Abstract: A pyrex tank for heating corrosive solutions is formed with a main body portion having an open top and with a small annular cavity portion depending from the bottom of the main body portion. A heater unit comprising a heating element enclosed in a quartz tube is securely mounted in an upright position on a support. The tank is positioned on the support with the central opening of its annular cavity receiving the quartz tube of the heating element. The solution in the main body portion of the tank is heated in the annular cavity portion thereof by convection. A thermocouple supported in an upright position on the support is inserted through the open lower end of an upright tube fixed to the bottom wall of the tank and extending upwardly into the interior thereof.