ACTION O F SODIUM A N D POTASSIUM AMALGAMS ON VARIOUS AQUEOUS SOLUTIONS BY GUSTAVE B'ERNEKES
INTRODUCTION I n working with magnesium upon different aqueous solutions, TommasiI found that there is a difference in the rate at which hydrogen is liberated. His investigations were of a qualitative character. Solutions of salts of the following formulz were tried by this investigator: NaCl, KC1, LiC1, NH4CI, CaC12, BaC12, SrC12, FeC13, FeS04,CrC13,NaS04,CuCI2, CdClz, PbCIZ,HgC12, PtC14, AuC13, and CuS04. G. Lemoine2 noticed that magnesium liberated hydrogen more rapidly from aqueous solutions of its salts, than from pure water, or solutions of other salts. The same fact was noticed by H. Mouraour.3 At the suggestion of Prof. Kahlenberg, Mr. 0. W. Brown and Dr. H. V. Black made some preliminary experiments in this laboratory for the purpose of comparing the rates at which magnesium liberates hydrogen from various aqueous solutions. They, however, discontinued their work on this subject, and it was then taken up by Prof. Kahlenberg himself, whose results have recently been published.4 T h e question then presented itself to Prof. Kahlenberg whether other metals would act in a similar way towards solutions of their salts, and at his suggestion I undertook to solve this question. Sodium and potassium naturally suggested themselves for such investigations, as both metals decompose water at ordinary temperatures. But on account of the violence of the reaction, and because the metals are so easily oxidized, their amalgams were used. With but few exceptions, which will
,
Bull. SOC.Chim. Paris (3) 21, 885-887 (1899). Comptes rendus, 129,291 (1899). Ibid. 130, 140 (1900). *Jour, Am. Chem. SOC.25, 380 (1903).
61 2
Gustave Fevnekes
be mentioned below, these amalgams have not hitherto been used for this purpose, although a great amount of work has been done to determine the constitution of ama1gams.I T h e tendency of most investigators seems to have been to consider anialgams as definite chemical compounds rather than as solutions of the metals in mercury. RaeyerZseems to have been the only one who made investigations as to the rate at which hydrogen is evolved from various aqueous solutions by the action of sodium amalgam. He investigated the behavior of solutions of sodium hydroxide, sodium sulphate, sodium chloride, sodium carbonate, and the sodium salts of the following organic acids : isophthalic acid, succinic acid, benzoic acid, acetic acid, tartaric acid, citric acid, and malic acid. He claims no great quantitative accuracy for his results, however, and simply gives the relative rates without any further explanation how the experiments were made. Baeyer found that the order of action was as follows, the substance causing fastest action being mentioned first : Sodium isophthalate Sodium sulphate ' ' succinate " chloride ' ' benzoate " carbonate '' hydroxide (ten drops) '' tartrate '' hydroxide (one drop) " citrate acetate " malate He found that water acts slowly at first, then faster, and at great concentrations of sodium hydroxide slower again. Sodium chloride, sodium sulphate, and sodium acetate act like water, whereas sodium carbonate retards the action. Of the organic salts Baeyer says :On the constitution of amalgams see : Guntz. Comptes rendus, 122, 465-467 (1896) ; 131,182-184 (1900) ; V. Merz and Weith. Ber. chem. Ges, Berlin, 14, 1438 (1881) ; F. Haber. Zeit. phys. Chem. 4 1 ~399 (1902) ; G. Meyer. Zeit. phys. Chem. 7, 477 (1891) ; J. Schumann. TVied. Ann. 43, IOI125 (1S91) ; Zeit. phys. Chem. 3, 443 (1889) ; Aug. Schoeller. Zeit. Electrochemie, 5, 259 (1898) ; W. Kerp. Zeit. anorg. Chem. 17, 284-309 (1898) ; M. Le Blanc. Zeit. phys. Chem. 5 , 467 (1888) ; Rud Boettger. Jour,prakt. Chem. I, 303 (1834) ; 3, 283 (1836) ; Georg Langbein. Zeit. phys. Chem. 36, 746 (1900) ; Gouy. Jour.de Phys. 4, 320-321 (1895). Liebig's Ann. 251, 265 (1888).
