Gustav Cornelius Gurlitt (1820-1901) was a German composer. His output was prolific, ranging from songs and teaching pieces to operas, cantatas, and symphonies. His teaching pieces for piano are particularly noteworthy.
These engaging Mid Intermediate studies are great for developing finger speed and dexterity. I suggest learning them as quick studies (spend about a week on each exercise). As I have transposed each exercise into every white note major key, you may like to choose a different key for each exercise.
Online resources: You can view all the Supersonics Plus resources available for this book here
(turn your phone sideways to view the samples)