How to get a data value between node tags

Relatively new to XPath, but really need a help and appreciate your hand.

I have following XML file piece:

<div id="current">

     <b> Current Data Ratio:</b>
     17.35
     <span class="neg">-0.23 (-0.84%)</span>
     <div id="timestamp">4:29 pm EST, Fri Jan  9</div>
</div>

I want to get data value 17.35. My XPath code below:

     Node external_node = (Node) xPath.evaluate("//div[@id='current']", xmlDocument, XPathConstants.NODE);
    if(null != external_node) {
        NodeList nodeList = external_node.getChildNodes();
        for (int i = 0; null!=nodeList && i < nodeList.getLength(); i++) {
            Node internal_node = nodeList.item(i);
            if(internal_node.getNodeType() == Node.ELEMENT_NODE)
                System.out.println(nodeList.item(i).getNodeName() + " : " + internal_node.getFirstChild().getNodeValue()); 

        }
    }

then what I get is:

b : Current Data Ratio:

span : -0.23 (-0.84%)

div : 4:29 pm EST, Fri Jan  9

the data 17.35 cannot be obtained. I changed Node type to Node.TEXT_NODE like this:

if(internal_nod.getNodeType() == Node.TEXT_NODE

then I get nothing returned. Then I tried to use text() function, it seems no help either. Any help needed.