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: Six epidemiologic studies in the United States and Europe indicate that habitual use of phenacetin is associated with the development of chronic renal failure and end - stage renal disease ( ESRD ) , with a relative risk in the range of 4 to 19 .
### Output Text:
Six epidemiologic studies in the United States and Europe indicate that habitual use of <span class="chemical">phenacetin</span> is associated with the development of chronic renal failure and end - stage renal disease ( ESRD ) , with a relative risk in the range of 4 to 19 . 