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: Proteinuria was evident at day 5 , peaked at day 7 and persisted to day 27 .
### Output Text:
Proteinuria was evident at day 5 , peaked at day 7 and persisted to day 27 . 