USE OF MIXED BUFFER MATERIALS 497 



used in culture media. The buffer solutions are sterilized with 

 thymol, formaldehyde, chloramides, etc. Heretofore investiga- 

 tors interested in these lines have had to use several different solu- 

 tions to get hydrogen ion concentrations between 10~ 2 and 10 -12 

 for example. As the preparation of each solution requires con- 

 siderable care and some of these materials are decomposed by 

 molds, fungi and bacteria, the solutions had to be renewed every 

 few weeks. From our work and that of Prideaux we believe that 

 one solution containing asparaginic 5 acid and orthophosphoric 

 (or pyrophosphoric) acid in equimolecular quantities suffices to 

 cover the entire range between 10" -1 and 10~ 13 in practically a 

 straight line or smooth curve relation between the hydrogen ion 

 concentrations and the number of molecules of alkali added to 

 the mixture of the two acids. We also avoid the use of the boric 

 acid employed by Prideaux which is undesirable in most biologi- 

 cal work. The buffer or culture solutions can be made and kept 

 sterile by making the original solutions decidedly alkaline at ordi- 

 nary temperatures instead of in autoclaves and afterwards adding a 

 (sterile) strong acid in known amounts to secure solutions having 

 higher hydrogen ion concentrations. This method is advanta- 

 geous when the alkali or acid and other materials present interact 

 and change the hydrogen ion concentration when heated in an 

 autoclave. 



In making a titration curve on such a strongly akaline solution 

 of the salts of two acids (in equimolecular proportion) we rec- 

 ommend the feature of adding to the alkaline solution in the hy- 

 drogen electrode vessel another solution containing the aspara- 

 ginic and phosphoric acids (in equimolecular proportions and in 



furnish sterile buffer tablets, with or without admixed standardized quantities 

 of different indicators, which cover all pH values from 1 to 14 in steps of 0.2 pH. 

 These sterile tablets are added to sterile culture media or to water to give the 

 desired pH values, and have been found very useful in saving time and securing 

 accurate results. 



5 The asparaginic acid can be replaced very advantageously in culture media 

 by I equivalent of formic acid, f equivalent of acetic acid, and one equivalent 

 of aminoacetic or equivalent acid. For buffer solutions this aminoacetic acid 

 can be replaced by phenolsulphonic acid, thymol, or other suitable and stable 

 substances having ionization constants around 10 -10 . 



