Dryness in the storage room is secured by a sheet metal floor under the ice, usually galvanized iron, which forms a large pan or vessel, in which all meltage water is collected. Water is very destructive to the ice, and the warm air is kept away from the top of the ice to prevent the moisture from being condensed there and settling on the ice. When the ice is low in the ice chamber, vapor may accumulate in the space above the ice. A ventilator in the top of the room is of service in conducting this away from the ice and keeping it dry. The water from the melted ice will absorb air and gases so it is spread out over as large a surface as practicable, and the air is conducted over it to be purified. [Illustration: FIG. 67. GROUND FLOOR.] There are several plans by which these general features are observed, in the construction of cold storage houses, some of which have been made the subject matter of patents. The plans shown in the illustrations embrace the essential features of good cold storage construction. These plans do not conflict with any patented devices, and will prove adequate for all practical purposes. [Illustration: FIG. 68. SECTION OF HOUSE. FIG. 69. SECTION OF WALL. PRINCIPLES OF COLD STORAGE CONSTRUCTION.] THE GENERAL ARRANGEMENT OF COLD STORAGE HOUSES may be, as shown in the illustrations, Figures 67–70, for any size. Large houses require a girder and posts under the center of the ice floor, and the air flues are best made double; one set at each side, with a drain on each side of the girder along the center of the room. The construction of the walls vary. Walls filled with sawdust, charcoal, tan bark or other non-conducting materials, have been in use for many years. Carefully conducted tests, however, have conclusively proved that a wall of this description is inferior to a wall which contains dead air spaces, felt or paper linings, a section packed with mineral wool and an outer circulating air space. [Illustration: FIG. 70. EXTERIOR VIEW OF COLD STORAGE HOUSE.] [Illustration: FIG. 71. SECTION VIEW OF COMBINED ICE HOUSE AND DAIRY.] The wall shown in Fig. 69 gives good satisfaction. It comprises air spaces, _A_, which are open to the outer air at the sill, and at the top open into the loft under the roof. Dampers _D_, in Fig. 68, are placed at the bottom, so they can be closed when desired. The next section, _B_, Fig. 69, is of dry sawdust, packed in place between walls of matched boards; the outer surface of these walls is lined with prepared water proof paper. The inner section, _E_, contains dead air spaces, which are about twelve inches square. The inner wall is of matched lumber and the outer one is of weather boards.