On the (Constitution of Certain Organic Salts of Nickel and Cobalt as they Exist in Aqueous Solution. By O. F. Tower* ("Reprinted from the Journal of the American Chemical Society, \ Vol. XXIV, No. io. October, 1902. ON THE CONSTITUTION OF CERTAIN ORGANIC SALTS OF NICKEL AND COBALT AS THEY EXIST IN AQUEOUS SOLUTION . 1 By O. F. Tower. Received July 2, 1902. It has been shown in a former paper that the molecular con- ductivities of aqueous solutions of nickel and cobalt tartrates are exceptionally small, and furthermore that the apparent molecular weights derived from the freezing-point method considerably ex- ceed the molecular weights calculated from the simple formulas of the salts . 2 It was suggested that these unusual results could be accounted for oh the assumption of polymerization. The formula, COONiOOC I I CHOH CHOH I I CHOH CHOH I I COONiOOC was given as expressing possibly the constitution of a molecule of nickel tartrate. Such a molecule would very likely be much less dissociated in solution than a simple molecule. In order to investi- gate this problem more fully these same methods have been ap- plied to the tartrates of other metals and to the nickel, cobalt, and magnesium salts of certain other organic acids. These salts were prepared from pure chemicals of standard make. The solutions were made by treating an excess of the carbonate or oxide of the metal with a sufficiently dilute solution of the acid. In a few instances the hydroxide of the metal was employed. On account of the slight solubility of most of these organic salts, the quantity of salt in solution after the acid had become neutralized was almost never equivalent to the quantity of acid taken, because some of the salt was precipitated while the action was going on. It was therefore necessary to determine the amount of salt actually present in the solution in each case. The temperature of the solution has considerable effect on the solubility 1 Read at the Pittsburg meeting of the American Chemical Society. 2 Tower : This Journal, 22, 501 (1900). ORGANIC SALTS OF NICKEL AND COBALT. IO13 of these salts. This effect has already been described for nickel and cobalt tartrates, 1 and is similar for the other salts used, although in most cases less pronounced. Heat seemed to decrease the solubility, so that all solutions were made up in the cold or at a temperature not exceeding 50°. The action of the dilute acids was very slow at these low temperatures. To accelerate it the solution was constantly shaken until the reaction was neutral. This required only about fifteen minutes with magnesia and the freshly precipitated hydroxides of nickel and cobalt, while for the carbonates of nickel and cobalt an hour or more was frequently necessary. Solutions of barium tartrate were prepared by neu- tralizing a solution of barium hydroxide with tartaric acid. Solu- tions containing more than 1 gram-molecule of barium tartrate in 80 liters were supersaturated. Measurements with these super- saturated solutions revealed no abnormal behavior, which is also the experience of others. Attempts were made to prepare solu- tions of calcium and zinc tartrates. These salts are, however, so insoluble that the solutions obtained were too weak to render the measurements of any value for the purpose of comparison. The measurements of the electrical conductivity of the tartrates reported in my former article were made with a small combination Wheatstone-Kohlrausch bridge only 25 cm. long. All the meas- urements which follow were made with a meter bridge, which had been carefully calibrated. The conductivities of the tartrates of nickel and cobalt were therefore redetermined with the new appa- ratus. The temperature at which all the determinations were made was 18 0 ± o.i°. The conductivity of the water used varied from 2.0 to 3.0 X I0~ 6 . This has been deducted from the specific conductivity in every case. The results with the salts of tartaric, malic and succinic acids are given in Table I : v is the number of liters in which a gram-molecule of the salt was dissolved ; M is the molecular conductivity in reciprocal ohms. In the former article the equivalent conductivity was given, but since some of the salts probably exist in a polymerized condition, the molecular con- ductivity is given as affording a better basis of comparison. 