INDUSTRIAL AND ENGINEERING
342
Figure 4 indicates that the cathode efficiency of a bath that is low in silver is markedly affected by both temperature and current density. At a high temperature the cathode efficiency increases with current density (within the range studied), but a t lower temperatures the cathode efficiency decreases with current density. If the temperature is approximately 75" C., the efficiencies a t current densities of 1 to 1.8amperes per sq. dm. are similar to those of the more concentrated bath. TABLEI. STATIC
POTENTIALS IN
SILVER SOLUTIOXS
(All baths contained 520 grams per lite: of sodium iodide per liter of citric acid) Ag Ed' OBSVD. lAg+] x 10-12 K Gra?ns/liter 23.78 0.389 9.55 11.21 0.402 7.06 4.63 0.412 5.31 2.15 0.423 2.46 1.07 0.438 1.47
and GO grams
x
10-15
1.42 1.78 4.60 4.03 5.00
SILVER-ION CONCEKTRATION. Table I lists the measured silver-ion concentration of baths whose total silver content had been determined. It should be noted that the respective concentrations of sodium iodide and citric acid are the same in each of the baths. I n calculating the instability constant values of the AgI; ion from the equation
no attempt was made to evaluate the effect of the citrate ion, whose presence may partly explain the lack of constancy of K .
CHEMISTRY
Vol. 27, No. 3
CONCLUSIONS The sodium iodide-citrate bath satisfies the requirements for a good plating solution: 1. The deposit is fine-grained and adherent. No quantitative study was made of the throwing power, but there appeared t o be uniform deposition even on irregularly shaped articles. 2. The permanency of the bath is indicated by the fact that it gave as good deposits after standing exposed to the atmosphere for 4 months as when newly prepared. 3. The anode corrosion is good. When operated at cathode efficiencies of 80 per cent and higher, the silver content of the bath increased. 4. The bath is easily prepared.
The silver content, as well as the silver-ion concentration of the more concentrated bath, approximates the values of a cyanide bath as found by Frary and Porter (4). LITERATURE CITED Audrieth and Yntema, J . Phus. Chem., 34, 1903 (1930). Egeberg and Promisel, Trans. EZectrochem Soc., 59, 287 (1931). Frary, Ihid., 23, 64 (1913). Frary and Porter, Ihid., 28, 307 (1915). Hellwig, Z . anorg. Chem., 25, 157 (1900). Leader, J . Inst. of Metals, 22, 11, 305 (1919). McKee, Mann, and Montillon, Trans. Am. Electrochem. Soc., 53, 333 (1928).
Mather and Blue, Ibid., 31, 285 (1917). Mather and Kuebler, Ibid., 28, 417 (1915). Newbery, E., J . Chem. Soc., 105, 2419 (1914). Sanigar, Trans. Electrochem. Soc., 59, 307 (1931). Schlotter e t al., Z . Metalllcunde, 25, 107 (1933). Simpson and Withrow, J . Am. Chem. Soc., 32, 1571 (1910). Taft and Barham, J . Phys. Chem., 34, 929 (1930). RECEIVED November 30, 1934. Originally submitted Derember 9, 1933.
Double Decomposition and Oxidation of Inorganic Compounds under Pressure Transformation of Heavy Spar into Barium Carbonate V. N. IPATIEFF~ AND C. FREITAG, Bayerische Stickstoff-Werke, A,-G., Berlin, Germany The reaction of double decomposition of barium I p a t i e f f bomb, and air was OLUTIONS of chromium sulfate and soda, under pressure and certain inpumped in until the pressure salts are transformed in reached 100 atmospheres. The the presence of air under dicated conditions, proceeds to completion at reaction was allowed to proceed pressure into salts of chromic 320" I n order to obtain g7 Per cent bansacid and, conversely, salts of for 12 hours a t 300" to 350" C. formation of barium sulfate into carbonate under At the end of the reaction the chromic acid under pressure of the conditions, it is necessary to use twice the whole of the chromium oxide hydrogen are reduced to chrowas oxidized to the calcium salt mium salts, forming under cerequivalent amount of soda. It may be concluded, of chromic acid, CaCr04. t a i n conditions complex comtherefore,f r o m the data obtained that other metallic These experiments showed p o u n d s ( 1 ) . The reaction of sulfates which are insoluble in water can be that, under pressure, even stable oxidation of chromium hydroxide transformed completely info the corresponding and very little reactive oxides are in a n alkaline medium has been capable of readily entering variinvestigated (2)and the optimum carbonates. ous reactions and yielding deconditions have been found for transforming this hydroxide into sirable products. In order to salts of chromic acid-potassium chromate and potassium verify such a conclusion, the reactions of double decomposition of barium sulfate and soda were investigated. The re-. dichromate. Oxidation experiments were made on commercial green sults completely corroborated the authors' assumptions. chromium oxide (insoluble in acids) by means of air under The first experiments were made with powdered heavy spar pressure in the presence of the hydrate of calcium oxide (from the firm of de Haen, Germany) and solutions of soda (milk of lime). One hundred grams of chromium oxide and saturated a t boiling temperature. I n each test 58.4 grams of an excess of calcium hydroxide were placed in a rotating heavy spar were used, and the amount of soda used was at but later the quangreater than its 1 Present address, Universal Oil Products Company, 310 South Michigan tity was doubled, The reactions were carried out a t 320" to Ave., Chicago, Ill.
