METAL-AMMONIA COMPOUNDS IN AQUEOUS SOLUTION. 1069 CXI. -Metal-Ammonia Compounds in Aqueous Solu- tion. Part III. Salts ofthe Alkaline Earth Metals. By H. M. DAWSON and J. MCCRAE. DRY calcium chloride forms with ammonia a complex salt, but we have no direct evidence that this complex is capable of existence in solution. Raoult (Ann. Chinz. Phys., 1874, [v], 1, 263) has shown that the solubility of ammonia in concentrated calcium nitrate solution is greater than in pure water, and Konowaloff (J. RUM. Phys. Chem. Soc., 1899, 31, 985; CAem. Centr., 1900, i, 938) has found that the partial pressure of ammonia over an ammoniacal solution of calcium chloride is less than that over a pure aqueous solution of the same concentra- tion. Konowaloff's observation has been confirmed by Gaus (Zeit.anmg. Chem., 1900, 25, 236). There is in these results an indication that the dissolved calcium salt (the calcium ion) is capable of fixing ammonia. We have extended our experiments on the distribution of ammonia between aqueous salt solutions and chloroform to solutions containing salts of the alkaline earth metals, I n our first communication (Trans,, 1900, 77, I250), we have given results with calcium chloride, but these are to be regarded as preliminary experiments. The method of experimentation has already been sufficiently described (this vol., 495). The experiments were carried out at 20°, and the results given on p. 1070 have been obtained : If these results are compared with those obtained for the salts of the alkalis on the one hand, and with the salts of copper, zinc, cadmium, and nickel on the other, it will be observed that, speaking generally, the salts of the alkaline earth metals occupy a position between these two groups.In general, the absorptive power of solu- tions of the alkali metal salts for ammonia is less than that of pure1070 DAWSON AND MCCRAE : METAL-AMMONIA COMPOUNDS IN strength of aqueous solution. Concentra- tionof NH,ii the aqueous litre. grams part, per I I Calciuiii chloride : 1-0 1.0 1 '0 1 '0 0 -8 0 '4 0-2 0.2 1'0 1 *o 8-340 6.739 5 -045 8'525 8.574 8.534 8.516 8.523 11 '790 14-970 0.297 0.241 Strontium nitrate : 4.959 8-287 Barium bromide : Barium chloride : 1.0 0 -8 0-4 0.8 0.8 0.8 0.4 8 '284 8 *305 8.307 3.290 4'882 9'871 13.303 Concentra- tion of NH, in the CHCI,, gram per litre.c2. 0.3031 0.3090 0 '31 52 0.3175 0.3177 0-4201 0'5443 0.31 72 0.2535 0'1892 0.1894 0.3204 0.3293 0.3279 0.3263 0.1290 0'1912 0'3971 0'5298 Coefficient, C2 k'. - cl. 28.13 27'74 27.97 26.82 26.82 28-05 27.51 26.29 26'59 26-67 26-18 25.86 25.15 25.33 25.46 25-51 26-14 24.85 25.11 2oeScient foi pure water when concen tration of NH, in CHCI, is c2. k. 26.24 26.23 26'22 26 *22 26 '22 25 -96 25.65 26 *22 28-26 26.30 26 *30 26.21 26'19 26.19 26.19 26-33 26.29 26 *03 25-73 k-k' -. n - 1-89 -1.89 - 2'12 - 3-00 - 3 '00 - 2-09 - 2.02 - 0.07 - 0.31 - 0.37 + 0.40 1 '45 + 1 '06 1 -07 1 *82 1 -02 1'45 1.47 1'42 water, and we have already shown that thia diminution of absorptive power is approximately proportional to the concentration of the dis- solved salt, The influence of these salts waB found to be greatest for potassium salts, and least for lithium salts, the order of magnitude being potassium, sodium, ammonium, lithium.The experimental data represmt the superposed influences of physical action and the forma- tion of chemical complexes, and from the negative values obtained forAQUEOUS SOLUTION. PART 111. 1071 - k' with some of the lithium salts we conclude that in these cases the fixation of ammonia in the form of chemical complexes more than counterbalances the lowering of the absorptive power which would result from the purely physical action of the dissolved salt, The alkaline earth metals approximate in their behaviour to the alkali metals. For the barium salts investigated, the physical action preponderates, whereas in the case of the calcium salt, this physical action is more than counterbalanced by the formation of complex calcium-ammonia ions.These two opposed actions are of approxi- mately equal magnitude for the strontium salt investigated, and in consequence, the value of the distribution coefficient differs but little from that for pure water and chloroform. The arrangement of the alkaline earth metals in the series barium, strontium, calcium, corresponds with that of the series given above for the alkali metals. The tendency to form complex ammonia ions on the part of calcium is greater than that observed in the case of any of the alkali metals, but it is still very small in comparison with that found for the metals copper, zinc, cadmium, and nickel, k' was found to be constant for the The value of the expression - alkali salt solutions when both the salt and the ammonia concentra- tions varied.This constancy is in harmony with the conception that the preponderating action of the dissolved salt is of a physical nature. When the formation of ammonia complexes is very considerable, as with copper, zinc, cadmium, and nickel salts, then this expression is by no means constant. Examination of the previous table shows that - k' is not nearly so constant as in the case of the majority of the alkali salt solutions investigated, and this is probably explainable by the greater tendency towards the formation of ammonia complexes exhibited by the calcium, strontium, and barium salts. Finally, we may compare our results with those arrived a t by Konowaloff (Zoc.cit.) and by Gaus (Zoc. cit.). Konowaloff's results were obtained by determining the partial pressure of normal ammonia solution containing 1 gram-equivalent of salt per litre at 60°, and those of Gaus by determining the same at 25' with solutions which were normal with respect to ammonia and 0.4 normal with respect to salt. The following table contains the values of P, - P, P, being the ammonia pressure over pure water, and P that over the salt solution. For the comparison we make use of an approximate value of ____ which is a mewure of the total action. In k - n n k - k' n1072 DAWSON AND MCCRAE : METAL-AMMONIA COMPOUNDS IN BaCl,. SrCl,. Sr(N03),. CaCI,. 2 2 2 2 Konowaloff., ............. P l - P +1.05 -1.1 -1.2 -3.6 Gaus .................... P, - P - 0.02 -0.29 - -0.77 Distribution method ... - + 1.3 - -0.3 - 2.0 k - k ' n The agreement between the three series is as close as might be ex- pected, the only anomaly being that Gaus finds for barium chloride a negative value, whilst the experiments of Konowaloff and ourselves give a positive value. THE YORKSHIBE COLLEUB, LEEDS.