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: RESULTS : Impairment of cognitive function was observed 6 to 8 hours after administration of haloperidol on Day 2 but was not evident 23 hours after dosing .
### Output Text:
RESULTS : Impairment of cognitive function was observed 6 to 8 hours after administration of <span class="chemical">haloperidol</span> on Day 2 but was not evident 23 hours after dosing . 