COOLING, STORING, AND SHIPPING MILK. 15 



pounds for the insulated tank, 65 pounds for the wooden tank, 101 

 pounds for the concrete tank, and 126 pounds for the galvanized- 

 iron tank. 



THE CONSTRUCTION OF MILK TANKS. 



Milk tanks should be so constructed as to minimize the loss in cool- 

 ing effect through radiation from both water and ice. They should 

 also be easy to construct, durable, and easy to clean. The best insulat- 

 ing materials are those that contain the greatest amount of entrapped 

 air in the smallest space. Other factors, however, such as space occu- 

 pied, structural strength, uniformity of insulating value, and ability 

 to withstand moisture, should be considered in the selection of the 

 insulating material. The material should not absorb moisture readily, 

 because as soon as it is water-soaked its insulating value is impaired 

 and it will rot. The insulation should be light, easy to work into 

 place, and should occupy little space. 



The height of the cooling tank depends upon the height of the cans 

 to be used. Provision should be made so that the water on the outside 

 of the cans will always be as high as the milk inside. An overflow 

 pipe to regulate the height of the water, and a drainage outlet in the 

 bottom of the tank so that the water may be emptied when it is de- 

 sired to clean the tank, should be provided. Narrow strips on which 

 to set the milk cans should be placed on the bottom of the tank in 

 order to permit the water to flow under as well as around the cans. A 

 frame should be made of 2 by 2 inch material, laid 2 inches apart, so 

 that it will fit snugly in the bottom of the tank. It may be made to fit 

 tightly by means of wooden wedges. 



THE INSULATED CONCRETE TANK. 



For use on the farm an insulated concrete tank will usually be found 

 to be the most efficient and satisfactory in every respect. In building 

 a tank of that kind the walls should have a total thickness of from 8 

 to 10 inches, divided into a 2 to 4 inch outer wall of concrete, next to 

 which is placed a 2-inch layer of insulating material and an inside 

 concrete wall of 4 inches. The concrete mix should consist of 1 part 

 Portland cement, 2 parts clean, sharp sand, and 4 parts broken stone 

 or gravel. Hydrated lime equal to 10 per cent by weight of the cement 

 should be added to the mix for the purpose of making the tank water- 

 proof. The outer wall should be constructed first, then the insulation 

 should be set in hot asphalt or gas-house tar and its inner surface 

 coated with the same material and allowed to dry thoroughly before 

 the inner wall of concrete is built. The inside wall of the tank should 

 be carefully troweled to force back all particles of stone or gravel, 

 thus insuring a smooth inner surface. 



In constructing the tank, if built partly underground as shown in 

 figure 12, an outside form extending only from the surface of the 