1 Tower : loc. at., pp. 504 and 515. 1 13 q- 3 3 ioi4 O. F. TOWER. Tabi,E I. Nickel tartrate. Cobalt tartrate. V. M. v. M.' V. M. V. mP 10.35 9-2 I 3-46 12.0 25.38 25-4 31-05 32.2 2 X IO.35 13.8 2 XI 3-46 16.4 2 X 25.38 34-5 2 X 3!-05 43 -o 4 X 10.35 20.7 4 XI 3-46 22.7 4 X 25.38 47-4 4 X 31-05 57 -i 8 X 10.35 30.6 8 XI 3-46 29.8 8 X 25.38 63-5 8X31-05 74-4 16 X 10.35 44.4 T6XI3-46 45 -o 16 X 25.38 83.2 16X31-05 96.0 32 X 10.35 62.8 32X13-46 61.2 32X25.38 105.6 32X31-05 120.6 64 X 10.35 81.5 64 XI 3-46 81.3 64 X 25.38 i 33 -o 64X31-05 150.2 Magnesium tartrate. Barium tartrate. V. M. v. M. ' V. M. V. M. 19-95 67.4 24.37 7I.9 20.03 58.5 21.27 59-3 2 X 19-95 82.0 2 X 24.37 87.7 2 X 20.03 70.4 2 X 21.27 72.8 4 X 19-95 98.I 4 X 24.37 103.0 4 X 20.03 85.2 4 X 21.27 88.6 8 X 19-95 114.6 8 X 24.37 II9.2 8 X 20.03 105. 1 8X21.27 106.4 16 x 19-95 130.5 16 X 24.37 135 . 1 16 X 20.03 125.6 l6X 21.27 126.5 32 X 19-95 145.8 32X24.37 150.0 32 X 20.03 143.O 32X21.27 147-3 64 X 19-95 160.7 64X24.37 165.9 64 X 20.03 161.4 64 X 21.27 167.1 Manganese tartrate. Nickel malate. 1 Cobalt malate. V. M. v. M. ^ V. M. V. M. 37-79 66.9 4 I .71 68.8 14-77 14.5 18.44 23.6 2 X 37.79 81.5 2 X 41.71 83.8 2 X 14.77 17.7 2 X 18.44 28.8 4 X 37-79 98.5 4 X 4 I- 7 1 99-7 4 X 14.77 22.0 4 X 18.44 36.0 8 X 37-79 II4.5 8 X 41.71 117.0 8 X 14.77 28.2 8 X 18.44 45-2 16 X 37.79 132.5 16 x 41.71 133-5 i 6 Xi 4.77 37-1 16 x 18.44 58.1 32 X 37.79 148.3 32X41.71 148.9 32 X 14-77 51.0 32 X 18.44 74.6 64 x 14.77 69-9 64 X 18.44 94-3 Magnesium malate. Nickel succinate. V. M. V. M. V. M? 9-74 43-3 18.42 62.2 19-57 62.7 2 X 9-74 54-7 2 X 18.42 75-9 2 X 19-57 76.9 4 X 9-74 67.4 4 X 18.42 9I.7 4 X 19-57 92.5 8 X 9-74 83.0 8 X 18.42 108.8 8 X 19-57 109.5 16 X 9-74 IOO. I 16X18.42 125.9 16 X 19-57 126.6 32 X 9-74 118.3 32 X 18.42 143.0 32 X 19-57 145-2 64 X 9-74 135.0 64X18.42 158.4 64 X 19-57 160.3 128 + 9.74 149.O Cobalt succinate. Magnesium succinate. V. M. v. M. V. M. V. mP 17.29 65.0 20.25 68.2 14.31 76.6 15.70 77.6 2 X 17.29 78.3 2X20.25 82.2 2 X 14.31 88.7 2 X 15.70 90.0 4 X 17.29 93.O 4X20.25 97.1 4 X 14.31 102.8 4 X 15.70 104.2 8 X 17-29 Io 9-7 8X20.25 113.6 8 X 14.31 117.4 8 X 15.70 119.8 16 X 17-29 126.6 16X20.25 130.2 16 X 14-31 131-9 16X15-70 134.6 32 X 17-29 145-0 32X20.25 148.0 32 X 14-31 146.2 32 X i5-7o 149.0 64 X 17.29 159.0 64X20.25 162.3. 64 X 14.31 158.8 64 x 15.70 160.8 1 ? nl 7 on ? solution of each salt of malic acid could be prepared with the small quan- tity of this acid on hand. ORGANIC SALTS OF NICKEL AND COBALT. IOI5 From these results interpolations have been made graphically foi v.— 16, 32, etc., by plotting curves with the molecular con- ductivities as abscissas and the logarithms (base 2) of the dilu- tions, v, as ordinates. The interpolated values are given in Table II. In cases where the conductivity was determined in two separate solutions only the average is given in the table. The re- sults of Walden 1 for magnesium salts of these acids are given for comparison. They have been reduced to the same units and temperature. The temperature coefficient used for this purpose was 0.027, the average value found by Arrhenius 2 for sodium salts of organic acids. Table II. Molecular conductivity of tartrates. Mag- Magnesium. v. Nickel. Cobalt, nesium. (Walden.) Barium. Manganese. 16 12.3 .... 63.0 3 2 18.1 30.5 77.5 .... 66.8 63.2 64 25.8 41. 