THE TRANSFORMATION FROM BLUE TO ROSE COBALTOUS HYDROXIDE BY HARRY B. WEISER AND W . 0. MILLIGAN
The addition of excess alkali to a solution of cobaltous salt gives a deep blue gelatinous precipitate which later turns to rose cobaltous hydroxide. Under certain conditions the highly hydrous precipitate appears green rather than blue. Winkelblech’ concluded that the blue precipitate was a basic salt and that the green coloration often observed, was the result of partial oxidation. The first conclusion was disproven by Hantzsch* who showed that both the blue and rose precipitates were cobaltous hydroxide. The difference in color was explained by assuming that the blue is COOHzO and the rose Co(OH)*. Weise9 questioned the accuracy of this assumption and suggested that the variation in color may be due to a difference in particle size. The cause of the various colors of the hydroxide has been the basis of recent independent studies by S t i l l ~ e l land , ~ by Huttig and K a ~ s l e r . ~ As a result of microscopic and x-ray examinations of the precipitates formed by the interaction of alkali and cobaltous salts under varying conditions, Stillwell concludes that the rose hydroxide, which is the stable form, is the only crystalline modification of the hydroxide. The green and blue are considered to be amorphous precipitates, the green being the color by transmitted light and the blue being a reflected color-a Tyndall blue resulting from the scattering of light by the minute particles, the size of which is of the order of the wavelength of blue light. Stillwell added CoC12to KOH in amounts greater than I mol of the former to 1.5 mols of the latter and allowed the precipitate to age in the mother liquor. The color of the precipitate changed from green to blue to rose, the final product probably being a definite crystalline basic salt. Stillwell raised but did not settle the question as to whether the alleged basic salt was the same or different from Habermann’s peach-blossom colored compound, CoC12.3Co0 3. gH206formed by adding ammonia to boiling cobaltous chloride. Stillwell confirmed Benedict’s’ observation that small amounts of hydrous nickelous oxide or hydroxide precipitated with the cobalt hydroxide retard the change from blue to rose. Weisera suggested that the specific stabilizing Ann., 13, 155 (1835). Z. anorg. Chem., 73, 304 (1912). “The Hydrous Oxides,” 149 (1926). J. Phys. Chem., 33, 1247 (1929). 5 Z. anorg Chem., 187, 16 (1930). 6 Monatshefte, 5 , 432; J. Chem. SOC., 48 A, 351 (1885). ’ J. Am. Chem. Soc., 26,695 (1904); cf. Test and Scoles. Proc. Indtana Acad. Sci., 34, 163 (1914). “The Hydrous Oxides,” 148 (1926). 2
TRANSFORMATION FROM BLUE TO ROSE COBALTOUS HYDROXIDE
723
action of the nickelous hydroxide on the blue cobaltous hydroxide is connected with the similarity in the crystalline structure of the two corresponding oxides. Stillwell accepts this in principle, but believes that both hydroxides are amorphous. “Hydrous nickelous oxide when freshly precipitated is laminar and amorphous and therefore stabilizes the laminar form of cobaltous hydroxide and inhibits crystal growth retarding the blue to rose change.” Thus Stillwell comes out definitely in support of the view that the difference in color between the blue or green compound on the one hand and the rose on the other, is due to isomerism, the former being the amorphous form and the latter the crystalline form of Co(0H)z. In marked contrast to this point of view, Huttig and Kasslerl claim as a result of x-ray analysis of the blue and rose compounds, that both are crystalline, and have identical crystal structures. The difference in color is attributed to particle size alone, the blue being the more finely divided. Five years ago2 the hope was expressed that x-ray analysis methods would solve the question as to whether the difference in color between the blue is due to isomerism or t o particle size. I n view of the fact that two observers, working independently, reached opposite conclusions by these methods, it is obvious that a third independent series of observations is in order. The present paper purports ( I ) to study the stabilization of the blue cobaltous hydroxide, ( 2 ) to determine whether the color differences among the cobaltous hydroxides is due to isomerism, to particle size, or to both, (3) to formulate a mechanism for the transformation from blue to rose cobaltous hydroxide, and finally (4) to establish the nature and composition of the compound formed by ageing, in the mother liquor, the hydrous precipitate formed by the interaction of alkali with excess cobalt chloride.
