Adulterations of tung oil with cheaper materials have been determined, grease, fish oil and mineral oil being the adulterants principally used, and before rosin oil rose to its present height in price it also was quite a favorite for the purpose. To determine the purity of the oil it is necessary to find the specific weight, the saponification number, the iodine value and the Hebner number also. Here is a table of oils and fats: -

Nsa Sana oil is closest to tung oil in its general behavior.

In the following table will be found the results obtained in the determination of chemical and physical constants of tung oil by the most noted authorities on the subject: -

To ascertain the presence of other vegetable oils in tung oil a good test is as follows: - A sample of appreciable volume of the oil is saponified with Na O H and the resulting soap disintegrated with H2S4O, the precipitate, well washed and the fatty acid that has been separated is well dried. This must not melt below 97 degrees Fahrenheit, for if it does it may be taken for granted that other oils have been present in the sample. While in many varnishes the presence of tung oil can be readily determined by its characteristic odor, this is not always an infallible guide, because in many well prepared varnishes that contained from 20 to 25 per cent of tung oil the odor has been absent. Still in most varnishes of moderate selling price, even when, on account of a strong turpentine odor, the presence of tung oil is not at once noticeable, it will reveal itself by its odor on setting up when the turpentine has evaporated.