Tung oil, even when mixed with other vegetable oils, gelatinizes under great heat. The jelly from pure tung oil is insoluble, while adulterated tung oil requires a greater degree of heat and the jelly can be liquefied again with addition of turpentine or benzine and other solvents of this character.
Reaction (by Zucker.) Five c c m tung oil are mixed with 2 c m m each of carbon bisulphide and sulphuric chloride. If the tung oil is pure it will go into a jelly, otherwise it will remain liquid.
Chloroform Iodine Test. One gram of tung oil dissolved in 5 cmm chloroform and then mixed with 5 cmm of a saturated solution of chloroform iodine will gelatinize immediately. When 2 grams of tung oil are used in this mixture, instead of one, the mass will be so firm that it may be pulverized.
Eladin Test (by Ulzer.) Ten grams of tung oil are mixed with 5 grams of nitric acid (42 degrees Be) and one gram mercury and agitated until the mercury is dissolved, then allowed to stand 20 minutes and again agitated or shaken for about a minute. Drying oils become solid under this test in from one to three hours, while non-drying oils remain liquid.
Sulphuric Acid Reaction (by Flatt). One drop of concentrated sulphuric acid on pure tung oil forms at once a dark brown skin, which envelops the acid. This skin becomes black in a very few seconds. This reaction does not take place with raw or bleached linseed oil or other vegetable oils, that might be employed for admixtures with tung oil, but may take place with boiled or bodied linseed oil, but in that case the added drying mediums would be readily detected.
Test for Rosin. A sample of the suspected oil is warmed with 70 per cent alcohol, when the rosin will go into solution, while tung oil is insoluble.
Test for Rosin Oil. Dissolve a sample of suspected oil in its own volume of acetic acid anhydride and add sulphuric acid. When rosin or rosin oil is present there will be a wine red or violet red discoloration of the mixture. (E. W. Boughon at the Seventh International Congress of Applied Chemistry.)
Test for Mineral Oil. When a few drops of the suspected oil are mixed with an alcoholic solution of KOH (hydrated potash), the solution will be clear if the oil is pure, otherwise if mineral be present it will be turbid.