REACTION STANDARDIZATION 21 



The salt and the peptone are best put in a mortar, and adding about i ounce 

 of the meat infusion we make a pasty mass; then we gradually add the remaining 

 infusion until solution is complete. It is sometimes recommended to use a tempera- 

 ture of soC. to facilitate the solution of the peptone. This is not necessary, and 

 if the temperature is not watched closely it might go up to 65C. or higher and we 

 should lose the clearing albuminous material from its coagulation. Of this rather 

 cloudy solution take up 10 c.c. with a pipette and let it run out into a porcelain dish. 

 Add 40 c.c. of distilled or rain water and about six drops of a 0.5% phenolphthalein 

 solution. (Phenolphthalein, 0.5; dilute alcohol, 100 c.c.) Bring the contents of 

 the porcelain dish to a boil and continue boiling for one or two minutes in order to 

 expel all CO 2 . Now from a burette filled with decinormal sodium hydrate solution, 

 run in this solution until we have the development of a faint but distinct pink in the 

 boiling diluted bouillon which is not dissipated on further boiling. 



It is more satisfactory to take burner from beneath the porcelain dish just before 

 running in the N/io solution, again boiling so soon as a pink color is obtained. Hav- 

 ing obtained the light pink coloration we read off the number of c.c. or fractions of a 

 c.c. of N/io sodium hydrate solution added to produce the color. This number 

 gives the acidity of the bouillon in percentage of N/i acid solution. 



Percent acid means that so many c.c. of N/i acid added to 100 c.c. 

 of the medium at the neutral point would give that percentage reaction. 

 Thus ij-^ c.c. of N/i HC1 solution added to 100 c.c. of medium at o, 

 would give us ij^% of acidity or + 1.5. (Accurately 98^2 c - c -) 



Percent alkaline means so many c.c. of N/i sodium hydrate solution added to 

 100 c.c. of the medium at the neutral point. Thus a %% alkaline medium would be 

 one whose alkalinity would correspond to the addition of ^ c.c. of N/i NaOH to 100 

 c.c. of the medium at o. It is written 0.5. 



If we took 100 c.c. of the medium and put it in a beaker and then ran in N/i 

 NaOH solution from a burette, it will be readily understood that if we had to add 

 3^2 c.c. of N/i NaOH to obtain the pink color, it would show that the acidity of the 

 100 c.c. of medium, being tested, corresponded to 3.5 c.c. of N/i acid solution, 

 and that its acidity was equal to 3^% of N/i acid solution, or that its reaction was 

 +3-5- 



As N/i NaOH solution is too corrosive for general use in a burette, and as 10 c.c. 

 of medium is more convenient to work with than 100 c.c., we use a solution one- 

 tenth the strength of the N/i NaOH and we take only one- tenth of the 100 c.c. of 

 medium. In this way it is the same from a standpoint of directly reading off our 

 percentage reaction as if we had 100 c.c. of medium and used N/i NaOH solution. 

 The A. P. H. Association recommends 5 c.c. of the medium and the use of N/20 

 NaOH. As the N/io NaOH is always at hand for titrating gastric juice, the N/io 

 is used instead. 



Should it be found difficult to carry on the titration while boiling the end reaction 

 may be fairly accurately determined in the cold. Deliver into a beaker from a 

 pipette 10 c.c. of the bouillon and make up to 50 c.c. with distilled water and add 5 

 drops of 0.5% phenolphthalein solution. Then run in N/io NaOH from a burette 

 and continue to add the N/io NaOH solution from the burette, drop by drop, until 



