=An Automatic Regulator= of practical value is that devised by Ruegheimer. It consists of a glass tube, =A=, =A¹=, =A²=. =A¹= is closed with an indiarubber stopper, through which passes a glass tube =B=, the lower end of which is cut off at an angle. It is attached to the gas supply pipe. The tube =C= is connected to the burners. To =D= is attached, by means of rubber tubing, a glass bulb =F=, which is placed inside the drying-box. =G G= is mercury, and =H= a rubber stopper by which the pressure on the mercury and quantity of air in =F= may be regulated. The action of the instrument is obvious. The gas passes down =B=, over the surface of the mercury and by the tube =C= to the burner. On the bulb =F= reaching a certain temperature, the mercury will allow just sufficient gas to pass from the tube =B= to maintain the box at a given heat. If it should fall, the mercury recedes from the aperture of the tube =B=, a larger quantity of gas passes to the burner, and the temperature is restored to a normal degree. If the air in the ball =F= expands to too great an extent, the mercury rises, and would eventually entirely close the aperture and cut off the gas supply, unless the tube =B= is provided with a small hole acting as a by-pass. The tube =B= may be moved up and down through the rubber stopper at =A¹= as a means of adjustment. [Illustration: _Fig. 3._] M. Thiel, of Paris, uses a very convenient drying-box, which, with his permission, is here explained. In a brick-lined receptacle under the laboratory floor lies the water-heating apparatus, which is constructed of sheet copper, and is capable of containing about four litres of water, utilised in the production of steam for heating the box. _a_, fig. 3, is the pipe passing through the wall into the drying-box; _b_ is the gas supply pipe to the two atmospheric burners. Fig. 4 represents a plan of the drying-box; _c c c c_ the perpendicular sides of the same, _a a a_ gives a plan and position and arrangement of the earthenware heating pipes lying in a serpentine form at the bottom of the box, entirely covered with dry sand, and this again covered, as before described, with tissue paper. _b_ is the outlet of the steam pipe. _d d d d_ are movable horizontal iron bars with adjusting screws, on which the plates are levelled. The box is covered by a hinged lid, which is raised about a couple of inches during the drying to allow the air to circulate. The dimensions of the box will be determined by the size of the plates to be used, several of which may be placed side by side. Its height is about half a metre inside, and the plates are placed about its centre. [Illustration: _Fig. 4._]