I have to do a lab next week in which I repeat the Franck-Hertz experiment. I am reasonably sure that I understand most of what I need to do, but I'm just a little unsure on a couple of points, and would appreciate some guidance if anyone is knowledgeable with it. The instructions say that the tube must be heated to ~180°C. I assume that this is to vapourise the mercury, and get it to a suitable pressure? Is there any other reason? I was looking online for an answer, and a lot of the pages said that the tube should under no circumstances be heated above 205°C. Is there any specific reason for this? I may have further questions as my research continues. Any help on this would be greatly appreciated.