370 Transactions. — Chemistry and Physics. 



different weights of resin, so it is evident that these acids are 

 soluble to a limited but definite degree in water, as I used 

 nearly the same volume each time for the determination of 

 HI. After the bromine had been absorbed, and before titrating 

 with Na 2 S 2 3 , I added excess of KI. After the starch blue 

 had been bleached with Na 2 S 2 3 it returned on standing in the 

 light, and this went on slowly, in some cases for many days. 

 When kept in the dark there was practically no change. This 

 residual action amounted to more than 0.6 c.c. decinormal 

 Na 2 S 2 3 , and was seen both in the resin and in the oils dis- 

 tilled from it. I took some of the reduced solution before the 

 blue had had time to reappear, added litmus, and neutralised 

 with decinormal NaOH. Then I blew through it, but instead 

 ■of turning red it only turned purple, the red of the litmus 

 rbeing masked by the blue of the starch iodide. This shows 

 that it is not only HI, but the excess of KI also, which is 

 •oxidized bv some constituent of the resin, with liberation 

 •of I. 



The following is the way in which I derived the figures for 

 the third and fourth columns : — 

 Suppose x grams of Br are taken. 



Let P = part of resin unaffected by Br ; 

 wH = H atoms replaceable by wBr ; 

 yBv = weight of Br which can be added to com- 

 pound : 

 PmH + :rBr = P(nBr) - (?/Br) + nBr + (x — 2n — y)Br. 



yBv = scBr - 2»Br - (x - In - y)Bx 

 (x — %n — y)Br is the excess of Br determined as free I. 

 77.Br is the Br determined as HI. 



To get the total absorption I substract the weight of Br 

 calculated from Na 2 S 2 3 from the weight originally taken and 



, , Br 100 



calculate „, — -r- — -. x —r ' 



Weight ot resin 1 



From the weight of Br used in getting the total percentage 

 absorption I now take twice the weight of Br calculated as 

 HBr, and reckon out the percentage absolution of the remainder 

 with the weight of resin taken. By subtracting the latter per- 

 centage from the former I get the percentage of Br replacing 

 II in the resin and appearing as free HI. I used all ordinary 

 precautions to keep the solution dry, such as heating and dry- 

 ing the flasks before adding Br, and keeping the standard 

 Br solution and resin-oils over CaCl 2 . 



