142 MARKET DAIRYING 



discharging the air, which is removed from the system 

 by starting the compressor and pumping the air out, the 

 operation of gas cylinder being just the reverse of that 

 when it is working ammonia gas. It is practically impos- 

 sible to get all the air out of the entire system by this 

 means, so that some other course must be taken to remove 

 'any remaining air after the compressor has been started 

 at regular work. This can be accomplished by admitting 

 the ammonia a little at a time, permitting the air to escape 

 through a purge valve, the air being thus expelled by dis- 

 placement. The cylinder containing the anhydrous am- 

 monia is connected to the charging valve by a suitable 

 pipe, and the valve opened. The compressor is then kept 

 running slowly with the suction and discharge valves wide 

 open and the expansion valve closed. When one cylinder 

 is emptied put another in its place, being careful to close 

 the charging valve before attempting to remove the empty 

 cylinder, opening it when the fresh cylinder is connected 

 up. 



"From sixty to seventy-five per cent of the full charge 

 is sufficient to start with so that the air may have an 

 opportunity of escaping with as little loss of ammonia as 

 possible. An additional quantity of ammonia may then be 

 put in each day until the full charge has been introduced. 

 When the ammonia cylinders have been emptied and a 

 charge of, say, seventy-five per cent of the full amount 

 has been introduced, the charging valve is closed and the 

 expansion valve opened. The glass gauge on the am- 

 monia receiver will indicate the depth of ammonia. The 

 appearance of frost on the pipe leading to the coils and 

 the cooling of the brine in the tank will indicate that 

 enough ammonia has been introduced to start with. It is 

 sometimes difficult to completely empty an ammonia cylin- 



