Hi parixcia - it's always nice to include the full clue, number of letters & any you've placed, so that people without the puzzle can more readily help you - thanks! :-)
hello lie-in King , sorry, the full clue and number of letters would have been helpful, must be the sun affecting my brain. (italian chemist whose law says that equal volumes of all gasses contain the same number of molecules at the same temperature and pressure) A???a???). no need to apologise for mis- spelling of my name . regards Patrixcia