474,925. Automatic control systems ; transformers; inductances. HERRMANN, R., and SKUTTA, T. May 15, 1936, No. 13780. Convention date, May 15, 1935. [Classes 38 (ii) and 38 (iv)] [Also in Groups XIII, XXIX, and XXXVII] Temperature.-The heater for the generatorabsorber of a refrigerating-apparatus is controlled automatically by electromagnetic means including a permanently-heated body the magnetic permeability of which varies with its temperature, and which is intermittently cooled by the evaporation of refrigerant therein to render the heater inoperative. In a machine comprising a generator-absorber A having an electric heating element 4, condenser B, and an evaporator C the lower part of which extends into a brine tank 27 in a refrigerator cabinet, the control means 39 is embedded in the insulation of the cabinet and comprises a magnet core 44, Fig. 2, of soft iron in the gap 48 of which is disposed a mercury switch 46, and which is provided with an excitation coil 45, and a condensate container 39<11> permanently heated by an electric element 41, and connected by pipes 38, 42 to the evaporator and a vessel 43 in the brine tank respectively. In the absorbing position shown in Fig. 2, the container 39<11>, which may be made of an alloy of 70 per cent iron and 30 per cent nickel, is cooled by the evaporation of condensate collected therein during the previous generating period and its permeability raised thus reducing the magnetic flux across the gap 48 of the magnet core and causing the float 47 of the switch to rise and the mercury level therein to fall and break the circuit through the heating element 4. Upon completion of the evaporation of the condensate in the container, the latter warms up and its permeability decreases and at the same time the magnetic flux across the gap increases thus pulling down the float of the switch and raising the mercury level so that the circuit through the switch is completed. In order to accelerate the change-over from absorption to generation a part of the condensate flowing into the container may be allowed to pass into the vessel 43 in the brine tank 37. In a modification, the magnet core is of U-shape and the container is disposed across the mouth of the core and encircled by a choke-coil in series with the heating element 4. In another arrangement, the magnet core is in the form of a rectangle 44<11>, Fig. 4, which constitutes a transformer having a primary winding 45<1> and a secondary winding 45<11> in series with the heating element 4. When the container 39<11> is cooled the flux through the limb carrying the secondary winding is reduced as also is the current through the winding and the element. When, however, the container warms up both the flux and the current increase. In a further arrangement, the magnet core and the condensate container are combined in an annular body around which is wound an excitation coil, and which is formed with a ring-shaped condensate chamber and a central bore for a tube containing the mercury and the float. In this case, one end of the heating element is permanently connected to the mercury in the tube, while the other is connected to a terminal with which the mercury contacts when it rises in the tube. Fig. 6 shows a further modification in which the generator-absorber is heated indirectly by a liquid, e.g. glycol, circulating through an annular space 25<1> heated by a burner 51 the gas supply to which is controlled by an electromagnetically controlled valve 62. In this case, the mercury switch is replaced by an armature 47<11> attached to the spindle 61 of the valve 62, and the condensate container 39<11> is heated by the products from an auxiliary burner 58 which heats a thermo-electric battery 59 supplying current to the excitation coil 45 of the magnet core and the coil 63 of an electromagnet controlling a valve 64 in a byepass 541 supplying gas to the burner 58 and a pilot jet 60. In operation, the valve 64 is held open by hand until its electromagnet becomes effective, whereupon the main valve 62 is opened.