52 General Bacteriology. 



maining gas is considered as hydrogen; bring this into the open arm, remove the thumb 

 and introduce alighted match. Air mixred with the hydrogen present causes a slight ex- 



TT 



plosion. Express the amount of CO2 and H. in the form of a proportion. ^ = . 



CU2 



REFERENCES. A. 203; McF. 54; M. & R. 86. 

 SPECIAL DIRECTIONS. Use B. coli, also try B.-subtilis. 



EXERCISE XLIX. DETECTION OF ACIDS (Wurtz). 



GENERAL DIRECTIONS. 



a. Melt a tube of lactose agar (gelatin can be used) and add enough of a sterile, blue 

 litmus solution to give it a distinct color, cool to 42 C., inoculate it with an acid- pro- 

 ducing organism and pour in the usual manner. 



b. When the agar has solidified invert the dish and place it in the incubator. 

 REFERENCES. McF. 54. 



SPECIAL DIRECTIONS. Use B. coli and incubate at 38 C. 



EXERCISE L. QUANTITATIVE DETERHINATION OP ACIDS. 



GENERAL DIRECTIONS. 



a. Inoculate 5 test-tubes of glucose bouillon (or milk) with an acid-producing 

 organism. 



b. At periods 24 hours apart remove, with a sterile pipette, 5 cc. of the medium from 

 each and titrate with a twentieth normal potassium (or sodium) hydrate solution, using 

 phenolphthalien as an indicator. 



c. Plot the results, expressing the number of cc. of hydrate solution as abscissae 

 and the daily intervals as ordinates. 



SPECIAL DIRECTIONS. Use B. coli and incubate at 38 C. 



EXERCISE LI. DETECTION OF NITRITES IN CULTURES. 



GENERAL DIRECTIONS. 



a. Make a culture of a reducing organism in a test-tube of the nitrate solution 

 (XXXVII. g.). 



6. Incubate at 28 C. for 1 week, add 1 cc. of each of following solutions: 



1) Sulphanilic acid (para-amido benzenesulphonic acid) 0.5 gm. Acetic acid (sp. 

 gr. 1.04) 150 cc. 



2) -amido-naphthalene acetate. Boil 0.1 gram of solid a-amido-naphthalene in 

 20 cc. of water, filter the solution through a plug of washed absorbent cotton, and mix 

 the nitrate with 180 cc. of diluted acetic acid. All water and vessels used must be free 

 from nitrites. (Leffman and Beam.) 



The presence of a nitrite is indicated by a pink color. 



c. A tube of the original medium should be incubated and tested as a control. 



REFERENCES. A. 215; McF. 56. 



SPECIAL DIRECTIONS. Use Bacillus vulgaris. (Hauser.) Mig. 



EXERCISE LII. DETECTION OF AMMONIA. 



GENERAL DIRECTIONS. 



a. Make bouillon culture and incubate. 



