with our CZ. Greenwald's constants for oxalic acid and malonic acid are included in the last column of Table VI11 together with tlinse which wc liavc calculated from Snnins' observations OII succinic and azelaic acids. For these calculatioiia we used the method of the present paper. Sitnms' constants must be reduced slightly to translate. them from ,U = 0.07 to 0 20 'TIE activity correction is -log ? ' i h i I 67 922 1935). ( e ) sbzd 68, 1341 (19RO)
The present report concerns studies of reactions that have been made under the fusion point and is limited to double decompositions involving only Na+, K', Kb+, CsT, C1-, Br-, and I- (see reactions l-ls, Table I). The variation of the speed of reaction with time a t a fixed temperature has been studied and also the variation of the speed with temperature for a fixed time. In five cases what appear to be equilibrium mixtures have been obtained and these mixtures have been studied in some detail. Materials and Experimental Procedure The salts used were Analytical Reagents with the exception of cesium chloride and bromide, which were prepared from the nitrate according to the method of Wells.3 The salts were fused and ground to a fine powder and kept in a desiccator until wanted. -4fter heating the various salt pairs a t temperatures and for lengths of time indicated in the proper place, all mixtures were examined by the method of X-ray crystal analysis as previously described.*" It is, in general, more difficult to obtain good films from salt mixtures which have been heated under the fusion point rather than above the ( 3 H L We% l m J 5rt
131 46, 186 (1891)
SOLIDALKALIHALIDEREACTIONS BELOW FUSION
Oct., 1938
fusion point. In many cases the material being examined does not appear to be in the proper crystalline form. The crystals are perhaps too small or are strained and for these and, no doubt, other reasons yield patterns consisting of a limited number of lines that are in many cases difficult to read. In addition to these difficulties, quantitative results from equilibrium studies are difficult to obtain because the formation of solid solutions is not as common as above the fusion point. It is often possible, however, to draw definite conclusions from surprisingly few data.
Results I n Table I are listed the results obtained for reactions 1 to 18 a t 400' when the heating was continued for thirty-six hours. What previously has been called the stable pair (indicated in Table I by the letter a) was heated in each case and the resulting mixtures were analyzed (by means of the X-ray beam) for evidence of reversal toward the reciprocal pair (indicated in the table by the letter b). As was to be expected from previous work above the fusion point most of the stable pairs showed little or no evidence of any tendency toward reversal. Reactions 3, 5 , 8, 9, 11, 14, and 16 showed unmistakable evidence of some reversal. The results obtained from heating the reciprocal pairs are shown in column b. All of the reactions with the exception of 10 and 14 proceeded partially or completely toward the stable pair. Reaction 10 possibly did also since it seems likely that reaction would have preceded the formation of a solid solution. The formation of
2321
this solid solution at 400' was not expected since i t was known that neither the mixture KBr-KC1 nor the mixture RbC1-KC1 forms a solid solution a t 400". The cube edge obtained is only 0.001 A. different from that of either component of the reciprocal pair but the interference diagram obtained can scarcely be the patterns of potassium bromide and rubidium chloride superimposed on each other since in this case interference lines with odd ordered indices would have been obtained such as 111 and 311 and no such lines were obtained. The situation was made even more interesting by reason of the fact that the stable pair, when heated a t 400°, produced only patterns of potassium chloride and rubidium bromide. It is, of course, quite possible that a solid solution of compounds that are just being formed may occur more readily than will be the case for a mixture of these same compounds after they have already been formed. The results in Table I indicate that reactions 3, 5 , 8 , 9, 11 and 16 should also reach an equilibrium if heated long enough a t 400'. Several of the reactions were examined at higher temperatures. When the reciprocal pair of reaction 14 (KI-RbBr) was heated a t 480" for thirty-six hours there was evidence of considerable reaction whereas a t 400' no evidence of reaction was found. The lowest fusion temperature of this mixture was found to be about 608'. When the reciprocal pair for reaction 2 was heated a t 480' for thirty-six hours the extent of the reaction was found t o be 62% as calculated from the resulting solid solution of rubidium
TABLEI SHOWING THE RESULTSOBTAINED BY HEATINQ VARIOUS SALT PAIRS AT 400' Reaction
Accepted cube edge aa
1 a. NaCl KBr b. NaBr KC1 2 a. NaCl RbBr b. NaBr RbCl 3 a. NaCl CsBr b. NaBr CSCl 4 a. NaCl KI b. NaI KCI
5.628 6.570 5.94 6.280 5.628 6.86 5.94 6 ,570 5.628 4.29 5.94 4.110 5.628 7.052 6.46 6.280
aa
Reciprocal pair-b Remarks
5.629 6.561 5.947 6.288 5.628 6.868 5.946 6.582
5.971 4.182 5.628 7.032 6.46
Partial reaction
FOR 36 HOURS X-Ray Observations Stable pair-a a0 Remarks b
No reversal
Partial reaction
5.631 6.860
N o reversal
Partial reaction
5.628 4.265
Partial reversal
Partial reaction
b
,
Little or no reversal
2322 ~ A B I1 , ~ ~( ComEuded)
Accepted cube edge
aR
Reaction
5 a. R'aCl RbI b. NaI RbCl r; d . NaCl CSI h Nal CsCl 7 a hTaRr KI b NaI KB r X a NaBr RbI b. XaI RbBr 9 a. NaBr (2.1
Sal C.B1 10 d Kci RbBr 1) KRr RhCI 1 1 it. KC1 CsBr 1). KBr CSCl 12 a. KCl Rbl b. KI RbCl 13 a. KC1 CsI b. KI CSCl 14 a. KBr RbI 1,
1, 1R a
b. 16 a.
h. 17 a
1).
628 32.5
5.622 7 320
X-Ray Observations
Reciprocal pair-b Remark,
a"
Almost complete reaction
46
b
570
E
1328
5.637 4 X4
Complete rrartion
5 937 6 998
;\lrno\t complrte reaction
1 .yLJ 11 4t:
1 110 94 7 052
?)'
5 626 7 327 6 575 5.628 4 558
3 937 6 995
Stable pair--a Remarks
Partial reversal
No reversal
-4 very little reversal
t, 41,
I>
.570
3 94 7 323
I,
b
Partial reaction
I,
Some reversal
7 257
ri 31;
n 86 .i 94
6 00 I
4 502 ii 46 I 28
4 51-i
I:
280
0 E l
b
Partial reaction
Some reversal
4 508
Solid
s
