=Condensing Water.=--In Chapter II reference was made to the condensing water for refrigerating system. This is important because the lower its temperature, the less the pressure will be created which means the less the power must be exerted in the production of the mechanical refrigerating effect. The water flowing over the condenser carries the heat to the sewer. Thus the heat from the carcasses, the sun heat on the walls of the building, the actinic rays through the windows, the heat from the men employed within, that from the electric lights within, and that absorbed from the earth upon which the building stands must all be collected and eventually passed into the sewer. =Absorption Equipment.=--Absorption refrigeration equipment is used to some extent in packing house work, but its complexity makes unnecessary an attempt of its description in this work. =Unit Basis.=--The unit basis of refrigeration commonly used in expressing quantity is tons of refrigeration, meaning the tons of refrigerating duty that can be performed per day of twenty-four hours. The standard measurement per ton as adopted by the American Society of Refrigerating Engineers, is a cooling effect equal to 288,000 B.t.u., being equivalent to the extraction of this quantity of heat from any substance. It has been established by the Bureau of Standards that in freezing one pound of water at 32° F., to ice at 32° F., 143.5 British thermal units of heat must be withdrawn from the water. For convenience in practice the fractional part is ignored, and 144 B.t.u. per pound of water is accepted as standard in calculations. =Computing From Unit Basis.=--If 144 B.t.u. are withdrawn from each pound of water at 32° F. to convert the water into ice at the same temperature, the melting of the pound of ice at the same temperature must re-absorb an equal heat in the process of freezing, consequently the melting of one ton (2,000 pounds) of ice to water at the same temperature would absorb 2,000 × 144 B.t.u., or 288,000 B.t.u., the accepted standard for computing the heat absorbed in the performance of one ton of refrigeration duty. In ice melting this absorption of heat is _latent_, not sensible to the thermometer, as no change is apparent by thermometer test in the temperature of the ice and the water, nevertheless an appreciable _cooling_ of surrounding is measurable by thermometer wherever ice melting takes place; for example, in an air-tight room, or in contact with solid substances, or with liquids, having a higher temperature than 32° F.