It is way off topic but a quick search reveals these were manufactured by Chicago Flexible Shaft Co. Chicago, Ill. Apparently it takes a 7x2x2 "carbon brick" supplied by the manufacturer, the directions I read say to "Put a piece of coal in a brisk fire until it is red through and through. Remove and after the flame has died away place in drawer and insert in heater which will require no further attention." This coal brick supposedly would last from 12-16 hours and a half brick 6-8 hours. the asbestos lined chamber radiates heat through the vents to warm the feet, they were advertised for use in buggies, sleighs, wagons and "touring" cars in the early 1900s'

W.M.