Garrett K. Johnson1 University of Missouri Columbia. MO 65201
I Preparation and Analysis of Solid Solutions I
in the Potassium Perchlorate-Permanganate
I t is well known t h a t a n ion of either sign, X, in a n ionic crystal lattice can he replaced randomly b y a different ion, Y, provided X a n d Y d o n o t differ greatly i n structure a n d size (1-3). This replacement is especially favorable if t h e pure end members. sav A X a n d AY. of t h e series of solid solutions : \ I N . \ ' I Ihmr idtmtiwl crystal structures and t h u s h ~ l o n n711 I I I P .3mr -1):1te eruun r isomorphism). Suth :I pair is K('lOn KMn04. ~ ; , t hofthese salts cristallize in orth&hnmbic space group P h n m a n d their lattice parameters differ b y n o more t h a n 3%a h n g a n y axis ( 4 , 5 ) .T h e mutual miscibility of these two compounds was shown t o form a continuous series b y Greenberg a n d Walden ( 6 ) ,t h e lattice being relatively indifferent in its accommodation of b o t h C104- a n d M n 0 4 ions. Solid solutions are found widely among mineral species and also amone some common lahoratorv chemicals, t h e two best known he;& t h e alums and t h e ~ u t t o salts. n he phenomenon is utilized imolicitlv i n m a n y radiochemical separation procedures a s weil a s in t h e production of metal dloys. I n s t a n d a r d gravimetric analytical methods, solid solution components sometimes contaminate precipitates-for example, C1- in AgRr and KCIOa in BaS04. I n t h e last case t h e istlmorphous replacement involves both positive a n d negative ions since substitution requires charge compensation. T h e ubiquity of solid solutions suggests t h e need for a n experiment t h a t advanced students can perform in order t o become familiar with this kind of compositional behavior of crystalline materials. S t u d e n t s of mineralogy nowadays a r e more accustomed t o this aspect of solids t h a n are students of chemistry. 'rlw pre.+nt t.ul)cr:n~entirlsu ic,cunr; ;sttentism upon w l u 11trnequilihrin :rnd tlw pr
