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Scientific Proceedings (125) 



removal of phosphates and carbonates by precipitation with 

 barium and filtration. These methods may be adopted by the 

 bacteriologist, but are time-consuming. If many cultures are 

 to be titrated the element of time is very important. Of almost 

 equal importance to the bacteriologist is the ability to make de- 

 terminations with small samples of material. Bacterial cultures 

 present a special problem in some respects. Their color and 

 turbidity are not easily matched by artificial controls. They may 

 contain other buffer substances than phosphates and carbonates. 

 We have tried to reduce the formol titration of bacterial cultures 

 to its simplest terms. Color and turbidity may be overcome and 

 much greater accuracy in judging a colorimetric end point may 

 be attained by the use of a comparator block and Clark and Lubs' 

 indicator solutions. The error due to the presence of buffer 

 substances may be eliminated by starting and ending the titration 

 at the same hydrogen ion concentration. If the isoelectric zone 

 of an amino acid or ammonium salt overlaps the zone of neutrali- 

 zation of its methylene derivative this may be done with perfect 

 results. This is the case with glycine, alanine, asparagine, am- 

 monium chloride, ammonium lactate and probably with others 

 not studied. In the case of the other amino acids titrated there 

 is no actual overlapping of the zones, but there are certain hydro- 

 gen ion concentrations at which the zones approach each other 

 closely. The overlapping of the zones or their points of nearest 

 approach are not at the same hydrogen ion concentration for all 

 the substances titrated. It was determined empirically in the 

 case of standard bouillon and bouillon cultures of various bacteria 

 that maximum formol titrations were obtained when the reac- 

 tion of the sample was reduced to P H 8.0, formalin added, and 

 the mixture immediately titrated back to P H 8.0. The results so 

 obtained were reasonably close (within about 6 per cent.) to 

 those obtained by titration from P H 7.0 to P H 8.0 after removal 

 of phosphates and carbonates by precipitation with barium and 

 filtration. The details of the method recommended are in press. 



" Ilenriques, V., and Sorensen, S. P. L., Z. f. physiol. Chem., 1910, lxiv, 

 120. 



