APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 23 



boxes, a lower room may answer the purpose. As an illustration of 

 the saving of material in construction and in refrigeration, let us 

 consider two cold-storage rooms, each of 1,000 cubic feet capacity; 

 one room to be in the form of a perfect cube, 10 by 10 by 10 feet = 

 1,000 cubic feet; the other room to be 10 by 6 feet by 16 feet 8 inches 

 = 1,000 cubic feet. The total square feet of surface in the first room 

 is 600; the total square feet of surface in the second room is 653; 

 therefore, for the same cubical contents, the second room has 8.8 

 per cent more radiating surface and will require 8.8 per cent more 

 material in construction. 



The cold-storage room should be where it is protected as much as 

 possible from the direct rays of the sun. Unless some natural pro- 

 tection is afforded, such as trees or buildings, the cold-storage room 

 should be in the northeast corner of the building. 



In the construction of a new plant advantage should be taken 

 of the actual condition surrounding the proposed building site. 

 Very often considerable may be gained by proper location of the 

 building and arrangement of machinery. 



For insulation of cold-storage rooms the reader is referred to the 

 matter under the heading "Insulation." 



PRINCIPLES OF MECHANICAL REFRIGERATION. 



When a solid or a liquid changes its state or condition, as when a 

 solid is converted into a liquid or a liquid into a gas or vapor, the 

 change of state or condition is in each case accompanied by the 

 absorption of heat. This absorption of heat, as previously explained, 

 is called "latent heat;" that is, heat that can not be measured 

 by a thermometer; and in order to transfer a substance from one 

 state to another it is only necessary to supply or extract heat. For 

 instance, if we take 1 pound of ice at zero temperature, Fahrenheit 

 scale, and apply heat, the temperature will rise until it reaches 32°. 

 If we continue the application of heat the ice will begin to melt, and 

 after we have supplied sufficient heat the 1 pound of ice will have 

 changed to water at 32° F., the same temperature at which the ice 

 commenced to melt. If the application of heat is continued the 

 water will grow warmer, but at a slower rate. It now takes about 

 double the amount of heat to raise the 1 pound 1 degree as water that 

 it did to raise the 1 pound 1 degree as ice. In other words, the speci- 

 fic heat of water is approximately double that of ice. 



When sufficient heat has been added to raise the 1 pound of water 

 to a temperature of 212° F., another critical point is reached at 

 which further application of heat to the water, under atmospheric 

 pressure, will not increase its temperature, but changes it into steam 

 at a temperature of 212°. Figure 9 shows graphically the relation 

 of heat to temperature. 