1 93.0 92.3 81.2 78.0 128 37.1 55.5 109.8 107.8 98.5 94.2 256 52.0 72.4 125.5 124.5 II7-3 no. 7 512 70.4 94.2 140.8 138.9 136.2 127. 1 1024 93.0 118.0 156.0 151.5 155.0 143.9 Molecular conductivity of malates. Magnesium. r. Nickel. Cobalt. Magnesium. (Walden.) l6 14.8 22.8 51. 1 32 l8.I 27.8 63.6 64 22.6 34.2 78.2 80.9 128 29.3 43.O 95.O 96.9 256 38.5 55.2 II3.4 II3.9 512 53.O 7O.7 129.2 I30.5 1024 72.3 9O.3 I46.O I45. 1 Molecular conductivity of succinates. Magnesium. v. Nickel. Cobalt. Magnesium. (Walden.) 16 59-5 63.7 78.2 32 73-o 76.8 90.7 64 88.0 91.2 104.8 106.8 128 105.2 107.9 120.2 121.6 256 122.3 I2 4-6 134.7 135.6 512 139.7 142.4 148.9 147-8 io2 4 155.6 157-5 l6o - s 158.6 1 Ztschr. phys. Chern i, 537 (1887). 2 Ibid., 4, 99 (1889). ioi6 O. F. TOWER. The molecular conductivities of the tartrates of magnesium, barium and manganese do not vary from one another more than may be expected for different salts of the same acid. The con- ductivities of the tartrates of nickel and cobalt are, however, so small as to be of an entirely different order. The same is true of the conductivities of the malates of nickel and cobalt. The con- ductivity of magnesium malate is somewhat less than that of the tartrate, as was also observed by Walden. The conductivities of the succinates of nickel and cobalt present no abnormal behavior when compared with the conductivity of magnesium succinate. Determinations of the lowering of the freezing-point were made with the apparatus described in my former article. Determina- tions of the freezing-point of the same solution never varied more than o.ooi°, but the freezing-points of two solutions made up as nearly alike as possible gave larger differences. Since the solu- tions used were rather dilute, a difference of two or three thousandths of a degree would frequently make a difference of ten or twenty units in the molecular weights calculated from them. So much reliance cannot therefore be placed on the absolute or on the relative value of the results obtained by this method, as on those obtained by measuring the electrical conductivity. The depressions of the freezing-point together with the apparent molecular weights calculated from them are given in Table III. Table III. Nickel tartrate. Cobalt tartrate. Substance in IOO cc. Grams. Depression . Apparent mol. wt. Substance in 100 cc. Apparent Grams. Depression. mol. wt. I.8795 0.139° 260 O.6739 0.062° 207 1.7205 0.121 273 0.6505 0.059 207 I.6450 0.117 268 O.3370 0.037 173 0.8602 0.081 202 0.3252 0.036 170 0.8225 0.076 206 0.1685 0.021 153 O.430I 0.042 193 O.1626 0.021 146 Magnesium tartrate. Barium tartrate. 0.8642 0.139° Il 8 0.7136 0.063° 216 0.8428 0.137 117 0.3568 0.036 189 0.4321 0.079 104 0.3568 0.039 174 0.4214 0.076 106 0.1784 0.020 170 0.2160 0.045 91 0.1784 0.021 162 Manganese tartrate. Nickel malate. 0.6130 0.083° 141 I. 2912 0.147° 167 ORGANIC SALTS OF NICKEL AND COBALT. 1017 Manganese tartrate. Nickel malate. Substance in Substance in IOO cc. Apparent IOO cc. Apparent Grams. Depression. mol. wt. Grams. Depression. mol. wt. O.5805 0.078° 142 0.6456 0.086° 143 0.3075 0.046 127 O.3228 O.050 123 O.2902 O.041 135 Cobalt malate. Magnesium malate. I.0360 0.114° 173 I.6060 0.244° 125 0.5180 0.068 144 0.8030 0.130 Il8 O.259O 0.040 123 O.4015 0.079 97 Nickel succinate. Cobalt succinate. 0.9488 0.169° 107 I.OI25 0.176° no O.893I 0.160 106 0.8646 0.156 106 O.4744 0.095 95 O.5062 0.094 103 0.4466 0.082 104 0.4323 0.084 98 O.2233 0.049 87 . O.253I 0.057 85 Magnesium succinate. 