.6 5.6 j.6 5.6
I0 10
IO
IO
1 iiiie,
111
riiii~~.
grams.
I
u.I493
2
0.3019
3 4 5
0.4925
0.4371 0.5029
Using the dish anode, with the same electrolyte, and diluting to about Co cc., these results were obtained : SO.
I 2
3
4 5
Cu present i n grams.
0.4884 0.4884 0.4884 0.4884 0.4884
Volts.
Aniperes.
7 i 8
10-15
Tiiiie,
mins.
y t . of c u i i i grams.
10-16
4 3
S
10-16
5
8 8
IO
2
0.4883 0.4884 0.4887 0.4634
10
I
0.2010
l h e character of the deposit was the same as when the spiral was used. Curve I 1 is constructed from these results. II-heii the spiral anode was used and nitric acid added as electrolyte, the best results obtained were those in which cc. of the acid was added to 2j cc. of the copper sulphate solution, and the liquid diluted to 12j cc. \\-ith boiling water, (2j cc. of the solution contained about 0.4876 gram of copper). Brilliant, crystalline, adherent deposits were obtained. SO. I
2
3 4
Volt%.
8 S
S
S
~iiipet-c,.
'Time,
of cu in grams.
wt. iiiiii+
/
15
7 S S
I5
0.48jS 0.4877
'5
0.4s;~
10
0.48;s
Thc following time curve determinations show that ten minutes are required for complete precipitation. T"
Volt5
I
S S
3 4
S S
..
I ime,
\vt of iiiiiis
Cll
i n gi-anib.
7- 8
I
0.1507
2
0.251s
7-i
3 4 4 6
0.3418 0.3960 0.4486 0.4654
S
04
1
7-1 I
S S
7-12
S
I
j-lu
7 - I I .
IO
w
0 4875
111 for graphic represeiitation Using the dish anode with the same electrolyte, the deposition of 0.4817 gram of copper \\-as complete in six minutes, with a pressure of S volts ant1 16 amperes.
463
ELECTROLYTIC D E T E R M I X A T I O K S A X D SEP.lRATIOSS
When 25 cc. of copper sulphate solution, containing 0.4967 gram of copper, to which was added 1.2 grams of ammonium nitrate and 25 cc. of ammonia, were diluted to 125 cc., heated to boiling, and electrolyzed, complete precipitation, using the spiral anode, required about fifteen minutes, as per table below and Curce I V .
Copper-
No. I 2
3 4
5 6
7 8
Volts.
8 8 8 8 8 8 8 8
Curves
Amperes.
9 9 9 9 9 9 9 9
a n d 11p.
Time, mills. I 2
3 4 5 7 IO
I5
W t of CII i n gramb
0.1508 0.2520 0.3455 0.4023 0.4422
0.4802 0.4914 0.4963
464
J GLIA IANGNESS
'I'lie deposits
ere bright and adherent.
ii-ith the same electrolyte 0.4824 gram of copper was deposited in six minutes with six volts and a current of 17 amperes, using the 11ciii'anode. The dish anocle was also employed in depositing copper from a cyanide 50111tiOtl. A slight excess of potassiwn cyanide was added above that required to precipitate the copper and redissolve the precipitate. To that solution were added I O cc. of ammonia, and i n six minutes, using 7 volts and 15 amperes, 0.4883 gram of copper was deposited in a beautiful burni.shed form.
Silver. Silver gave the most satisfactory results. The silver from a nitrate solution was precipitated and redissolved in potassium cyanide, and an excess of two grams of potassium cyanide added in each determination, the solution diluted as usual, heated almost to boiling, and electrolyzed. The following table and corresponding curve (Xo. V ) show results obtained by the use of the spiral anode. so.
\.olts
Amperes
I
5
2
5 5
2.8 2.8 2.9 2.8
3
4
5 6 7
5 5 5 5
2,s
'Time, mins.
0.2046 0,3391 0.48j8 0.5043
I 2
3 4
2.8
5 7
2.8
I0
Wt. of Ag i n grams.
0.522j
0.5270 0 . 5301
The precipitation was complete in ten minutes. The deposits were chalk-white, and spongy in the bottom of the dish, but adherent. IYith the nee!' anode, using a portion of the same solution, ant1 atltliiig three grams of potassium cyanide, the 0.53 gram of silver was ,lepositetl in two minutes, all but a very small quantity of which was precipitated during the first minute. See Ciirete V I constructed from the results which follow : Tiiiie,
tvt. of 4 R
SO.
l-olti:
Ampere.;.
1
3
10
4
0,5304
2
5
6
1
0.5306
3
3
8
3
4
7
9
2
0.5306 0.5301
3
5
9
I
0.5116
iiiiiis.
iii grams
?'lie grc;it differences in current strength in the above series are due iiiainl!. to the variation in distance betiveen the electrodes, a small decrease i:i c!iitancc causing a large rise of the curreiit. the pressure being kept i'i
ll~S!~~Ilt.
ELECTROLYTIC IJETERMISATIOSS A N D SEP.1RA’TIOSS
Silver-
2. 4. G .
g.
10.
NI i n a t es. Nickel. A few determinations of nickel from a solution containing ammonium sulphate show that half a gram of that metal may be precipitated in five minutes using the dish anode. To 25 cc. of the nickel solution, containing 0.5004 gram of the metal, were added 3 grams of ammonium sulphate dissolved in water and 20 cc.
466
J U L I A LPiNGNESS
of ammonia, the solution then diluted to 60 cc. and heated almost to boil1ng. KO.
Amperes.
.1line. mills.
wt. of h-i
Volts.
6 6. j
11-16
6
0. 5005
11-14
3
O.