Experimental A . Stabzlization of the Blue Hydroxide. Blue cobaltous hydroxide usually passes over to the stable rose hydroxide in the presence of excess alkali. Hantzsch pointed out that this transformation is retarded by the presence of a slight excess of CoClz and Benedict reported the stabilizing action of Ni(0H) 2 precipitated simultaneously. Hantzsch showed that the excess CoClz was adsorbed. This was confirmed by Stillwell who attributed the stabilizing action to the inhibition of crystal growth by the adsorbed salt. The stabilizing action of nickelous hydroxide was attributed to a similar cause. The presence of the sulfates of ferrous iron, zinc, manganese, magnesium, chromium, copper, and aluminum; and the nitrates of lead, cadmium, thorium, and strontium are said by Chatterji and Dhar3 to have little or no stabilizing effect. Since the stabilization is the result of adsorption it seems altogether unlikely that only the salts of cobalt and nickelous hydroxide should have a Z. snorg. Chem., 187, 16 (1930). 149 (1926). Chem. News, 121, 253 (1920).
* “The Hydrous Oxides,”
HARRY B. WEISER AND W. 0. MILLIGAN
724
stabilizing action on the blue to rose transformation. Actually a number of substances were found not only to retard but actually to stop the change. The results of these observations will be given in the following paragraphs. Effect of Cobaltous Chloride. For the sake of comparison, observations were made of the color changes which take place in the C O ( O H )precipitated ~ in the presence of an excess of CoC12. Approximately 0.5 gram of C O ( O H ) ~ was precipitated by mixing solutions as indicated in Table I in an apparatus designed for rapid uniform mixing of solutions.‘
TABLEI Effect of CoClz on the Stability of Blue Co(0H)z 2M NaOH, j cc; total volume, z j cc) M COCll cc
5 see.
blue blue blue blue 9 blue IO blue I 1 blue I 2 blue I 3 blue I 4 blue I 5 blue 5 6 7 8
5 min.
some rose light blue green green green green green some green dark blue dark blue dark blue
I
Color after day
rose light blue green green green green light blue light blue light blue some lavender some lavender
3 days
8 days
rose light blue green green green light blue lavender lavender lavender 1a v en der lavender
rose green blue green light blue lavender lavender lavender lavender lavender lavender lavender
Similar experiments carried out with air-free solutions and kept out of contact with the air gave identical results. For corresponding conditions the color changes were essentially the same as those reported by Stillwell. The formation of a green hydroxide in the absence of air disproves Winkelblech’s conclusion that the green color necessarily results from oxidation. Stillwell showed, however, that a green coloration is obtained by partial oxidation of the blue compound. Eflect of Mannitol. Since cane sugar is apparently adsorbed by the hydrous oxides of copper2 and iron3 it was suggested that certain carbohydrates and higher polyhydroxy alcohols might retard the transformation of the unstable blue to the rose cobaltous hydroxide. That such is the case is shown by the following results. Using the same procedure as in the previous experiment, varying amounts of mannitol were added to the reaction mixture previous to precipitation. The observations with CoClz in excess and with NaOH in excess are given in Tables 11 and 111, respectively. Weiser and Middleton: J. Phys. Chem., 24, 48 *Graham: Phil. Trans., 152, 283 (1861). Riffard: J. Chem. SOC.,27, 292 (1874).
(1920).
