I urgently need you, Writeacher, to check these sentences. Thank you very much in advance.

1)He uses a particular salt, adds it to other components and brings it to the boil. Once the boiling (better ebullution??) has subsided (ceased?), he drinks the potion. First, he suffers the most horrible agonies...
2) Hyde is physically smaller because he's evil side has always been repressed by his good one. (one is necessary=:
3) He is aware he has turned (transformed himself is possible?) into an evil, horrible, tenfold more wicked man.
4) The soldiers succeed in putting on their gas masks except (but) the poet's friend, who is not fast enough to get on his gas mask.

1)He uses a particular salt, adds it to other ingredients, and brings it to a boil before turning off the heat. Once the boiling has stopped, he drinks the potion. First, he suffers the most horrible agonies...

2) Hyde is physically smaller because his evil side has always been repressed by his good side.

3) He is aware he has turned into an evil, horrible, very wicked man.

4) The soldiers succeed in putting on their gas masks except for the poet's friend, who is not fast enough getting on his mask.