THE MILK CONTRACTOR 315 



passes over them, down the surface of the board. Sometimes the upper 

 tubes are constructed for cooling with water while the lower ones are 

 made of special ammonia piping for direct-expansion ammonia from a 

 refrigerating machine. By employing direct expansion instead of brine 

 for the final cooling the use of a brine pump, brine tank and coils or brine 

 cooler is obviated and the attendant losses avoided. Screw plugs are 

 provided at both ends of each tube so that the tubes can be thoroughly 

 cleaned, a necessary provision because many waters deposit an incrusta- 

 tion of mineral salts within the tubes, thus impairing their conductivity 

 and so their cooling efficiency. 



In the spiral-conical coolers the water enters at the bottom and travels 

 in a spiral course through a small tube around a tinned copper shell or 

 cone and discharges at the top into a cavity beneath the bowl or milk- 

 distributing reservoir, whence it overflows into the outlet pipe. The 

 milk is fed from the bowl into the outer surface of the cone and flows 

 spirally downward over the cold surface of the water tube to a trough at 

 the bottom of the cone whence, it is discharged into a receiving can at 

 approximately the temperature of the cooling water. Thus efficiency is 

 gained by the retarding effect of the spiral path of the milk, by bringing 

 the milk in its progress downward in contact with a surface that grows 

 constantly cooler and by the construction of the spiral itself which is such 

 as to spread the milk in a thin film over the maximum of surface in the 

 corrugations toward the bottom. 



The advantages claimed for this type of cooler are compactness of 

 design, occupancy of a minimum of floor space per unit of capacity, high 

 cooling efficiency, accessibility for cleaning and a convenient mantle 

 enclosure. 



The demand for absolutely enclosed coolers has led to the use of tubu- 

 lar coolers. They are identically the sam'e machines as the tubular heat- 

 ers that are used for pasteurizing milk but instead of heating the milk 

 in the inner tube or tubes with hot water it is chilled with cold water or 

 brine. The milk in the inner tubes circulates in a direction contrary to 

 that of the water so that the milk in its progress is brought into contact 

 with colder and colder water. These coolers are economical and efficient 

 and besides protect the milk from contamination from the air, prevent the 

 considerable loss that occurs with open coolers from evaporation, may be 

 sterilized under pressure and since they are erected in sectional units 

 may be expanded as the business grows. The drawbacks are that the 

 milk may be contaminated by leakage and that it is difficult to draw off 

 all of the milk at the end of the run. These coolers are in use in some of 

 the largest and best plants. 



Many of the above types of coolers can be used as regenerative coolers, 

 by running the cold milk en route to the heaters through the upper sections 

 of the cooler, thereby reducing the temperature of the hot milk from the 