TRANSFORMATION FROM BLUE TO ROSE COBALTOUS HYDROXIDE
725
TABLEI1 Effect of Mannitol on the Stability of Blue Co(OH)2 in the Presence of Excess CoC12 (M CoC12,6 cc; z M NaOH, 5 cc; total volume, 2 5 cc) M Mannitol cc 5 seconds 0.0 0 .I
0.25
0.5 I .o 2.0
3 .o 9.0
5 minutes
light blue dark green dark green dark green dark green dark green dark green dark green
blue blue blue blue blue blue blue blue
Color after I hour
I
day
IO
blue-green light green green green green green green green green green green green green green green green
days
green green green green green green green green
TABLEI11 Effect of Mannitol on the Stability of Blue C O ( O H )in ~ the Presence of Excess NaOH
(M CoClZ,4 cc; z M NaOH, 6 cc; total volume M Mannitol cc
Mol ratio Mannitol : Co
0.001
0.0002
0.01
0.0025
0 .I
0.025
0.2
0.05
0.5
0. I25
I .o
0.25
2 .o
0.5
3.0 4.0
0.75
5.0
1.25
I
.o
5
Color a t start
blue blue blue blue blue blue blue blue blue blue
25
cc)
Observations
rose in I O minutes rose in 1 2 minutes rose in 18 minutes still some blue after 4 weeks no change in 4 weeks no change in 4 weeks no change in 4 weeks no change in 4 weeks no change in 4 weeks no change in 4 weeks
It is clear from these observations that a very small amount of mannitol will completely inhibit the transformation from blue to rose Co(0H)z even in the presence of an excess of NaOH, which ordinarily favors a rapid change. All of these observations were made a t room temperature. To determine the stabilizing effect a t higher temperatures the sample prepared as in Table I11 containing z cc of M mannitol was heated on a water bath at 92' for 8 hours. No noticeable change in color was observed. Effect of Several Sugars, etc. The influence of a number of sugars, polyhydroxy alcohols, gelatin, etc. on the blue to rose transformation have been summarized in Table IV.
HARRY B. WEISER AND W. 0. MILLIGAN
726
TABLEIV Effect of Several Substances on the Stability of Blue C O ( O H )in ~ the Presence of Excess NaOH (M CoC12, 4 cc; 2 M NaOH, 6 cc; total volume, 2 5 cc) Stabilizer added (o.rg.)
Color after z weeks
Maltose Lactose Xylose Arabinose Sucrose Galactose Dextrose Dulcitol Sorbitol Raffinose Glucose penta-acetate Egg albumin Gelatin NiC12
Original deep blue Original deep blue Original deep blue Original deep blue Original deep blue Original deep blue Original deep blue Original deep blue Light blue Original deep blue Light blue, some rose Some rose by the end of I hour Mostly rose by the end of I hour Mostly rose by the end of I hour
E$ect of Potassium Suljate. Hantesch observed that the blue precipitate formed in the presence of a small excess of CoS04 was more stable than that formed in the presence of CoCl,, probably because of stronger adsorption of the sulfate than of the corresponding chloride. This suggests that the addition of sulfates might retard the blue to rose transformation, even in the presence of excess alkali. This was testeri out with the results shown in Table V. It is obvious that the salt retards distinctly the blue to rose transTABLEV Effect of KzSOaon the Stability of Blue Co(0H)z Solutions mixed Color after 2M
KOH cc 5 5
M Satd. CoCll H20 KzSO, 5 sec. cc cc cc 4
11
o
4
o
11
blue blue
IO
min.
rose blue
30min.
16 hrs.
rose light blue
rose some rose
24
hrs.
rose rose
formation when present in large excess. That the retarding effect is not more marked as compared with CoS04 is probably due to very much weaker adsorption of K2S04than of CoS04.
B . Adsorption o j Sugars by C O ( O H ) ~ . Since the sugars exhibit such a marked stabilizing effect on the blue Co(OH)2 even when present in low concentration, it would follow that the sugars should be strongly adsorbed. The following experiments show that this is the case:
TRANSFORMATION FROM BLUE TO ROSE COBALTOUS HYDROXIDE
727
In a I O O cc flask were placed amounts of CoClz and sugar solutions as listed in Table VI; then I I cc of NaOH was added; and finally more water to the I O O cc mark on the flask. The contents of the flask were shaken thoroughly for a few minutes and then centrifuged. A portion of the supernatant solution was withdrawn and analyzed for sugar. The analysis of sugars were made with a Reichert Soleil-Ventzke saccharimeter. The following normal weights were used: 100 Ventzke degrees equivalent to 26.00 grams of sucrose; 32.857 grams of lactose; 12.474 grams of maltose; and 16.507 grams of raffinose.' No attempt was made to use a different normal weight for different parts of the scale as the correction is small. Thus a t 5 Ventzke degrees, the normal weight of sucrose is given as 24.90 grams. Temperature corrections were made.
