PHYSICAL AGENTS 



137 



Fig. 96. — An electric milk purifier (pasteurizer). The milk flowing from 

 cup to cup completes the circuit when the current is on. The effect is cer- 

 tainly a heat effect. Sparking occurs at the lips of the cups. 



Fig. 97. — One of the ten filter beds of the Columbus water- filtration plant 

 with the filtering material removed. Sand is the filtering material. All 

 of the beds together have a capacity of 30,000,000 gallons daily. 



