238 GENERAL MICROBIOLOGY 



the stock solution of chloride of lime and the water to be 

 purified? Why is a minimum time limit set? 



What other means are used for the chemical steriliza- 

 tion of water? Are these efficient? 



What is the Hazen theorem? Its explanation? 



What other uses has chloride of lime in sanitation? 



16. Give all data and observations in full. State any 

 conclusions to be based on the above and point out any 

 practical applications. 



REFERENCES 



HOOKER: Chloride of Lime in Sanitation (1913), pp. 7, 12-34, 34-77. 



WESBROOK, WHITTAKER and MOHLER: The Resistance of Certain 

 Bacteria to Calcium Hypochlorite. Reprint from Jour, of Amer- 

 can Public Health Association, Vol. I (1911). 



WHITTAKER: Field Equipment for Laboratory Work on Water 

 Supplies. Reprint from Journal of American Public Health Asso- 

 ciation, Vol. II (1912), pp. 948-954. 



EXERCISE 4. TO DEMONSTRATE THE EFFICIENCY 

 OF THE BERKEFELD FILTER CANDLE AS A MEANS 

 OF WATER PURIFICATION 



Apparatus. Berkefeld filter candle complete with cylin- 

 der; water-power vacuum pump; filter flask with rubber 

 stopper into which the filter candle fits; one liter sterile flask; 

 eight tubes of salt-free gelatin for water analysis; eight 

 Petri dishes; sterile 1 c.c. and 10 c.c. pipettes; dilution 

 flasks; distilled water 



Method. 1. Set up the filtering apparatus, connect 

 with the vacuum pump and wash the filter by running 

 through it 500 c.c. of boiling, distilled water. 



2. Place a cotton plug in the cylinder and in the side 

 arm of the filter flask; sterilize the filtering apparatus as set 

 up, in the autoclav. 



3. Collect a liter of polluted river water from a point 

 near the opening of a sewer. 