TABLEVI Adsorption of Sugars by Blue C O ( O H ) ~ [Solutions mixed (total volume IOO cc): I O cc 0.9937 M CoClz equivalent to 0.9247 g Co(0H)z; I I cc 2.23 hl NaOH (excess NaOH 0.045 hf); sugar solutions as listed below] Sugar cc Sucrose 0.9899 M
5.00 IO.00 20.00
Concentration in mols/liter Initial Final 0.0351 0.0495 0,0990 0.0736 0.1980 0 .I j66
Adsorption in mols sugar/mol Co(OH)* 0 .I45 0.255
0.415
Lactose o , 3 I I 5 11
40.05
0.0312 0.0623 0.1248
50.00
0 .I 5 5 7
10.00
20.00
Maltose
0 .I Z O I
0.0160
0 .I59
0.0323
0.302
0.0758 0.0986
0,493
0.574
hl
20.00
0.0240
70.00
0.0841
0.0138 0.0627
0.103 0.215
20.00?
0,0514
0.0358
0.' 5 7
jo
0.1286
0.1067
0.220
20.00
0.0277
0.0970
0.0232 0.0833
0.0452
70.00
Maltose o
2572
31
002
Raffinose 0.1386M
International Critical Tables, 2, 335 (1924). In these experiments 20.00 cc of 0.4980 M CoCll were used.
0.138
H A R R Y B . WEISER AND W. 0. M I L L I G A S
728
The effect of the excess NaOH and NaCl on the solution was determined and found to be negligible for the purposes of these experiments. Thus 2 s cc of a 0.9899 molar sucrose solution diluted to 100 cc gave a saccharimeter reading of 32.36 Ventzke degrees. I n the presence of the same amounts of KaOH and NaCl as in the adsorption experiments, the reading was 3 1 . 7 7 degrees. This difference of 0.59 degree corresponds to O.OOJ, mol of sucrose
0
"I
Equilibrfum Concentration
Mols p e r L
FIG.I Adsorption of Sugars by Blue Co(OH)*.
per liter or to an adsorption of approximately 0.004 mol sucrose per mol Co(0H)2. The adsorption data are given in Table VI and are shown graphically in Fig. I . It will be noted that typical adsorption isotherms are obtained in each case. All the sugars are strongly adsorbed, even a t relatively low concentrations. The order of adsorption is: lactose > maltose > sucrose > raffinose. C . X - R a y A n a l y s i s o j Cobalt Hydroxides. Before considering the mechanism of the transformation from the blue to rose cobaltous hydroxide and the inhibiting of this process by adsorbed substances, it seems advisable t o report the results of x-ray analysis of the several preparations. X-ray diffraction patterns were obtained by the powder method using a General Electric Diffraction Apparatus. The following preparations were examined :
TRANSFORMATION FROM BLUE TO ROSE COBALTOUS HYDROXIDE
729
1. Rose C O ( O H ) ~ The . sample was precipitated in the cold with excess NaOH and allowed to stand for I j minutes until the transformation from blue to rose was complete. After washing with water by the aid of the centrifuge until peptization started,' it was washed once with alcohol, dried a t 60' and ground in an agate mortar. There was no indication of any oxidation. The x-ray pattern was obtained at once. 2. Blue Co(OH)z, drzetl. The sample was precipitated in the presence of a slight excess of CoC12 and was washed at once and dried like I . After grinding, the color mas a blue-gray. I t was probably oxidized slightly. It stood over CaC12 for j months before its diffraction pattern was made. 3. Green Co(OH)2, dried. The sample was prepared and treated exactly as 2 except that a larger excess of CoClz was present during the precipitation. I t was decidedly green in color. 4.Blue Co(OH)z, niozst, not sfnbdired. This sample was prepared like 2 , except it was not washed or dried. Some rose was visible at the end of the x-ray exposure. 5 . Blue Co(OH)2,mozst, stabzlzzed. This sample was prepared as described in Table 111, using 0 . 2 cc of mannitol solution as a stabilizer. It was sealed in a glass tube without washing or drying and the x-radiogram made. The preparation still possessed the original blue color after one month,
TABLEVI1 X-Ray Diffraction Data for the Rose, Blue, and Green Co(OH)2 I.
2.
