at 25° is (mols./1000 mols. of water) MgSO4, 11.6; NaSO4, 26-0; NaCl, 26.3. Diverse numbers obtained by other investigators are quoted. J. S. CARTER. Univariant Thermal decomposition of chloro-salts of metals of the platinum group. systems. G. GIRE (Ann. Chim., 1925, [x], 4, 183221). The univariant systems MM'CI solid = M' solid+2MCI solid+2Cl2 gas-Q, where M=Na or K and M'=Pt, Ir, or Rh, have been studied by measurements of the dissociation pressures of the salts over wide ranges of temperature. All the reactions are shown to be completely reversible within the temperature limits of the investigation. The dissociation of potassium chloroplatinate becomes apparent at about 600°, the curve (log p-1/T) consisting of two straight lines intersecting at 774°, the latter portion of the curve being inclined at a greater angle to the abscissæ axis, due to the heat of fusion of the potassium chloride (m. p. 774°), the system above this temperature being of the type solid solid+liquid+gas-Q'. The values for the heats of reaction Q and Q' determined from the curve are 38-6 Cal. and 46-0 Cal., respectively, whence the value of the molecular heat of fusion of potassium chloride (Q'-Q-S) is 7.4 Cal. This is higher than the value determined directly (cf. Schemtschuschny and Rambach, A., 1910, ii, 204), the difference being due to the heat of solution of the potassium chloroplatinate, which is found to dissolve in fused potassium chloride. The dissociation pressure of potassium chloroplatinite (cf. Vezes, A., 1899, ii, 492) is initially much higher than that of the chloroplatinate at the same temperature, but rapidly approximates to the latter. The dissociation of sodium and barium chloroplatinates (cf. Gire, A., 1922, ii, 551) was not investigated up to the m. p. of the chlorides, and hence the curves are straight lines. Dissociation is apparent at about 500° and 400°, respectively, the pressure reaching 1 atm. at 717° and 676°, respectively. The curve for potassium chloroiridate resembles that for the chloroplatinate, since the liquid phase is again introduced. Dissociation is observed at 575°, and intersection of the two portions of the curve occurs at 774°, the values of Q, Q', and S being 36-1, 41-2, and 5.1 Cal., respectively. Measurements of the dissociation pressures of an intimate mixture of potassium chloroiridate and potassium chloride corresponding with 2K,IrCl+2KCI 2K,IrCl+Cl2 gave 764° as the m. p. of potassium chloride in this system, whence the values for Q, Q', and S are 32-1, 23-3, and 4.4 Cal., respectively, the low value for S being due to the negative heat of solution of the chloroiridite in the fused potassium chloride. Sodium chlororhodate shows measurable dissociation at 600°; the two portions of the curve intersect at 790°. The heating curve of the mixture shows a second arrest at 904°, the m. p. of the sodium chlororhodate, whence Q, Q', and S have the values 35-3, 46-0, and 45-35 Cal., respectively. J. W. BAKER. Thermal decomposition of chloro-salts of metals of the platinum group. Calorimetric investigations. G. GIRE (Ann. Chim., 1925, 4, 370-409).-Measurements have been made of the heats of solution of various salts of the type M,M'Cl, the thermal decomposition of which has been already studied (cf. preceding abstract), and of the heats of the reactions M2M'Cl+2Co-M'+2CoCl2+2MC1+q, whence, since the heat of the reaction 2Co+2Cl2= 2CoCl2+q is 94-8 Cal. (Thomsen, J. pr. Chem., 1877, 15, 435; Pigeon, A., 1894, ii, 455), the heats of formation of MM'Cl, could be determined. The heats of solution, obtained by direct measurement, for potassium, sodium, and barium chloroplatinates (anhydrous) are, respectively, -12.15, +7-10, and +9-05 Cal. (-1-06 Cal. for the hexahydrate of the of formation of the solid salts, +91-2, +79-6, and barium salt), and the corresponding molecular heats +82-1; and for the dissolved salts, +88.7, +90-50, Thomsen and Pigeon (loc. cit.) that the heats of formand 88-70 Cal., respectively. The hypothesis of ation in solution of all the chloroplatinates from the