ACTION O F ANALGAMS UPON SOLUTIONS (REPLYTO G. McP. SMITH)
BY GUSTAVE FERNEKES
I n a recent article, G. McP. Smithr criticises the explanation given by me of the phenomena described in a paper on the action of sodium and potassium amalgams on various aqueous solutions." Smith in an attempt to harmonize the facts observed by nie, with the theory of electrolytic dissociation has drawn some rather hasty conclusions from very meager experimental evidence. I n this paper I purpose to show that the great number of experiments which I have performed, and also the few additional ones of Smith, can not only be readily explained without the aid of the electrolytic dissociation theory, but that it is impossible to explain the majority of them by means of that theory. Smith made potassium amalgam from sodium anialgani, by acting upon the latter with a concentrated solution of potassium chloride ; and vice versa he made sodium amalgam from potassium amalgam, treating the latter with a concentrated sodium chloride solution. H e further repeated some of the experiments of Schumann,3 preparing barium and magnesium amalgams from sodium amalgam, by acting upon the latter with solutions of the corresponding salts. T h e only new fact which Smith has discovered is, that sodium amalgam can be prepared from potassium amalgam by the method described above. Without attempting to make sodium amalgam from calcium, barium or magnesium amalgams, by treating these amalgams with a concentrated sodium chloride solution, Smith nevertheless proceeds to the following general statement,4 ('But nowhere have I seen that sodium amalgam has been prepared from potasJour, Phys. Chem. 8, 208 (1904). Ibid. 7, 611 (1903). Wied. Ann. 43, 1 0 1 (1891). 1. c. p. 213.
Action o f Amalgams upon Solutions
567
sium amalgam or from magnesium amalgam, etc., as should be possible according to the ionic theory and the law of mass action.” I repeated Smith’s experiments with sodium and potassium amalgams] and obtained the same results which have been mentioned above. I also prepared barium and calcium amalgams in the same manner described by Schumann. I then attempted to replace barium in its amalgam by sodium or potassium] treating the amalgam with a concentrated sodium chloride or potassium chloride solution. T h e experiments were performed as follows : 50 g of barium amalgam were placed in an Erlenmeyer flask, and covered with a strong solution of potassium or sodium chloride. T h e solution was allowed toremain in contact for from four to five hours. T h e solution was now poured off and the amalgam carefully washed with water. A very dilute hydrochloric acid solution was now poured upon the amalgam until the evolution of gas ceased. After this solution had been poured from the mercury into a beaker, the barium was precipitated by means of dilute sulphuric acid, filtered, ignited and weighed. T h e filtrate was evaporated to dryness in a platinum dish and the residue weighed. This residue was either sodium or potassium sulphate. A blank experiment was performed with pure barium amalgam. 508 of the amalgam contained 0.5724 g barium and 0.0160 g sodium. 50 g of this same amalgam after having been treated for four hours with a concentrated sodium chloride solution contained 0.4517 g barium and 0.0131 g sodium. T h e amalgam . when allowed to act on a very concentrated potassium chloride solution for five hours, contained 0.5263 g barium and 0.0138 g potassium. A few more experiments were now performed with solutions of potassium sulphate ,and also with sodium sulphate. T h e object in these cases was to throw insoluble barium sulphate out of solution, and thus give the potassium or sodium a better chance to combine with the mercury. T h e difficulty which presented itself here is quite apparent. Barium sulphate
would form at the surface of the amalgam and prevent further action. I therefore shook the amalgam violently with the solution, and continued this shaking with a n occasional renewal of the solution until no more turbidity occurred. But when I now examined the amalgam I found neither barium nor alkali metal present. To complete this series of experiments, I tried various temperatures up to 40' C with the same result as above. This shows conclusively that barium in its amalgam is not replaceable by either sodium or potassium by the method which Smith thought possible by the ionic theory. That barium actually acts on the solution is shown by the analyses, but it js also seen that the corresponding quantities of sodium or potassium did not combine with the mercury. It might be added here that I did not attempt to remove the small quantity of sodium in the barium amalgam, because I did not think it would interfere with the outcome of these experiments. -In subsequent experiments I removed