LUBS AND CLARK: NEW HYDROGEN-ION INDICATORS 615 



with water. The dye collected as a black viscous mass at the bottom 

 of the beaker. The water was poured off and the viscous mass which 

 hardened upon cooling was boiled with alcohol to remove the remain- 

 ing thjanol. Upon cpoling to room temperature the thymolsulphone- 

 phthalein was filtered off as greenish crystals. Yield about 5 grams. 

 These crystals can be recrystallized from alcohol. (1) 0.3288 gram 

 gave 0.1490 gram BaS04; (2) 0.4224 gram gave 0.2118 gram BaS04; 

 S. calculated for C27H30S 05,6.88 per cent; S found (1) 6.21 per cent/^ (2) 

 6.88 per cent. 



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

 between Ph 8 and Pr 9.75. The useful range lies between Ph 8.00 and 

 Ph 9.50. Throughout this range the differentiations are extremely 

 sharp. For colorimetric purposes a dilution of 0.1 gram of indicator 

 in 200 cc. alcohol and 50 cc. water was used. Use 3-6 drops. This 

 indicator covers practically the same range as phenolphthalem, and 

 probably can be substituted for the latter to advantage in many cases. 

 This point will be decided as soon as we have completed our work on 

 the magnitude of the protein and salt errors of these new indicators, 



a-NAPHTHOLSULPHONE-PHTHALEIN 



Preparation. — Five grams of the acid chloride, 5 grams of freshly 

 fused and dehydrated zinc chloride and 6 grams of a-naphthol were 

 thoroughly mixed. The reaction began at once. A dark green melt 

 was formed. This was heated to 70° with constant stirring and held 

 at this temperature for about ten minutes. Upon longer heating, the 

 dye tends to go over into a substance which is probably an oxidation 

 product and which gives a green color in alkaline solution. The melt 

 was extracted with water to remove the zinc chloride. The residue 

 was then extracted thoroughly with ether in order to remove the ex- 

 cess of naphthol. It was then dissolved in cold alkali and the solution 

 filtered. The indicator was reprecipitated by the addition of strong 

 hydrochloric acid, filtered with suction, washed with water containing 

 hydrochloric acid and air dried. When dry the indicator has a dark 

 green color. Without further purification and after drying at 120° 

 in vacuo, 0.5154 grams gave 0.2345 grams BaS04; 0.2736 grams gave 

 0.1239 grams BaS04. Theoretical for C27H18SO5, 7.06 per cent S. 

 Found (1) 6.24 per cent, (2) 6.21 per cent. 



Properties. — The color changes are from yellow to blue over the 



15 Incomplete fusion suspected in this case. Further analyses were not made 

 because of limited supply of indicator. 



