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: In both groups a potassium deficit developed , with proportionally larger losses from the extracellular than from the intracellular compartment .
### Output Text:
In both groups a <span class="chemical">potassium</span> deficit developed , with proportionally larger losses from the extracellular than from the intracellular compartment . 