212 



GENERAL MICROBIOLOGY 



that the unknown disinfectant undiluted is 5 times the strength of 

 the undiluted phenol.* 



11. Determine the approximate phenol coefficient of 

 mercuric chloride according to the results of your experi- 

 ment. How does this compare with results in literature? 



12. What are some of the principal factors involved in 

 the examination of disinfectants (pp. 12-20, Hyg. Lab. Bui. 

 No. 82). How would each of these come into consideration 

 in actual practice? 



METHOD OF MAKING DILUTIONS OF DISINFECTANT FOR 



TEST 



1 part of 5% phenol +1 part distilled water =2.5% phenol. 

 1 part of 5% phenol +4 parts distilled water = 1.0% phenol. 

 1 part of 5% phenol+9 parts distilled water = 0.5% phenol. 



1 part of 1 : 500 HgCl 2 + l part distilled water =1 

 1 part of 1 : 500 HgCl 2 +3 parts distilled water = 1 

 1 part of 1 : 500 HgCl 2 +9 parts distilled water = 1 



1000 HgCl 2 . 

 2000 HgCl 2 . 

 5000 HgCl 2 . 



METHOD OF RECORDING RESULTS 



Disinfectant. 



Time in minutes during which culture is exposed to 

 action of disinfectant. 



13. Give data and results in full. Draw any conclusions 

 that properly follow and point out any practical applications. 



* In a large class it would be interesting to have determined the 

 phenol coefficient of the chromic acid cleaning solution and of the 10% 

 sodium hydroxide used for cleaning glassware, as each is recommended 

 for immersing slides, cover-glasses, etc. contaminated with bacteria. 