ation in solution of all the chloroplatinates from the value obtained is 89 Cal. instead of the value 85 Cal. chlorides are the same is thus verified, but the mean given by the earlier investigators. Sodium chlororhodate crystallises with 12 mols. of water, thus confirming the formula Na,RhCl, 12H2O assigned to it by Gutbier and Hüttlinger (cf. A., 1908, ii, 200). The heats of solution of the hydrated and anhydrous the heat of formation of the solid salt is 74-4 Cal. salts are, respectively, -20-56 and +7-70 Cal. and The heats of solution of potassium chloroiridate and chloroiridite, K,IrCl, are -13.12 and -7.90 Cal., respectively. Reduction of the chloroiridate either with cobalt or chromous chloride occurs in two stages: 2K,IrCl+2KCl=2K,IrCl+Cl2-Q and 2K,IrCl=2Ir+6KCl+3Cl2+Q, the second stage being too slow to permit of calorimetric measurements. heat of the first reaction was obtained by the addition An approximate value, -29 to 30 Cal. (low) for the of 5% of potassium chloride to the solution to suppress the second reaction. The solubility of potassium chloroiridate is 0.66 g. and 1-12 g. per 100 g. of water at 0° and 20°, respectively. From the dissociation curves obtained (cf. preceding abstract) the value a mean value of 0.0325 being obtained (that for sodium of Q/T is deduced for each of the systems studied, chlororhodate is slightly lower). Similar calculations applied to the published data for a large number of other univariant systems give Q/T=0.032 for compounds of the type MCI, NH,, 0.028 for the dissociation of hydrates, and values varying between 0.028 and 0-034 for other systems, whilst the dissociation of auric chloride, a reaction similar to those studied, gives a value 0-0326: hence for each group of similar reactions Q/T has a definite value which, in disagreement with Nernst's hypothesis, seems to be independent of temperature. The application of the results to the constitution of the salts on Werner's theory is discussed. J. W. BAKER. (MLLE.) G. MARCHAL (J. Chim. phys., 1925, 22, Thermal decomposition of metallic sulphates. 493-517). The thermal decomposition of anhydrous magnesium sulphate can be detected at about 880°; from this temperature to beyond the m. p. (1155°), the total pressure of the dissociation products follows the normal logarithmic law. At 1190°, the total pressure is 212.6 cm. of mercury. From the sulphur dioxide partial pressures at equilibrium the mean value of the heat of dissociation into magnesia and sulphur trioxide over the range 1000-1100° has been calculated as 66.07 cal., whilst that obtained from thermochemical measurements is 65-6 cal. Beryllium sulphate dissociates appreciably at 565° and the dissociation follows the reaction 5BeSO, SO3,5BeO+ 480. Up to 785°, the sulphur trioxide equilibrium pressure is represented closely by the equation log Pso,=-14-907/7-14.10 log.T+57-97, whence the calculated values for the heat of decomposition over the range 700-800° has a mean value of 41 cal. compared with 49-8 cal. given by thermochemical measurements for the direct decomposition to the oxide. The fact that over the temperature range 590-775° the dissociation pressure of aluminium sulphate is considerably higher than that of beryllium sulphate suggests a possible method for the separation of the two metals. The double sulphate of potassium and magnesium melts at 750°, but does not commence to dissociate appreciably until 895°; this agrees with the thermodynamic deduction that its dissociation pressure should be considerably lower than that of magnesium sulphate. The double salt of potassium and beryllium melts at 900°. Dissociation can be detected at 700-710° and the dissociation curve is normal up to about 975°, but at higher temperatures, owing to the solution of potassium sulphate in the fused double salt, the pressure is diminished. The calculated mean value of the heat of decomposition up to the m. p. is 65.2 cal., above which temperature it is 58-8 cal. The value obtained from thermochemical measurements is 58.5 cal., from which it follows