80 BACTERIOLOGY. 



important is the neutralization. Ordinarily, this is ac- 

 complished with the saturated sodium carbonate solu- 

 tion, and the reaction is determined with red and blue 

 litmus papers, and for the beginner this method serves 

 most purposes. 



The sodium carbonate solution is not so good, how- 

 ever, as a strong solution of caustic soda or potash, 

 because the carbonic acid liberated from the sodium 

 carbonate is frequently seen to give rise to confusing, 

 temporary acid reaction which disappears on heating, 

 nor is litmus the most reliable indicator to employ. 

 To obviate this, Schultz (Centralb.f. Bakt. u. Parasit- 

 enkunde, 1891, Bd. x., Nos. 2 and 3) recommends exact 

 titration with a solution of caustic soda. For this pur- 

 pose a 4 per cent, solution of caustic soda is prepared. 

 From this a 0.4 per cent, solution is made, and with it 

 the titration is practised. After the bouillon has been 

 deprived of all coagulable albumin and blood-coloring- 

 matter by boiling and filtration, and has cooled down 

 to the temperature of the air, its whole volume is ex- 

 actly measured. 



From it a sample of exactly 5 or 10 c.c.is then taken, 

 and to this a few drops of one of the indicators com- 

 monly employed in analytical work are added. Schultz 

 recommends 1 drop of phenolphtalein solution (1 

 gramme phenolphtalein in 300 c.c. of alcohol) to 1 

 c.c. of bouillon. The beaker containing the sample is 

 placed upon white paper, and the dilute caustic soda 

 solution is then allowed to drop into it, very slowly, 

 from a burette, until there appears a very delicate rose 

 color, which indicates the beginning of alkaline reaction. 

 A second sample of the bouillon is treated in the same 

 way. If the amounts of caustic soda solution required 



