114 DAIRY LABORATORY GUIDE 



and discharge valves wide open and expansion valve 

 closed. As soon as one cylinder is empty replace 

 with another, being careful to close the charging 

 valve before attempting to remove the empty cylin- 

 der; opening it when the fresh cylinder is connected. 

 From 60 to 75 per cent of the full charge is sufficient 

 to start with, so that any air not having been removed 

 may escape with as little loss of ammonia as possible. 

 Add a small amount of ammonia each day until full 

 charge has been introduced. The glass gage on the 

 ammonia receiver will indicate the amount of am- 

 monia present. The appearance of frost on the pipe 

 leading to the coils and the cooling of the brine or 

 air in refrigerator in the tank will indicate that 

 enough ammonia has been introduced to start with. 

 It sometimes requires applications of heat to entirely 

 empty the ammonia cylinder. One part of water will 

 absorb 800 parts of ammonia gas, therefore for use in 

 case of accident keep a vessel of water handy. After 

 starting compressor at the proper speed and adjusting 

 regulating valve, note temperature of delivery pipe, 

 and if there is a tendency to heat open it wide, and 

 vice versa. With too light charge of ammonia the 

 delivery pipe will become heated. The refrigerating 

 room should be about 15 degrees lower than the brine 

 being used, and the temperature of the water dis- 

 charged from the ammonia condenser should be about 

 15 degrees lower than that of the condenser. By 

 placing the ear close to the expansion valve the 

 ammonia can be heard passing through it. If the 

 sound is uniform and continuous the machine is 



