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: METHODS : Mannitol ( 18 % solution ; 1 g / kg ) was administered as a bolus to patients ( ten had malignant glioma , seven brain metastases and four meningioma ) about 30 minutes before craniotomy .
### Output Text:
METHODS : <span class="chemical">Mannitol</span> ( 18 % solution ; 1 g / kg ) was administered as a bolus to patients ( ten had malignant glioma , seven brain metastases and four meningioma ) about 30 minutes before craniotomy . 