APRIL 15, 1938
ANALYTICAL EDITIOK
20 1
The consistencies of the six saturants were as folloivs:
TABLEI. WIDTHOF RING Saturant
Penetration
Saturant
Penetration
HI H2 H3
30
S1 82 d3
150-175 150-175 150-175
R .? 40
O n Coating -1 Saturant
After 1 day
Mm.
The picture- at the top of Figuie 2 shoa- the two panels before they were placed in the oven. The second set, immediately below. shows their condition after exposure for one day a t 110" F.; the third and fourth sets, after 3 and 6 days' exposure, respectively. It will be observed that no discolored ring was formed on either coating around saturant H1. However, saturants H3, P2, and S3 developed rings on both coatings, while saturants H2 and S1 developed rings on coating B but not on coating A . The rings widen with time to a definite maximum, and when the test is conducted at 110' F. they are of sub-tantially maximum width a t the end of 3 days. The average width of ring for each of the twelve combination. illu~tratedin Figure 2 is given in Table I.
Hard
H1
Soft
H3 dl 92 63
Hi
0 0 0 0 0 1: 0 0 0.25 0.9
.Liter After 3 days 6 days Mm. .Mm. 0 0 0 0 0 25 0.0 0 7 1 3
0 0 0 0 0 3 0.0 0.: 1
,
On After 1 day Mm 0 0 025 1 2
0.73 1.8 2.6
Coating E 4fter After 3 days 6 d a y s
Mm.
Mm.
0 0 035 2 0 1.0 2.9 2
0 0 065 2 2 1.0
,
3.4 5 0
Several years of practical experience with the exudation test have led to the conclusion that while it is safest practice to use only saturants and coatings t h a t show no ring whatever in that test, no visible bleeding n-ill occur in roofings made with a saturant and coating that in the standard exudation test a t 110" F. develop a ring not wider than 0.5 mm. I~ICEITED J a n u a r i 12 1038
Internal Electrolysis without Diaphragms Determination of Small Amounts of Nickel, Cobalt, and Copper in Ores Poor in These Metals J. J . LISRIE
AND
L. B. GINSBURG
Institute of Nonferrous ICletals, Moscow 17, c'. S. S . R.
T
HE authors ( 7 ) have slion-n the advantages of internal
electrolysis over external electrolysis in the determination of small amounts of metals, and have pointed out that a very simple apparatus without diaphragm may be substitut'ed for the complicated apparatus. proposed by a number of author; (1, 2, 4, 6, 11, 12), ~ i t h o u timpairing t'he accuracy of the analysis (6, 9, 10). I n addition (1) having selected a suitable anode, we obtaiii a definite potential difference not exceeded a t any moment during the course of the electrolysis but very slowly and gradually diminishing by 0.1 to 0.2 volt. Therefore by internal electrolysis it is possible to make separations which by external electrolysis require a constant' control of the cathode potential and a suitable apparatus. (2) The chief oxidizing process occurring a t the anode is the dissolution of the anode with the formation of the corresponding ions of this metal in the solution. This eliminates many difficulties of electrolysis due to the oxidation a t the anode of a number of ions to their higher valency states. We are therefore justified in hoping that small amounts of nickel and cobalt may be separated from large quantities of iron and from chromium by this method. This was the chief purpose of the present vork.
0.44 volt) would indicate that nickel and cobalt would be deposited on the platinum cathode, if the anode were an iroii plate. The potential difference. 0.19 x-olt. is sufficient for such a deposition. However, because of the very small overvoltage of hydrogen on nickel and cobalt. these nietals cannot be deposited by electrolgsib in an acid medium, TI-liilein ammoniacal solutions they form complex ions, as a result of which their potentials are shifted and hecome more negative than in an acid medium.
-4pparatus The apparatus for internal hydrolysis used by the authors is shown in Figure 1 (and in Figure 1 of an earlier article, 7 ) . The cathode is a Fischer's platinum gauze; the anode is a metallic plate of iron, zinc, or aluminum, depending on the metal to be yecipitated and on the conditions of precipitation. To secure a ull contact, the electrodes are firmly held together by a copper or aluminum clamp, which replaces the copper wire formerly used ( 7 ) and somewhat simplifies manipulations. The places of contact must a1way.c he well cleaned n-ith emery paper before proceeding to work. Determination of Nickel and Cobalt The normal potentials (E,) of nickel, cobalt, and iron (Em, s,+-, 0.25 volt; Eco;co --, 0.255 \rolt: E p e , pB- + ,
FIGURE1
IZDI STRIAL ASD ESGINEERISG CHEMISTRY
202
The authors failed to separate nickel and
VOL. 10, NO 4
nickel by the precipitate affects the res u l t s of determination.