all but a slight trace of sodium in the anialgam. As Smith's objections were found not to hold for barium amalgam, it could be used for the purpose of testing thecorrectness of Pr'of. Kahlenberg's theory. According to this theory we should expect barium amalgam to act more slowly upon a solution of potassium or sodium chloride than upon pure water, because each molecule of the salt would influence the surrounding molecules of water by chemical attraction. By the ionic theory we should expect no difference in the rate of reaction. I t was found that water acted about three times as fast upon barium amalgam as did a solution of potassium chloride. These facts in themselves are sufficient to prove that the view held by Prof. Kahlenberg is correct. But to show that Smith has omitted consideration of the important factor, chemical attraction, in explaining the replacements in the mercury, I performed another experiment to show how essential this factor is. A solution containing equimolecular quantities of sodium and potassium chlorides was allowed to act on sodium amalgam,
Action of Amalgams upon Solutions
569
After fifteen minutes, the amalgam was examined, and found to contain only potassium, although more sodiurn than potassium was present in the solution at the end of the experiment. T h e experiment was now performed with potassium amalgam and the same solution. Again only potassium was found in the amalgam. This proves that potassium has a greater affinity for mercury than sodium. This fact is further born out by regarding the heats of formation which it might be well to present in this connection.
+ + +
-+ + +
Na Hg = HgNa 10300 cal. Na Hg, = Hg,Na 21600 ' ' (3) K Hg+ = HggK 20300 (4) K Hg,, = Hg,& 34200 I t appears from these data that by choosing the potassium or sodium in the proper proportions to the mercury, the heat of formation of the potassium amalgam may be made to exceed that of sodium amalgam or vice versa. This is particularly evident when we regard reactions ( 2 ) and (3). From these therriiochemical data Berthelot has explained the replacement of sodium in sodium amalgam by potassium in a potassium hydroxide solution, and it did not require the assumption of ions to account for the facts satisfactorily. I t is true that the law of mass action asserts itself in these, as in all chemical reactions, but Smith's attention need hardly be called to the fact that this law is entirely independent of the ionic theory, and was known long before that theory existed. T h e reason why barium in barium amalgam is not replaced by sodium or potassium from solutions of their salts is perfectly obvious. In the case of barium amalgam there evidently exists a compound whose heat of formation so far exceeds that of either sodium or potassium amalgam, that a replacement by these metals is in no manner possible. We may therefore bring even saturated solutions of sodium or potassium chloride into contact with barium amalgam without effecting a replacement. Calcium will probably act in a similar way to barium. From the fact I)
(2)
+
Bertbelot.
+
Comptes rendus, 88, 1335 (1,879).
( (
570
Action of Amalgams @on Solutions
that barium has such a strong affinity for mercury we should expect the vapor tension of the solution of barium in mercury to be depressed correspondingly. I n looking over the results obtained’ for the molecular weight of barium and calcium where mercury was used as a solvent, I found that it was about onehalf that obtained by other methods. Ostwald says that he could not harmonize these facts with the existing views. According to Prof. Kahlenberg’s theory the explanation is again very simple. I have thus shown in this paper that the reciprocal replacement of metals in mercury is not always possible as might be expected from (‘ the ionic theory and the law of mass action.” That a retardation of the evolution of hydrogen by the action of an amalgam which is not thus replaceable, upon a solution is nevertheless observed. Furthermore the replacements which do take place in the amalgams can be explained on a purely thermochemical basis and the laws of chemical attraction. But before concluding this paper, it might be well to ask Smith how he would explain by the ionic theory the anon~alous behavior of sodium hydroxide solutions towards both sodium and potassium amalganis. These phenomena he seems to have overlooked entirely. Besides this there is still the great number of solutions of organic compounds which he has failed to mention. All the above facts again show how limited the application of the ionic theory is toward the general subject of solutions, and they have tended very much to strengthen my belief in the theory which Prof. Kahlenberg holds. Michigan College of Mines, Houghton, August, 1904. Ostwald.
Solutions, p. 193.
