th in td instead of bold

[EmanuelFaria]

Some papers use th to create bold text. This is a horrible illiteracy. Somehow I need to create a simple xpath that selects and change this.

  <td align="center" rowspan="1" colspan="1" class="td">8</td>
    <td align="center" rowspan="1" colspan="1" class="td">8.26</td>
    <td align="center" rowspan="1" colspan="1" class="td">0.21</td>
    <td align="center" rowspan="1" colspan="1" class="td">beta-Phellandrene</td>
   </tr>
   <tr class="tr">
    <td align="center" rowspan="1" colspan="1" class="td">9</td>
    <td align="center" rowspan="1" colspan="1" class="td">8.46</td>
    <th align="center" rowspan="1" colspan="1" class="th">8.41</th>
    <th align="center" rowspan="1" colspan="1" class="th">para-Cymene</th>
   </tr>
   <tr class="tr">
    <td align="center" rowspan="1" colspan="1" class="td">10</td>
    <td align="center" rowspan="1" colspan="1" class="td">8.96</td>
    <th align="center" rowspan="1" colspan="1" class="th">30.90</th>
    <th align="center" rowspan="1" colspan="1" class="th">gamma-Terpinene</th>
   </tr>
   <tr class="tr">
    <td align="center" rowspan="1" colspan="1" class="td">11</td>
    <td align="center" rowspan="1" colspan="1" class="td">9.48</td>
    <td align="center" rowspan="1" colspan="1" class="td">0.47</td>
    <td align="center" rowspan="1" colspan="1" class="td">Terpineol</td>
   </tr>