PHYSICAL AGENTS 



139 



Fig. 101. — An electric milk purifier (pasteurizer). The milk flowing 

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

 is certainly a heat effect. Sparking occurs at the lips of the cups. 



Fig. 102. — 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. 



