describe the atmosphere, including the actual temperature in the jury room.

Initially most of the jurors appeared to be relaxed and confident of a guilty vote. After the Henry Fonda character (HFC) voted not guilty the atmosphere became hostile towards the HFC and he was on the defensive ironically feeling he was being obligated to prove innocence rather than the others being required to prove guilt. Slowly jurors began doubting the boy's guilt and some of the holdouts for guilty became very angry using personal prejudice and experiences to defend their arguments. In the end all logical arguments for guilty were found to be flawed and only the personally biased arguments remained. The last two holdouts had a eventually had a change of conscience and voted not guilty with the rest.

Just to add, as I recall, the weather is hot, and there is no air-conditioning. Some of the men are irritable and the room seems claustrophobic.