(_f_) Several portions of the oil are placed upon a porcelain slab and separately treated with a few drops of concentrated sulphuric acid, nitric acid, and a solution of potassium dichromate in sulphuric acid, and notice taken of the colours produced, comparative tests being simultaneously made with olive oil of undoubted purity. (_g_) The presence of sesamé oil is readily detected by the formation of a deep green colour when the oil is agitated with a mixture of equal parts of nitric and sulphuric acid. (_h_) Upon mixing samples containing cotton-seed oil with an equal volume of nitric acid (40° B.) a coffee-like colour is produced. Olive oil gives a pale green, rape and nut, a pale rose, and sesamé oil a white-coloured mixture. The presence of rape- and cotton-seed oils may also be detected as follows:--Dissolve 0·1 gramme silver nitrate in a very little water, and add about 4 c.c. of absolute alcohol. This solution is added to the sample of olive oil to be tested, the mixture well shaken and put aside for one or two hours; it is then to be heated for a few minutes. If cotton-seed or rape-seed oil is present, the oily stratum which separates on standing will exhibit a brownish-red or blackish colour, due to the reduction of silver. Olive oil fails to cause an appreciable coloration. Experiments made by the author with samples of olive oil containing 10 per cent. of cotton-seed and rape-seed oils furnished the following results:--On standing one hour, without heating, the mixture containing cotton-seed oil showed a slightly dark colour, that adulterated with rape-seed oil a decidedly dark colour; upon the application of heat, the former exhibited a dark-red colour, while the latter turned quite black.