S
c*
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I ST R Y
March, 1935
330" C. in a 2-liter rotating autoclave into which various gases were pumped. The data obtained in these experiments are collected in Table I. TABLEI. EXPERIXENTS ON SPARAND SODA EXPT. No. 140 142 145 146 147
NazCOa Hz0 Grams Grams 30 125 30 125 60 250 60 250 60 250
TEMP.
h1AX.
TR.439-
TION
SURE
BaBOr
Hours 4 4
dtm. 180
5 5 4
180
DURA- PRES- FORMED
C. 320-330 320-330 320-330 320-330 300
180 180 60
GAS
INTRODUCED
%
Atm.
31.5 51.8 93.0 85.0 90.5
50 COz 50 Hz 50 Hz 50 air
tests were made with dilute solutions of soda. The addition of an excess of water made unnecessary the participation of any other gas in the reaction medium. The data obtained in the tests with varying concentrations of soda solution are given in Table 11. For comparative purposes the action of soda upon heavy spar was investigated also in a glass retort equipped with a reflux condenser without additional pressure. The results of these tests are given in Table 111. TABLE111. RESGLTS OF EXPERIYESTS AT ATMOSPHERIC PRESSURE
None
OF WATER TABLE11. E:FFECTOF EXCESS
ExPr. No. 148 151 153 160 155 157 159
Na2COs Crams 30 30 30 30 45 45 45 60 60 60
162 16t 166
168
60
H20 Grams 250 175 150 125 250 175 150 300 500 750 1500
TEMP. O
c.
300 320 300-325 320 300 320 320 320 320 320 300
hIAX. DURA- PRES-
(Duration of experiments, 5 hours) TR.ANS-
SURE
Bas04
Hours 5 5 4 4 3 3
Atm.
%
70 90 90 100 90 100
47.0 53.3 57.6
4 4
4
4 4
... ...
96.5
...
97.2
The experimental results show that under pre,,qwre a considerable transformation of the sulfate into the carbonate salt takes place. K h e n a double instead of a single equivalent quantity of soda was used in the reaction, the conversion reached 93 per cent. ((Thepercentage of conversion was actually greater on account of impurities contained in the heavy spar used.) The introduction of various gases did not affect the course of reaction of transformation; only the introduction of carbon dioxide gas led the reaction in the opposite direction. In view of the fact that in the large autoclave (2000 cc. capacity) some evaporation of the water occurred Kith the resultant precipitation of crystals of sodium carbonate, further
Wood
cut
149 150 152 161 154 156 158 163 165 167 169
50.6
80.5 87.7 86.5 91.4 97.5
100 100
EXPT. No.
FORMED
TION
TRAXSFORMED
NazC03 Grams
45 45 45
H20 Grams 250 175 150 125 250 175 150
60 60 60 60
300 500 750 1500
30
30 30
30
BaSOi
% 23.7 28.8 22.5 25.0 32.2 37.2 38.2 41 5 38.9 38.6 36 8
As the data in Tables 11 and I11 show, the percentage of conversion of barium sulfate is greater in each case under a higher pressure than under ordinary pressure. Dilution of the soda solution plays a minor role in the degree of transformation of barium sulfate, but apparently it is limited only to a certain extent. The usage of a 100 per cent excess of soda makes possible, under certain conditions, a complete transformation of barium sulfate into barium carbonate.
LITERATURE CITED (1) Ipatieff, V. N., and Mouromtsev, V., Ber., 60, 1980 (1927). (2) Ipatieff, V. V., Jr., and Platonowa, M. N., Ibid.,65, 572 (1932).
RECEIVED November 19, 1934.
bu Paul Honor&
THE WEST POWERHOUSEOF
343
THE
Dow CHEMICAL COMPANY