Action of Sodium and Potassium Awzalgams
613
Der negative Phenylrest scheint beschleunigend zu wirken, da BenzoEsaure dreimal soviel Wasserstoff entwickelt als essigsaures Natron. Am Auffallendsten ist aber der Gegensatz zwischen Bernsteinsaure einerseits und der Aepfel-, Wein-, und Citronensaure andrerseits welche zehnmal weniger Gas entwickelt als erstere. Dieses Verhalten scheint mir den Schliissel fur den rathselhaften Vorgang zu liefern. Diejenigen Sauren welche wie die Aepfelsaure ein alkoholisches Hydroxyl enthalten, befinden sich bei Gegenwart von Natronlauge vermuthlich als basische Salze in Losung wodurch die Fahigkeit des Salzes Natrium aufzulosen verringert wird Worauf diese Fahigkeit beruht ist mir unklar, da das passive Verhalten der Salze unorganischen Sauren die Erklarung des Vorganges durch Dissociation unwahrscheinlich macht.” In 1893, Svante Arrhenius‘ in electrolyzing aqueous solutions of salts of alkali metals, found that some time elapsed before hydrogen was given off from the amalgam formed at the cathode. Prom the standpoint of his theory, he attributed this to the ions of sodium or potassium in the solution which would hinder the entrance of more of these metals into solution in form of ions. EXPERIMENTAL WORK In studying the rate of reactions, the volumes of hydrogen liberated at given intervals of time were measured. This is a method which is common in measuring the rate of chemical reactions in which a gas is evolved.* The experiments were performed in the following way. Two hundred cubic centimeters of solution were poured into beakers 14 cm high and g cm in diameter. These beakers contained evaporating dishes 7 cm in diameter, on which were set eudiometer tubes whose upper ends were provided with stop-cocks above which the tubes were widened out so as to form funnels. These tubes also had small funnels inserted into their lower end by means of ((
Zeit. phys. Chem. 11, 805 (1893). Millon. Ann. Chim. Phys. ( 3 ) 6, 73 (1842); W. Spring. Chem. 2 , 13 (1888) ; Bredig. Ibid. 39, 125 (1902).
Zeit. phys.
614
Gustave Fernekes
rubber stoppers. By suction, the eudiometer tubes were filled almost to the top with the solution, and 5 cc of sodium amalgam was placed in the upper portion of the tube which had been thoroughly dried. T h e stopcock was now opened and the amalgam allowed to drop through the solution in the eudiometer into the evaporating dish, and the eudiometer was then quickly filled with solution by suction at the upper end of the tube as before. Bubbles of gas would be prevented from getting to the top before a reading could be taken. With a little practice this method gave fairly quantitative results. Some factors which might seem to be a source of error in these experiments must be mentioned. Small quantities of air might be carried down mechanically by the amalgam. Experiments performed with mercury alone showed that this quantity was very small. T h e amount was 0.02 of a cubic centimeter, which was as small a reading as could be estimated on the eudiometers employed. Then the fact must be considered that the height of the column of solution in the eudiometer tube exerts a downward pressure. T h e column is 4.4 cm high, which corresponds to about 3 mm of mercury. All readings are therefore 0.08 of a cubic centimeter too large. T h e solubility of the hydrogen also influenced the readings. Finally, slight variations of temperature could not be avoided. A change in temperature of I O C might change the total volume of 2 0 cc of gas by about 0.08 cc. I t can be seen from these data that the maximum error on 2 0 cc of gas evolved could amount to 0.1-0.15cc. As the solution of different salts in most cases showed a greater variation than this, they must be looked upon as real differences in the rates of liberation of hydrogen. T o prevent bubbles from adhering and accumnlating on the sides of the apparatus, the funnels, evaporating dishes and eudiometers were treated with a chromic and sulphuric acid mixture. Impurities on the surface of the amalgam were carefully guarded against, although impurities purposely introduced had no marked effect on the rate of liberation. T h e mercury used was obtained from Bausch and Lomb (Rochester, N. Y.) and
,
Action of Sodium and Potassium AmaZgams
615
was marked C. P. redistilled. It was cleaned before using according to the method of Bruh1.l T h e sodiuni was obtained from Schuchardt and was scraped free from oxide before using. The sodium amalgam was prepared by throwing pieces of sodium upon mercury in a covered porcelain casserole and then shaking until combination took place. A rather strong amalgam was first made an$this then diluted until 5 cc liberated 2 3 cc of hydrogen from water, i. e., 5 cc contained 0.0472 g of sodium. After being thus prepared, the skin of oxides was scraped off the top with a piece of filter-paper, and the amalgam was then poured into bottles which were well stoppered and kept under a bell-jar in a dry atmosphere. In this way the amalgam can be kept indefinitely without change of concentration. T h e potassium amalgam was prepared in a similar manner. When the amalgam was at the bottom of the evaporating dish, it had a diameter as measured by a pair of dividers of about four centimeters. This would give a thickness of 3.2 mm V
to this layer as calculated by the formula h = PT ’ where h = height, u =volume, and Y = radius. T h e evolution of hydrogen was watched and readings were taken every five minutes. Two or three samples of the same solution were run side by side in different apparatuses and only slight variations were noticed, which must be attributed to the causes mentioned above. In all cases where salt solutions were used, a little frosted white area was noticed on the amalgam from which the hydrogen seemed to emanate, and this was larger the more rapid the reaction. In concentrated potassium hydroxide or pure sodium hydroxide no such area was observed. It is very probable that these areas are simply small bubbles of hydrogen adhering to the mercury. T h e salts of the inorganic acids used were obtained from various sources. From Kahlbauni were obtained : KzSO,, NaC1, KCl, K N 0 3 , KBr, SrCIz, Na2HP0,, Na2PZ07. From Schuchardt : NaZS04,Na2B407,NaBr, KI, NaI, ordinary NaOH Ber. &em. Ges. Berlin,
12, 204
(1879).
