E. B. [CVNTRIBCTION FROM
THOMAS AND THE
LYMAN J. WOOD
Yol. 36
DEPARTMENT OF CHEMISTRY, ST.Louis UNIVERSITY1
A Study of Some Reactions between Dry Inorganic Salts BY E. B. THOMAS AND LYMAN J. WOOD I n a report made by the senior author a t the renver Meeting on certain salt mixtures it was shon n that potassium chloride and sodium Lromido interact with each other when the salts are fusrd, the reaction going practically to completion. This reaction has been studied in detail hoth belom and above the fusion point. Several other reactions have also been investigated by means of the x-ray spectrograph and are reported below.
over the use of all lines on the film as has frequently been done. In the first place it is obvious that interference lines corresponding to should interplanar distances greater than 2 not be used since the unavoidable error in measuring is approximately ten times as large as in the range selected. In the second place lines too far out from the zero are not convenient since any error made is multiplied by a very large factor in calculating the cube edge and also excessive time of exposure is required to ensure lines heavy Methods and Apparatus enough to measure accurately. Each mixture examined was weighed out careMack, Havighurst and Blake2 have shown fully, mixed thoroughly and heated in an electric that greater accuracy is obtained by calibrating furnace Fused mixtures were kept above the each section of the film, i. e., by selecting calibratfusion temperature for a few minutes, after ing lines in the same range as the unknown lines. which time they were taken from the furnace and The method described above has been shown poured onto a brass plate previously cooled in to produce accurate and reproducible results, ice watrbr. Immediately after pouring the molten as can be seen by referring to the data given mixture was stamped from above with another below. It goes without saying that all the lines cold plate The result was almost instantaneous (frequently as many as 18 or 20) were measured in crystallization order to determine the pattern or patterns present, 'The apparatus used for x-ray examinations all lines being accounted for in the manner shown was thl- General Electric Multiple Diffraction in Table I1 although space does not permit pubSpectrograph. The powder method was used lishing all in detail. The Wyckoff method of for all tests. The powdered sample was passed mixing the standard with the unknown could through a 200 mesh screen and sealed in a thinnot be used if sodium chloride was to be the walled glass tube having a maximum outside standard since many of the mixtures contained diametcr of 0.9 mm. The powder was exposed to the 110 o( doublet for 300 to 600 m. a. sodium chloride. In order to determine the hours, the x-rays being filtered through zirconia amount of error introduced due to the difference to make them nearly monochromatic. The film in densities of sodium chloride and an unknown radius was 20.3 cm. The unavoidable error is when the two are photographed on opposite believed to be about plus or minus 0.006 8. edges of the film, a trial run was made with pure for a cube edge of 5 to G A., which is about the potassium bromide as unknown and pure sodium accuracv reported by Davey' using a similar chloride as standard. A cube edge value of K3G7 A. was obtained for potassium bromide laboratory procedure. compared with 6.570 8., the preferred value A11 film measurements were made by direct reported in the "International Critical Tables.' ' comparisons with standard sodium chloride lines In some cases flour was mixed with the heavier on the opposite edge of the film, the NaCl 400, samples in order to minimize the effect of the 331 and -4% interference lines being used for difference in densities and also to cut down the this purpose. For accurate measurements of cube time of exposure. edges, lines corresponding to interplanar distances Experimental Results in the range of 1.3 to 1.6 A. (in the same range as thr st aritlard sodium chloride lines) were selected. In order to study in more detail tlic rcaction f h r autll(,is I w l i r \ c that t h i i method of deter- KC1 t KaRr + KHr -1NaCl iiicntioiied aim\(., riiiriitig I t i ( ciil)t t tl;rc has an irnpor tnrit advantagin 3 w i e r ( ~ fbinary mixtures of KC'I K B I , KCI I!
I I , , , ,
1'1,
I\?
?,14Ul
A.
121 h l d i k H < x ~ . I ~ 1u ri n t i R l l b r l t r r i 1m111'ust 4 6 , '>I,\ ~ l ~ l i L !