o 6,
DE~LHUIXATIOX IN P R E S E N COEF IROS.To eliminate THE
the influence of iron, the authors have tried combining i t 0 53with stable complex The attempt to de052 c o m p o u n d s by the posit nickel or cobalt 051. action of pyrophoson the cathode, using 50. phate, tal taric acid, cadmium and cliro049, oxalic acid, potassium mium plates in a 0 5 IO 15 20 25 30 35 40 Minutes cyanide, and sodium feebly acid and an FIGURE 2 fluoride. ammoniacal medium, The first three, as was also unsiiccessful, evidently because of an insufficient shown by numerous experiments, do not give complexes stable potential difference. L-sing a zinc anode, the t n o metals under the conditions and do not prevent the deposition of iron ere fully on the cathode. - deDosited. V i t h potassium cyanide, iron, nickel, and cobalt form such To a solution containing a definite amount of nickel and cobalt stable complexes that they are not deposited from the solusulfates, 10 grams of ammonium sulfate and 15 ml. of concention. The only complex-former yielding good results has trated ammonia were added, the solution was diluted to 150 to 200 ml. and heated to TO" C., and bound electrodes (Pt-Zn) were been found to be sodium fluoride, combining v i t h ferric iron placed in the solution. The electromotive force of this cell deto form a stable complex FeF6--- and exercising no influence termined by the compensation method at the beginning was found upon nickel and cobalt salts. to be equal to 0.60 t o 0.58 volt. After 30 t o 35 minutes (Figure 2) it gradually falls t o 0.50 volt, and then remains constant. To a solution containing nickel and ferric salts, acidified with Nickel and cobalt, are deposited quantitatively during this time. sulfuric or acetic acid, 2 grams of eodium sulfate or acetate were A test for the completeness of deposition, made by adding sodium added (to increase the electric conductivity of the solution); sulfide t o the electrolyte after the electrolysis, ahoived no t,racee the solution TYas diluted with water to 100 ml., and 50 to 60 ml. of nickel and cobalt. of a sodium fluoride solution saturated in the cold n-ere added. Then 2 t o 3 drops of phenolphthalein and ammonia were added TABLEI. DETERhIINATION O F NICKELAND COBALT FRON until a pink coloration appeared (a large excess of ammonia S O L ~ T I OOFN S THEIRSULFATES should be avoided as it diminishes the stability of the complex ferric fluoride). The solution was diluted to 200 ml., the elecFound --IntroducedKickel + trodes (Pt-Zn) were placed in it, and it was subjected to internal KO. Sichel Cobalt cobalt Xickel Cobalt electrolysis for 35 to 40 minutes. 7
Gram
1
9
10
11 12 13 14
15 16 17
18
0,002i 0.0027 0,002; 0.0027 0.0054 0.0060 0.0081 0.0107
....
0,0025 0.0025 0.0023 0.0025 0,0025 0,0025 0,002.5 0.0025 0.002i
Gram
Grom
Grank
0 0027 0 0028
n
onzfi
o on28
0 0054 0 0060 0 00i4 0.0083
.... 0,0025 0.0003 0.0003 0.00055 0,00055 0.0011 0.0011 0.001i 0.001i 0,0025
0:0030 0 0019 0.0031 0 0031 0 0030 0 003i 0 0042 0 0043 0 0052
.
,.
0.0027 0.0026 0,0026 0,0026 0,002: 0,0026 0,0025 0.0026 0.0027
Gram
.... ,... .... .. . ..., 0.0026 0.0003 0.0003 0 0005 0.0005 0.0011 0.0011 0,0017 0 .0 0 l i
0.0029
Nos. 7 a n d 8. Cementation on tlie anode. Nos. 9 t o 18. Cobalt determlned i n the deposit colorimetiica113, nickel, by difference.