that the value 6.4 cal. does not necessarily correspond with the heat of fusion of the salt. A. E. MITCHELL. Thermochemistry of beryllium. C. MATIGNON and (MLLE.) G. MARCHAL (Compt. rend., 1925, 181, 859-861). The heats of solution of some beryllium compounds in water and in solutions of hydrogen chloride, hydrogen fluoride, and sodium hydroxide are recorded. The following heats of formation are given beryllium oxide, 137-4 cal.; hydroxide, 209-3 cal.; sulphate, 276-9 cal. The results obtained illustrate the close chemical analogy between beryllium and aluminium. S. K. TWEEDY. Heats of combustion of normal substances. P. E. VERKADE and J. COOPS (Z. physikal. Chem., 1925, 118, 123-128).-A reply to the criticisms of Jaeger and von Steinwehr (A., 1925, ii, 126) that undue weight has been given to Dickinson's value for the heat of combustion of benzoic acid in view of the results obtained by other observers. Recent accurate determinations (Verkade and Coops, A., 1923, ii, 294; Schläpfer and Fioroni, A., 1923, ii, 832; Swientoslawski and Starczewska, A., 1922, ii, 616) are in agreement with Dickinson's value, and it is claimed that the results quoted by Jaeger and von Steinwehr are less trustworthy. In particular, the electrical method of determining heat values involves a systematic error. J. S. CARTER. Calorimetric researches. IX. Heat of combustion of d- and meso-tartaric acids, racemic acid, and some derivatives. J. Coops and P. E. VERKADE (Rec. trav. chim., 1925, 44, 983-1011; cf. A., 1925, ii, 490).-Ammonium hydrogen meso-tartrate (m. p. 167°) is prepared by adding solid mesotartaric acid to concentrated ammonia until neutral to methyl-orange; the same amount of the acid is then added and the solution evaporated and crystallised. meso-Tartramide (m. p. 187-187.5° with slight decomposition) separates slowly from a solution of ethyl meso-tartrate saturated with ammonia at 0°. The molecular heats of combustion at constant pressure (mol. wt. in mg.; 15° cal.) are: d-tartaric acid, 275-1; racemic acid, 273-0; meso-tartaric acid, 275-7; ammonium hydrogen d-tartrate, hydrogen racemate, and hydrogen meso-tartrate, 341-7, 339.5, and 341-2, respectively; methylammonium hydrogen d-tartrate and hydrogen racemate, 508.0 and 506-0, respectively; ethylammonium hydrogen d-tartrate and hydrogen racemate, 665-4 and 663-1, respectively; aniline hydrogen d-tartrate and hydrogen racemate, 1079-3 and 1077-3, respectively; benzylamine hydrogen racemate and hydrogen meso-tartrate, 1229.9 and 1231-5, respectively; d-tartramide, 427-0; mesotartramide, 426-4; d-tartaric diethylamide, 1064-1; racemic acid diethylamide, 1064-3; meso-tartaric diethylamide, 1065.3. The heat of racemisation of solid d-tartaric acid is thus 2.1±0.1 Cal. in the crystalline state and in dilute aqueous solution, the symmetrical intramolecular inactive acid has a greater free energy content than the asymmetrical optically active isomeride. meso-Tartaric acid has a larger heat of combustion, but a smaller dissociation constant than d-tartaric acid, in contradiction to the rule of Stohmann (J. pr. Chem., 1889, 40, 357). The heats of combustion of succinic, l-malic, and the tartaric acids show that replacement of a hydrogen atom by a hydroxyl group does not produce a constant difference, and hence the heat of combustion is not an additive quantity. Both racemic acid and hydrogen racemates are racemic compounds. W. HUME-ROTHERY. Both Calorific value and constitution. M. F. BARKER (J. Physical Chem., 1925, 25, 1345-1363).