THE NEW YORK JOURNAL OF PHARMACY 



sorbed by the thiosulphate. Realizing 

 the importance of simplifying this part 

 of the work, since an absolutely known 

 control was necessary, T endeavored to 

 make use of starch solution, which was 

 found to be impracticable. Several other 

 forms of indicators were used without 

 success, until the thought occurred to use 

 methylene blue. This proved to be a 

 decided innovation and succeeded in 

 eliminating this obstacle, which at first 

 seemed almost impossible. By the use of 

 methylene blue as an indicator in all sub- 

 sequent control determinations, concor- 

 dant results were obtained by independent 

 workers. In this manner the so-called 

 "personal equation'' or neutral persuasion 

 is reduced to a negligible amount. 



In order that further work in this 

 direction may be encouraged, the follow- 

 ing detailed example will give an idea as 

 to what to expect, throughout the method 

 of determination, when using methylene 

 blue as an indicator. An example in 

 standardizing the concentrated carbolic 

 acid solution follows : 



Take 5 c.c. of the above; add 25 c.c. of 

 water and 60 c.c. of the bromine solution 

 This gives a clear solution. Next add 

 10 c.c. of HCl, which produces a whitish 

 magna of tribromophenol, which floats 

 to the top of the solution, which solution 

 is of a yellowish color. Shake the vessel 

 occasionally during a half-hour, add 15 

 c.c. of distilled water for washing the 

 stopper, etc., which is carefully followed 

 with 10 c.c. of a 20% solution of potas- 

 sium iodide in water. 



This is again shaken for about ten 

 minutes. A reddish brown solution en- 

 sues with a light brownish precipitate 

 which floats to the top of the fluid, indi- 

 cating the presence of free iodine. Two 

 c.c. of chloroform are next added which 



dissolves the above precipitate and takes 

 on a violet color by absorbing the iodine 

 present and falls to the bottom of the 

 vessel. 



One cubic centimeter of a saturated 

 aqueous solution (6%) of methylene blue 

 is now added to the above mixture. This 

 immediately produces a dark yellowish 

 brown, to a greenish brown color (precip- 

 itate in colloidal suspension), depending 

 on the amount of free iodine present. The 

 solution is then titrated with the standard 

 thiosulphate solution using one c.c. por- 

 tions at first and later on in tenths of a 

 cubic centimeter, carefully added, and the 

 solution vigorously agitated for one min- 

 ute after each addition. The following 

 color phenomena will be observed : As 

 the end point is approached, a clearer 

 greenish color is imparted to the solution 

 and the chloroform is observed to give 

 up its violet color produced by the iodine, 

 and takes on a faint blue ; the solution 

 turning to a steel blue color, when sud- 

 denly the entire solution turns from a 

 greenish gray to a light blue as the end 

 reaction is reached. The end reaction is 

 strong and distinct. Vigorous agitation 

 is essential throughout the entire titration. 

 A perfect end reaction is one in which 

 the chloroform is of a pure white nature, 

 or has a bluish-white tinge, and the solu- 

 tion is clear with a light blue color. The 

 chloroform not only clears the solution 

 for titration by dissolving the precipi- 

 tated tribromophenol, but in this instance 

 it assists as an indicator, both as to the 

 elimination of the iodine and the produc- 

 tion of the blue color, since it dissolves 

 out of solution both of the above, leaving 

 it greenish in appearance until the reac- 

 tion is completed. 



In conclusion the following reasons are 

 submitted for the purpose of offering 



