PHP: Problems Instantiating Class

I try to create new object of a class called Isolate (this class is used to prevent XSS and other attacks via htmlspecialchars and so on).

So, I do it like this:

$data['name'] = $_POST['name'];
$data = $isolate->isolateArr($data);

And my Isolate class look like this:

class Isolate {
    public function isolate($var) {
        $iVar = htmlspecialchars($var);
        $iVar = mysql_real_escape_string($iVar);
        $iVar = stripcslashes($iVar);

        return $iVar;
    }

    public function isolateArr($arr) {
        foreach($arr as &$instance) {
            $instance = $this->isolate($instance);
        }
        unset($instance);
        return $arr;
    }

But as the result I have a warning like Missing argument 1 for Isolate. As I understand, it asks me for the argument for the first function, but I do not need to call the first one, I need to call the second (because I have an array in this case).

So, why does it always ask for the first function argument? There in no any __construct method, what is the point?

Thank you in advance!