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: Based on this model and on Bayes ' theorem , the predictive accuracy of identifying " nephrotoxic " patients increased from 0 . 17 to 0 . 39 .
### Output Text:
Based on this model and on Bayes ' theorem , the predictive accuracy of identifying " nephrotoxic " patients increased from 0 . 17 to 0 . 39 . 