2846 GLASSTONE AND RIGGS CO-X FOEBfA!L'ION CCCXCIV.-Complex Formation in Lead Nitrate Solu-tions. Part I I . The Quaternary System Potassium Nitrate-Lead Nitrate-Barium Nitrate- Water. By SAMUEL GLASSTONE and ERKEST J. RIGGS. THE primary object of the present work was to investigate the quaternary system lead nitratebarium nitrate-potassium nitrate-water a t 25" and at 50" and hence it was required t o have a knowledge of the three ternary systems KN0,-Pb(NO,),-H,O KN0,-Ba(NO,),-H,O and Pb(N0,)2-Ba(N0,)2-H,0 at the same temper-atures. The h t of these three systems has been investigated by Glasstone and Saunders (J. 1923 123 2134) a t 25" and 50"; the second has been examined at 9.1" 21.1" and 35" by Findlay Morgan, and Morris (ibid. 1914,105 779) and to a limited extent a t 25" by Foote (Amer.Chem. J . 1904 32 251); the 25"-isothermal for the third system was investigated by Fock (2. Kryst. 1897 28 337). Before the quaternary system was examined therefore Foote's measurements on the ternary system KNO,-Ba(NO,),-&O at 25" were exfended and the 50"-isotherm was determined completely ; Fock's work a t 25" was repeated because this author did not use the Schreinemakers residue method for the determination of the com-position of the solid phase and the 50O-isotherm for the syste TX LEAD "RATE SOLUTIONS. PABT II. 2847 Pb(N0,),-Ba(N03)2-H,0 was also determined. Finally the quaternary system Pb(N0,)2-Ba(N03)2-KN03-€&0 was investi-gated as completely as possible at 25" and 50". It was hoped to obtain through this investigation further evidence for the existence of a double or complex salt of lead nitrate and potassium nitrate, the presence of which has already been suspected in solutions con-taining these two salts (see Glasstone and Saunders loc.cit.). Lead and barium nitrates have an almost identical crystal structure (Vegard 2. Physik 1922 9 395) and separate from solutions con-taining both salts as a continuous series of mixed crystals; further, potassium and barium nitrates form a double salt 2KN03,Ba(N03), (Foote h. cit.) and consequently it was thought possible that when this double salt separated from a solution containing lead barium, and potassium nitrates there might be a tendency for it potassium nitratelead nitrate double salt with a similar structure which has no stable existence at the ordinary temperature to separate with it as a mixed crystal.This idea was based on the well-hown existence of ~ 0 7 H 2 0 in the form of a mixed crystal with FeS04,7H20, and %he recent preparation by Richards and Meldnun ( J . Amr. C h . Soc. 1921 43 1543) of Na,S0,,4€&0 which does not exist by itself as a mixed crystal with Na2Cr04,4H,0. The resulb of the present work indicate that lead nitrate can exist in some form which is isomorphous with either potassium nitrate or with the potassium-barium double nitrate; the most probable form is as the double salt 2KN03,Pb(N03), which hm no stable existence at the ordinary temperature but might separate as a mixed crystal with E X P E R I M E N T A L . General Prdure.-In the case of the second of the ternary systems mentioned above the procedure was the same as that followed in the first part of this work (Glasstone and Saunders h.cit.); for the third ternary system and the quaternary system, however owing to the deposition of mixed crystals it was essential that very little of the solid phase should separate and consequently the mixed solids were made fo dissolve in water at a temperature just above that at which the isotherm was being determined and the solution was stirred in a thermostat until sufficient solid for analyais had separated as the result of evaporation. Method of AnaZysis.