-Previous empirical expressions for calculating the calorific values of carbon compounds take little or no account of constitutive effects. The contributions of like atoms and of the CH2-group have been taken as constant, which, except in the case of hydrogen, is not permissible. The molecular calorific value of an organic compound depends on its constitution; that of carbon varies and becomes less as the disposition of valency bonds approaches that in the symmetrical tetrahedral positions. The thermal effects accompanying oxidation of the carbonyl group and the combination of a hydrogen atom with a hydroxyl group, deduced from the calorific values of diphenyl, benzil, and benzoin, are 60.7 Cal. and 12.9 Cal., respectively. The combustion of diatomic hydrogen is similar to that of hydrogen in a hydrocarbon, and since the calorific value of hydrogen is the same in all the organic compounds studied, it is adopted as the basis of calculation. The heat of combustion deduced for the carbon atom in methane (normal case) is 75.5 Cal.; for each of those of ethane, 83-1 Cal. This increase is ascribed to a decrease in the angle between the valency bonds accompanying the change from methane to ethane. In ascending an homologous series, this increase becomes less. Replacement of the four hydrogen atoms in methane by the same group (e.g., in tetramethylmethane) restores symmetry to the molecule and the central carbon atom attains the original value. The value of the change -C:C-→ CO2 is 97.7 Cal., of the same order of magnitude as the combustion of elementary carbon: similarly with "benzenoid " carbon. The linking -CC- has a value 120-5 Cal. in acetylene to 124-5 Cal. in dipropargyl. COOH The contribution of the carboxyl group is not equivalent to one carbonyl plus one hydroxyl group. Results point to mobility of a hydrogen atom giving rise to an additional potential OH hydroxyl, thus XH X.C<OH' → and favouring association. Discrepancies between calculated and observed values disappear when calorific values of the vapours of the acids are taken. The aldehydic group is equivalent to one carbonyl and one hydrogen group. Among the simpler aromatic hydroxy-compounds, only the dihydroxybenzenes are anomalous, possibly because of tautomeric effects. The results of various observers indicate that the benzene molecule is best represented by Ladenburg's prism formula. L. S. THEOBALD. Heat of solution of gypsum at the maximum solubility. E. LANGE and F. DÜRR (Z. physikal. Chem., 1925, 118, 129-139).-The heat of solution in water of gypsum has been determined at 22.5°, 27-8°, 33-4°, and 37-6°, the values for the molecular heats of solution being -590, -300, 0, and 230 cal., respectively. Contrary to the statement of Colson (A., 1925, ii, 37), the zero value for the heat of solution occurs at a temperature which, within the limits of experimental error, is that at which the solubility is a maximum. J. S. CARTER. expressing the vapour pressure of aqueous solutions of non-volatile solutes as a function of temperature and solubility has been deduced, using the degree of saturation as a fundamental method of expressing concentration. The equation has the form log AP =K[1/T-a(1-log S/b)], where AP is the lowering of the vapour pressure, T the absolute temperature, and S the degree of saturation, i.e., the ratio of the number of g. or mols. of solute in solution to the number present at saturation, in a given weight of solvent. K, a, and b are constants. The three postulates used in deducing this relationship are as follow: (1) the coefficient [(JP log AP)/{(1/T)}]s is constant (equals K), and (2) is independent of S, and (3) the coefficient [(@K log S)/{(1/T)}]AP-1 mm. is constant. Existing data are used to verify these. The relation is shown to hold for 31 salts, which include the commoner salts of the alkali metals and ammonia, the chlorides and bromides of the alkaline earths, and the sulphates of beryllium, nickel, copper, and zinc. The values of the constants, K, a, and b are also given for these salts. The value of a is the reciprocal of the absolute temperature at which a saturated solution has a vapour pressure lowering of 1 mm. From the above equation, there follow two generalisations, (1) the ratio of the lowering of the vapour pressure, at any degree of saturation, to that of a saturated solution, at a given temperature, is independent of temperature, and (2) the value of this ratio is a simple function of the degree of saturation, i.e., AP/AP=SKalb L. S. THEOBALD. Free energy of ions measured by capillary electrode. P. B. TAYLOR (Physical Rev., 1924, [ii], 23, 556).