Figure 3 shows that the potential difference a t the beginning is equal t o 0.57 to 0.60 volt, then it gradually diminishes, and after 35 to 40 minutes stops a t 0.42 volt. At this point no nickel is detected in the solution. The nickel deposited on the cathode has a dark color, and the results, as shown by Table 11,are too high, owing to the coprecipitat'ionoffluorides. OF NICKELIS THE PRESEUCE OF IRON TABLE11. DEPOSITIOX ASD FLUORIDES
Sn. 1
2 3
Table I indicates that in tlie absence of other metals nickel and cobalt are completely deposited on the cathode when present in amounts not exceeding 6 to 7 mg. A number of experiments (including iios. 7 and 8) have helped to establish that larger quantities of nickel and cobalt begin cementation on the zinc anode, leading to results that are too low. However, an active metal like zinc as the anode furnishes conditions suitable for the deposition of all the metals nobler than zinc, if present in the solution. I n the ores under investigation, only copper, chromium, and iron were present. Less than 3 per cent of iron does not interfere with the electrolytic deposition of nickel and cobalt, since under the conditions of the electrolysis i t is present in the form of a small precipitate of hydroxide, not decomposed by the current. With an iron content of over 3 per cent, the precipitate of hydroxide is so bulky that the adsorption of cobalt and
,--IntroducedSichel Gram
Iron Gram
0.002i 0.002i 0 002i
0.15
0.15 0.13
--Sickel i f t e r first deposition Gram
FoundAfter second deposition Gram
0,003'1
0 0026 0.0028 0,0026
0 0042
0.0047
To secure good results, the authors dissolved the deposit of nickel and redeposited it. The connected electrodes were removed from the electrolyte bath, washed with distilled water (by dipping for some seconds in a glass of water), then disconnected; the deposit of nickel was dissolved by immersing the cathode in a glass containing 20 ml. of sulfuric acid (1 t o 4), and the clean cathode was washed with hot water over the glass. After adding an excess of 10 to 15 ml. of ammonia, and diluting the solution to 150 to 200 ml., it was again subjected to electrolysis for 35 t o 40 minutes at 70" C. When deposition was complete, the electrodes were removed, washed vith water, and disconnected, and the cathode was washed with alcohol and dried at 80" t o 90" C .
As shown by the last column in Table 11,the results of the second deposition are satisfactory. I n Table I11 are compiled the results of nickel and cobalt determinations in the presence of iron under the conditions specified above.
.kNALYTIChL EDITIOK
APRIL 1.5, 1938
OF SICKEL AXD COBALT IN TABLE111. DETERMINATIOS PRESENCE OF LARGEAMOTXTSOF IRON
THE
(Cobalt in the deposit b a s determined colorimetricall>-;nickel, b y diffeience' Found --Introduced----Sickel So. Nickel Cobalt Iron cobalt Sickel Cobalt Gram Grain Gram Gram Gram Gram 0 0025 0.00012 0.00013 0.15 0.0026 1 0.0025 0 0003 0.15 o . o m 0 0025 2 0.0025 0.0003 0.0025 o.ooo.5 0.15 0.0080 3 0.0025 0 0005 0 0005 0.0030 0.0023 0 0005 0.15 4 0.0025 5 o.oo2j o.ooii 0.15 0 . 0 0 3 ~ 0.002.; 0 noli 6 0.0021 ... 0.15 0,0020 0.0020 0.0016 .... 0.15 0.0017 0.0017 7 8 0.0011 . . . 0.15 0.0011 0.0011 9 0.0006 ... 0.15 0 0006 0.000ii
+
To determine copper in ores by internal electrolysis (7), copper was deposited in an acetic acid solution in the presence of hydrazine (to eliminate the disturbing influence of ferric ions), using a lead plate as the anode. The method could not be applied without modification, since lead, passing to solution from the anode plate during the dc>termination of copper, would interfere with a further determination of cobalt and nickel, being deposited on the cathode with these metals. Volts
0,58jT 0.56
CHROMIUM No.
1 2 3
Sickel Found Gram
Oh..er vati,iri-
0.0027 0,0027 0.0027
0 0023 0.0020 0 0000
Xickel deposited in 1 hour Xickel deposited in 1 hour S o nickel a t all deposited
0 0034 0 0037 0 0079
D E T E R M I N A T I O N I N THE PRESEXCE O F CHRO.\IIUM
1
I
OF NICKELIS THE PRESESCE OF TABLE IV. DEPOBITIOS
--Introdured-Nickel Chromium Gram Grtzm
203
(AND
LARGEQCAKTITIESOF IROS). Since in many poor nickel ores the chromium content is only about 0.3 to 0.5 per cent, the authors had to study nickel and cobalt deposition by internal electrolysis in the presence of chromium. The experiments n-ere made with salts of tri- and hexavalent chromium, and helped to establish t'he fact that chromium is not deposited on the cathode, but that when present in small amounts i t retards the deposition of nickel and cobalt and in large amounts prevents deposition. The authors succeeded in eliminating the influence of chromium, oxidizing it, and precipitating i t by salts of barium (acetate or chloride) under the following conditions :
T o a solution containing salts of nickel, ferric iron, and hexavalent chromium, 5 ml. of acetic acid, 2 grams of sodium acetate (for greater electric conductivity of the solution), and 2 to 3 ml. of a 10 per cent solution of barium chloride were added (five times the quantity theoretically required for precipitation). The solution was allowed to stand for 5 to 10 minutes for a better separation of barium chromate; and without filtering off the precipitate 50 to 60 ml. of a saturated sodium fluoride solution were added; the solution !vas neutralized with ammonia by means of phenolphthalein, diluted t o 150 t o 200 ml. with water, heated to 70" C., and subjected to internal electrolysis as described above with a redeposition of nickel and cobalt from the amnioniacal sulfate solution.