616
Gustave Fernekes
by alcohol, CaCIZ, BaClZ, Na3A103, CH3COONa, KOH. T h e sodium hydroxide from metallic sodium was from Eimer and Amend. T h e results obtained are presented in the tables which follow. To facilitate comparison and to show the general trend of the results at a glance, they have also been plotted in the forin of curves, ordinates indicating minutes and abscissE the number of cubic centimeters of gas evolved. In most cases the readings were taken every five minutes. Normal, one-tenth normal and saturated solutions were employed. In sll tables the numbers indicate the volume of hydrogen gas evolved in cubic centimeters. The term normal solution as used here always means a solution containing one gram equivalent per liter. Table I with accompanying Fig. I represents results obtained by the action of sodium amalgam on solutions of sodium salts. The curve for water is also shown for the purpose of comparison. Among the salts which acted faster than water are : Na3A10?, NaHC03, NaZHPO4,NaZSO,, and NaOH. Those acting slower
TABLEI.
. - I& x c d
x
20 A V J 3 L f
12
7 c 0
0.3
i
-
0.5 , 0.6 I 1.4 0.8
-
1.0
-
1.1
3.0
1.2
1.3
-
-
4.8
-
-
Aclion of Sodium ana' Potassium Amatgams
617
TABLEI.-( Continued.)
5
0.2
IO
0.5 0.8
I5 20
25 30 35 40 45 50 55
I .o 1.2
1.5
1.8 2.0 2.2
'j
4.0
5.2
4.5
2.5
- I
2.7
-
I
-
: - I -
60
-
65 70
-
-
2.7
4.3 4.7 4.9 5.6
3.2
5.2
than water are : NaBr, NazB407,Na2S04, NaC1, NalP207, NaI, CH?COONa, and pure NaOH from metallic sodium,
61 8
Gustnve Fernekes
T h e solutions of salts acting slower than water will be taken up first. The slowest of these are the saturated solutions of sodium sulphate and the solution of sodium hydroxide containing 50 g to a liter. Only about 0.2 of a cubic centimeter of hydrogen was evolved at the end of an hour in these cases. Next to these stand the saturated solutions of sodium iodide and sodium pyrophosphate, which gave about I cc each in one hour. Saturated sodium chloride and normal sodium chloride liberated 1.5 cc and 1.3 cc of hydrogen respectively at the end of the same period. Sodium acetate stands next in the list. Normal sodium sulphate and one-tenth normal sodium sulphate again fall very close together, both liberating 2 cc of hydrogen at the end of an hour. T h e next in order is a tenth-normal sodium borate solution. One-tenth normal sodium bromide and sodium chloride solution stand nearest to water.
Pig. I Action of sodium amalgam on the aqueous solutions of sodium salts
Among those salts acting faster than water are the acid salts, normal and one-tenth normal sodium acid phosphate solutions, sodium acid carbonate and also sodium sulphite, normal and one-tenth normal sodium hydroxide. One would expect the acid salts to act faster on account of the replaceable hydrogen atbm, but this explanation can not hold in the case of sodium sulphite. Sodium hydroxide is an anomaly in the list of these
Action of Sodium and Potassium Amalgams
619
solutions. I t is seen that sodium hydroxide from metallic sodiiim acts very slowly, in fact as slowly as saturated sodium sulphate solution ; whereas sodium hydroxide from alcohol acts extremely fast, even exceeding that of a one-hundredth normal solution of hydrochloric acid (see Fig. 3). An explanation of
TABLE 11.
-I---
5
0
IO
0.I
I5
0.2
20
0.3 0.5 0.7 0.8
25
30 35 40 45 50
0.9
I .o
- I -
65
70
5
0.2
IO
I5
0.6 0.9
20
1.2
-
25
30 35 40 45
0.I2 0.2 0.25
0.3
50
55 60 - 1 - 1 -
1.6 2.2 2.7 3.2
4.0 4.5 5.2
-
-
620
Gustave Fernekes
this phenomenon will be given later. I t is seen, from these curves that in general the greater the dilution the faster the action, although a tenth-normal solution does not act ten times as fast as a normal one. In some cases in fact there is very little difference observable between the action of the saturated, normal and tenth-normal solutions ; such a case is sodiuni sulphate for instance. In other cases the difference asserts itself more distinctly, as is the case with sodium chloride and sodium bromide.
Action of sodium amalgam on aqueous solutions of potassium salts
Table I1 and Fig 2 represent the results of the action of sodium amalgam on solutions of potassium salts. Here again the acid salt, potassium acid carbonate, acts faster than water. Potassium iodide, bromide and sulphate act slower than water. Normal, tenth-normal and saturated solutions of potassium sulphate again act with about the same degree of readiness. Potassium chloride, iodide and bromide follow each other successively, the first being a saturated and the other two normal solutions of these salts. There is again a distinct difference between normal and tenth-normal potassium iodide,
Action of Sodium and Potassium Amalgams
62 I
and also between saturated and normal solutions of potassium bromide. Thus it appears that the bromides seem to act fastest, the chlorides somewhat slower, and finally the iodides and sulphates act very slowly. Solutions of equivalent strength of sodium sulphate, bromide and chloride seem to correspond very closely to those of potassium sulphate, iodide, bromide and chloride of the same strength. T h e similarity of the salts will fully account for this phenomenon. Tn solutions, potassium sulphate would combine with water with the same degree of tenhcity as sodium sulphate, althocgh a slight difference might be expected. TABLE 111.
