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: Pretreatment of rats with sodium salicylate , ED50 103 mg / kg ( 60 - 174 ) , and phenylbutazone , 59 mg / kg ( 50 - 70 ) converted the non - convulsant dose of pilocarpine , 200 mg / kg , to a convulsant one .
### Output Text:
Pretreatment of rats with <span class="chemical">sodium salicylate</span> , ED50 103 mg / kg ( 60 - 174 ) , and <span class="chemical">phenylbutazone</span> , 59 mg / kg ( 50 - 70 ) converted the non - convulsant dose of <span class="chemical">pilocarpine</span> , 200 mg / kg , to a convulsant one . 