155 



was taken as the end point. The results of these tests with 23 lots of 

 media are shown in Table II and Graph I. 



TABLE II. 

 Acidity op Media (*Calculated in Per Cent.) as Affected by Carbon Dioxide in Distilled Water. 



Agart (alone) 



Agar and 1 gm. starch 



Agar and 2 gm. starch 



Agar and 10 gm. soil 



Agar and ammonium nitrate 



Agar and 7.5 gms. gelatine -j 



Agar and .05 gms. peptone 



Agar and 1.0 gms. sodium asparaginate 



.\gar, 1 gm. starch and 10 gms. soil 



Agar, 1 gm. starch and 1 gm. (ammon. nitiate 



(b) ) 



Agar, 1 gm. starch and 7.5 gelatine - 



-\gar, 2 gm. starch and 7.5 gelatine 



Agar, 2 gm. starch and .05 gm. peptone 



Agar, 10 gms. soil and 1 gm. (ammon. nitrate). 

 Agar, 10 gms. soil, 2 gms. starch and 7.5 

 gelatine 



Lipman and Brown's "synthetic agar' 



J. Conn's (.sodium asparaginate agar). , . •! 



(1) CO2 

 Present 



Dilution 

 Water. 



.68% 



.69 



.72 



.39 



.76 



.72 (a) 



.83 

 1.00 

 1.03 



1.18 

 .66 

 1.10 

 1.58 

 1.15 

 .84 



.64 

 1.25 

 1.40 

 1.48 

 1.87 

 2 24 

 2^46 



(2) CO2 



Free 

 Dilution 

 Water. 



.07% 

 .08 

 .06 

 .00— 

 .58 

 12 

 .16 

 .08 

 .10 

 .04 



.44 

 .11 

 .16 

 .10 

 .08 

 .72 



.22 

 .28 

 .32 

 .36 

 1.38 

 1.40 



(3) 



Acidity 



,Due 



to COj in 



(1). 



.61 (c) 



.61 



.66 



..30 + 



.18 



.6'! 



.61 



.92 



.93 



.76 



.74 



.55 



.91 

 1.48 

 1.07 



.12 



.56 

 1.03 

 1.12 

 1.16 

 1.51 



.86 

 1.06 



(4) Actual 

 Acidity if 

 Corrected 

 to .80 by 



(1). 



(5) Actual 

 Acidity if 

 Corrected 

 to .50 by 



(1). 



alk. 



alk. 



alk. 



alk . 



acid 



alk. 



alk. 



alk 



alk. 



alk. 



alk. 

 alk. 

 alk . 

 alk. 

 alk. 



alk. 

 alk. 

 alk. 

 alk. 

 alk. 

 alk. 

 alk. 



*1.00% would mean the requirement of 1 cc. normal alkali for neutralization of 100 cc. of media. 



tFifteen grams of air dry agar basis of all media. 



(a) Each figure given represents one lot of media. No two lots of same media were made on same 



date. 



(b) Phenolphthalein is not the most desirable indicator to use when ammonium salts are present. 



(c) Distilled water prepared from soft water is often practically free from carbon dioxide. 



The table shows — 



(1) That the carbon dioxide normally present in distilled watex 

 prepared from hard water by a modern still affects the titration of media. 



(2) That the titration, due to carbon dioxide pre.sent in diluting 

 water may be much greater than the total titration of the acidity of 

 the media itself. 



(3) That the carbon dioxide does not affect the acidity of all media 

 in the same proportion. 



(4) Media adjusted by results of titrations made of aliquots diluted 



