iodine monochloride (ICl) in glacial acetic acid, which became known as Wijs's solution, dropping the reagent. Alternatively, J. Hanuš used iodine monobromide (IBr), which is more stable than ICl when protected from light. Typically, fat is dissolved in chloroform and treated with excess ICl/IBr. Some of the halogen reacts with the double bonds in the unsaturated fat while the rest remains. R-CH=CH-R' + \underset{(excess)}{ICl} -> R-CH(I)-CH(Cl)-R' + \underset{(remaining)}{ICl} Then, saturated solution of potassium iodide (KI) is added to this mixture, which reacts with remaining free ICl/IBr to form potassium chloride (KCl) and diiodide (). ICl + 2 KI -> KCl + KI + I2 Afterward, the liberated is titrated against sodium thiosulfate, in presence of starch, to indirectly determine the concentration of the reacted iodine. I2{} + \underset{(blue)}{starch}{} + 2 Na2S2O3 -> 2 NaI{} + \underset{(colorless)}{starch}{} + Na2S4O6 is calculated from the formula : Where: is the difference between the volumes, in mL, of sodium thiosulfate required for the blank and for the sample, respectively ; is the normality of sodium thiosulfate solution in Eq/ L ; 12.69 is the conversion factor from mEq sodium thiosulfate to grams of iodine (the molecular weight of iodine is ) ; is the weight of the sample in grams. The determination of IV according to Wijs is the official method currently accepted by international standards such as DIN 53241-1:1995-05, AOCS Method Cd 1-25, EN 14111 and ISO 3961:2018. One of the major limitations of is that halogens does not react stoichiometrically with conjugated double bonds (particularly abundant in some drying oils). Therefore, Rosenmund-Kuhnhenn method makes more accurate measurement in this situation. Kaufmann method Proposed by H. P. Kaufmann in 1935, it consists in the bromination of the double bonds using an excess of bromine and anhydrous sodium bromide dissolved in methanol. The reaction involves the formation of a bromonium intermediate as follows: Then the unused bromine is reduced to bromide with iodide (). Br2 + 2 I- -> 2 Br- + I2 Now, the amount of iodine formed is determined by back-titration with sodium thiosulfate solution. The reactions must be carried out in the dark, since the formation of bromine radicals is stimulated by light. This would lead to undesirable side reactions, and thus falsifying a result consumption of bromine. For educational purposes, Simurdiak et al. (2016) suggested the use of pyridinium tribromide as bromination reagent which is more safer in chemistry class