In case you missed it, please check out my post on major thirds.

Chromatic fourths and easy and fun:



And of course, this is one reason why you practice chromatic fourths:



You’ll notice that in certain spots you have to slide your second-finger from a black key to a white key. Try this exercise that alternates ascending with descending passages and isolates this occurrence:



I would imagine that Moszkowski’s Book III and IV would contain exercises similar to this. Exercises that focus on isolating spots with troubling fingering/hand positions. I would encourage you to experiment with similar exercises with all intervals. To start simply, practice switching directions! An example using minor thirds:



Stay tuned for part 5!