I saw once again on MMD, some information about this organ.  I think
that perhaps we are missing an understanding of the complete mechanism
because part of it is missing and we are afraid to deduce the rest of
the design.

I have a friend who once lived in India.  They used 'natural gas' for
cooking and perhaps for lighting.  They had a large pit in the ground
into which they placed (read: 'shoveled') elephant dung and other,
similar, compost-able material which I will refrain from describing.

In a short time, this pit was producing sizable quantities of 'natural
gas'.  To trap the gas, they placed a large, barrel-shaped drum in the
pit, open side down.  (Notice the similarity to the organ.)  A tube ran
from the top of the drum to the gas appliances.  Gases from the compost
collected under the drum, thereby raising the drum above the large
'bubble' of gas.  The pressure was controlled by the weight of the drum
(weight/surface area), with adjustment provided by rocks placed on top.
By the way, they didn't bother to add the odor producing agent which is
always in the gas we buy from our utilities, for obvious reasons.

So, let's look at the organ in the Moldova Museum.  I would suggest
that the stopper was not intended as a stopper at all.  And there is no
need to wonder about a device for a constant air supply, like a feeder
bellows, to the inner barrel.  Any small bellows would have been
connected to the hole where the stopper now is.  Someone would pump the
bellows until the inner drum rose a reasonable amount and then keep
pumping enough to keep it inflated.  Church organs of the time all had
much larger bellows that were manually operated.

If this were really a demonstration of some sort, the means to raise
the bellows would very likely have incorporated a one-way valve (also
common at the time) so that you could just lift the inner barrel and
release it to start the organ.

Incorporating a manual bellows would have been a very simple arrangement
and would have been just as simple to lose over the years.  With it,
the utility of the organ becomes obvious.

Regards,
Craig Smith