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 toxicity of Renografin 76 % was compared with that of Hypaque 76 % by selective injection of each into the right coronary artery of dogs .
### Output Text:
The toxicity of <span class="chemical">Renografin 76 %</span> was compared with that of <span class="chemical">Hypaque 76 %</span> by selective injection of each into the right coronary artery of dogs . 