Liquid optic or cooling element ?

Hi.
I just recived an Ebay buy. An old Leitz projector;

http://img152.imageshack.us/img152/3908/leitzivl2bd87coa5.jpg

It is a "Kinoprojektor, Diaprojektor für große Kino Dias, ohne
Objektiv
von Leitz Typ IV-BL"

But this animal is very different than other Leitz Typ IV-BL
projector
Boxes, it has a small box element , that looks as it is watertight
--- you can see it in the picture ,taken out, --- please ; has anyone
seen such element in a condenser before , what's it's porpus, if
Liquid has to be added, what liquid would that be -- oil, glyserine,
water, or any liquid at all ; it don't looks as the glasses each side
has any optic function. --- if it is just a cooling element, how would
that even work ?

P.C.

.