No. 31 brings together in one study many of the elements already presented earlier in the book: moving quickly in and out of the mid/low register, rapid slurred/tongued patterns, and both sudden and gradual dynamic changes.  I settled at a tempo somewhere around quarter=96, and my Cornopub edition suggests a tempo range of 84-112.  Verne Reynolds goes even further in The Horn Handbook, noting that No. 31 “is still another two-slurred, two-tongued exercise that can be practiced at various speeds, including a speed fast enough to justify using the double tongue.” (p. 61)