I left out the following sentences.
Thank you very much, Writeacher.
1) He feels tenfold more evil than Hyde but also more free.
2) He realizes a potion capable to split up his soul, to separate the good side from the evil one.
3) The image of his friend returns to the memory of the poet.
Some soldiers begin to fall down under the deadly gas.
4) When these agonies have stopped (not “stop”) he feels like he is out of a great sickness.
5) As Hyde he feels a sense of freedom, he is smaller and younger because his evil side is less exercised.
1) He feels he is ten times more evil than Hyde, but also more free.
2) He makes (or devises or creates) a potion capable of splitting his soul in two, to separate the good side from the evil one.
3) The poet remembers his friend.
(Active phrasing is ALWAYS better than passive.)
Some soldiers begin to fall because of the effects of the deadly gas.
4) When these agonies have stopped, he feels as if he has recovered from a great sickness.
5) As Hyde, he feels a sense of freedom. He is smaller and younger because his evil side is less exercised.