1346 RIVETT AND O’CONNOR SOME TERNARY CXXV.-Some Ternar,y Systems containing Alkali Oxalates and Water. By ALBERT CHERBURY DAVID RIVETT and EDMUND ARTHUR O’CONNOR. THERE has been considerable discussion a t various times regarding the alleged formation of certain double oxalates of the alkali metals. Wenzel is quoted by some early writers as maintaining the existence of t.he double salts K,C204,Na,C,04 and but Rammelsberg ( A I ~ . Pltys. Chem. 1850 [ii] 79 662) has thrown doubt on the one case and Souchay and Lenssen (,4nnalen, 1856 99 31) on the other. Foote and Andrew (Amer. Chent. J. 1905 34 164) drew the same conclusions as Rammelsberg and Souchay and Lenssen and claimed to have shown that these double oxalates do not exist a t 25O in the solid state. They state that the solid monohydrates of potassium and ammonium oxalates remain in equilibrium with a common saturated solution and that the same holds for anhydrous sodium and hydrated potassium oxalates.A few years later, Barbier (Bull. SOC. chim. 1908 [iv] 3 725) described a double oxalate of potassium and ammonium stating that it might readily be formed by adding a concentrated solution of potassium oxalate to a saturated solution of ammonium carbonate. The analysis he quotes points to a pure 1 :I anhydrous double salt. w 2 0 4 (NH4)2C204 SYSTEMS CONTAINIETQ ALKALI OXALATBS ASD WATER 1347 None of the authors mentioned made complete investigationa by the solubility method. Pooh and Andrew (Zoc. c&.) obtained a few solubility figures but to determine the solid phases present they relied on a general principle laid down in a previous paper (ibid.p. 153) that when two salts are mixed in varying propor-tions and treated with water a t a constant temperature the resi-due of undissolved solid remains constant in composition and the solution varies if a pure double salt is present whilst on the other hand the residue varies and the solution remains constant in composition when a mere mixture of the two single salts is present. This rule is liable to mislead if only because it does not take into account the possibility of the formation of mixed crystals (solid solutions). It has seemed worth while therefore to apply the solubility method more fully to some of these ternary systems of alkali oxalates in water. Knowledge of the solid phases present has been obtained by the customary graphic method of plotting in a triangular diagram the percentage compositions of pure solution and of the moist solid (or “residue ”) in equilibrium with it and extrapolating the straight line joining the two poinb to the com-position of the pure solid uncontaminated with adhering solution.The systems investigated are those containing potassium sodium, and ammonium oxalates in pairs with water. The solid phases of the individual salts stable a t these temperatures with their own aqueous solutions are respectively K,C,O,,H,O (NH,),C,O4,H20, and N%C20,. EXPERIMENTAL. I. System K,C,O,-(NH,),C,O,-H,O at 2 5 O and 50°. The system potassium oxalate ammonium oxalate and water has been examined at 2 5 O and 50° and the figures obtained are given in tables I and 11 respectively and plotted in Fig.1. $uitable mixtures of the salts (monohydrates) and water were heated in bottles which were sealed and placed in a thermostat, in which they were continuously rotated for about forty-eight hours. Undissolved solid was allowed to settle and clear solution drawn into a pipette through a small plug of cotton wool held in rubber tubing. A known weight was diluted to a suitable volume for subsequent analyses. Residues were obtained by pouring solu-tion and suspended solid on to a Buchner funnel drawing the solution through rapidly by means of a pump but disconnecting the pump before more than a very small amount of air had been 3 E 1348 RIVETT AND O'CONNOB SOME TIBRHARY drawn through the moist solid.A slight loss of waterr vapour a t 50° ia inevitable but with rapid working it can be made almost negligible. Total oxalate was determined by titration of a fraction of the stock aolution with standard potassium permanganate ammonium by distillation with alkali and absorption of ammonia in standard acid and potassium by difference. Concentrationa have been ex-pressed in percentages by weight but as densities have been deter-mined in all cases figures for concentrations in other terms are readily obtainable. TDLE I. 250. No. 1 2 R 2 3 R 3 4 R 4 6 R 5 6 7 8 9 R 9 10 R 10 11 R 11 12 R 12 13 14 16 16 Density. 