TABLEv.
DETERMISATION OF S I C K E L AXD COBALT I N THE PRESENCE O F CHRORIICM AND L.4RGE QUAXTITIES O F IRON
--
,Cobalt i n the deposit was determined colorimetrically; nickel b y differencri FoundIntroducedSickel So. Nickel Cobalt Iron Chromium cobalt Sickel Cobalt Gram Gram Gram Gam Gram Gram Gram 7 -
1
2
3 4 5 6 7 8 0 10 11 12 13 14 15
0.0005 0.0010
o.noi.;
0 .0 0 % i 0.0027 0 002i 0.0027
0.002i 0.0023 n.0025 0 0025 0,0023 0.0025 0,0023 0,0025
0.10 . . . . 0.10 . . . , 0.10 ,... 0.10 . . . . 0.10 . . . . 0.10 .. 0.10 . . . . 0.10 0.10 0'0003 0.10 0 0003 0 . 1 0 0 .n o n j 0 . 1 0 0.0005 0.10 0 . 000j 0 . 1 0 0.0003 0.10 ...,
0.009 0.009 n ,009 0.006 0.009 0.015 0.015 0.030 0.009 0.009 0.009 0.009 0.009 0.009 0.009
+
0 0005 0.0010 0 , 0014 0 0026 0 0026 0,0026 0,0027 0 0028 0.0023 0.0030 0.0030 0,0030 0 0030 0 0031 0 0030
0.0005
, . . . , . . .
0 0010 0 0014 ,. .... 0.0026 0.0026 ,... 0.0026 ... 0.002i 0,0028 .. . 0.0025 0.00?3 0 000: 0.0026 0 . 0 0 0 4 0 0026 0 , 0 0 0 4 0.0OY6 0 . 0 0 0 4 0.0026 0 , 0 0 0 3 0,0026 0.0004
:
The results given in Table V indicate that the method is satisfactory for ores of the usual chromium content.
Determination of Copper The third metal interfering with the deposition of nickel and cobalt by internal electrolysis is copper.
FIGURE 3
To overcome this difficulty the authors investigated two possibilities: (1) deposition of copper from an acid solution using a zinc plate as the anode and employing sodium fluoride to eliminate the influence of ferric iron, and (2) deposition of copper from a n acid solution with the aid of an iron anode. The first modification seemed especially attractive, as no new foreign metals mere introduced into the solution, and before determining nickel and cobalt only a neutralization. of the solution with ammonia was necessary. h number of experiments were carried out with solutions of salts of copper, nickel, and iron in an acetic acid and a feebly sulfuric acid medium (Table 'VI). TABLEVI.
