236 GENERAL MICROBIOLOGY 



EXERCISE 3. TO DEMONSTRATE THE EFFICIENCY OF 

 CHLORIDE OF LIME AS AN AGENT IN THE PURI- 

 FICATION OF DRINKING WATER 



Apparatus. Small can of commercial chloride of lime 

 (one can is sufficient for the class); 6 liter precipitating jar; 

 sterile 1.5 liter flask; 20 sterile Petri dishes; sterile 1 c.c. 

 pipettes; two sterile 100 c.c. volumetric pipettes; ten tubes 

 of litmus lactose agar; ten tubes gelatin; two litmus lactose 

 agar shakes; six dilution flasks, four 99 c.c. and two 90 c.c, 

 (distilled water) ; one liter of sewage. 



Method. 1. Using the large precipitating jar, prepare 

 a 6% solution of chloride of lime (by weight), using the 

 entire contents of a newly opened can. This stock solution 

 will contain about 2% available chlorine calculated on the 

 basis of 35% available chlorine in the commercial chloride 

 of lime. 



2. Mix well and allow to settle over night before pro- 

 ceeding with the experiment. 



3. Obtain the sewage in the large sterile flask. Save 

 a small quantity of the sewage in a sterile test tube for 

 microscopic examination. 



4. Make gelatin and litmus lactose agar plates of the 

 fresh sample, plating 1 c.c. and 0.1 c.c. direct, and dilutions, 

 1-100, 1-10,000 and 1-1,000,000 (five plates in each 

 medium) . 



6. Add 1 c.c. of the 6% solution of chloride of lime 

 (2% available chlorine) to exactly 1,000 c.c. of the sewage 

 in the sterile flask; shake vigorously for one minute and 

 allow it to stand one hour. This amount is over ten 

 times the amount necessary for sterilization, calculating 

 on the basis of 16 Ibs. of chloride of lime (containing 

 35% available chlorine) per million gallons of water. (See 

 table on page 11, Hooker's Chloride of Lime in Sanita- 

 tion.) 



6. Plate in gelatin and litmus lactose agar, using 1 c.c. 



