PROBLEM 106 



123 



Note. — A similar experiment should be tried with water from various sources. 

 Bottled drinking water, rain water, artesian well water, tap water, and water 

 collected from surface pools are suggested for possible experiments. 



Problem 106 : To determine some of the most effective pre- 

 servatives. 



Materials. — Test tubes containing beef bouillon and various 

 preservatives, salt, sugar, vinegar, formalin, boracic acid, alcohol. 



Method. — Expose the tubes to the air unplugged. Number the 

 tubes and label them. 



To No. 1 add nothing. 



No. 2 add J spoonful of salt. 



No. 3 add 1 spoonful of sugar. 



No. 4 add a saturated sugar solution. 



No. 5 add 1 spoonful of vinegar. 



No. 6 add a few drops boracic acid (saturated solution). 



No. 7 add | spoonful boracic acid. 



No. 8 add 5 drops formalin. 



No. 9 add 1 spoonful alcohol. 



Observations. — Note the appearance, odor, and color of each 

 tube at the end of three days, five days, one week, and two weeks. 

 Tabulate your results 

 as shown in accom- 

 panying chart. 



Conclusion. — 1. 

 What are the most ef- 

 fective preservatives? 



2. Which of the 

 above are permitted 

 bylaw? (See Hunter's 

 Civic Biology, p. 148.) 



3. On which solu- 

 tions did mold grow? 



4. Which preservatives prevented bacteria but not molds? 



5. Which preservatives prevented the growth of both bacteria 

 and molds? 



