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: The mortality rate among patients with ATT - ALF was high ( 67 . 1 % , n = 47 ) , and only 23 ( 32 . 9 % ) patients recovered with medical treatment .
### Output Text:
The mortality rate among patients with ATT - ALF was high ( 67 . 1 % , n = 47 ) , and only 23 ( 32 . 9 % ) patients recovered with medical treatment . 