164 MASS. EXPERIMENT STATION BULLETIN 167. 



Table V. — The Influence of Sterilization on Ph and the Formol Titrating 



Nitrogen. 



' Medium IV. without addition of acid and alkali. 



From Table V. it is evident that a general increase of Ph took place in 

 each medium, and it is least in the control: the marked and varied increase 

 of the formol titrating nitrogen in each medium occurred and the change 

 is parallel to the amount of the acid and alkali added. These changes 

 may be attributed to the different amounts of acid and alkali added, the 

 heat caused by the sterilization, and the variation in the original con- 

 centration. 



In order to eliminate these sources of error, and to secure more uni- 

 formity in the media, the author resorted to the following procedure: 

 instead of preparing Medium IV. as just stated, i: was made up according 

 to the following formula : — 



2 per cent. Liebig's meat extract. 

 2 per cent. Witte's peptone. 

 1 per cent. NaCl. 

 1,000 c. c. distilled water. 



This medium has been used for the preparation of different Ph, as the 

 formula indicates below. 



+ 



+ 



(?-^-) 



X 



Number of c. c. of the Required number of Number of c. c. H2O Total 



above medium c. e. n/5 HCl or n/5 to make up to the volume 



NaOH total volume 



of which 



X is the total volume of the medium which has the same constituents as 

 Medium IV. 



Y is the required amount of n/5 HCl or n/5 NaOH which has been deter- 

 mined to secure different Ph- 