DETERMISATIOh- O F COPPER I S THE PRESENCE O F i\jICKEL, COBaLT, AND IRON WITH A %INC ANODE, I N AN ACID &lEDIG&f ~J.olumegf solution, 200 m!. N o s . 1 t o 4 , 10 ini. of free acetic acid. XOS. 5 a n d 6, 10 drops of 1 to 1 free sulfuric acid) Copper Found After After 7 Introduced first second So. Copper Nickel Cobalt Iron deposition deposition Gram Gram Gram Gram Grain Gram
-
0 0026
0.0003 0.0005 0.0005 0 0003 0,0005
0.10 0.10 0 10 0.10 0 10
0.0026
0.0003
0.10
2 3 4
0 0026 0.0026 0 0026
5
0.0145 0.0145 0.0143 0,014.5 0.0145
6
0.0145
1
0,0026
0.0170 0 0163 0 0163 0 0163 S o t deterinined S o t det ermi lied
0.0139 0.0140 0.0144 0.0139 0 0139 0.0140
In all cases the copper first deposited was of a dark color, and its weight was too high. After dissolving the deposit from the cathode in dilute nitric acid and redcposition with the lead anode, the results in the majority of cases were too lov-. I n the electrolyte after the second deposition considerable amounts of nickel were detected. In addition, the zinc anode during the first deposition was coated &-it11a marked layer of copper, which seems to account for the too low ultimate results obtained for copper. Thus, the first modification proveid unsuccessful for the following reasons: (1) because of the large difference between , -- the copper is to a the potentials E z n , z n - + and E c ~cU considerable extent cemented on the anode; (2) in the
INDUSTRIAL AKD ENGINEERIKG CHEMISTRY
204
presence of copper, nickel is partly deposited with it, in spite of the relatively high acidity of the solution, as the overvoltage of hydrogen on the surface of copper plus nickel is obviously greater than that on the surface of pure nickel. To study the conditions of deposition of copper by the iron cathode (the second modification), a number of experiments were made in an acetic and a sulfuric acid solution (Table VII). TABLEVII. DEPOSITION OF COPPER BY -Introduced----Xo. Copper Nickel Gram Gram 1 0.0145 0 0025 0.0143 0.0025 0.0148 0,0025 4 0.0146 0 . 0 0 2 3 5 0.0145 0,0025 6 0.0145 0.0025 7 0.0145 0.0023 8 0.0145 0.0025 9 0.0145 0,0025 10 0.0145 0,0025 11 0.0143 0,0025 12 0.0145 0.0025 13 0.0146 0,0025
2 3
1 4 0.0145 15 16 17 18 19 20
0.0145 0.0145 0.0145 0.0145 0.0145 0.0143
0,0023 0.0023 0.0025 0 0025 0 0025 0.0023 0.0025
THE
IRON ANODE
(Volume of solution, 200 ml ) -Copper FoundAfter Erst After second Conditions Iron deposition deposition of Deposition Gram Gram Gram I n Acetic 4cid Solution . . 0.0132 . . 0.0132 . . )80, acetic acid, 4 ml. . . 0 0134 0.0130 i 0.0144 SO%acetic acid, 6 to 10 mi. 0.1044 o.io 0.0150 0.0132 0 . 1 0 0.0158 0,0136 Iron combined by sodium 0 , 1 0 0.0156 0.0132 fluoride: 80% acetic 0.0140 acid, 10 nil. 0 , 1 0 0.0158 0 . 1 0 0.0156 0 0132 0.10 0 . 1 4 6 . , , , 80% acetic acid, 10 ml. 0.10 0.144 . . . F e + + reduced by hydrazine I n Sulfuric A cid Solution .. 0 0143 H ? S O I ( l : l ) ,2 drops 0 0144 HzSOd (I::), 3 drops o:io 0 0137 ) Iron combined with N a F : 0.10 0 0136 H:SOi (+:I), 3,drops Iron combined with N a F ; 0.10 0 0143 0.10 0 0144 H9so;( i : i ) .2 t o 4 mi. 0.10 0.0144 ' I r o n reduced ' b y hydrazine
'' : '
::: }
i }
+,
I
I n a feebly acetic acid solution (experiments 1 to 4) copper is not entirely deposited. Good results are obtained only with an acidity of 6 to 10 ml. of 80 per cent acetic acid to 200 ml. of solution (experiments 5 and 6). T o eliminate the influence of ferric ions, combination Tvith fluoride or reduction by hydrazine mas used. I n the first case the copper deposited was black, and the results obtained were too high (experiments 7 to 11). I n these cases repeated depositions led to results that were too l o x , as in the fir?t modification. Klien Fe-++ was reduced by hydrazine, the results were satisfactory (experiments 12 and 13); the color of the deposit was pink. In a feebly sulfuric solution, in the absence of iron, copper is deposited quantitatively (experiments 14 and l5), an acidity of 2 to 3 drops of sulfuric acid (1 to 1) in 200 nil. being sufficient. Satisfactory results are obtained in this medium also in the presence of iron, if the latter has been reduced by hydrazine (experiment 20). Iron may also be combined with sodium fluoride, but in this case the acidity should be raised to 2 to 4 ml. of sulfuric acid (1 to 1) in 200 ml. (experiments 18 and 19).