-Using a cell with one mercury electrode contained in a capillary and completely polarisable, the other being reversible to the anion of the electrolyte, it is shown that T-To+Cf(V-Vo), where V is the fall of potential across the cell, Vo the E.M.F. of the reversible electrode, T the surface tension of the polarised electrode, To a constant, whilst C depends only on the concentration of the electrolyte. Curves may be constructed yielding values of the difference in free energy of the anion at two concentrations. The ratio of the change in free energy of the anion to that of the electrolyte is 0.50 for potassium and sodium chlorides, but 0-85 for potassium hydroxide above 0.1N. A. A. ELDRIDGE. Electrical conductivity in benzene solutions. S. JAKUBSOHN (Z. physikal. Chem., 1925, 118, 3136). The electrical conductivity of solutions of aluminium bromide monothiohydrate (AlBr3, H2S) over the concentration range 20-54% by weight increases with increasing concentration of solute; the values of the specific conductivities at 25° of the 20% and 54% solutions are 0.81 × 10-6 and 3.54× 104, respectively. The mol. wt. as determined by the cryoscopic method over the concentration range 1-22.5% increases with increasing concentration, being 271 in the 1% solution and 359 in the 22-5% solution. Electrolysis results in the cathodic liberation of hydrogen and the anodic deposition of bromine which reacts with the solvent to form bromine (compound, AB2, m. p. 66.5°; eutectics both melt at 66.5°); m-hydroxybenzaldehyde : picric acid (compound of undetermined composition, m. p. 90°; eutectics both melt at 86.5°); antipyrine: quinol (two compounds, A,B,, m. p. 130°, and AB,, m. p. 134°; eutectics, 102-5°, 118.5°, and 120.5°). Type III (compound formed which decomposes below the m. p.): Acetamide: salicylic acid (compound, AB; eutectic, 53°; transition point, 65°); anthracene: picric acid (compound, AB; eutectic, 110°; transition point, 151.8°); p-dinitrobenzene : α-naphthylamine (compound, AB; eutectic, 40°; transition point, 81°); p-dinitrobenzene: B-naphthylamine (compound, AB; eutectic, 87°; transition point, 91.2°); carbazole 2: 4: 6-trinitrotoluene (compound, AB; eutectic, 73.5°; transition point, 140°). C. HOLLINS. Equilibrium in the system potassium sulphate, potassium nitrate, water at 25°. R. INOUYE (Mem. Coll. Sci. Kyōtō, 1925, 8, 287-290). -The equilibrium conditions were deduced from analyses of both the liquid and solid phases. The solubilities of potassium sulphate and potassium nitrate are, respectively, 11.98 and 38.19 g. of salt in 100 g. of water. The solution saturated with respect to both salts contains 3.95 g. of potassium sulphate and 25·37 g. of potassium nitrate per 100 g. of water. L. L. BIRCUMSHAW. System silver sulphate aluminium sulphatewater at 30°. R. M. CAVEN and T. C. MITCHELL (J.C.S., 1925, 127, 2550-2551).-Mixtures of solutions of the two salts yield no crystalline compound at 30°. R. CUTHILL. Equilibrium in the systems aluminium sulphate copper sulphate water and aluminium sulphate ferrous sulphate-water at 25°. V. J. OCCLESHAW (J.C.S., 1925, 127, 2598-2602; cf. Caven and Mitchell, A., 1925, ii, 396).-No double salt is formed in the copper sulphate system. From has been isolated. the other system a double salt, Al2(SO4)3, FeSO4,24H2O, R. CUTHILL. Equilibrium in systems of the type Al2(SO4)37 M"SO, H2O. II. Aluminium sulphate nickel sulphate-water at 30°. R. M. CAVEN and T. C. MITCHELL (J.C.S., 1925, 127, 2549-2550; cf. A., 1925, ii, 396).-No double salt is formed in solution. R. CUTHILL. Ternary systems. III. Silver perchlorate, toluene, and water. A. E. HILL and F. W. MILLER (J. Amer. Chem. Soc., 1925, 47, 2702-2712; cf. A., 1922, ii, 555).