254 STATE BOARD OF AGRICULTURE. 



Eesearcli Associate F. W. Fabiau submits the followiug report : 



The work that I have been able to do along experimental lines has 

 necessarily been limited due to the lack of time at ni}- disposal after 

 discharging my obligations as a teacher. However, I have found time 

 to undertake several problems, some of which I am still working on 

 while others I have completed. 



Problem 1. Titration of Culture Media. 



This problem was undertaken in cooperation with G. L. A. Ruehle, Re- 

 search Associate, of this station, to compare three methods of titrating 

 culture media to determine the one giving the most uniform and satis- 

 factory results under all conditions. A general outline of the methods, 

 procedure and results obtained follow : 



A. The standard procedure: Add 5 cc. of the medium to 45 cc. of 

 distilled water,, boil for one minute to expel the COo and then titrate 

 in the presence of phenolphthalein until a faint but definite pink color 

 is obtained, the color remaining for five minutes. 



B. Driving off the CO2 from the water by boiling, then adding the 

 hot medium to be tested and finally titrating as before after the mixture 

 has become cold. 



C. Neutralizing the CO. in the water with an alkali, then adding the 

 medium to be tested and finally titrating to a permanent end point as 

 in the preceding methods. 



It Avill be noted that the principal distinction between metliod A and 

 the other two is that A requires titration when hot, while B and C re- 

 quire titration when cold. Methods A and B depend upon boiling to expel 

 the COo in the water, while C depends on neutralization of the CO.. 



The titrations by the three above methods were done at approximately 

 the same time. Duplicate determinations were made in each case, one 

 of the writers running method B and the hydrogen ion determination 

 by the colorimetric method, while the other ran methods A and C. The 

 titration of each medium were made with each method using all of the 

 eight difterent waters. It was desired to titrate standard laboratory 

 media having different reactions in water from different sources and 

 differing wideh^ in chemical composition. An N/10 acid potassium 

 phthalate solution was used to titrate back the excess alkalinity, it being 

 the only accurate acid solution available when the need arose. Car- 

 bonate free N/20 sodium hydroxide was used to titrate the acidity, 

 every precaution being taken to have the procedure uniform. The re- 

 sults of the titrations using the different methods and the various waters 

 and media will be found in tables 4, 5 and 6. 



THE MEDIA. 



All media were made according to Standard Methods. The nutrient 

 gelatin table 1, a and b, was made from meat infusion while all other 

 media were made from meat extract cubes. Half of each lot of media 

 was made acid while the other half was left unadjusted. 



