170 C. L. BRIGHTMAN, MEACHEM AND ACREE 



or optimum in value. We have already established some of 

 these limiting values of ionic concentrations for several wood 

 destroying fungi 2 and have begun to put the results into prac- 

 tical application in culturing the fungi, and in preventing the 

 decay of chestnut trees 3 and of wood pulp, 4 for example. 



The concentration of the hydrogen ions is a very important 

 physiological and chemical factor governing the growth of wood 

 destroying fungi. It is therefore essential to devise methods 

 for measuring this factor accurately, especially as a very great 

 effect on the growth is produced by small changes in hydrogen 

 ion concentration in the regions of maximum and minimum values 

 of tolerance. This is well illustrated in figure 1, which gives one 

 of the many sets of experiments worked out by Meacham which 

 will be reported later. 



The hydrogen electrode 5 and sulfonphthalein indicators 6 were 

 developed by Desha, Loomis, Myers, W. F. Clark, Slagle, White, 

 Lubs, W. M. Clark, Guy, Birge, Hopfield and the writers for meas- 

 uring hydrogen ion concentrations in solutions of weak and strong 

 acids and bases, in the presence of salts, and in general under 

 conditions such as we find in culture media. These methods 

 are probably the best known for measuring the hydrogen ion 

 concentration, but the presence of certain salts has an appre- 

 ciable effect on the apparent values obtained by both methods. 

 As the electrometric and colorimetric methods give different 

 results, it is necessary to learn the magnitude of the errors in- 



2 See preliminary report: Meacham, Science, 48, 499. 



3 Ibid, and several reports appearing later. 



4 See address by Acree before Buffalo Convention of Tech. Assn. Pulp and 

 Paper Industry, published in Paper, June, 1919. 



5 Science, 30, 624. Loomis and Acree: Am. Chem. J., 46, 585, 621. J. Am. 

 Chem. Soc, 38, 2391. Desha and Acree: Am. Chem. J., 46, 638. Myers and 

 Acree: Ibid, 50, 396. Clark, Myers and Acree: J. Phys. Chem., 20, 243. 



6 Acree: Am. Chem. J., 37, 72; 39, 155, 528. Slagle and Acree: Ibid, 42, 115, 

 and unpublished data on phenolsulfonphthalein. White and Acree: Science, 

 42, 1101; J. Am. Chem. Soc, 39, 648; 40, 1092; 41, 1190. White and Davis: Jour, 

 of Urology, 2, 107. Lubs and Acree: J. Am. Chem. Soc, 38, 2773, Lubs and 

 Clark: J. Wash. Acad. Sci., 6, 609; 6, 483. J. Bact., 2, 1, 109, 137. Birge and 

 Acree: J. Am. Chem. Soc, 41, 1031. Brightman, Hopfield, Meacham and Acree: 

 Ibid, 40, 1940. 