-Of the three binary systems silver perchlorate-water, water-toluene, and silver perchlorate-toluene, the first has already been investigated, whilst the second is difficult to study on account of the extremely low mutual solubility of the components. The third has now been investigated over the range -73.5° to 75°. At the lower temperature, the solubility of the salt is too small for detection; at 25° the saturated solution contains 50.3% of silver perchlorate and is thus unique for the combination of a highly polar solute with a non-polar solvent. Below 22-6°, the solid phase is the compound AgCIO,,C,H,, and the solubility falls very rapidly with falling temperature. The ternary system has been studied from the ternary eutectic at -94° up to 91-75°. In ascertaining the composition of the liquid phases, the salt was method. The data show the existence of seven determined directly and the water by an indirect quintuple points, each of which was characterised, and twenty 4-phase equilibria. In addition to the solubility curves for silver perchlorate, its hydrate, and its toluene compound, there are two binodal curves. One of these is submerged and does not reach any of the two-component axes at any temperature. The other binodal curve shows an abnormal distribution of silver perchlorate between the toluene and water phases, the salt being present almost entirely in the latter up to high concentrations, in spite of its great solubility in toluene. This may be due to complete dissociation in concentrated aqueous solution, but it is probable that compound formation and chemical affinities play a large part in all cases of distribution. The intersection of the two binodal curves at points other than their plait points gives rise to a three-liquid system, which is stable from -24.1° to 90°. A. GEAKE. System Na,SO-Na,Cl2-MgSO, MgCl, H2O. H. J. ROSE (Trans. Roy. Soc. Canada, 1925, [iii], 19, III, 33). The composition of the solution saturated with respect to thenardite, mirabilite, and astrakanite at 25° is: (mols./1000 mols. of water) MgSO4, 11.6; NaSO4, 26-0; NaCl, 26-3. Diverse numbers obtained by other investigators are quoted. J. S. CARTER. Thermal decomposition of chloro-salts of metals of the platinum group. Univariant systems. G. GIRE (Ann. Chim., 1925, [x], 4, 183221). The univariant systems M,M'CIe solidM' solid+2MCl solid+2Cl2 gas-Q, where M=Na or K and M' Pt, Ir, or Rh, have been studied by measurements of the dissociation pressures of the salts over wide ranges of temperature. All the reactions are shown to be completely reversible within the temperature limits of the investigation. The dissociation of potassium chloroplatinate becomes apparent at about 600°, the curve (log p-1/T) consisting of two straight lines intersecting at 774°, the latter portion of the curve being inclined at a greater angle to the abscissæ axis, due to the heat of fusion of the potassium chloride (m. p. 774°), the system above this temperature being of the type solid solid-liquid+gas-Q. The values for the heats of reaction Q and Q' determined from the curve are 38.6 Cal. and 46-0 Cal., respectively, whence the value of the molecular heat of fusion of potassium chloride (Q-Q=S) is 7-4 Cal. This is higher than the value determined directly (cf. Schemtschuschny and Rambach, A., 1910, ii, 204), the difference being due to the heat of solution of the potassium chloroplatinate, which is found to dissolve in fused potassium chloride. The dissociation pressure of potassium chloroplatinite (cf. Vezes, A., 1899, ii, 492) is initially much higher than that of the chloroplatinate at the same temperature, but rapidly approximates to the latter. The dissociation of sodium and barium chloroplatinates (cf. Gire, A., 1922, ii, 551) was not investigated up to the m. p. of the chlorides, and hence the curves are straight lines. Dissociation is apparent at about 500° and 400°, respectively, the pressure reaching 1 atm. at 717° and 676°, respectively. The curve for potassium chloroiridate resembles that for the chloroplatinate, since the liquid phase is again introduced. Dissociation is observed at 575°, and intersection of the two portions of the curve occurs at 774°, the values of Q, Q', and S being 36-1, 41-2, and 5.1 Cal., respectively. Measurements of the dissociation pressures of an intimate mixture of potassium