-The amounts of water in the saturated solutions and wet solids were determined by drying known weights first on the water-bath then in an air-oven at l l O o and finally at 130".The dry solid was then dissolved in water made up to a known volume and an aliquot portion taken for analysis. If the ~ ~ O ~ Y ~ ( N O ~ ) 2848 BLASSTONE AND RIGBS COMPLEX FORMATION solution contained only potassium and barium nitrates the barium was precipitated directly M sulphate with sulphuric acid and the barium sulphate was washed dried and weighed. When the solu-tion for analysis contained lead and barium nitrates only hydrogen sulphide was passed into the warmed solution until all the lead was precipitated; the precipitate of lead sulphide was filtered off, washed with a solution of hydrogen sulphide and the barium in the filtrate estimated as sulphate. The amount of lead was usually found by difference but in several cases the sulphide was dissolved in hot dilute nitric acid and the lead estimated as sulphate by the method described in Treadwell’s ‘‘ Quantitative Analysis ” (1919, p.174). When the solution to be analysed contained all three nitrates both the lead and the barium were determined by the methods described above and the potassium was obtained by difference. The analytical method was tested beforehand on mixtures of known weights of the various nitrates and found to be quite satisfactory IN LEAD NFI!BATE SOLUTIONS. PdaT II. R&.-These are all given at3 percentages. /--KNO,. 27.39 27.67 17-14 9-13 3.80 0.00 *14-8 k0,. 45.45 44.88 44.66 40.3 1 35-75 30-08 28-86 24-14 18.76 10-53 3.93 0.00 2849 KN0,-Ba(NO,),-H,O at 25".Solution. Rest. Ba(NO,),. H,O. KNO,. Bs(NO,),. H,O. Solid phase. - / -.-- -. -0 0.00 72.61 - - -2.44 69-89 78-65 4-84 16.51 KNO + D.S. 4-88 77.98 39-31 49.67 11.02 D.S. 6.6 78-6 - - - D.S. + Ba(NO,), 6-57 84.30 1-18 92.26 6.56 Ba(NOS)* 7.72 88.48 1-05 91-18 7.77 I9 9.28 90-72 - - -D.S. refers to the double salt 2KNO,,Ba(NO,),. * Taken from Foote Eoc. cd. 99 Solution. c BWO,),. 2.34 4-22 5.11 5.64 6.99 10-16 10-81 10.43 10.14 10-92 12.73 14.63 KN03-7 H,O. 52-21 50.90 50.23 54-05 57.26 59-76 60.33 65-43 71-10 78-55 83-34 85-37 -Ba(NO,),-H,O at Rest. . - .. ___ KNO,. Ba(NO,),. 87.05 0.65 84.20 1.25 74-36 3-87 42.78 50.55 42-38 46.05 41-56 50.93 2-18 92-55 0.02 95.39 2-28 93.48 1-33 95.39 1.07 95.85 - -50".H,O. 12.30 14.55 21-77 6.67 11.57 7-51 5-27 4.59 4.24 3.28 3.08 -Solid phase. I&O + D.S. D.S. D S . + Ba(NO,), =o, S Y Ba(NOd2 The results obtained for this system are represented in Fig. 1. Pb( NO,),-Ba( NO,),-H,O at 25". Solution. Pb(N0a)p Ba(N0A. 34.60 1.39 31-13 2.65 22.73 4.23 16.21 5.29 8.96 6.66 6-26 7-31 1.63 8.64 -Solution. - Pb(N0a)v Rs(h'O,)z 40.82 2.57 37-78 3.83 29.31 6-38 17-05 9.12 10.34 11-05 5.72 12-85 -7 HtO. 64-01 66.22 73-04 78-50 84-38 8643 89.73 Rest. Solid phese. Pb(NOa)a* 8 1-83 66.90 38.08 15.06 10.15 3.44 -Ba(NO,)p 11.26 18.90 56.67 80-02 84.28 89-54 -Y HSO. 6.91 14.20 5-25 4-92 5-57 7.02 -Pb(NOJ2.87.54 76-56 39.27 15.44 10.42 3-59 -Ba(NO;h. 12-46 23-44 60.73 84-66 89-58 96-41 -Pb (NO,) 2-Ba (NO,) 2-H,0 at 50". Rest. Solid phase. _- - - -_ H,O. Pb(NOa)z. Ba(N0,):. HSO. P/b(NO,h. Ba(XO;)*. 