Unknown early lava lamp that needs fixing

Can anyone help me with this. Does anyone know what this is or how to fix it. The orange liquid is supposed to bubble up and back down again when the light is on and generates heat. However I switched it on for the first time in 10 years and it worked for 20 minutes then stopped, so I think the liquid is exhausted in some way. I think it dates from the 60s and I bought in a flea market around 1990