How for instance is a minimum temperature to be kept? Chiefly, by insulation--this is a strictly mechanical term understood by motorists and engineers and must be understood by the housewife, who is a domestic or kitchen engineer if she is anything. The low temperature is kept by keeping out the outside heat and keeping in the inside cold! After much experiment, it has been found that the walls, floors and doors of every refrigerator must have at least one air space, from six to nine layers of insulating material consisting of pebbled cork, or certain patented materials, mineral wool, asbestos and various layers of porous substances which keep out the outer warm air and prevent the cold air from escaping. (See illustration.) Well insulated refrigerators backed up against boilers, stoves or vats maintain a temperature far below 58 or 60 degrees; some, the best, maintaining 50 degrees. AS TO ICE CHAMBERS The ice compartment should be above, and to one side, so that the cold air from the melting ice can descend, as is the custom of cold air, and can rise again as it gets heated in its contact with the provisions and pass up over the ice, be cooled and pass down again with its collected odors through the drain. This is what is called air circulation, and when the ice box is properly constructed, and when the ice compartment is kept full, the air is in constant motion, traveling over and over again up and down and around the food and ice. This constant activity of the air is what insures an odorless condition, unmouldy and cold food. [Illustration: _Courtesy of Bohm Syphon Co._ NOR COLD NOR HEAT CAN GET BEYOND THESE FORTIFICATIONS PORCELAIN ENAMEL LINING ONE PIECE DEAD AIR SPACE INSIDE WOOD LINING BLACK WATERPROOF PAPER WOOL FELT PAPER FLAXLINUM INSULATION OUTSIDE WOOD CASE] In the best refrigerators the ice chamber extends a few inches below the door and is lined with the highest grade of smooth galvanized metal, lock jointed, and is without seams and sharp edges. In some refrigerators the wall between the ice compartment and the provision chamber is slatted, in some there is a space at the top, in others, holes are bored, top and bottom, to permit the free egress of the circulating air. These methods are good in varying degrees. The main things to be kept in mind are: 1. Does the air circulate enough to prevent any moisture accumulating in the refrigerator? Can salt be kept dry and granular in it for one hundred hours? 2. Does the refrigerator keep below 60 degrees, or better between 45 and 50 degrees? Will a damp cloth dry quicker inside than outside of it, because of the rapid circulation and dryness of the air? 3. Do matches keep dry and can they be lighted by being struck on its walls? (This shows whether the ice box is dry!) 4. Does the milk taste of cheese or the butter of the soup?