VOL. 10, NO. 4
excess of hydrazine and ferrous iron ions should be oxidized. If hydrazine is not used, and iron has been combined with fluoride, an additional oxidation is still necessary, since the solution contains ferrous iron, due to the dissolution of the iron anode. The oxidation was brought about by means of bromine, the excess of which was eliminated by boiling. Then the solution was cooled, sodium fluoride (a saturated solution) or solid ammonium fluoride was added, and nickel and cobalt were determined under conditions described above. The results are given in Table VIII, which shows that copper, nickel, and cobalt are deposited quantitatively. The method is very accurate] but the oxidat,ion of hydrazine, if used, proved slow. As in internal electrolysis, previous to the deposition of copper, a reduction of ferric iron occurs in the solution a t the expense of the current itself [at' the cathode, 2 Fe+++ 2 e +. 2 Fe+-; at' the anode, Fe (from the anode) - 2 e -t Fe+'], the authors decided to try depositing copper in the presence of iron without any other reducing agents by increasing the time of electrolysis and by a greater dissolution of the anode. I n the presence of less than 0.1 gram of iron, such a method has given good results. With a higher iron content considerable cementation of copper on the anode occurs because of the excessive time of electrolysis.
+
+4luminumAnode Although aluminum has a very negative normal oxidation potential] Eo = -1.34, an aluminum anode in internal electrolysis behaves like an iron anode : without depositing nickel and cobalt, it deposits copper very well. Aluminum does not increase the content of ferrous ions in the solution, to be later oxidized, and its solubilit'y in a 1 per cent acid is less than that of iron. During electrolysis, aluminum dissolves t,o a very small extent, which diminishes the consumption of fluorides for combining iron and aluminum before the nickel and cobalt determination. The cementation of copper on aluminum is exceedingly small: on a smooth polished aluminum surface it has not been observed a t all; on a rough surface, i t is negligible. As a result of these investigations, the authors have developed the following procedure for analysis of ores containing small amounts of copper, nickel, and cobalt.
Procedure
I n tlie absence of chroniiuin or when it is present in quantit,ies less than 3 mg., the procedure is as follow: DETERilISATION OF COPPER. The ore sample, 0.5 or 1 gram, depending on the nickel content (the amount of nickel in the sample should not exceed 6 mg.), is treated with 10 ml. of hydrochloric acid (d = 1.19), then with TABLE F'III. DETER~IINATIOS O F COPPER, NICKEL, AND COBllLT 5 ml. of nitric acid (d = 1.4); 5 t o 6 ml. of sulIN THE PREsEXCE OF LARGE AhfoUNTs O F IROS furic acid (1 to 1) are added, and the whole is (Xos. 1 t o 3 iron reduced bp hydrazine: nos. 4 t o 7 iron combined with fluoride. Cobalt evaporated in a dish t o fumes of sulfuric acid. determined colorimetrically by the method of Lurie and TroitzkajA (3); nickel, b y To the slightly cooled residue 20 to 30 ml. of difference) \mter are added, and the mixture is boiled t o disConditions of DepobitIntroduced ___ --Found--No. Coppei Sickel Cobalt Iron Copper Sickel Cobalt ing Copper solve salts. Then the solutjon is neutralized with Gram Gram Gram Gram Gram Gram Gram ammonia to the first appearance of a permanent 1 0.0145 0 0023 0.0003 0 10 0 0144 0.0026 0 0003 aceticacid precipitate of ferric hydroxide, which is dissolved with a few drops of dilute (1 to 1) sulfuric acid, 2 0.0145 0 0023 0 0003 0 10 0 0143 0 . 0 0 2 4 0.0004]'% 3 0 . 0 1 4 5 0 . 0 0 2 5 0.005 0 10 0 0144 0.0020 0.0003 HlSO.1 ( l : l ) ,5 drop, t o an excess of 4 ml, being added, The contents of 200 ml. the dish are transferred to a 400-ml. beaker, di4 0 . 0 1 ~0 0026 o 0003 n 10 0 0129 0 . 0 0 2 0 0 0004' luted with hot water to 200 ml.9 and heated t o 5 0.0129 0 . 0 0 2 ~ 0 . 0 0 0 3 0 10 o 0 1 2 ~ 0.00zz 0 0003 H?SO, (1:1), 4 n!l. t o 6 0,0129 0.0026 0.0003 0 . 1 0 0 0 1 2 ~ O . O O ~ G 0.0004 200 mi. of solution 60" to 70" C. (If the iron content exceeds 0.1 i 0.0129 0.0026 0.0003 0 10 0 O l ? Y 0.00'26 0.0005 gram, it is reduced by adding 1 gram of hydrazine.) After placing the connected electrodes (Figure 1) in the soluThus> the authors hare Obtained "" lnethods for the cathode and an iron or tion Lvitha previously n-eighed deposition of copper by internal electrolysis with an iron anode aluminum plate serving as the anode, electrolysis is carried on for in the m-esence of nickel (cobalt')and iron: in a 4 to 5 Der cent 30 minutes at 60" to 70' C. Then 10 to 20 ml. of water are added and the electiolysis is continued for 10 mmutes more. When acetic acid solution in the Dresence of hvdrazine. and in a dePosltlon 1s complete (the Part of the electrode covered 1 per cent sulfuric acid solition in the presence df fluorides again with the liquid should remain pure), the electrodes are or hydrazine. After the deposition of copper and before the removed from the beaker, Jvashed over the beaker with a jet determination of nickel and cobalt in the electrolyte] the of water from a nashing bottle, and diwonnected; the cathode 7 -
