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: The serum sodium at this time was 120 mmol / L , serum osmolality was 263 mosmol / kg , urine osmolality 410 mosmol / kg and urine sodium 63 mmol / L , consistent with a diagnosis of SIADH .
### Output Text:
The serum <span class="chemical">sodium</span> at this time was 120 mmol / L , serum osmolality was 263 mosmol / kg , urine osmolality 410 mosmol / kg and urine <span class="chemical">sodium</span> 63 mmol / L , consistent with a diagnosis of SIADH . 