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: Hysterosalpingography was performed on both patients and , in 1 instance , an abnormal x - ray film was reflected by the gross appearance of the uterine cavity found in the surgical specimen .
### Output Text:
Hysterosalpingography was performed on both patients and , in 1 instance , an abnormal x - ray film was reflected by the gross appearance of the uterine cavity found in the surgical specimen . 