0.9808 0.207° 90 0.8942 0.185 81 0.4904 0.115 8r 0.4471 0.098 76 0.2452 0.065 72 In order to render tjiese results more readily comparable, by means of graphical interpolation the molecular weights have been calculated for dilutions of 16 and 32 liters. These figures together with the molecular weights calculated from the simple formulas of the respective salts are given in Table IV. Table IV. Tartrates. Malates. Succinates. Mol. wt. from formula Values interpo- ( . . lated from \ ^ ‘ Table III |^ = 3 2 *-- 207 207 172 286 203 230 244 122 196 207 109 234 143 3 191 19 1 156 164 179 120 140 150 100 3 3 175 175 140 108 hi 82 100 103 77 From this table it is seen that all the salts yield in the more con- centrated solutions apparent molecular weights considerably less than the molecular weights calculated from the formula, except the tartrates and possibly the malates of nickel and cobalt. Ac- cording to the dissociation theory we should expect all of the salts in solutions of this concentration to give apparent molecular ioi8 O. F. TOWER. weights much less than the true ones. The nickel and cobalt salts just mentioned, which give such high molecular weights, are the ones calling for special explanation. These exceptional results yielded by the freezing-point method are, however, in line with the conductivity determinations with the same salts. An adequate explanation of this peculiar behavior of the tar- trates and malates of nickel and cobalt is difficult to find. It was Walden 1 who first pointed out, working with magnesium salts, that the dissociation of the salts of dibasic acids with bivalent metals as measured by the conductivity was of a very different nature from the dissociation of the neutral sodium salts of the same acids. Bredig 2 has attempted to explain this difference on the assumption that the molecules of a salt, MgAc (Ac being the radical of a dibasic acid), split up into complex ions of the nature Mg x /Ac + >Ac and Mg\ — Mg/ X Ac as well as the simpler ones Mg and Ac. As the dilution increases the complex ions gradually tend to decompose into the simpler ones. The behavior of nickel and cobalt tartrates and malates has been shown to be very different from that of the magnesium salts of the same metals. The suggestion was made in the article to which reference has already been made, that the abnormal behavior of the tartrates of nickel and cobalt might be ascribed to polymerization of the molecules. The same would also apply to the malates. The molecule of nickel tartrate, for example, in solution would have the formula COONiOOC I I CHOH CHOH I I CHOH CHOH I I COONiOOC and would be dissociated in concentrated solutions into complex ions and as dilution proceeds into simpler ones in a manner similar to that indicated above for magnesium salts, the dissociation, how- 1 Loc. cii., p. 529, el seq. 2 Ztschr. phys. Client., 13, 202 (1894). ORGANIC SALTS OF NICKEL AND COBALT. IOig ever, being much less. This explanation differs from that of Bredig for magnesium salts in assuming the existence of double molecules in solution as well as of complex ions, and seems to have support in the apparent molecular weights derived from the freezing-point method. The application of Ostwald’s formula for basicity, as developed by Walden 1 for dibasic salts of bivalent metals, throws but little light on this question. The formula is A — Cnpi^ where A is the difference between the equivalent conductivities at v — 32 and v = 1024, n x is the basicity of the acid radical, n 2 is the valence of the metal, and C is a constant, equal usually to 10 or a little less. Only molecular conductivities are given in Table II so that the difference between the values at v — 32 and v — 1024 must be divided by two to make it comparable with the difference obtained with equivalent conductivities. When this is carried out for the nickel and cobalt salts the basicity is found to be two, just the same as when applied to the magnesium salts. Since, how- ever, the formula is wholly empirical, the results obtained by using it cannot be accepted without other support in the face of the values derived by the freezing-point method. If the Ostwald rule shows anything in this instance, it is rather to be interpreted as indicating that the complex ions decompose but little below the dilution, 1024. 