Athanor

You may also be inſtructed, That when you are diſtilling of Aqua fort. and that the Coals in the Athanor are almoſt gone out (which happens hardly in 10 or 11 hours) then lift up the Cover from the Athanor, make it full again with Coals and cover it, elſe the Fire will go out, and all will be cold, as Oportunity it ſelf will teach thee and make thee to remember.

Source: wiktionary

The Furnace call'd an Athanor, was invented to keep a conſtant Heat for Fourteen Days, a Month, Twelve Months, or more, as ſome Chymical Operations require, which may be augmented or decreaſed, by opening or ſhutting the Regiſters, as you pleaſe, and according to the Magnitude of the Tower, requires no Attendance above once in twenty four, fourty eight, or one hundred Hours.

Source: wiktionary

The long and tedious operations of the ancient chemists rendered it a desirable requisite, that their fires should be constantly supplied with fuel in proportion to the consumption. The athanor furnace was peculiarly adapted to this purpose.

Source: wiktionary

The Magus should not, therefore, live exclusively in his laboratory, amidst his Athanor, his elixirs, and his pantacles. […] A magical operation should invariably be followed by a rest of equal duration and an analogous diversion, but one contrary in its object.

Source: wiktionary