var column = 2,
    sum = 0,
    tables = document.getElementsByTagName('table');

for (var i = 0, i < tables.length; i++) {
  var table = tables[i];
  var rows = table.getElementsByTagName('tr');
  for (var j = 0, j < rows.length; j++) {
    var row = rows[j];
    var cells = row.getElementsByTagName('td');
    for (var k = 0, k < cells.length; k++) {
      var cell = cells[k];
      if (k == (column - 1)) {
           if (cell.firstChild) {
          sum += parseInt(cell.firstChild.nodeValue);
        }
      }
    }
  }
}

console.log(sum)