56-61 77-06 9.54 13.40 88.31 11.69 58-39 63.40 26-10 10.50 69-02 30.98 64-37 40.31 55.14 4.55 41.25 58-75 73.83 78-61 8-92 83-87 7-21 8.78 91.22 81-60 6-60 87.70 5.70 6.67 93.33 - I - - 2850 GLASSTONE AND ~ Q B S COMPLEX FORMATION The results obtained for this system we represented in the usual mmner in Fig. 2. In the columns headed " solid phase " me given ma. 2. H20 FIG. 3. FIG. 4. 25' yo Pb(NO,) in Pb(NO,) + Ba(NO,) in solutions. Circles rqreent point8 from the ternary system; square.8 points from the q u a t e m r y aystem.the compositions of the mixed crystals which separate from the various solutions in the dry state ; these results were obtained fro IN LEAD KITRATE SOLUTIONS. PART II. 2851 the amlpb of the wet solid by allowing for the amounts of salt present in the adherent mother-liquor. Fig. 3 gives the gram-percentage of lead nitrate in the mixed crystals against the gmm-percentage of lead nitrate in the total salt dissolved in the solution from which the crystals separate at 25" whilst Fig. 4 gives the corresponding curve at 50". KN03-Pb(N03)2-Ba(N03)2-H20 at 25". Solution. Dry solid. 7- - KNO,. Pb(N0,)- Ba(NO,)*. H,O? &Ow Pb(N0,)I. Ba(NO,).. phases. 15.26 2.12 6-05 76-57 43.23 0.10 56.67 D.S.+ M.C. 17.39 11-44 3-40 67.77 41-98 0.43 57.59 ,, 15-99 13.82 4.76 65-43 43.45 0.80 55.75 ,, 16.01 21.25 4-33 58-41 43-51 1.70 54.79 ,, 15.65 26.59 4.06 53-70 0.88 31-36 67.76 ,, 17.87 35.90 2.46 43.77 23-10 14.95 61.95 ,, 23-41 37.68 2.11 36.80 23.78 38-10 38.12 25.75 34-65 1.16 38.44 69.45 4-42 26-13 D.S.? M.C.+ I(N0, 26.78 23.26 1.76 48.20 92-31 0.61 7.08 99 27-23 15-28 2-32 55-17 96.06 0-23 3.71 Y Y 27.69 9.85 1.87 60.59 92-13 0.10 7-77 1 3 27.74 4-95 1.92 65-39 63.28 0.30 36.42 25.22 40.46 0-72 33.60 45.44 51-86 2-70 mo:'+ M.C.25-00 39.84 1-18 33-98 2-11 28-02 69.87 Y Y 25-00 38.00 1-59 35.41 10.61 76.19 13.20 9 9 24-91 37-48 1.80 35.81 94.90 1.31 3.79 9 , 25.74 32.63 1.92 39.71 91.23 1-36 7.41 D.S.+ -0, M.C. refers to Pb(NO,),-Ba(NO,) mixed crystal. KN03-Pb(N03)2-Ba(N0,),-H,0 at 50".Solution. Dry solid. ENO,. 27.40 28.28 32-61 35.48 36.91 38-06 39-43 40.90 41-39 41-86 33.25 33-41 32-64 Pb(NOa)** 15-89 27.00 38-93 33.62 29-22 24-98 19-96 14.64 13.01 10.35 40.88 40.19 39-82 Ba(NOdI. 8.11 6-68 2.15 2-01 2.24 2.59 2-85 3-32 3.44 3-69 1-02 1-51 2-40 - HZO. 48-60 39-04 26-31 28-89 ' 3 1.63 34.37 37-76 41-14 42.16 44.10 24.85 24-89 25.14 7 mow 1-04 9.4 1 15-02 91-53 92.65 65.31 57-61 64-03 71.12 97.69 53.25 34.54 46.76 Pb(NOt)r 6.15 11-94 47-42 1-02 0-00 1-62 0.94 0.65 0-44 0.19 43-15 35.58 46-12 B ~ ( N o ~ . Phases. 92.81 D.S.+ M.C. 78-65 ,, 37-56 7.45 D.S.? KNO, 7-35 9 , 33.07 Y Y 41.45 Y Y 45.32 9 , 28-44 9 , 2-12 3-60 KNO:'+ M.C.29.88 9 9 7.12 9 , The two isotherms in this quaternary system have been drawn from the above results by the method of Schreinemakers as this was found to give the least confusing diagram and are represented in Fig. 5. The points A By and C represent the composition of ternary liquids which are in equilibrium with two solid phases-potassium nitrate and double salt double salt and lead nitrate and potassium and lead nitrates reapectively-whilst the points on the 5 D 2852 GLASSTONE AND RIGGS COMPLEX FORMATION curves AD BD and CD give the composition of quaternary solutions in equilibrium with double salt and potassium nitrate double salt and mixed crystal and potassium nitrate and mixed crystal re-spectively.The point D represents the composition of the quater-nary isothermal invariant solution. The composition of the dry solid given in the above tables was obtained by calculating from the analysis of the solutions the amounh of the three nitrates dissolved in the water which was present in the wet solid and deducting FIG. 