You already seem to be able to successfully run XPath queries, so I skip the PHP code and immediately fall into the XPath part.
Not sure what you mean by "content", so I offer several alternatives:
You want all text nodes inside the <div/> :
//div[@class="content_text"]//text()
You want all XML, including elements:
//div[@class="content_text"]
Both return a set of results, be sure to focus on it.
source share