MECHANICAL REFRIGERATION 303 
sufficient to start with so that the air may have an oppor- 
tunity of escaping with as little loss of ammonia as possi- 
ble. 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 ex- 
pansion valve opened. The glass gauge on the ammonia 
receiver will indicate the depth of ammonia. The appear- 
ance 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 some- 
times difficult to completely empty an ammonia cylinder 
without first applying heat. The process of cooling being 
the same when the ammonia expands from the cylinder 
into the system as when leaving the expansion valve, a 
low temperature is produced and the cylinder and con- 
nections become covered with frost. When this occurs the 
cylinder must be slightly warmed in order to be able to 
get all the ammonia out of it. The ammonia cylinders, 
when filled, should never be subjected to rough handling 
and are preferably kept in a cool place free from any lia- 
bility to accident. The fact that ammonia is soluble in 
water should be well understood by persons charging a 
refrigerating system, or working about the plant. One 
part of water will absorb about 800 parts of ammonia gas 
and in case of accident to the ammonia piping or machine, 
water should be employed to absorb the escaping gas. 
Persons employed about a plant of this kind should be 
provided with some style of respirator, the simplest. form 
of which is a wet cloth held over the mouth and nose. 
“After starting the compressor at the proper speed and 
adjusting the regulating valve note the temperature of 
