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: Further increase in infusion time resulted in further reduction in the odds of convulsions to 99 . 8 % reduction at 240 min .
### Output Text:
Further increase in infusion time resulted in further reduction in the odds of convulsions to 99 . 8 % reduction at 240 min . 