Rose
Blue (dry)
9 hours
din
2.75 2.37
8 5 IO
I . 590
8 6
1.504
4
I.3jO
I
1.318 1.183
3
1.140
0.1
1.108 1.068
0.1
1.780
4.66 4.00 2.66 2.37 1.78; 1.555 1.316
6 6 IO
4 0.5 0.6
3.93 2.63 I . j36 1.315
8 hours
I
din
8
4.66
2
IO
4.00
2
I 0.5
0.1
0.1
0.918
0.1
j.6 3.93
8 8
IO
2.63 1.536
4
1.459
0.1
1.574
3
I.2Ij
0.1
0.1
Cf. Tower and Cook: J. Phys. Chem., 26, 728
5. .
Blue (moist and stabilized) 20 hours db/n 1 A
2.66 2.34 1.752
0.5
1.014
1
A
2
0,948
1
Blue g o i s t )
8 hours
din A
1
A
4.66
3. Green (dry)
(1922).
3
IO
5
1.000
0.1
0.937
0.1
HARRY B . WEISER AND W. 0. MILLIGAN
730
The planar spacings were read off the several x-radiograms and the intensities (I) were estimated visually on such a scale that I O means the most intense line, and 0.1 means a line that is just visible. These results are tabulated in Table VI1 and given in chart form in Fig. 2 . The time noted in the table is the time of exposure to the x-rays in making the x-radiogram. From the observed data there appears to be no doubt that blue Co(OHI5 exists in a crystalline form different from rose Co(0H)Z. I t will be noted
I I
2 1
,
3 I
1
4
II
I
,
0
FIG.2 Diagram of the X-radiograms of Cobaltous Hydroxides. ( I ) Rose; (2) Blue (dry); (3) Green (dry); (4) Blue (moist); (5) Blue (stabilized). Samples contain some Rose.
that the dried blue and green samples ( z and 3 ) all have the same planar spacings except for some lines which correspond to the rose preparation, I . It would be expected that these samples would contain some rose. Some rose was visible in sample 4 a t the end of the x-ray exposure. However, the moist blue sample, stabilized with mannitol, retains its original deep blue color and is probably free from any of the rose form. The latter sample contains NaCl, NaOH, and a small amount of mannitol, but these are in solution and therefore do not influence the x-ray pattern. A comparison of the diffraction pattern for the stabilized blue hydroxide, with those for samples 2 , 3, and 4, discloses that the spacings are nearly identical for all samples after the lines in 2 , 3, and 4 belonging to the rose, are cancelled off. These observations not only show the existence of two crystalline forms of Co(OH)* but disclose that the blue and green samples are identical in crystal structure. The results appear to disprove Stillwell'sl conclusion that the blue and green precipitates are amorphous. The similarity in crystal structure between the blue and green preparations supports Stillwell's view J. Phys. Chem., 33, 1247 (1929).
TRANSFORMATION FROM B L U E T O ROSE COBALTOUS HYDROXIDE
73 I
that this color difference is not due to isomerism. His claim that the green is the color by transmitted light,, and the blue is a Tyndall blue, is probably correct. Huttig and Kassler' were correct in concluding that both the blue and the rose hydroxides are crystalline. They were altogether wrong however, in their deduction that the two are identical in crystal structure, and the difference in color is due to particle size. I t is probable that the blue sample which they examined with the x-rays contained so much rose that t,hey completely overlooked the fainter lines belonging to the blue form. T h e Mechanism of the Blue to Rose Transformation and the Stabilization of the Blue Hydroxide. In view of the marked adsorption of certain sugars by blue Co(0H)z and the marked retarding action of relatively small amounts of the sugars, there is little doubt but that the two phenomena bear to each other the relation of cause and effect. I t will be recalled that the order of adsorption of the sugars investigated is: lactose > maltose > sucrose > raffinose. I t is of interest to note that the peptizing action of sugars, as a result of adsorption, on hydrous ferric oxide2 follows the same order. A similar peptizing action of the adsorbed sugars on the blue Co(OH)2 was noted. In some cases the sol formed originally was thrown down completely only after centrifuging for an hour a t 3000 r.p.m. The probable mechanism of the transformation of the blue to rose hydroxide consists