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: For PA training , latencies ( seconds ) were recorded for entry from a suspended platform into a Plexiglas tube where a shock was automatically delivered .
### Output Text:
For PA training , latencies ( seconds ) were recorded for entry from a suspended platform into a Plexiglas tube where a shock was automatically delivered . 