y question is about Determination of Iodine Value in Fats & Oils experiment. I can't seem to get the right IV for coconut oil (Iv = 7-11 range). I followed the procedure used by American Oil Chemists Society, but still I'm getting an IV value of around 1.

Question

y question is about Determination of Iodine Value in Fats & Oils experiment. I can't seem to get the right IV for coconut oil (Iv = 7-11 range). I followed the procedure used by American Oil Chemists Society, but still I'm getting an IV value of around 1. 
The volume of titrant for blank that I got is around 21 mL of 0.1 N Na2S2O3, while with the sample is 18-19 mL.

Accdg to Dr. Bob, it's possible the blank is contaminated. What's the usual volume for blank? Thank you.