CLARK AND LUBS: INDICATORS FOR CULTURE MEDIA 483 



ANALYSES 



I. 0.1456 gram gave 0.0881 gram AgBr. 

 II. 0.1865 gram gave 0.1158 gram AgBr. 

 Calculated for C27H 2 sBr20 5 S, 25.6 per cent Br. 

 Found, I, 25.8 per cent; II, 26.4 per cent. 



TABLE 1 



Color Changes and Approximate Ranges of the Various 

 sulphone-phthaleins 



INDICATOR 



Thymolsulphone-phthaleinf 



Tetrabrom-phenolsulphone-phthalein. 

 Tetrachlor-phenolsulphone-phthalein* 

 Dibrom-o-cresol-sulphone-phthalein . . 

 Dibromthymol-sulphone-phthalein.. . . 



Phenolsulphone-phthalein 



o-Cresolsulphone-phthalein 



Phenol-nitro-sulphone-phthalein* 



a-NaphthoIsulphone-phthalein 



Thymolsulphone-phthalein 



Thymol-nitro-sulphone-phthalein* 



Carvacrolsulphone-phthalein* 



* These compounds were prepared only in small amounts. Upon investiga- 

 tion we found that they showed no advantage over compounds more easily pre- 

 pared. On this account we did not attempt to find the best conditions for their 

 preparation, and for this reason the details of methods for their preparation are 

 not given. 



t This indicator shows color changes in both alkaline and acid solutions. 

 Between P "£ 3 and P ^ 8.0 its solution is yellow in color. 



CHEMISTRY. — The colorimetric determination of the hydrogen- 

 ion concentration of bacteriological culture media. 1 William 

 Mansfield Clark and Herbert A. Lubs, Bureau of Ani- 

 mal Industry. 



In a previous note 2 we described some new indicators which 

 are especially useful in colorimetric determinations of hydrogen- 

 ion concentrations. In the present number of this Journal we 

 present some further notes. 



1 From the research laboratories of the Dairy Division, Bureau of Animal 

 Industry. Published by permission of the Secretary of Agriculture. 



2 Ltjbs, H. A., and Clark, W. M. Journ. Wash. Acad. Sci., 5: 609. 1915. 



