496 M. R. MEACHAM, J. H. HOPFIELD AND S. F. ACREE 



no very great change under average conditions for bacteriological 

 work around 25°C. because the hydrolysis is fairly slow and the 

 first acid group of orthophosphoric acid has an ionization con- 

 stant about equal to that of the second acid group of pyrophos- 

 phoric acid (1.1 X 10 -2 ). As work with solutions more acid than 

 C H = 10 -2 will be rare, the hydrolytic cleavage (of anions and 

 molecules) can be represented by the equation : 



NaH 3 P 2 7 + H 2 -* NaH 2 P0 4 + H 3 P0 4 



From this equation and the above ionization constants it is seen 

 that there is no appreciable change in the hydrogen ion concen- 

 tration. The preparation of mono-, di-, tri-, and tetra-salts 

 from pure pyrophosphoric acid and the rate of hydrolytic cleav- 

 age of each will be studied carefully in this connection. The 

 change of the tetra-salt into the orthophosphate by the action of 

 alkalies will also be studied. 



It is highly desirable that the hydrogen electrode be employed 

 more widely in the study of the ionization constants of such acids 

 and in the study of the acidity of such regulated culture media 

 before and after the growth of organisms on such media. Professor 

 Abbott and Professor Bray have most generously consented to 

 our work in this field as accessory to their own investigations, 

 which are practically the only authoritative records of the ioni- 

 zation constants of these acids, especially pyrophosphoric acid. 

 We consider their work to be of a very high order of merit and it 

 is hoped that further studies in the application of these materials 

 in culture media and the studies by use of the hydrogen elec- 

 trode and spectrophotometric methods will be of importance. 



It should be pointed out that the use of the above mixture of 

 asparaginic (aminomalonic, acetoacetic, etc.) acid and ortho- 

 phosphoric acid (or pyrophosphoric acid) or equivalent mixtures 

 simplifies very greatly the work involved in measuring the useful 

 ranges of indicators, comparisons with culture media, and related 

 fields. This applies to both the buffer solutions 4 alone and those 



4 The Grahame Chemical Company now sells a sterile single buffer solution 

 which remains constant indefinitely and covers all pH values from 1 to 14 very 

 accurately and replaces the 5 or 6 buffer solutions employed heretofore. They also 



