| 摘要 |
552,910. Ventilation. CONCRETE UTILITIES, Ltd., and MARQUES, C. A. Oct. 31, 1941, No. 14000. [Class 137] [Also in Group XI] Resistance wires 2 are embedded in concrete, cement, artificial resin or other plastic material 1, and the slab then arranged in a concrete enclosure 4 with an air space 6. The resulting units may be placed at spaced points on a floor in the doorway of a building. In a modification, Fig. 5, wires 17 are embedded in a block 18 having a slot 19 which provides ventilation in a building. |
