I left out the following sentences. Thank you very much.
1) His dictionary definition of a horse underlines how Mr. Gradgrind has choked his Bitzer's imagination.
2) The black of the soot (can soot be replaced by ash and smoke?).
3) Dickens compares the up-and-down movement of the piston of the steam engine (and not steam engine's piston) to the (shaking??) head of an elephant in a state of melancholy madness.
4) In contrast with Sissy (incorrect, better: Unlike Sissy), Bitzer is light haired and light eyed.
5) He calls his students by their number in the class register.
1. "...has choked his Bitzer's imagination." Should "his" be in there?
2. yes
3. "the steam engine's piston" is smoother
4 and 5 - OK