384 Proceedings of the Royal Society of Edinburgh. [Sess. 
The dilute solutions were made by diluting measured volumes of the strong 
solutions in standard Charlottenburg apparatus. They were then titrated 
again against the thiosulphate solution. 
In order to decide whether such extremely dilute solutions really contain 
the amount of active iodine added and determined by titration, the 
dilution was carried one step further and the following experiments made. 
The actual solutions used ranging from T to ‘001 normal iodine, a -0001 
Fig. 2. — Iodine Concentration Cell, showing Stoppered Electrodes. 
normal iodine solution was therefore prepared and was titrated against a 
*0001 thiosulphate solution, which was made by dilution in the same 
apparatus. 25 c.c. of the iodine solution were decolorised by 23’5 c.c. of 
the thiosulphate solution. It was also found that 1*5 c.c. of the iodine 
solution were required to give a perceptible colour with starch. This 
result was then compared with the E.M.F. readings. The E.M.F. readings for a 
solution of T normal iodine against *001 normal iodine, and of T normal iodine 
against *0001 normal iodine, were taken, the following values being obtained 
— all solutions containing T15 molecules of potassium iodide in 1000 c.c. : — 
T-'OOl = # 0749 volts, 
T-O001 jg T054 volts, 
