It is evident that this oven could be used with an atmosphere of carbon dioxid or of air, provided the gas for heating were derived from a separate source and the tube between E and F broken. In a drying oven designed by the author, the movable top is made with double walls and the space between is joined to the steam chamber by means of a flexible metallic tube, thus entirely surrounding the drying space with steam. =25. The Ulsch Drying Oven.=—A convenient drying oven is described by Ulsch which varies from the ordinary form of a water-jacketed drying apparatus in having a series of drying tubes inserted in the water-steam space. [Illustration: FIGURE 16. ULSCH DRYING OVEN.] The arrangement of the oven is shown in the accompanying figure. The water space is filled only to about one-third of its height. When the heat is applied the cock _c_ is left open until the steam has driven out all the air. It is then closed and the temperature of the bath is then regulated by the manometer _e_, connected with the bath by _d_. The bottom of the manometer cylinder contains enough mercury to always keep sealed the end of the manometer tube. The rest of the space is filled with water. At the top the manometer tube is expanded into a small bulb which serves as a gas regulator, as shown in the figure. The gas is admitted also by a small hole above the mercury in the bulb, so that when the end of the gas inlet tube is sealed enough gas still passes through to keep the lamp burning. With a mercury pressure of thirty centimeters the temperature of the bath will be about 105°. The walls of the bath should be made strong enough to bear the pressure corresponding to this degree. The drying can be accomplished either in the cubical drying box _a_ or in the drying tubes made of thin copper and disposed as shown in the figure. The natural draft is shown by the arrows. The substance is held in boats placed in the tube as indicated. The air in traversing the tube is brought almost to the temperature of the water-steam space in which the tube lies. The natural current of hot air can easily be replaced by a stream of dry illuminating or other inert gas.