In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Of our control group ( n = 50 ) , 21 patients ( 42 % ) were established hepatitis .
### Output Text:
Of our control group ( n = 50 ) , 21 patients ( 42 % ) were established hepatitis . 