542 - Reading-Course for Farmers. 



In order to understand the construction of a barn for the purpose of 

 maintaining a proper temperature, it is necessary to get certain concep- 

 tions concerning heat and cold. Every one is famihar with the process 

 of cold storage by refrigeration and understands that for successful cold 

 storage either by ice or other artificial means, it is necessary to insulate 

 thoroughly the room which is to be kept cold. It is important to under- 

 stand that if a room and its contents are cooled say to 20^ ¥., and it were 

 possible to insulate the room that there would be no exchange of tem- 

 perature with its surroundings, the temperature would remain constant 

 forever. The only way that the room can rise in temperature is by pene- 

 tration of heat from the exterior. In the same w^ay, if a room and its 

 contents are heated to a temperature of 80° F., it can cool off only by 

 the heat of the room escaping into the surrounding spaces. Further, if 

 the outside temperature is at 50° F., the units of heat involved in lower- 

 ing the temperature to 20° F., or raising it to 80° F., would be the same. 



The importance of thorough insulation in maintaining the temperature 

 of the room is therefore obvious and cannot be too thoroughly insisted 

 on for this purpose, although, as will be shown directly, the necessity of 

 pure dry air makes complete insulation impossible even were it mechan- 

 ically possible. The exchange of temperatures between the rooms of a 

 building and the surrounding air may be brought about in two general 

 ways: (i) By the conduction of the heat through the surrounding walls, 

 and (2) by an actual exchange of air between the exterior and the 

 interior. Walls should be made of such materials and so constructed 

 that they will both prevent the conduction of heat and also the free ingress 

 and egress of air. Glass is a good illustration of a substance which will 

 conduct heat rather rapidly but will entirely prevent the passage of air. 

 Therefore, an excess of glass is objectionable because it allows the too 

 rapid cooling of the room at night. 



Since still air is a poor conductor of heat, dead air spaces are ex- 

 tremely desirable. This is illustrated on railway trains when double 

 windows do not frost over as single windows do in cold weather. It is 

 important, in order to secure the proper result, that these air spaces 

 should be perfectly tight, so that there is no exchange of air between the 

 spaces and the surroundings. This is perhaps the greatest fault in the 

 construction of dead air spaces. In Farmers' Reading-Course Bulletin 

 No. 23, ]\Ir. Cook discussed a method of securing insulation which he 

 has found satisfactory. Perhaps in all structures, but particularly in 

 barns, the exchange of air, rather than conduction, is the most important 

 reason for the change of temperature. 



Even when no regular system of ventilation exists, the air sifts in 

 around doors and window casings and through cracks and crevices often 