2 If then the tartrates and malates of nickel and cobalt are polymerized in aqueous solution, the molecules of the succinates are surely not, for their conductivities are normal and the apparent molecular weights found by the freezing-point method also pre- clude any such condition. This seems to show that the presence of the hydroxyl groups in the tartaric and n?alic acids may have some influence in inducing polymerization of the nickel and cobalt salts. There appears to be ground for this in the fact that the results obtained with the tartrates reveal a greater degree of polymerization than those with the malates ; that is, the polymer- izing influence is apparently greater where two hydroxyl groups are present than where only one is present. 1 Loc. cit. 2 From the electromotive force of a cell containing a 1 / 5 0 molecular solution of nickel tartrate only about one-tenth of the nickel was found to exist in the ionic state. Tower : Loc. at.. p. 511. 1020 O. F. TOWER. That the presence of an hydroxyl group is the determining in- fluence in causing polymerization of the nickel and cobalt salts receives, however, no support from the results obtained by apply- ing methods similar to the above to the malonates and tartronates of nickel and cobalt. Conductivity and freezing-point determina- tions were carried out with these salts and also with the magne- sium salts of the same acids. The malonic acid was a preparation of Merck. The tartronic acid was made from dinitrotartaric acid according to Demole . 1 The yield was small, which accounts for only one set of determinations having been made. Molecular con- ductivities are given in Table V, and depressions of the freezing- point in Table VI. Table V. Nickel malonate. Cobalt malonate. V. M. v. M. V. M. V. M. 15.61 23.7 20.55 23.3 12.82 28.5 19.17 30.6 2 X 15.61 27.3 2 X 20.55 26.9 2 X 12.82 33-2 2 X i 9- I 7 35-7 4 X 15-61 32.1 4 X 20.55 31.8 4 x 12.82 39-6 4 X 19. J 7 42.4 8 X 15-61 39.9 8X20.55 39.O 8 X 12.82 48.6 8 X 19-17 52.3 16 X 15-61 49.4 16 X 20.55 49.5 16 X 12.82 61. 1 16 X 19.17 64.9 32 X 15.61 64.0 32 X 20.55 64.0 32 X 12.82 78.4 32 X I 9- I 7 81.5 64 X 15.61 80.2 64 x 12-82 96.0 Magnesium malonate. Nickel tartronate. V. M. V. M. V. M. 8.02 34.6 1 1 . OO 38.2 30.50 29.7 2 X 8.02 42.7 2 X II. OO 47.1 2 X 30.50 34-7 4 X 8.02 51-7 4 X 1 1. 00 59-2 4 X 30.50 40.3 8 X 8.02 64.7 8 X 1 1. 00 73-2 8 X 30.50 46.9 16 X 8.02 77-5 16 X 11. 00 88.7 16X30.50 54-5 32 X 8.02 93-8 32 X 1 1 .00 106.9 32 X 30.50 63.8 64 X 8.02 110.9 64 X 11. 00 126.8 Cobalt tartronate. Magnesium tartronate. V. M. V. M. 28.10 36.5 15-77 42.O 2 X 28.IO 43-3 2 X 15-77 51-3 4 X 28.10 50.6 4 X 15-77 61.9 8 X 28. 10 58.7 8 X 15.77 74-8 16 x 28.10 68.5 16 x 15.77 89.2 32 X 28.10 79*4 32 X J5-77 105.7 64 X 15-77 122.5 1 Ber. d. 1 them. Ges., 10 , 1789 (1877). ORGANIC SALTS OP NICKEL AND COBALT. 1021 TABLE VI. Nickel malonate. Substance in 100 cc. Apparent Grams. Depression. mol. wt. I.0300 O.150 0 131 C.7824 O.141 106 0.5150 0.090 109 0.2575 O.054 9 1 Magnesium malonate. 1.5750 O.298 101 1.1477 O.233 94 0.5738 0.134 82 0.2869 0.075 73 Cobalt tartronate. 0.6302 0.119 101 0.3151 0.071 85 0.1576 0.043 70 Cobalt malonate. Substance in 100 cc. Grams. Depression. Apparent mol. wt. i -1995 0.201° 114 0.8402 O.169 95 0.5998 O.H5 99 0.2999 O.066 86 Nickel tartronate. 0.5798 0.102 108 0.2899 O.065 85 0.1450 O.O39 7 i Magnesium tartronate. 0.9944 0.200 95 0.4972 O.I2I 78 0.2486 O.072 66 To bring- the results of these two tables to a uniform basis, interpolations have been made graphically, exactly as in the pre- ceding cases. These interpolated values will be found in Tables VII and VIII. Table VII. Molecular conductivity. , s Malonates. Tartronates. V . Nickel. Cobalt. Magne- sium. Magnesium. (Walden.) Nickel. Cobalt. Magne- sium. l6 23.O 30.0 43 *o .... 