I
XL;
XL;
-u
3 x
XL;
,u'
EU
u 5" x x -5
1
1.9
0.5 1.2
3.0
25
11.0
4.8 7.0 10.0 12.0
4505 ~-
14.0 16.3 18.0
-
-1-1
0.3 0.7
0.2 I. I
1.1 2.0
2. I
1.9
2.7
3.5 4.5 5.8
2.5 3.0 3.5 4.0 4.4
1.5
9.0 10.0
I
4.7
,
2.0
-
7.1 8.5
-
-
10.2
11.3
_-
,
-
13.5
- 1 - 1 -Table I11 and Fig. 3 represent the results obtained with still other solutions which were treated with sodium amalgam. Nitric and hydrochloric acids were tried. T h e former was reduced and did not give 23 cc of gas. One-hundredth normal hydrochloric acid acted even slower than normal sodium sulp5ite. This shows that even though a salt might contain a very slight excess of acid as an impurity, it would make very little difference in its rate of reaction. One-fourth normal solu75 1
622
Guslave Fernekes
tion of calcium, strontium and barium act slower following the increase of their atomic weights. T h e rapidity with which they act is not proportional to their atomic weights, however. These results are influenced by the formation of the difficultly soluble hydroxides.
>
Fig. 3 Action of sodium amalgam on solutions of various other conipounds
The only other curve represented in this chart is that of ammonia. A normal ammonia solution acts faster than water, but very much slower than a sodium hydroxide solution of equivalent strength. Table IV and Fig. 4 present the results yielded by the action of potassium amalgam on various solutions. Normal and tenth-normal sodium hydroxide purified by alcohol again acted faster than all the others. Water was acted upon more violently by potassium amalgam than by sodium amalgam of the same strength. Here again solutions of the sulphates acted slower than those of the iodides or chlorides. I t might be said that potassium amalgam acts more violently on most solutions than does sodium amalgam. T h e most interesting curves in these figures are the ones which represent the dction of ordinary sodium
Action o f Sodium and Potassium A m a l g a m
TABLEIV.
s .
.
x
g Y
x
0" ad
0.2
0.2
0.5
0.5 0.7
1 .o
1.3 35 45 4500 1
--
65 701 75 -
I ^
10.1 20. I
1.0 1.1
2.0
2.6 3.9 4.7 5.5
0.5 3.5
4.0
1
4.8 5.7 6.2
-
~
,
~ -
~
1
~
-
1.4 1.7
-
-
-
-
-
d d
3 __
0
x"
5 IO
I5 20 25
30 35 40 45 50 55 60 65 70
hydroxide solution on both sodium and potassium amalgams. As has been mentioned.before, there is little or no action of these amalgams on a solution of pure sodium hydroxide prepared from
624
Gustave Fernekes
metallic sodium. T h e fact that sodium hydroxide from metallic sodium retards the action, and sodium hydroxide purified by alcohol hastened the evolution of hydrogen was somewhat puz-
Fig. 4 Action of potassium amalgam on solutions of potassium and sodium salts
zling, and so analyses of both sodium hydroxides were made, which gave the following results : Sodium hydroxide purified by alcohol
NaOH 40, CaO FeO
so,
c1 Heavy metals
85.31 1.75 0.26
trace trace trace none
%
Sodium hydroxide from metallic sodium
90
%
none none trace none none none
Various impurities were now purposely introduced into the solution of sodium hydroxide from metallic sodium to see whether they would accelerate the reaction. T h e chlorides of aluminum, calcium and iron (both ferrous and ferric) were successively introduced into the solution, as was also sodium sulphite. T h e addition of iron salts increases the rapidity of the action somewhat, although this increase is so slight that it does not account for the enormous rate observed with sodium hydrox-
Action of Sodium and Potassium Amalgams
625
ide purified by alcohol. Small quantities of sodium sulphite introduced had little effect. A normal solution of the latter salt acted rather vigorously, but still very much slower than a solution of sodium hydroxide (purified by alcohol). At this point Prof. Kahlenberg suggested another line of work which diverted my attention from the above work for a time. On inspecting the list of substances tried by me, he noticed that it contained but few organic compounds. The solutions of organic compounds that had been tried, such as aqueous solutions of amyl alcohol, ethyl alcohol, glycerine and canesugar (see tables that follow) were acted upon much more rapidly by sodium amalgam than was pure water. The fact that amyl alcohol which is not copiously soluble in water, nevertheless showed an increased activity suggested that other organic compounds which are very slightly soluble in water might produce a similar acceleration of the chemical action in question ; and so a goodly number of organic substances that are but very slightly miscible with water were tested. The following compounds employed were obtained from Schuchardt : methyl alcohol, propyl alcohol, glycerine, grapesugar, cane-sugar, milk-sugar, dextrine, pentane, amylene, paraffine, M. P. 30' to 37" C, benzene, toluene B. P. 110" at 744 mm, $-xylene B. P. 136.5' at 744 mm, naphthalene, thymol, cumenol, menthol, camphor, terpineol, acetonitrile, tri-propylamine, butylamine, di-amylamine, aniline B. P. I 85", toluidine €3. P. 195.5' at 151 mm, diphenylamine, dibenzylamine, benzamide, benzylamine, pyridine, quinoline, blood albumen and egg albumen. From Kahlbaum were obtained : ethyl alcohol, amyl alcohol, acetone, hexane, petroleum ether, phenol, borneol, mesitylene, and naphthylamine. The acetanilide was of Merck's manufacture, and the carbon bisulphide came from Bausch and Lamb. The water used in these experiments was distilled from a tinlined copper still of about eight liters capacity and condensed in a block-tin spiral. Barium hydrate was added to the water before it was distilled. This would combine with the carbon di-