APRIL 15, 1938
ANALYTICAL EDITION
is washed with alcohol, dried for 5 minutes a t 80" to 90" C., and weighed. The difference in the weight of the cathode shows the copper content of the sample. DETERMINATION OF NICKEL AND COBALT. After the deposition of copper, bromine is added to the electrolyte until the solution is brown; the solution is then boiled t o remove the excess of bromine and to reduce the volume of the solution to 100 ml. After cooling the solution slightly, 50 to 60 ml. of a sodium fluoride solution saturated in the cold (about 4 per cent) are added, 2 to 3 drops of phenolphthalein are then added, and the solution is neutralized with ammonia until a pink coloration develops (a brown precipitate where the first drops of ammonia fall is evidence of insufficient sodium fluoride; in such a case a little more sodium fluoride solution is added). The solution is heated to 70" C., the electrodes are placed in it (the cathode being a platinum gauze, and the anode a zinc plate), and the solution is subjected to electrolysis for 30 to 35 minutes (the completeness of deposition is tested by adding water). If the bromine has been poorly removed, the deposition of nickel and cobalt may be somewhat retarded, and 0.2 to 0.3 gram of sodium sulfite should be added to the solution. After nickel and cobalt have been completely deposited, the electrodes are removed, washed by dipping in a beaker of distilled water, and disconnected, and the cathode is dipped in a beaker containing 20 ml. of sulfuric acid (1 to 4). When t'he deposit is dissolved, the cathode is taken out and washed with hot water over the beaker. To the solution 10 to 15 ml. excess of concent,rated ammonia are added and the solution is diluted to 150 to 200 ml. and heated t o 70" C. The electrodes (Pt-Zn) are connected again, the cathode having been previously weighed, and placed in the solution, which is subjected to electrolysis for 35 to 40 minut,es. When deposition is complete, the electrodes are removed and disconnected, and the cathode is washed with alcohol, dried for 5 minutes at 90" to 100" C., and weighed. The increase in the weight of the cathode s h o w the sum of nickel plus cobalt,. COLORIMETRIC DETERMIXATION OF COBALT (8). The deposit on the cathode is dissolved in 20 ml. of nitric acid (1 to 1). The cathode is washed with hot water over the beaker, and the solution is evaporated to dryness. The evaporation is repeated once more, after adding 10 ml. of hydrochloric acid; the residue is drenched with 1 to 2 ml. of hydrochloric acid (1 to 1) and diluted with a few milliliters of hot water. To the solution, which should have a volume of about 10 ml., a few crystals of ammonium thiocyanate and a little sodium sulfite are added. It is heated (at 70" to 80" C.) until green (the color of a nickel salt). Upon cooling, 1 gram of sodium pyrophosphate, 1 to 2 drops of phenolphthalein, and dilute (12 per cent) ammonia are added, the latter being introduced in drops, until the color of the solution has changed to pink. Then 5 grams of ammonium thiocyanate are added (the pink coloration disappears), the solution is diluted to 15 ml., and thoroughly shaken; 15 ml. of pure acetone and 1 to 2 drops of dilute ammonia are added, and the whole is vigorously stirred for 1 to 2 minutes. The solution is allowed to stand for 2 to 3 minutes and poured into an Eggerz test tube. T o another test tube the same reagents are introduced in the same quantity, and a standard cobalt chloride solution is added from a buret until the color, after stirring, matches that of the test solution. From the number of milliliters of the standard solution of cobalt salt added, the cobalt content of the sample is calculated. The nickel content of the sample is calculated by deducting the cobalt content found from the sum of nickel plus cobalt, obtained by internal electrolysis.