in the solution of the minute blue crystals in the excess alkali followed by reprecipitation of the less soluble, larger, rhombic crystals of the rose isomer. The addition of strongly adsorbed substances such as mannitol, various sugars, etc., surrounds the blue particlea with a protective layer which inhibits or prevents the isomeric transformation. In the presence of excess cobalt salt, the isomeric transformation is prevented not only by strong adsorption of the salt but by the tendency to form a basic salt as described in the next section. In the absence of alkali, the solvent action of the mother liquor is insufficient, to bring about the isomeric change, even a t temperatures considerably above room temperature; on the other hand, in the presence of alkali, without the presence of a stabilizing substance, the transformation is quite rapid at higher temperatures. D. Basic Cobalt Chloride. As already noted in Table I, the aged precipitate formed by adding excess CoClz t o sodium hydroxide solution varies in color from green to blue to rose (lavender) depending on the age and the excess amount of CoClz in the mother liquor. This confirms the observations of Stillwell. X-ray diffraction patterns were made of the following preparations: 1 . Aged Green-Blue. To 5 cc of z KaOH solution was added 6 cc of I M CoC12 solution. After eight days, the green-blue precipitate was removed from the mother liquor by centrifuging, but was neither washed nor dried. Z. anorg. Chem., 187, 16 (1930). Dumanski, et al: Kolloid-Z., 51, 62, 7 2 2 (1930).
210
(1930); 54, 73 (1931); J. Rim. Phys.-Chem. SOC.,
HARRY B. WEISER AND W. 0. MILLIGAN
73 2
2. Aged Green. This was prepared in the same way as the preceding sample, except that 7 cc of CoC12 was used. 3. Aged Rose (Lavender). This precipitate was prepared and aged in the same way as the two preceding ones, except that 1 5 cc of CoClt was used. Stillwell calls this material “aged rose”; it is, however, more of a bluish-rose which we have designated as lavender. 4. Lavender, Dried. The precipitate prepared as number 3 was washed with water by the aid of the centrifuge until a sol began to form and finally with alcohol. It was dried at 60’. The planar spacings and the intensities of the lines of the several preparations are given in Table VI11 and shown diagrammatically in Fig. 3.
TABLEVI11 X-Ray Diffraction Data for the Green, Blue, and Lavender Aged Precipitates I.
2.
Blue-Green (moist) 18 hours d/n I
Green (moist) 18 hours
4 66 4.00
2.74 68 2.37 2 .oo 2
1
d p
A
A
4
5
7.0 6.0
5.6 4.6
9.0
4.01
4.0
9.0
2.69 2.37
10.0
10.0
3.0
5.0
2
.oo
6.0 4.0
,806
0.I
707 1 ’ 574
0 . 2
4.0
1.775
5.0
I
1.695
0.2
I.
1.575 1 531 1.498 1.344 1.313 1.229 I , 178
4.0
4.0
,086
0.2
,023 I ,009 0.940 0.898
0.1
1.533 1.491 1,453 1.350 I ,310 I . 230 1,176 I ,084
0.I
I
,024
0 . 2
0.I
I , 003
0.I
I I
3.0 3.0 I
.o
2
.o
0.I 0.I
0. I
0.752
0. I
0.718
0. I
3. Lavender (moist) 18 hours I d/n
0.1 0.1
2.0 2
.o
0.I 0.I 0.I
5.6 2.69 2.30
4.
Lavender (dry) 8 hours d/n 1
.s
8.0
5.5
9.0
2.77
8.0 6.0
to.0
2.28
10.0
.o
2.14
0.1
1.948 1.820
3.0
2.07
I
1.96 1.831 1.711 I ,613 1 ’ 536 1,458 1.391 1.367 I . 286 1.247 I . 208 I . 167 I . 136 I . 107 I ,066 I . 028 0.986 0.947 0.929 0.883 0.839 0.796 0.756
2.0
3 .o 5.0
2.0
3.0 3.0 0.5 2
.o
1.0 I .o
0.5 0.I
0.j
1.701 1.610 1.535 1.513 1.390 1.367 1.285 1.248 1.134 1.103 1.062
0.1
0.1
0.2 0.2
0.1 0.1
0.1 0.1 0.1
0.1
0.1 0.1
0.3 0.I 0 .I 0 .I 0. I
0.1
0.1 0.I 0.I
0.I
more very faint lines present
TRANSFORMATION FROM BLUE TO ROSE COBALTOUS HYDROXIDE
733
A comparison of the above diffraction data with those for the blue, and the rose hydroxides, Table VII, discloses that the lavender precipitate is a different compound, probably a basic salt as suggested by Stillmell. To determine whether this was the case or whether it was a third isomeric form of CO(OH)~,the carefully prepared, washed, and dried sample (4 above) was analyzed for cobalt and chloride. The cobalt was determined by electrodeposition of the metal and the chloride was estimated as AgCl. The data are given in Table IX.