5. Ba"O,)* KNO, WNO,), these from the total amounts found by the analysis of the dried residue. An examination of the results given above for t'he quaternary system shows that when the two solid phases in equilibrium with saturated solution should consist only of potassium nitrate and double salt there is also present a small amount of lead salt; the results are so consistent as to rule out the possibility of experimental error.The presence of lead has been confirmed by washing the wet solids with a little water and grinding the residue at 30-35" with a solution containing roughly 25% of potassium nitrate and 2 IN LEAD NITRATE SOLUTfONS. PART 11. 2853 of barium nitrate which dissolves lead nitrate very readily. The solid was then filtered off and ground up with a fresh portion of the solution; this process was repeated several times but even after ten treatments the solid residue still contained an appreciable quantity of lead salt. These results indicate that lead nitrate in some form is separating as a mixed crystal either with potassium nitrate or else with the double salt. The most probable explana-tion is that the double salt 2KN03,Pb(N03)2 which has no stable existence alone under ordinary conditions is separating out from solution as a mixed crystal with the barium double salt of s i m h formula.Other explanations are of course possible but they seem to be less probable. In order to obtain if possible further evidence for the existence of the double salt of lead and potassium nitrates the results for the systems from which the potassium-barium double nitrate and mixed crystals of lead and barium nitrates separate were examined &B follows. It was msumed as a first approximation that all the potassium nitrate in the solid phase was in the form of the double salt with barium nitrate and so the aaount of barium nitrate present as double salt was calculated; the residual barium nitrate was assumed to be present as mixed crystal with lead nitrate.In this way the ratio of lead nitrate to barium nitrate in the mixed crystal was determined and compared with the ratio of these two salts in the quaternary solution. The results are given below. Pb(NO*) Pb (NO,), Pb(NO,) + Ba(NO,) %* '0° Pb(NO,) + Ba(NO,) %* 25' Solution. Mixed crystal. Solution. Blixed crysfal. 94-69 82.49 94.75 72.35 86.76 32.00 82-62 15-09 77-07 12-78 66.20 6.32 25.95 10-67 These results have been plotted in Figs. 3 and 4 for 25" and 50" respectively for the purpose of comparison with the results for the ternary system. It is seen that for a given ratio of lead nitrate to barium nitrate in the solution the mixed crystal separating from the ternary solution contains relatively more lead than does that separating from the quaternary system ; if a lead-potassium nitrate double salt had been present then the reverse would have been expected. It is possible however that the presence of pohsium nitrate in the solution alters the ratio of lead to barium in the mixed crystal and so no definite conclusiom can be drawn frgm the results. Summary. (1) The ternary systems KN0,-Ba(N0,)2-H20 and Pb(N03),-Ba(NO3),-H2O have been investigated a t 25" and 50". 5 D * 2854 KNECHT AND EIIBBERT THE BE€IAVIOUR OF GLUCOSE AND (2) The quaternary system KN03-Ba(N03)z-Pb(N03)z-H20 has been investigated at 25" and 50". (3) There is shown to be some evidence for the existence of a double salt 2KN03,Pb(N0,), in the form of a mixed crystal with the double salt 2KNO3,Ba(hTO3),. UNIVERSITY COLLEGE EXETER. [Received November 3 4 1925.