-
626
Gustave FerneRes
oxide and also liberate the ammonia which would be contained in the first 300 to 400 cc of distillate. T h e water would also be free from any grease. T h e importance of the latter fact will become apparent from the data that follow below. The solutions were usually made up in the afternoon and allowed to stand over night. T h e experiments were made the next morning. T h e substances thus remained in contact with the water for 16 to 18 hours. While working up the solutions they were frequently shaken. T h e shaking was invariably repeated before using them. Paraffine and vaseline were melted just before pouring them into the water. Many of the results found were confirmed by Mr. F. L. Shinn. Duplicates and sometimes three samples of the same solution were run side by side. The results of the different samples agreed very closely, and the average of the values obtained is given in the tables. It might be well to add that the physical properties of these solutions were of course not appreciably different from those of pure water. The viscosity, surface tension (by Traube's method) and the electrical conductivity were tested, as were also the refractive power and the rotatory power, though the refractometer and polariscope are of course less sensitive instruments, relatively, and it was not to be expected that such very dilute solutions as here used could be distinguished from pure water by means of these. Table V and Fig. 5 represent results obtained with solutions of hydrocarbons on sodium amalgam. T h e solutions were prepared by shaking up the water with a great excess of the hydrocarbon. A glance at Table V shows that all the solutions act faster on the amalgam than pure water. It may be observed further that in most cases the rapid action seems to start after the lapse of five minutes, and in some of the cases ten, fifteen, or even more minutes are necessary, before rapid action begins. Solutions of hexane, terpineo1,I heptane, and xylene act more rapidly after five minutes. Solutions of naphthalene, petroleum This substance is a terpene hydrate and ought, strictly speaking, not be classed as a hydrocarbon.
Action of Sodium and Potassium Amalgams
627
TABLEV.
B w 3 F9
0
3w
i 0.9 5.4 11.0 15.5 18.0
0.5 1.6
0.3
5.5
3.5 7.5 ro.5 r4.o r6.o r7.8
20.7
10.3 14.8 17.8
21.3
19.9
-
-
-
-
-
-
-
-
~
0.7
1.8
2.7
0.4
8.8
0.9 2.5 4.0 6.0 8.5
11.0
11.0
13.0 15.0
13.0
I .o
195
2.5 5.0
_.
-
-
_
15.0
- 17.0 _- -
r9.3
_ 0.2
0.2
0.6 0.8
0.65 1.1
3.7 4.9 6.0 6.7 7.5
-
9.2 10.5
11.6
-
ether and benzene do not show an increase of action until ten minutes have elapsed. A solution of paraffine began to act rapidly after twenty minutes ; one of mesitylene after twenty-five, and vaseline after thirty minutes. Toluene gives a curve which is very nearly a straight line, althouhg it has a slight bend after the five minute
Gustave Fernekes
628
mark. T h e increase of action can be readily seen (Fig. 5) by the sudden bend in the curves. After this bend the curve con-
of the
action -___
-
e,
e,
9;
3
aPci z v.
f?v
x 5
I .o
IO
I5
4.0 7.0
20
10.0
25 30 35 40 45 50 55 60
13.5 16.0 18.0
-
-
0.2 I .o
2.4 5.0 -
10.0
13.0 15.5 17.0
-
0.5 2 -5 4.0 5.5 7.0 9.0 11.5 14.0 16.0
-
0.2
0.2
1.9 1.6 2.6 3.5 4.5 5.5 6.2 8.6 7.1 7.5
0.5
-
I .o
1.5 2.0
2.5 3.0 345 4.0 5.0 5.5
-
Action of Sodium and Potassium Amalgams
629
of half-saturated solutions of the same hydrocarbons on sodium
amalgam. These solutions were made up in the following manner: a liter of water was saturated with the hydrocarbon by constant shaking for some time. T h e hydrocarbon was then allowed to collect on the surface of the liquid, and then separated from it by means of a separating funnel. Five hundred cubic centimeters of this solution thus saturated was then diluted up to a liter. T h e strength of these solutions was then one-half that
Fig. 6 Action of sodium amalgam on half-saturated solutions of hydrocarbons
of the saturated solutions. T h e action of these half-saturated solutions on sodium amalgam was in all cases slower than was the action of saturated solutions. In most cases the rate of liberation of hydrogen was more than half as fast as in saturated solutions. A half-saturated solution of terpineol, however, liberated even less than half the quantity of hydrogen that was liberated by a saturated solution of the same compound at the end of the same period of time. T h e curves do not follcw each other in the same order as in Fig. 5. A saturated solution of terpineol acts faster than a saturated solution of heptane or naphthalene. On comparing half-saturated solutions of the
