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: Creatinine clearance , maximum urinary osmolality and 24 hour urine volume have been tested in 50 affectively ill patients who have been on long - term lithium for more than one year .
### Output Text:
<span class="chemical">Creatinine</span> clearance , maximum urinary osmolality and 24 hour urine volume have been tested in 50 affectively ill patients who have been on long - term <span class="chemical">lithium</span> for more than one year . 