USE OF MIXED BUFFER MATERIALS 495 



of cornmeal, beans, malt, beef and other nutrient substances, as 

 well as upon the acid or basic products formed by the fungi. 

 An equimolecular mixture of asparaginic (or aminomalonic or 

 acetoacetic) and pyrophosphoric acid (Ki = 1.4 X 10 -1 , K 2 = 

 1.1 X 10- 2 , K 3 = 3 X 10- 7 , K 4 = 3.6 X 10~ 9 ) also gives nearly 

 a straight line relation between the hydrogen ion concentration 

 and the number of molecules of alkali added (fig. 3). The use 

 of pyrophosphoric acid in this connection is to be recommended 

 for the reason that Bray and Abbott (1909) have found the ioni- 

 zation constants of the third and fourth acid groups to have the 

 above mentioned unusual values. It is clear that there would be 

 nearly a straight line relation between the number of molecules 

 of alkali added and the hydrogen ion concentration between 

 about 10~ 6 and 10~ 10 . This is a very important region in the 

 study of seawaters and many natural waters and other solutions 

 which are slightly alkaline and it is doubtless familiar to many 

 that there are practically no organic carboxylic acids having 

 ionization constants between 10~ fc and 10~ 9 or 10~ 10 . The sec- 

 ond acid group of maleic acid has an ionization constant about 3 

 X 10 ~ 7 , and the second acid group of benzylmalonic acid has an 

 ionization constant 4.9 X 10 -7 . Outside of phenols and similar 

 substances, there are no organic acids with ionization constants 

 below these values until we come to the aminocarboxylic acids 

 such as asparagin, aminoacetic acid, etc. with ionization con- 

 stants around 10 -9 and 10 -10 . An inorganic substance like pyro- 

 phosphoric acid is therefore very welcome to cover this very 

 important range and it has the added advantage that it is not 

 readily decomposed by bacteria or fungi as are the organic acids. 

 Furthermore it does not precipitate out the calcium and magne- 

 sium from natural waters or culture media. The only apparently 

 undesirable feature of pyrophosphoric acid is that the work of 

 Abbott (1909) has shown that in acid solutions pyrophosphoric 

 acid is hydrolyzed into the orthophosphoric acid and that the 

 rate of hydration increases with increasing hydrogen ion concen- 

 tration. It is therefore certain that in very acid culture media 

 containing pyrophosphoric acid there would be a change into 

 orthophosphoric acid. It is clear, however, that there could be 



JOURNAL OF BACTKRIOLOGY, VOL. V, NO. 5 



