How do I cite a quote from a book without the actual book?

I am writing my college application essays and I want to use a quote from Ayn Rand's The Fountainhead that I found on the web. I have read the book, but do not have it with me. I am not sure how to cite it besides indicating in the actual essay where the quote comes from. Do I need to put an annotation at the end in MLA format? If so, how I do that without the book? How am I supposed to figure out which page or even chapter the quote came from?