Here's a link to pictures of an almost (but not quite) identical one on ebay


http://www.ebay.co.uk/itm/Old-Vtg-National-Pressure-Cooker-Presto-Forty-Cooker-/120761605855#ht_2502wt_1185


From which it looks as if heating anything is going to be marginal but if any heating is going to be useful it will be of the base - and it shows a neoprene seal in the lid that is the likely cause of the problem - so now I need to jimmy up some extra length handles and go to!