630
Gustave Femekes
same compounds it will be observed that a solution of terpineol acts slower than solutions of naphthalene or heptane. T h e curves representing the results for solutions of toluene and mesitylene follow in the same order in Fig. 6 as in Fig. 5. T h e results in these two tables very strongly favor the view that these hydrocarbons are actually in solution. The presence of a certain quantity of the hydrocarbon in the water increases the rate of reaction on the sodium amalgam. If only one-half the concentration of the hydrocarbon is used in the water we might expect this solution to act more nearly with the rate that pure water acts. Further it might be expected that the action would be one-half as rapid as with the saturated solution, if we compare the rates of both the saturated and halfsaturated solutions with water. All solutions represented in Table V I satisfy the first requirement, i. e., they all act slower than saturated solutions of the same hydrocarbons. The second requirement is, however, only approximately satisfied. T h e rate of action is sometimes greater, and in a few instances half that of the concentrated solutions. Table VI1 and Fig. 7 present results obtained by using amines and various organic compounds containing oxygen. T h e amines are placed at the right-hand side of the figure. T h e solutions used were all saturated unless otherwise stated. Glycerine solution containing four molecules to a liter acts extremely fast, the action starting rapidly from the very beginning. Amyl alcohol and methyl alcohol solutions (the latter containing two gram-molecules per liter) show a slight bend in the curve which means an initial slow action. T h e same is true of ethyl alcohol containing four gram-molecules per liter. Methyl alcohol with zoo g per liter acts very much slower than the same solution containing two niolecules per liter. It is comparable with the sodium salts of inorganic acids which have already been discussed. One would expect propyl alcohol to act like methyl and ethyl alcohols on account of its similarity to these. Different concentrations of propyl alcohol in water were, however, not tried. Ether acts extremely fast. T h e total amount
Action of Sodz'uvz and Potassium Amakams
631
of gas evolved in this case was greater on account of the vapor pressure at the temperature of the experiment. Solutions of TABLEVII.
4.0
8.0
3-2
12.0
15.5
18.5
20.7
-
-
___
___
1.2 2.0
0.4
2.8 3-5 4.7 6.0 13.0
1.4 1.7
-
1.0
~
3.0 5.5 6.9
-
0.2
0.3 0.7
2.5 4.0
2.7
-
7.0
-14-
- I -
'-I- - I - ; -
-
10.2
13.0 16.5
-
1.2
5.0
7.6 9.2 12.0
13.8 16.5 17.6
0.6 1.5 3.0 4.0 5.2 6.8 8.5 10.8 12.5
-
0.7 1.4
0.2
0.2
0.2
0.6
0.3
0.9
0.5 0.9
0.7
2. I
2.7 3.4 4.1 4.5 5.2 5.9 6.6
1.2
0.3 0.4 0.5 0.7
1.2
1.7
10.0
-
12.7
1.6 2.2
2.7 3.2 4.0 4.5 5.1
-
6.7 .-
-
1.6 1.8
0.8 0.9
2.2
1.3
2.7 3.1 3.6 4.1
I .o 1.1 1.2
-
1.35 1.4
1.5 1.6
I. I
2.3 2.7 3.2 4.0 5.0 5.8
-
7.0
4.6 5.3
8.0 9.0
-
-
10.0 11.0 12.0
632
'
Gusiave Pevnekes
thymol, cuniinol, camphor, and menthol all act faster than water, and they all show a sudden bend in the curve where rapid action commenced. A saturated solution of phenol acts but little faster than water.
Fig. 7 Aqueous solutions of amines, alcohols, and miscellaneous oxygen compounds
Saturated solutions of the amines, aniline, toluidine, and xylidine act with about the same speed upon the sodium amalgam as does water. Toluidine and xylidine even retard the action somewhat. T h e same results were obtained with many other amines and amides tried, the action of the water on the amalgam being hardly influenced by these substances. It might be of interest to add a number of substances, whose action on the anialgam was tried at dilutions of one gram per liter. Fig. 8 and Table VI11 present the results obtained with these dilute solutions. Glycerine, cane-sugar and butyl alcohol still show a more rapid action at this dilution than pure water. T h e solution of glycerine, however, acts slower than a solution of the same substance where four molecules per liter were used (Fig. 7). A grape-sugar solution acts with about the same speed as water. Acetone, milk-sugar and amyl alcohol solutions retard the action of the amalgam. Again referring to Fig. 7, one may observe that a saturated amyl alcohol solution
Action of Sodium and Potassiunz AmaZgams
633
acts very fast. T h e curve in this figure (Fig. 8 ) shows that amyl alcohol retards the action when only one gram is used to a liter of water. The fact that solutions which are as dilute as this still affect the reaction is very remarkable. A solution of cane-sugar containing one grain of sugar per liter can hardly be detected by the sense of taste. Glycerine, phenol, and the alcohols can, however, be tasted quite distinctly at this dilution. T h e latter may also be detected by the'sense of smell. The dilu-
TABLEVIII. Butyl
Min.
