616 LUBS AND CLARK: NEW HYDROGEN-ION INDICATORS 



range of Ph 7.50 to Ph 9.00. Very sharp differentiations can be se- 

 cured over this range. As an indicator solution use 0.1 gram dissolved 

 in 50 cc. alcohol and add 150 cc. distilled water. Use 1-2 drops. 



TETRABROM-PHENOLSULPHONE-PHTHALEIN 



Preparation. — This compound was prepared as described by White. ^® 

 Two grams of phenolsulphone-phthalein were suspended in 20 cc. of 

 glacial acetic acid and to the suspension were added 10 grams of bro- 

 mine dissolved in 10 cc. of glacial acetic acid. The flask was allowed to 

 stand, with occasional shaking, for several hours and then the excess 

 of bromine was removed by means of an air current. The precipitate 

 was filtered off with suction, washed with cold acetic acid, recrystallized 

 from the same and air dried. 



Properties. — The color changes are from yellow to purple and occur 

 over the range Ph 3.50 to Ph 4.50. The indicator solution was made 

 by dissolving 0.1 gram in 250 cc. alcohol. Use 3-5 drops. 



BROMTHYMOL-SULPHONE-PHTHALEIN 



Preparation. — This indicator was prepared in the manner described 

 for the analogous phenol compound. It is obtained as yellow granular 

 crystals. We are investigating its chemical constitution and will 

 publish our data shortly. 



Properties. — The color changes are from yellow to blue and occur 

 over the range Ph 6.00 to Ph 7.25. As an indicator solution use 0.1 

 gram dissolved in 250 cc. of alcohol. 



Work is now in progress to prepare other new indicators of the 

 sulphonephthalein type. We have already prepared phenol-nitrosul- 

 phone-phthalein, but have not purified it sufficiently to give an accurate 

 description of its properties. 



The authors take this opportunity to express their gratitude to Dr. 

 L. W. Jones, Dr. S. F. Acree, and Dr. E. C. White for specimens of 

 indicators and to Mr. H. A. B, Dunning for valuable suggestions. 



SUMMARY 



The following new indicators of the methyl red type have been pre- 

 pared by us: Monoethyl red, diethyl red, monopropyl red and dipropyl 

 red. Besides these new indicators we have also prepared and investi- 

 gated the following indicators of the methyl red group which had been 



"White, Disser. Univ. of Wisconsin. 1915. 



