Case 3. The oil is apparently vegetable in origin. Take, as before, the " actual density" :— Now proceed to use the reagents in the capsules, putting 5 drops of the reagent (from the dropping-tubes) into 10 drops of oil, and stirring ; note the following effects : 1. Barium polysulphide goes very pale-yellow only with inferior olive, ground-nut, and castor ; and greenish with hempseed and very bad olive. The density throws out castor and hempseed, and only ground-nut and inferior olive are left. Try zinc chloride, when olive gives a green, and ground-nut s yellow. Confirm ground-nut by saponifying, and throwing up the fatty acids with hydrochloric acid. Then dry them, and dissolve in 4 parts of alcohol of 85°. To this, add an excess of rectified spirit, when, if ground-nut-oil be present, white flakes of arachidic acid will deposit ; these may be collected, dried, and weighed. By treating pure ground-nut-oil side by side, the percentage of it in a mixture may be deduced.
2. Zinc chloride gives a green or greenish-yellow with olive, rape, colza, almond, linseed, and cotton. Olive and colza are green, linseed yellow or greenish-yellow, rape yellow, cotton (when heated) brownish, while almond is milky with a greenish tinge. The density excludes definitely linseed and cotton ; it remains to distinguish between the others. Try stannic chloride, when, if a green be produced, it is rape or colza; olive and almond respectively give faint-yellow or no colour. If it be not rape or colza try phosphoric acid, which will decolorize almond-oil, and turn olive-oil green. To distinguish between linseed and cotton, if required, try sulphuric acid ; linseed goes orange-yellow, while cotton goes deep reddish-brown.
8. Sulphuric acid. There only now remain to be considered poppy- and nut-oils. The former becomes dark-brownish by agitation with sulphuric acid, while the latter only goes orange-yellow.
Having thus ascertained, by the density and reactions, the purity of the oil, and named it, the next case is that of a mixed vegetable oil ; it is here that the experience comes into play. Tho most valuable help [in addition to the " actual density," and the full tables of reactions of all the oils hereafter appended (see pp. 1472-5), as devised by Chateau, and somewhat modified by the present writer, who uses by preference a different reagent for the first group], consists in the following process, originally proposed by Maurnene". 50 grm. of the oil are carefully weighed into a tube, the temperature is taken with the long delicate thermometer (No. 15), 10 c.c. of absolute sulphuric acid (reagent No. 12) are added from a pipette, and the whole is rapidly stirred with the thermometer until it ceases to rise, and the number of degrees through which it has gone np are registered. According to the originator, we should get the following results, in about 2 minutes, the results being constant if the acid be used of the same strength, and the surrounding tempera ture be kept equable :— The phenomenon is easily defined and observed, and gives distinctions much more characteristic than those yielded by any of the former methods. The phenomena remain the same if two oils are
mixed together. Thus two measures of olive-oil and one of poppy-oil should show: 2 vol. olive-oil = 2 x 108 = 216 1 vol. poppy-oil = 1 x 187.5 = 3 vols. mixture, 103.5° F.
Or 1 vol. = 134.5° F.
and the experiment really gives this result, as has been ascertained by repeated trials with this and other mixtures.
In practice, the present writer did not succeed well with this process, for although he occasion ally came up to these figures, yet the use of so hygroscopic an article as absolute sulphuric acid is always uncertain ; he is, therefore, now in the habit of using the following process :— Preserve some pure sulphuric acid, of sp. gr. 1.845, in a well-stoppered and capped bottle, never leaving the stopper out for more than the moment required to extract some of the contents. Get a tin vessel about 5 in. deep and capable of holding at least 2 qt. of water. Have some glass tubes on feet, capable of standing heat, about 11 in. in diameter, and holding about 7 oz. of liquid. Have the acid in a bottle 6 in. high, with a thermometer inside. Counterbalance the tube, and weigh in accurately 50 firm. of the oil. Raise the water in the tin vessel to 28° (82° F.), immerse both the sulphuric acid bottle and, the tube in the water, and place the long thermometer inside the latter. As soon as both the acid and the oil are at a temperature of 27° (80° F.), draw out 10 c.c. of the former with a pipette, and let it flow gradually (at the rate of 1 c.c. every 5 seconds) into the latter without touching the sides, stirring all the time with the thermometer. After all the acid is in, continue to stir rapidly for exactly minute, keeping the tube in the water with one hand and stirring with the other, and then move the thermometer more slowly, noting the exact degree at which it ceases to rise. From that, deduct 80, and the difference is the amount of rise. Treated in this way, and using a definite hydrated acid, the rise of temperature is not quite so great, but it is (at least in the writer's hands) much more constant. With him, olive-oil gives a rise of 106° F., rape-oil of 131° F., and so on, very nearly in proportion to the original figures. It cannot, however, be too strongly impressed that every one using this process must fix his own standards according to his own method of working, and that a pure standard oil should always be done in precisely the same manner immediately before the suspected article. For this reason, the writer prefers not to give his own tables of results, as no two persons, unless actually working side by side, will ever get absolutely identical figures.