l8 STORRS AGRICULTURAL EXPERIMENT STATION. 



NaOH to the solution until the material is in the very faintest 

 degree alkaline. In other words, we add just enough NaOH 

 to pass the neutral point, as shown b)^ its action upon red and 

 blue litmus papers. 



After the neutralization we add the white of an egg and boil 

 for three-quarters of au hour. In this boiling we make use of 

 a 50 per cent, solution of calcium chloride, which boils at about 

 112° C. Placing the dish containing the gelatin solution in a 

 bath of this mixture we can leave the material to boil over a 

 moderate gas flame without danger of burning; considerable 

 care is necessary, however, to regulate the gas flame so that 

 the solution does not boil over. 



2. Water, . . . ^oo cc. 



Dry litmus (in cubes), 48 grams. 



The litmus is steeped in the water for three hours or more 

 at a temperature of about 60° C. to dissolve as much of the 

 active material as possible. The solution is then filtered. 



After solution i has boiled with the white of an egg for 

 three-quarters of an hour it is mixed with the filtered litmus 

 solution 2, the two together making the bulk up to about a 

 liter, and water is added if necessary to replace the water 

 which has been evaporated. The solution is then warmed 

 slightly, though not above 60°, in order to avoid as much as 

 possible the changes in the litmus which high temperatures 

 produce. The solution is then filtered through absorbent cot- 

 ton, distributed in sterilized tubes, about 8 cc. in each, and is 

 ready for final sterilization, which is carried on as usual by 

 steaming on three successive days. The sterilization always 

 has a tendency to change the color of the litmus to a reddish 

 brown, but the blue color is restored after the litmus cools and 

 stands for a few hours in contact with the air. When finally 

 sterilized and cooled the solution should be a deep blue color, 

 so that when poured out into petri dishes the color is quite 

 -Strong. We have found that the litmus of commerce is quite 

 variable in strength, since 3 per cent, of litmus (30 grams) 

 is sometimes sufficient to give the required blue color, while 

 in other cases it requires 40-50 grams. We have found that 

 as a rule 48 grams produces as good a color as can be desired, 

 but sometimes, if the litmus is exceptionally strong, a smaller 



