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: Of the 3 patients , 2 were ingesting acceptable doses of elemental calcium ( 1 g and 2 g daily , respectively ) in the form of calcium carbonate .
### Output Text:
Of the 3 patients , 2 were ingesting acceptable doses of elemental <span class="chemical">calcium</span> ( 1 g and 2 g daily , respectively ) in the form of <span class="chemical">calcium carbonate</span> . 