views of the apparatus the box front 12 includes louvers 13 facilitating dissipation of heat from the block 4 housed in the box and conveniently displays the fuse f 1 and led 1 sides 9 39 9 39 join the box front 12 to the back 9 the box bottom 14 shown in fig7 may comprise a plurality of inwardly directed flanges serving to support the block 4 while allowing full communication between the ambient air and the bottom ends 7 of the ducts 3 the outstanding efficiency of the instant apparatus is attributable to the constriction of the air into extremely small volumes as it passes by convection upwardly through the ducts 3 in the thermal and electrical insulating material of the block 4 the refractory block is preferably formed of zro 2 and sio 2 and as shown in the illustrated embodiment includes a substantial number of the relatively closely disposed bores or ducts 3 formed therein in a vertical manner the illustrated apparatus is formed with a total of 56 such ducts 3 but obviously larger or smaller blocks 4 may be used having a correspondingly greater or lesser number of ducts in any case the respective ducts 3 which actually perform in a manner similar to capillary tubes in receiving vertically advancing and discharging the ambient air each measure substantially 2 mm in diameter in a block which has a height of approximately 70 mm the appropriate heating convection and sterilization of air as treated by the disclosed apparatus.