Recognizing linseed oil

Any oil mixed with sulfuric acid heats up.
Semi-dry oils reach a temperature of 85°C, and linseed oil -- 100°C.
When we add 10 g of sulfuric acid to 50 g of unknown oil, after 2 minutes we get the highest temperature.
If the temperature is 110 ÷ 120°C, then we know that we are dealing with linseed oil, free of impurities.

Iodine number

Unsaturated acids absorb iodine.
The number of iodine absorbed is called the "iodine number."
For domestic linseed oil, this number is 170 (for American linseed oil - 200).
If the iodine number is low, it indicates the presence of numerous impurities.