20 GENERAL METHODS 



marks the end-point. The calculation is again c.c. for c.c. From 

 the calculated strength figure out the amount of dilution necessary 

 to make an exactly N/10 Na2S2Os solution. 



(c) Iodine Solution. Measure out 25 c.c. of iodine solution in a 

 beaker and dilute with 200 c.c. water. Run in the N/ 10 thiosulphate 

 solution from a burette until the iodine color becomes pale yellow. 

 Then add 2 c.c. starch solution; the first drop that causes the blue 

 color to disappear marks the end-point. The calculation is again 

 c.c. for c.c. From the calculated strength figure out the amount 

 of dilution necessary to make an exactly N/10 iodine solution. 