NaC1, NaCl-SaBr and NaC1-KBr of various compositions were made up and examined with the x-ray spectrograph. All of these salts cryscallize in the sodium chloride type of lattice and the cube edges range from 5.628 A. for NaCl to (i..iTO A. for KElr. The chemicals used were of c. P. quality fcx all mixtures. The results obtained arc shown in Table I.
continuous series of mixed crystals between 500 and 660". R. Nacken6 found that for a mixture of 6.5 mole per cent. of sodium chloride and 35 mole per cent. of potassium chloride the solid solution which exists a t higher temperatures unmixes a t slightly under 500" and that pure sodium chloride exists just under 300" and pure potassium chloride somewhat below 250 ".
TABLE 1 RESULTS OF X-RAYANALYSISOF BINARYMIXTURES Mixture number
19a
Cornpahition ill mole %,
Indices h k I d in
NaCl 50 400" KC1 60 420 422 42 KBr 85 400 KC1 1.5 420 422 2W KBr 50 400 KCl 50 420 422 43 KaBr 50 400 KaC1 SO 420 422 1Y S a C l 85 400 S a B r 15 331 420 44 S a c 1 50 400'' KBr 50 420 422
A. .. .
1.257 1,149 1.634 1.461 1.333 1.007 1.436 1.309 1.452 1.300 1,186
1.421 1.302 1.271
Phase I Cube edge = a ,
..
5.fi28 5.628 6.536 6.534 6.530 6.428 6.426 6.416 5,808 5.814 5.810 5 . ti84 5.676 5.684
Phase 11 Indices h k 1 din
Remarks
For pure NaCY a = 5.G?8 No KCl diss. For a solid s o h . of this compn. a = 6.526 For a solid s o h . of this compn. a = 0.425 For a solid solti. of this compn. a = 5.784 For a solid s o h . of this compn. a = 5.674 NaCl appears to be sl. sol. in KBr.(a = 6.5i0)
Cuhe
A. edge
= a
Remarks
400 1 . 5 i l 6,284 For pure KCl 420" . . . . . , a = 6.280 422 1.282 6.280 No NaCl diss. No lines for a second phase obs.
No lines for a second phase obs. h'aC1 lines detected (faint)
No lines for a second phase obs.
... , , , 2222" , . . , . . For pure S a C l 1.464 6.548 420 1.260 3.834 a = j . 6 2 8 1.338 6.554 ... ... Double line, i. e., a line from each pattern occurred a t about this position and hence neither could be measured accurately.
Vegard:' investigated the system KC1-KBr arid found it completely miscible in all proportions in the solid state. L-egard's results have since been confirmed by other workers* and in the present work (Mix Xo. .I% and KO. 2W, Table I). From his work with KG1-KBr mixtures Vegard was able to state the "Additivity Law." Although it is by no means certain that the "Additivity Law" holds for all substitutional solid solutions, it does seem to hold very well for the type of solid solution dealt with in this paper. One of the purposes of the present work has been to see how well x-ray 'measurements from this type of salt mixture can be explained in terms of the "Additivity Law." Its validity has therefore been assumed. I t was already known that sodium chloride and potassium chloride are a t most only a very little soluble in each other in the solid state a t room t t . r i q ) c w t i i r - c . . (;. 'I'arnmanri5 reported a
Havighurst, Mack and Blake4d using x-ray diffraction methods, report that about 2% of sodium chloride dissolves in potassium chloride and a few per cent. of potassium chloride in sodium chloride a t room temperature. These conclusions were based upon two measurements which appear to be wholly inconsistcnt with each other. In this work i t was found possible to check one of these two measurements to within 0.001 -4. (Mix No. 19a, Table I), from which results i t is concluded that sodium chloride and potassium chloride are almost if not completely insoluble in each other in the solid state a t room temperature. Sodium bromide is reported to form a solid solution with sodium chloride up to 35y0 sodium b r ~ m i d e . ~ "Results are shown in Table I for a 50 mole per cent. mixture of sodium bromide and sodium chloride (No. 4 3 ) . It is to be obw-vcd tlint t h e cube tdge for the solid solutiori Inrger tlinn the c~alculatt.rl x due, the i I ) s t ' I t-tf 0 1
V,,h