Acetone
5
-
I .o
0. I
0.2
IO
0.4 0.8
1.9 3.2 4.8 6.2 9.5 11.3 '3:5 15.5 17.5 18.j
0.3 0.6 0.8 r.0 1.3 1.5
0.8
-
-
15 20
I .o
25 30 35 40 45 50 55 60 65
1.3 1.8
70
Phenol
2.2
-
3.5 4.2 4.8 5.2 6.0
-
1.5
-
~
-
7.8
-
-
2.8
_ -
-
~
11.5
-
-
'5.5
Canesugar
Milksugar 0. I
-
~~
Min.
Glycerine
Grapesugar
IO
0.5 I .8
0. I I .o
I5
4.2
1.8 3.2 5.4 7.9 10.3 13.0 14.5 16.j
5 20
7.3
25
11.0
30 35 40 45 50 55 60
14.4 17.0 19.4 20. j 22.0
-
0.6 0.8 1.1
1.4 1.8 2.0
-
3.2 4.3
-
634
Gustave FenzeRes
tion at which various substances can still be detected by the sense of taste has been very carefully studied by Prof. Kahlenberg.' I t is clearly shown in this article that a substance must be soluble in order that it may be tasted, and furthermore it js shown how extremely delicate must be the reaction between the solution and the nerve endings which govern the sense of taste.
Solutions in which one gram of the substance was used per liter of water
A five-thousandth normal solution of silver nitrate and a twothousandth normal solution of mercuric chloride could still be tasted. There is no doubt that there are substances which can be tasted in still greater dilutions. T h e sense of taste also assists us in detecting the presence of hydrocarbons in solution. I t is a well known fact that water shaken up with benzene or toluene will retain a distinct taste characteristic of the respective hydrocarbon used. From these facts we can draw the conclusion that the hydrocarbons and other compounds frequently regarded as in"The action of solutions on the sense of taste." Read before the Wisconsin Academy of Sciences, Arts and Letters a t its meeting at Milwaukee, December, 1897.
Action of Sodium and Potassium Amalgams
635
soluble, actually go into solution. T h e action of these solutions on sodium amalgam can serve as a method of detecting the presence of minute quantities of these compounds in water. T o remove all doubt that the action might be due to finely suspended particles of these hydrocarbons, a number of experiments were performed. Precipitated barium sulphate and calcium carcium carbonate were employed. But the action of the amalgam on water containing these finely divided substances was not increased. An explanation of these facts is now incumbent. Viewed from the standpoint of catalytic actions it is possible to classify all these reactions under two heads. First there are those substances which, dissolved in water, retard the action of the amalgam so that the spegd with which the latter liberates hydrogen is less than with pure water. These substances are negative catalytic agents ” and include most of the salts of the inorganic acids and also some organic compounds. Then there are those substances which in solution increase the action of the amalgam. These substances are positive catalytic agents ” and include most of the organic substances employed, especially the hydrocarbons. T h e term catalytic action of course does not give an explanation of these phenomena, but it merely serves as a convenient term for the classification of these results. As we are here dealing with solutions entirely we are confronted with the problem to find an explanation as to the nature of these solutions. It would seem that the action of the sodium and potassium amalgams on solutions of sodium and potassium salts should be fully accounted for by the ionic theory of Arrhenius. As stated above, this investigator attributed the slow action of sodium qmalgam, for example, on solutions of sodium salts to ions of sodium in solution, which by mass action would prevent the entrance. of more sodium ions into the solution. Although this theory is very plausible in the case of solutions of sodium salts with sodium amalgam, it fails to explain the slow action of the same amalgam on solutions of potassium salts. It is just as difficult to explain the slow action of potassium amalgam on solutions of sodium salts by this theory. T h e increased action ((
((
636
Gustave FemeRes
of the sodium amalgam on water containing organic compounds in solution cannot be accounted for by this theory, and the problem of finding the cause for the anomalous behavior of the amalgam on these solutions would remain unsolved. Numerous examples of the untenability of the ionic theory have been found since its establishment in 1887, and it is especially the series of investigations which have been carried out in this laboratory for a number of years under the direction of Prof. Kahlenberg, which show conclusively that this theory has outlived its nsefulness. Prof. Kahlenberg has also been the first to suggest a new theory, which not only explains satisfactorily the facts whose interpretation required the complicated ionic theory, but which also throws light upon the whole subject of solutions, explaining the facts whose interpretation by the old theory was difficult or absolutely impossible. Chemical affinity, the affinity between solvent and dissolved substance, and the formation of a true chemical cotnpound whose properties are different from either constituent form the basis of this new theory. It will be seen how siniple the interpretation of the behavior of the amalgam on the different solutions is. To begin with, the solutions of the sodium and potassium salts of inorganic acids, whose action on the amalgams could not be explained by the ionic theory, will show how well the new theory applies. A solution of sodium chloride should retard the action of the sodium amalgam according to the ionic theory, because sodium iops in the solution will tend to prevent the entrance of more sodiutn in the ionic state. On the other hand, a solution of potassium chloride should not retard the action of the sodium amalgam. T h e potassium ions can offer no resistance to the entrance of sodium ions. A glance at Figs. I and z will however, show that potassium chloride retards the action, and furthermore that a normal potassium chloride solution retards about as much as a normal solution of sodium chloride. Prof. Kahlenberg’s theory satisfactorily explains this by assuming that potassium chloride has about the same affinity for water as has sodium chloride on account of the similarity of the two salts.