25.5 32.0 42.3 32 26.5 34.7 52.6 .... 29.9 37.8 51.5 64 3I.2 41.2 65.7 62.9 35 -i 44-7 62.4 128 38.2 51.2 79-5 77-5 40.8 52.2 75-3 256 47-8 64.0 95-9 95-4 47-3 60.3 89.9 512 80.4 IT 3-9 II 4.7 59-2 70.4 106.3 1024 77-2 99*3 i 35 .o 134.9 64.3 81.2 123.0 Table VIII. Malonates. Tartronates. , » ^ ( A „ Magne- Magne- Nickel. Cobalt, sium. Nickel. Cobalt, sium. Molecular weight from formula 161 161 126 177 177 142 • Values interpolated (v= 16 121 104 87 94 from Table V. \z; = 2> 2 101 9 1 77 106 98 77 It is seen in these cases as heretofore, that the nickel and cobalt salts possess lower molecular conductivities and higher apparent molecular weights than the corresponding magnesium salts. Al- 1022 ORGANIC SALTS OF NICKEL AND COBALT. though the conductivities of all these salts are less than for the corresponding succinates, still the relative differences between the conductivities of the nickel, cobalt, and magnesium salts are about the same as in the case of the succinates. No such differences exist, as were found between the conductivities of the tartrates and malates of magnesium and those of the corresponding nickel and cobalt salts. The conductivities of the magnesium salts of malonic and tartronic acids are considerably less than the con- ductivities of any of the other magnesium salts investigated. This was noticed by Walden in the case of the malonate. B redig’s ex- planation of such behavior has already been referred to. The im- portant point to notice in connection with these last results is, however, that the conductivities of the nickel and cobalt tartron- ates are not appreciably less than the conductivities of the same malonates, although tartronic acid possesses an hydroxyl group. Any explanation of the conduct of these salts based on the pres- ence of an hydroxyl group in the molecule, therefore, appears to be untenable. Before letting the question rest here, however, a few consider- ations bearing upon the point under discussion will be mentioned. The strength of the acids of the succinic acid series (i. e., succinic, malic, and tartaric acids), as is well known, increases with the number of hydroxyl groups present, Ostwald’s affinity constants being for succinic acid 0.0066, for malic acid 0.0395, f° r tartaric acid 0.097. 1 The hydroxyl groups have therefore a distinct effect on the strength of the acids. In the case of malonic and tartronic acids a very different effect is observed. The Ostwald constant for malonic acid is 0.158 and for tartronic acid 0.107 ; that is, the intro- duction of an hydroxyl group has here decreased the strength of the acid. Such being the facts with regard to the acids, it seems probable that salts of the succinic acid series might show very different gradations in properties from the same salts of the malonic acid series. Then before asserting that the presence of the hydroxyl groups in malic and tartaric acids has no effect on the behavior of their nickel and cobalt salts, it is necessary to ex- tend investigations similar to these to the salts of the glutaric acid series or some higher one. Such work is contemplated in the future. 1 The values given are for K = 100L See Ztschr. phys. them 3, 418 (1889). ORGANIC SALTS OF NICKEL AND COBALT. 1023 Iii conclusion, however, it may be stated that aqueous solutions of nickel and cobalt salts of dibasic organic acids offer greater resistance to the passage of the electric current than solutions of similar salts of the other metals investigated, notably magnesium, and that this resistance is exceptionally great in the case of the tartrates and malates of nickel and cobalt. This abnormal be- havior of the last-named salts is also confirmed by the results ob- tained with the freezing-point method for determining molecular weights. Western Reserve University, Cleveland, O., June, 1902.