o FIG. 3 Diagram of the X-radiograms of Precipitates formed b ageing Co(OH)* in CoC12 Solution. ( I ) Green Blue. (2) Green; (3) Lavender (moist); (47 Lavender (dried). The Lavender kecipitates are chiefly t’he Basic Salt, CoCI2.3CoO.3.5 HnO.
TABLE IX Analysis of the Basic Cobalt Chloride
0.2990 0.1162
0.1687
56.44
56.42
0.0788
16.8
16.98
The results. show that a definite, crystalline, basic salt is formed, the composition of which corresponds to Habermann’s basic cobalt, chloride, C O C ~ Z . ~ C O O , ~ .formed ~ H Z Oby , the action of ammonia on a hot solution of COClZ. summary
The conclusions to be drawn from this investigation may be summarized as follows: I . Cobaltous hydroxide Co(0H)t exists in two isomeric crystalline forms as evidenced by x-ray analysis.
HARRY B. WEISER AND W. 0. MILLIGAN
734
2 . Cobaltous hydroxide may be blue, green, or rose in color. The green and blue preparations, CY Co(OH)2, are identical in crystalline structure, while the rose, fi CO(OH)~,is distinctly different. 3. Conclusions I and z are contrary to those of Stillwell who believed that the blue and green hydroxides are amorphous, and to those of Huttig and Kassler who believed that the blue and rose are identical in crystal structure, the difference being due to variation in particle size. It is probable that the blue sample subjected to x-ray analysis by Huttig and Kassler contained so much rose that the fainter lines belonging to the blue form were completely overlooked. 4. The blue and green preparations owe their difference in color to a difference in physical character. The green is the color by transmitted light and the blue is probably a reflected color, a Tyndall blue (Stillwell). 5 . a Co(0H)z is the instable form. In the presence of alkali it dissolves and reprecipitates in the less soluble, stable 3!, modification. 6. The a to fi transformation can be prevented or retarded by the presence of strongly adsorbed substances in the solution from which the a form precip itates. The blue form is stabilized indefinitely by small amounts of mannitol, sorbitol, dulcitol, sucroBe, lactose, maltose, xylose, arabinose, raffinose] galactose] and dextrose. The transformation is retarded by cobalt salts (Hantzsch), Ni(OH)z simultaneously precipitated (Benedict), albumin, gelatin and sulfates. 7. Adsorption isotherms of various sugars with CO(OH)~as adsorbent are given. The adsorption is strong even in relatively low concentrations, as would be expected from the marked stabilizing action of the compounds. The order of adsorption is: lactose > maltose > sucrose > raffinose. The peptizing action of the sugars as a result of adsorption on hydrous ferric oxide (Dumanski) follows the same order. 8. Cobaltous hydroxide in contact with a solution of CoC12 undergoes color transformations from green to blue to lavender. The blue and green substances are mixtures of CY CO(OH)~,P Co(OH)2, and a basic salt CoC12,3C00.3.5H20. The lavender compound formed on long standing is the pure basic salt. 9. The color transformations and the composition of the various colored substances formed by the interaction of alkali and CoClz may be represented as follows: cx Co(0H)z Excess CoC12 CY C O ( O H ) ~ Excess alkali P Co(0H)s P Co(OH)z t Blue, Green --+ Rose COC~~.JCOO.;. gH10 Green
1
Co(0H)z P Co(0H)z + C0C12.3C00.3.5Hz0 CoC12.3C00.3.5HzO Lavender Blue
CY
The Rice Institute, Houston, Zexas.