Acfion of Sodium and Poiassium .4matgams
637
T h e water would in each case be held with the same degree of tenacity, and the action of the sodium amalgam on the new compound would in each case suffer an equal retardation. T h e same explanation of course holds in the case of potassium and sodium salts in general if we compare isotonic solutions of these salts. T h e theory also accounts for the same phenomenon observed with potassium amalgani (see Figs.). T h e similarity in the ebullioscopic and cryoscopic behavior and the electric conduction of solutions of sodium and potassium salts can also be readily interpreted by this theory. A new chemical compound then is formed between the water and the salt which, if similar, will also have similar action on the respective amalgams. There still remains the list of organic solutions, the results of which on sodium amalgam are represented in Figs. j to 8. As the majority of organic compounds are considered undissociated in aqueous solution, the ions can not be held responsible for the peculiar behavior of these solutions on sodium amalgam. By the application of the new theory presented above the results can, however, be readily explained. T h e formation of a compound of the solvent and dissolved substance is again assumed. T h e compound must in this case be extremely unstable toward sodium amalgam, as is shown by the rapid inroads that the latter makes upon the solution. T h e action as has been mentioned, was in most cases more rapid than with pure water. T h e assumption of such an unstable compound is nothing extraordinary. Nuinerous instances of the great reactivity of such unstable compounds are known. I t will suffice here to mention but one instance to illustrate what is meant. Kitrous oxide, for example, is a more reactive compound than are either of the elements of which it is composed. Everybody knows that a splinter of wood will burn even more violently in nitrous oxide than in pure oxygen. These facts give the clue for the explanation of the anomalous behavior of these organic solutions, and justify the view that the rapid action of these organic solutions is due to such unstable compounds. It is also clearly shown by comparing the results presented in all the tables that
638
Gustave fiernekes
the rate of action of inorganic as well as organic solutions on the amalgams is not proportional to the number of dissolved molecules. A one-tenth normal sodium chloride solution does not act ten times as fast as a normal solution of fhe same salt. A half-saturated solution of any of the organic solutions does not act half as fast as a saturated solution. This simply means that the first particles of a substance going into solution are attracted more strongly and held more firmly by the water than are the particles which enter w5en the solution is already partially saturated. T h e firmness with which the particles are held by the water diminishes with increasing concentration. Therefore the particles which enter when the solution is already partially saturated will not influence the rate of action of this solution on the amalgam as much as the first particles which went into solution. This then accounts for the fact that in most cases of the inorganic salt solutions very little difference appears between the rate of action for different concentrations of the same salt. It is for the same reason that a half-saturated solution of a hydrocarbon, for example, acts slower than a saturated one, but not with half the rate. There is still one more fact to be explained, and that is the sudden increase of action on the amalgam of most organic solutions. This sudden increase is shown in the figures by the sudden bend in the curves. This can also be easily interpreted by the new theory. T h e amalgam in acting on the solution forms sodium hydroxide. It is very probable that this sodium hydroxide brings about this increase in action. A compound formed by the action of the three substances water, hydrocarbon and sodium hydroxide need only be assumed in these cases to explain these phenomena. At this place, attention must again be called to the rapid action of sodium hydroxide purified by alcohol, on both sodium and potassium amalgams. T h e results of this action are presented in Figs. I and 4. A probable explanation of these results follows, from what has been stated above ; small quantities of organic substance may be present in this sodium hydroxide. The combination of the water, sodium hydroxide and the organic substance again might cause this rapid action which was observed.
Action o f Sodium aizd Potassium Amalgams
.
639
All the results obtained by the action of the different solutions on sodium and potassium amalgams are now satisfactorily explained by Prof. Kahlenberg’s theory. A few of the possibilities of applying this theory to phenomena which are closely allied to these results should be mentioned. I t has been convenient to term these actions catalytic actions. T o solve the nature of catalytic reactions is one of the most important problems of modern chemistry. Catalysis plays an important r81e not only in pure science, but also in inany branches of chemical industry. T h e manufacture of indigo from naphthalene, and the manufacture of sulphuric acid are only two of the numerous reactions which are termed catalytic. Many of these catalytic reactions find a ready explanation by the application of this new theory, and by w i n g the term solution in the broad sense which includes*solid, liquid and gaseous solutions, it is not improbable that all catalytic actions can be explained satisfactorily. It is then simply the attraction between solvent and dissolved substances and the formation of a true chemical compound which is more or less stable and which may be made up of more than two substances, which has been set down as the cause of the different rates of reaction. To how great an extent this theory will be substantiated by further investigation cannot be foretold a t the present time, but its simplicity must certainly appeal to all who have followed the development of the ionic theory and are cognizant of its weaknesses. Many very able investigators have been aware of the meager evidence upon which the theory of Arrhenius has been built up and have repeatedly set forth views similar to Prof. Rahlenberg’s. None, however, took a firm stand to uphold these views nor did they attempt to confirm thein experimentally. 1 wish at this place to express my sincere gratitude to Prof, Kahlenberg, not only for the many compounds which he placed at my disposal, but also for the many suggestions and the advice which he offered me throughout the work. Laboratory of Physical Chemistry, University of Wisconsin, Madison, July, 1903.
