NOTES
Feb., 1940
449
the inclusion of foreign material in barium sulfate where KHand KDare the dissociation constants of precipitates is a sorption on the initially formed the acid in H2O and D20, increases with decreasprimary crystallites. The growth of these will be ing acid strength.l The ratio of the apparent such that most of the initially sorbed material first dissociation constants of proto- and deuterodoes not find its way out of the internal “mosaic” carbonic acid has been accurately determined to structure of the macrocrystal (cf. also Darwin,6 be 2.68 a t 2.5O.l This does not agree with the predicted value of 3.6 obtained from the function Smekal,6Balarewl). This point is supported by our experiments in given by Rule and La Mer and recently conwhich the precipitates were treated by prolonged firmed by Martin and Butler. However, the boiling with dilute sodium hydroxide (0.02-0.01 acid strength should not be judged from the ap.V). In Fig. 2 the percentage of ammonium salt parent dissociation constant. In aqueous solution carbon dioxide is hydrated distilled over as ammonia is plotted against the time of distillation. It is very significant that, in only to a small extent forming rather strong metathis case, ammonia distils over very slowly, ten to carbonic acid. The relationship between K1, the fifteen hours being needed to expel most of i t . This hydration constant, K,, the true first dissociation is incompatible with adsorption on the external constant and Ka, the apparent first dissociation surface of the macrocrystals only. It can only be constant, is explained on the assumption that the contaminating salt is mainly present on an internal surface of the macrocrystal. The results of the distillation If hydration of carbon dioxide is assumed to be experiments would, moreover, be difficult to rec- the same in DzO as in H2O (the solubilities are oncile with the existence of secondary insoluble very nearly identical) then. KHt/KDt = 2.68. compounds (Karaoglanow’) or of solid solutions. I t has been possible to determine the total amount I t is highly improbable that, in these cases, the of carbonic acid in solution since carbon dioxide total ammonia could be expelled by treatment does not react immediately with water. In with an alkali as dilute as 0.01 N sodium hydrox- conjunction with conductivity data the true diside. sociation constant has been estimated therefore to It is not quite simple to visualize a satisfactory be 4 X 10-4.3 From the smooth curve plot of mechanism of the formation of macrocrystals -log KH against‘ KH/KDthe value of 2.9 is now which possess a mosaic structure. Kolthoff obtained for the ratio. This compares more suggests that the electrolyte, adsorbed on the pri- favorably with 2.68 than with 3.6, the value premary nuclei, will influence crystallization in such dicted on the basis of the apparent dissociation a way that the lattice of the eventually formed constant. macrocrystals will contain many imperfections. (1) Rule and La Mer, THISJOURNAL, 60, 1974 (1938); Martin and Another way of visualizing the formation of a Butler, J . Chcm. Sac., 1366 (1939). (2) Curry and Hazelton, THISJOURNAL, 60, 2773 (1938). mosaic structure would be found in the assump(3) Strohecker, 2. Nahrungsm. Untersuch. H y g . U’arenkundc, 31, tion that the primary crystallites will grow to- 121 (1916); Buytendyk, Brinkmdn and Mook, Biochem. J . , 21, 576 gether on certain faces to irregular macrocrystals (1927). DEPARTMENT OF CHEMISTRY which possess a large internal surface. (5) C. G. Darwin, Phil. Mag., 27, 315, 675 (1914); 43, 800 (1922). (6) A. Smeksl, Physik. Z., 27, 837 (1926): Ann. Phrs., 9s) 1204 (1927). (7) G. H. Walden, Jr., and M. U. Cohen, THISJOURNAL, 67, 2597 (1935); P. R . Averell and G. H. Walden, Jr., ibid., 69, 907 (1937).
CHEMISTRY DEPARTMENT OF MELBOURNE UNIVERSITY MELBOURNE, AUSTRALIA RECEIVED AUGUST2,1939
Dissociation of Carbonic Acid in Ordinary and in Heavy Water BY G. ALEXANDERMILLS
In general, acids are considerably weaker in heavy than in ordinary water. The ratio KH/KD,
DARTMOUTH COLLEGE N. H. HANOVER,
RECEIVED NOVEMBER 7, 1939
Chlorination of 1-Hexyne in Reactive Solvents.
I11 BY R. 0. NORRIS AND G . F. HENNION
Previous paper^^'^ from this Laboratory describe the chlorination of l-hexyne in various (1) Paper XXXVI on the chemistry of substituted acetylenes and their derivatives; previous paper, THISJOURNAL, 61, 2897 (1939). Also paper 5 on halogenation in reactive solvents: c f . , i b i d . . 61, 1460 (1939). (2) Verbanc and Hennion, i b i d . , 60, 1711 (1938). (3) Norris, Vogt and Hennion, i b i d . , 61, 1460 (1939).