chloroiridate and potassium chloride corresponding with 2K,IrCl+2KC1→ 2K,IrCl+Cl2 gave 764° as the m. p. of potassium chloride in this system, whence the values for Q, Q', and S are 32-1, 23-3, and 4.4 Cal., respectively, the low value for 8 being due to the negative heat of solution of the chloroiridite in the fused potassium chloride. Sodium chlororhodate shows measurable dissociation at 600°; the two portions of the curve intersect at 790°. The heating curve of the mixture shows a second arrest at 904°, the m. p. of the sodium chlororhodate, whence Q, Q', and S have the values 35-3, 46-0, and 45-35 Cal., respectively. J. W. BAKER. Thermal decomposition of chloro-salts of metals of the platinum group. Calorimetric investigations. G. GIRE (Ann. Chim., 1925, 4, 370-409).-Measurements have been made of the heats of solution of various salts of the type M,M'Cl ̧, the thermal decomposition of which has been already studied (cf. preceding abstract), and of the heats of the reactions M,M'Cl+2Co-M'+2CoCl2+2MC1+q, whence, since the heat of the reaction 2Co+2Cl2= 2CoCl,+q is 94-8 Cal. (Thomsen, J. pr. Chem., 1877, 15, 435; Pigeon, A., 1894, ii, 455), the heats of formation of M,M'Cl, could be determined. The heats of solution, obtained by direct measurement, for potassium, sodium, and barium chloroplatinates (anhydrous) are, respectively, -12-15, +7-10, and +9-05 Cal. (-1.06 Cal. for the hexahydrate of the of formation of the solid salts, +91-2, +79-6, and barium salt), and the corresponding molecular heats +82-1; and for the dissolved salts, +88-7, +90-50, and 88-70 Cal., respectively. The hypothesis of ation in solution of all the chloroplatinates from the Thomsen and Pigeon (loc. cit.) that the heats of formation in solution of all the chloroplatinates from the chlorides are the same is thus verified, but the mean value obtained is 89 Cal. instead of the value 85 Cal. given by the earlier investigators. Sodium chlororhodate crystallises with 12 mols. of water, thus to it by Gutbier and Hüttlinger (cf. A., 1908, ii, 200). confirming the formula Na,RhCl, 12H2O assigned The heats of solution of the hydrated and anhydrous the heat of formation of the solid salt is 74-4 Cal. salts are, respectively, -20-56 and +7-70 Cal. and The heats of solution of potassium chloroiridate and chloroiridite, K,IrCl, are -13.12 and -7-90 Cal., respectively. Reduction of the chloroiridate either with cobalt or chromous chloride occurs in two stages: 2K,IrCl+2KCl=2K,IrCl2+Cl2-Q 2K,IrCl=2Ir+6KCl+3Cl2+Q, the second stage being too slow to permit of calorimetric measurements. heat of the first reaction was obtained by the addition An approximate value, -29 to 30 Cal. (low) for the of 5% of potassium chloride to the solution to suppress the second reaction. The solubility of potassium chloroiridate is 0-66 g. and 1.12 g. per 100 g. of water at 0° and 20°, respectively. From the dissociation curves obtained (cf. preceding abstract) the value a mean value of 0.0325 being obtained (that for sodium of Q/T is deduced for each of the systems studied, chlororhodate is slightly lower). Similar calculations applied to the published data for a large number of other univariant systems give Q/T=0.032 for compounds of the type MCI, NH, 0.028 for the dissociation of hydrates, and values varying between 0.028 and 0.034 for other systems, whilst the dissociation of auric chloride, a reaction similar to those studied, gives a value 0.0326: hence for each group of similar reactions Q/T has a definite value which, in disagreement with Nernst's hypothesis, seems to be independent of temperature. The application of the results to the constitution of the salts on Werner's theory is discussed. and J. W. BAKER. (MLLE.) G. MARCHAL (J. Chim. phys., 1925, 22, Thermal decomposition of metallic sulphates. 493-517). The thermal decomposition of anhydrous magnesium sulphate can be detected at about 880°; from this temperature to beyond the m. p. (1155°), the total pressure of the dissociation products follows the normal logarithmic law. At 1190°, the total |