205
ducing excessive SO4ions to the solution.) After this, 30 per cent barium chloride solution is added until barium sulfate is completely precipitated. The precipitate is filtered off through a filtering crucible with suction and washed with a small amount of hot water. The fltrate is evaporated down to a volume of 100 ml., cooled, neutralized with ammonia, and acidified with acetic acid (an excess of 3 t o 5 ml. of 80 per cent acetic acid). T o make sure precipitation of barium chromate is complete, 1 to 2 ml. more of barium chloride are added; the mixture is allowed to stand for 10 minutes, and without filtering off the precipitate a sodium fluoride solution is added. The further procedure is similar to that in the absence of chromium. The method has been verified on two samples of ore (Table IX)* The results obtained precisely check with those obtained by the usual methods. Aside from the elements enumerated, the following were found in ores: EiOz, 41 to 42%; FezOa, 18 to 19%; A 1 2 0 3 , 22%; CaO, 8 to 9%; Pb, 0%; Zn, 0%; As, 0%; Sb, 0%; Cr, 0.4%; Sn, 0%; S, 27;; TV, V, Mn, absent; Mg, 2.5%.
Conclusions h'ickel and cobalt cannot be deposited by internal electrolysis with a n iron, cadmium, or chromium anode, because of the shifting of potentials of these metals in an ammoniacal medium. The internal electrolysis method for the deposition of nickel and cobalt with a zinc anode gives accurate results. I n order to deposit nickel and cobalt in the presence of ferric iron, a sodium fluoride iron complex must be formed, which is not decomposed in a feebly ammoniacal medium. Up to 3 mg. chromium does not interfere with the determination of nickel and cobalt by internal hydrolysis; with more than 3 mg. of chromium the deposition of nickel and cobalt is retarded or ceases altogether. The interference of chromium is eliminated by precipitating it as barium chromate. When copper is present, it should be separated first. The separation of copper froin nickel by internal elwtrolysis with the aid of a zinc anode in a feebly acid medium is not feasible, because of the eo-deposition of nickel with copper on the cathode. Copper may be deposited and determiiied in a 1 per cent sulfuric acid solution with the aid of an iron or aluminum anode. Less than 0.1 gram of iron does not interfere JTith the deposition of copper; a larger quantity of iron must be combined with sodium fluoride or reduced by hydrazine. The determination of nickel, cobalt, and copper by internal electrolysis lyithout diaphragnis in ores poor in these metals yields very accurate results, agreeing with those obtained by more complicated methods.
I n the presence of more than 3 mg. of chromium, copper is deposited in the same \yay as in the absence of chromium.
Literature Cited (1) Clarke, B. L., Wooten, L. .I.,and Luke, C. L., ISD. EKG.CHEM.,
TABLEIX. So.
-Sample Copper
%
SALY LYSIS
5 2 Found in-Nickel Cobalt
%
OF
ORES
Anal. E d . , 8, 411 (1936). M.,A n a l y s t , 55, 312, 495, 680 (1930). Fife, J. G., Ibid.,61, 681 (1936); 62, 30 (1937). FranCois, M., Ann. chim., (9) 12, 176 (1919). Hollard, A , , Bull. S O C . chim., 29, 116 (19033. Kolossow, JV. I., and Lurie, J. J.,Trade Stand:ird U. S.S. R., Sonferrous Metals, Fasc. 45 (19341. Lurie, J. J., and Ginsburg, L. B., ISD. ESG. CHEX, Anal. Ed., 9, 424 (1937). Lurie, J. J., and Troitzkaja, 11.I., Ilfilcrocheniie, 22, 101 (1937). Lurie, J . J., and Troitzkaja, h f . I., Z . m o l . Ciiem., 107, 34 (1936) : Zavodsliaya Lab., 5, 1426 (1936). Lurie, J . J., and Troitakaja, X. I., Ibid.,6, 39 (1937). Sand, H. T.S.,- i n d u s t , 55, 309 (1930). Sand, H. Y.S., and Collin, E. M.,Ibid., 56, 90 c1931).
( 2 ) Collin, E.
-Sample 3G Found inCopper Sickel Cobalt
%
(3) (4)
(5) (6) (7)
Then ferrous iron is oxidized n-ith bromine, as described above, 0.5 gram of ammonium persulfate is added, and the solution is boiled 10 minutes or until the oxidation of C r + + +to CrzOl-- and the decomposition of the excess of ammonium persulfat'e are complete. (The oxidation of Fe++ and C r + + +with ammonium persulfate should not be made at the same time, to avoid intro-
(8) (9)
(10) (11) (12)
RECEIVEDDecember 13, 1937.
