MANUFACTURED ICE AND FREEZING MIXTURES 169 



pressor to the valve, E. The low side comprises the portion 

 from the valve, E, to the compressor. Referring to the table 

 (Art. 194), we see that at a pressure of 34 Ib. the boiling point 

 of ammonia is 5F. In operating the ice plant, the regulating 

 valve is usually so set that the pressure on the low side of the 

 valve, i.e., in the pipes in the brine vat, is maintained at 

 about 34 Ib. Since the temperature of the brine is usually 

 from 10 to 15 above the temperature of the pipes, the 

 temperature of the brine is about 16 or 18F. 



197. Purity and Cost of Manufactured Ice. Practically all 

 impurities of every kind are removed from the water by dis- 

 tilling it before it is placed in the cans to be frozen. Even 

 though air be the only impurity present when freezing takes 

 place, the ice will be filled with small bubbles and therefore 

 will be clouded and opaque. It is the presence of a very small 

 amount of air which the water reabsorbs before freezing can 

 take place, which gives the center of the ice cake the whitish, 

 opaque appearance familiar to all users of artificial ice. Even 

 small quantities of dissolved solids generally give the ice a 

 yellowish or brownish tinge. When frozen in cans by the 

 method here described, only pure water can give clear, color- 

 less ice; therefore, only distilled water is used. As far as 

 possible the exhaust from the engine which runs the com- 

 pressor is used. Since this does not furnish sufficient water, 

 generally, steam from the extra boiler mentioned above (Art. 

 193) is also condensed and used. 



In the southern portion of the United States and in many 

 northern portions which are remote from bodies of fresh 

 water, manufactured ice can be produced at less expense 

 than natural ice can be obtained. The average cost of pro- 

 ducing artificial ice is now generally considerably less than 

 $1 per ton. The cost to the consumer is, however, much 

 more than this, owing to the expense of handling and the 

 large loss due to melting which necessarily accompanies its 

 distribution during warm weather. 



198. Freezing of Ice Cream. The freezing of ice cream 