1.021 1.040 -1.058 1.068 1.087 1.1 07 1.124 1.128 1.137 --1.166 1.185 1.204 1.217 ---1.216 1.216 1.216 Percentage composition of solution or residue (R).K2C2OI. -2.67 0.44 4.32 2-41 6.6 1 2-75 9-48 2.62 12.10 14.18 16.37 16.54 2.14 19-39 4-37 21.9 6.70 24.3 13.4 26.9 26.3 26.8 27-2 (NH*),CZO'~ 5-01 4-72 81.3 66.4 61.1 72-3 4.48 4-38 4-16 4.01 3-78 3.68 3-67 3.32 3-10 2.90 2.76 80.4 '76-4 76.2 61.9 1.83 0.85 c H20. 96.0 92.6 18.3 91.2 41.2 89-1 36.1 86.4 26.1 83.9 81.0 80.9 79-9 17.2 77.3 19.2 78.0 19.2 72.8 24.7 7 1.3 71.0 72-3 72.8 Solid phases. (NH,),C*O,H,O. Solid solution o SYSTENS UONTBZNINQ ALKALI OXALATES AND WATER. 1349 TABLE 11.50°. NO. 1 2 3 R 3 4 R 4 6 R 6 6 R 6 c 8 9 R 9 10 Percentage composition of solution or residue (R). h Density. K4C20,. (NH4),C,04. q0. 1.034 - 9.63 90.4 1.080 7.99 8-44 834 1.136 1-164 1.187 1403 1.254 ---16.20 4.20 17.99 6-72 22.4 13.3 24.4 16.2 30.4 7.10 6-79 6-10 6.76 4-78 70.0 66.7 55.9 66.3 76.7 26.8 76.2 27-6 7 1.6 30.8 69.8 28-5 64-8 1.261 31.0 3.34 65-7 1.262 31.6 2-64 65.9 7 76.6 0.47 24-0 1.252 33-1 - 66.9 FIU. 1. With the exception of some of the reaidues these rwults are plotted in Fig. 1 and show distinctly that only two solubility 3 E" 1350 RIYETT AND O’OONNOR SOM’E TERNARY curves are obtainable a t each of these temperatures the two meet-ing sharply a t a quadruple (or condensed triple) point.There is no evidence a t all of the existence of a double salt. On the other hand it is quite apparent from the relations between compositions of solutions and corresponding residues (shown only for 50°) that the solid phase present in those complexes in which excess of ammonium oxalate is taken (curve CB) is not this pure solid but contains in addition some potassium oxalate. The pro-portions of the two in the solid vary according to the composition of the solution in equilibrium and the evidence is definite that mixed crystals of the two salts are produced. The more potassium oxalate there is in the solution the more there is in the solid. The same must hold with regard to the solids in equilibrium along the curve A B .These solids will be mainly potassium oxalate with steadily increasing proportions of ammonium oxalate. The amounts of ammonium oxalate in solutions along this curve are, however so small that a slight error in the analysis of the residue may make the extrapolation method uncertain in showing the solid phase. Some of the mixed crystals were dried by draining on a porous tile in a closed $essel immersed in the thermostat. Analysis proved the two constituents of these mixed crystals to be the respective monohydrahs. The form of the isotherms with a sharp change of direction a t B shows that two distinct solid phases must be present at this a univariant point. It follows that the series of mixed crystals is not complete but that there is a limit to the solubility of each solid in the other.The compositions are also not given by such points as B and E in Fig. 1 those of the exact solid solutions in equilibrium with the corresponding liquid solutions a t the other ends of the tie-lines. Some of the crystals may have had a core of the pure maih con-stituent so that the mean composition represented by D and E may be low in potassium oxalate as compared with the solid solu-tion itself. All that is established is the existence of mixed er ystals . The work of Foote and Andrew (Zoc. cit.) is not quite extended enough to show this. They obtained only the points A B and C a t 25O. It has been found impossible t o repeat the work of Barbier (Zoc. cit.) which pointed to the formation of an anhydroua double salt IC,CzO4,(NH4),C20,.By following closely the method which he desoribed for isolating the compound crystals were precipitated which after drying on a porous tile contained 81.1 per cent. of These limits have not been determined SYSTEMS (JONTAININB ALKALI OXALATES AND WATER. 