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<br />Effects of Insoluble Ma[erial on Cavity Shape <br />The salt used in all experiments con- <br />tained insoluble material, mainly anhydrite, <br />in quan[i[ies from approximately 1~ to more <br />than lOJo. The amount was fairly consis[enr <br />in specimens from a given source. In sev- <br />eral cases [he bulk of the impul•ities was <br />concentrated in parallel bands, several <br />inches thick, as shown in Fig. 15. <br />The collet[ion of this material on the <br />cavity bottom ac[s as a barrier and grea[ly <br />reduces the ra[e of solution in that area. If <br />most, but no[ all, of this material is re- <br />moved from the cavity while washing, the <br />bottom of the cavity will assume a conic <br />shape whose sides slope at an angle equal to <br />the angle of repose of [he insoluble material. <br />in the case of anhydrite, [his is approxi- <br />mately 34°. <br />O[her effects of insoluble material on <br />cavity shape tend to average out over the <br />washing process and become relatively in- <br />significan[, except when the anhydrite <br />stringers or bands are sufficiently [hick [o <br />provide barriers. In such cases greater ir- <br />regularityof the surface resul[s. With se- <br />vere banding of anhydrite, i[ would be <br />2.0 <br />1.6 <br />r <br />f-- <br />a 1.2 <br />U <br />ta.. <br />~, 0.8 <br />w <br />a <br />u~ <br />0.4 <br />0 <br /> <br />0 20 40 60 80 100 120 140 <br />W, LBS/ FT3 <br />Figure 14. Specific Gsa~~~,~y vs. Specific Weigh[, <br />Figure 15. Otcuaence of Insoluble >fatesiaL <br />307 <br /> <br />