A larger device used for cooling milk is a tank of running water (Figs. 61-_a_-_b_). The water flowing thru this tank commonly flows into another tank used for the watering of stock. Cans with inverted covers like those illustrated are waterproof, because the air is caught inside them so that it cannot get out for the water to replace it. It does not require a large stream of water to renew that in the tank and keep it cool. The efficiency of this device depends entirely upon having a supply of cold water available. [Illustration: FIG. 61-_a_. Cross-section of cooling tank.] =130. Refrigerating Plants.= Refrigerating plants are sometimes installed in private dwellings. These consist of a motor and a machine for compressing gas, a chamber which is to be cooled, and sometimes coils of pipe containing brine. When the gas--for example, ammonia or carbon dioxide--is compressed, it heats the pump which compresses it. That is, when a liquid or gas is being compressed, it gives up heat. When a liquid or gas expands, it takes heat from somewhere. In refrigerating plants, the expanding gas is made to take the heat either directly from the refrigerator or storeroom, or from brine which is then used for cooling the refrigerator or room. Refrigerating plants require the same care as pumps, motors and refrigerators. [Illustration: FIG. 61-_b_. Cooling tank.] =131. Water Coolers.= Since ice is not always pure, it is necessary to use cooling devices which do not permit it to come into direct contact with the water. One type of water cooler consists of a can set in an ice box with a pipe leading to the outside so that the box does not have to be opened every time that water is wanted (Fig. 62). This can should be made so that it may be removed, washed and scalded. Another cooler consists of a tank or water bottle placed on the outside of a refrigerator or box of ice with a pipe leading thru the refrigerator or box of ice (Fig. 63). The water flowing thru the pipe is cooled. The pipe ends at the outside of the ice box with a faucet to let out the water. This cooler cools only the water flowing into the pipe instead of the entire tank of water. [Illustration: FIG. 62. Water cooler containing water tank.] [Illustration: FIG. 63. Sectional view of water cooler.] =132. Care of Water Coolers.= Put only clean, pure water into the coolers, and keep them clean by flushing them out occasionally with boiling water. CHAPTER XVIII FANS AND VENTILATORS =133. Selecting a Fan.= With the coming of electricity into the home, fans have become practical home devices. Do not buy a fan or other electrical device without ascertaining whether the current is direct or alternating, and what voltage is needed to run it. Most city homes are now supplied with current ranging between 105 and 115 volts, so most fans are made for that. Fans will run on a small wire like that used for lighting. [Illustration: FIG. 64. Blower.] [Illustration: FIG. 65. Stationary fan.]