1351 ammonium oxalate 5'8 per cent. of potassium oxalate and (by difference) 13.1 per cent. of water. After washing with a solution of ammonia as recommended by Barbier the proportion of potassium oxalate decreased slightly. It appears certain that this precipitate consists of mixed crystals of the two hydrates. It is of interest to note that Souchay and Lenssen (Zoc. cit.), following Wenzel's instructions for preparing the alleged double salt obtained crystals which they stated to be ammonium oxalate, but containing 0.9 per cent.potash. 11. System Na,C20,-(NH,),C,0,-H,0 at 2 5 O and 50". Sodium oxalate differs from both the potassium and ammonium salts in crystallising anhydrous from aqueous solution; hence it is less likely that mixed crystals will be formed between it and either of the other two. The figures in tables I11 and IV show that neither double salt nor mixed crystals occur in the sodium-ammonium system a t 2 5 O or 50°. The method of analysis was similar to that adopted for the previous system. TABLE III. 26O. Percentage composition of solution or residue (R). No. 1 2 3 R 3 4 6 6 7 8 9 R 9 10 11 Density. 1.027 1.030 1.033 1.037 1 to39 1.043 1.047 1.043 1.035 1.028 1.021 --Na,C,04.3.73 3-69 3-65 3-50 3.51 3.46 3.41 2.86 1-82 0.40 0.89 63.9 -(m4)2cZ04. H 2 0 . - 96.3 0.74 95.6 1.49 94.6 0.53 35.6 2-48 94.0 2-89 93.6 3-77 92.8 4.74 91.8 4-76 92.4 4.81 93-4 66.9 32.7 4.88 94.2 6-01 96.0 Solid phases. Na,C,O, 1352 NO. 1 2 3 4 R 4 5 6 R 6 7 8 R 8 9 10 11 Density. 1.023 1*M1 1.036 1-044 1.049 1.066 1.063 1.059 1.051 1,042 1-034 --I TABLE IV. 50°. Percentage oomposition of solution or reeidue (R). r A \ Na,C,O,. (NH&C,Op H2O. 96-6 4-54 -4-46 1.59 94.0 4.37 3.14 92.5 4.28 4.64 91.1 70.0 1-47 28.5 4-29 6.12 89.6 4-13 7.86 $8.0 66.7 3-64 39-8 4.05 9.19 86.8 3-57 9-21 87-2 €047 63-4 36.1 2-44 9.32 88.2 1.25 9-46 89.3 9.63 90.4 -Fra.2. Solid phases. Na,Ca04. The results are plotted in Fig. 2 where on account of the sparing solubilities of the two components only a single angle of the triangle is shown. The residues are omitted. 111. System .- K,C20,-Na,C20,-H20 at 25O. Foote and Andrew (Zoc. c i t . ) concluded that anhydrous sodium oxalate and the monohydrate of potassium oxalate can exist sid SYSTEMS CONTAJBINQ ALKALI OXALATES AND WATER. 1363 by side in equilibrium with a common saturated solution and the figures in table V plotted in Fig. 3 confirm this showing that neither double salts nor mixed crystals are formed. Solutions and residues were analysed by determining total oxalate by titration and total anhydrous salts by weighing after evaporation and dry-ing a t 125O a t which itemperatwe potassium oxalate monohydrate is readily dehydrated.As the amount of sodium oxalate present is always relatively small this indirect method is less accurate than that employed in the previous two cases. FIG. 3. N O . 1 2 3 4 R 4 5 6 R 6 7 8 9 10 Density. 11215 1.218 1.223 1.226 1.228 1,178 1.136 1.084 1-067 1.026 -K,C;04. 27.2 26.8 26.3 26-2 81.9 26.1 19-6 14.4 7-00 8-10 3.99 -Na2C2O4. H2O. - 72.8 0.77 72.4 2.17 71.6 0.73 17.4 2.50 71.4 1-71 7,2.0 3.21 77-2 65.3 27.7 3.21 82.4 3-40 88.6 3.71 92-3 3.7 1 96.3 TAfiLi. -v. 25" Percentage composition of solution or residue (R). K,C204,7H20 and Na2C,01. Na,C,O4 1364 PRICE THE DEUOMPOSITION OF Summary. (1) It has been stated by some authors and denied by others that potassium and ammonium oxalates form a double salt. Iso-therms have been obtained a t 2 5 O and 50° and show that a t these temperatures mixed crystals of the monohydrates are formed. (2) Anhydrous sodium oxalate has been shown to exist in equil-ibrium with ammonium oxalate monohydrate and a common, saturated solution at 2 5 O and 50°. Neither double salts nor mixed crystals are formed. (3) The same has been shown to be the case at 2 5 O with anhydrous sodium oxalate and potassium oxalate monohydrate. W N I V E I C S ~ ~ ~ OF MELBOURNE. [ReeCived Nwember lat 1919.