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: These findings have been compared with norms and with values of the same tests from screening prior to lithium , available for most of our patients .
### Output Text:
These findings have been compared with norms and with values of the same tests from screening prior to <span class="chemical">lithium</span> , available for most of our patients . 