508. Furfurol Reaction with Sesame Oil.—Olive oil and sometimes butter are mixed with the cheaper body, sesame oil. The latter is detected with certainty, from the red coloration it gives when mixed with furfurol and hydrochloric acid. Instead of furfurol, some body yielding it when subjected to the action of hydrochloric acid, viz., sucrose or a pentose sugar, may be used. It has been found by Wauters, however, that an alcoholic solution of two grams of furfuraldehyd in 100 cubic centimeters of alcohol is the best reagent. One-tenth of a cubic centimeter of this reagent is used for each test.[509]
The test is made as follows: The quantity of the furfuraldehyd solution mentioned above is mixed with ten cubic centimeters of hydrochloric acid, and there are added, without mixing, an equal volume of the suspected oil. On standing, a red coloration is produced at the zone of separation of the two liquids. If the oil be sesame, the coloration is produced instantly. As little as one per cent of sesame in a mixed oil will show the color in two minutes. The manipulation is also varied by shaking together the reagents and the melted butter. Turmeric, which is sometimes used in coloring butter, also gives the rose-red color when treated with hydrochloric acid, but turmeric supplies its own furfuraldehyd. It is easy to distinguish therefore the coloration due to sesame oil, which is developed only when furfuraldehyd is present, from that due to the turmeric, which is produced without the aid of the special reagent.
509. Butter Colors.—Where cows are deprived of green food and root crops, such as carrots, and kept on a poorly balanced ration, the butter made from their milk may be almost colorless. To remedy this defect it is quite a common practice to color the product artificially. Almost the sole coloring matter used in this country is anatto.[510] Other coloring matters which are occasionally employed are turmeric, saffron, marigold leaves, yellow wood (Chlorophora tinctoria), carrot juice, chrome yellow (lead chromate) and dinitrocresol.
The use of small quantities of anatto, turmeric or saffron is unobjectionable, from a sanitary point of view, but this is not the case with such a substance as lead chromate. The detection of anatto or saffron in butter may be accomplished by the method of Cornwall.[511] About five grams of the warm filtered fat are dissolved in about fifty cubic centimeters of ordinary ether, in a wide tube, and the solution is vigorously shaken for from ten to fifteen seconds, with from twelve to fifteen cubic centimeters of a very dilute solution of caustic potash or soda in water, only alkaline enough to give a distinct reaction with turmeric paper, and to remain alkaline after separating from the ethereal fat solution. The corked tube is set aside, and in a few hours, at most, the greater part of the aqueous solution, now colored more or less yellow by the anatto, can be drawn from beneath the ether with a pipette or by a stopcock below, in a sufficiently clear state to be evaporated to dryness and tested in the usual way with a drop of concentrated sulfuric acid.
Sometimes it is well to further purify the aqueous solution by shaking it with some fresh ether before evaporating it, and any fat globules that may float on its surface during evaporation should be removed by touching them with a slip of filter paper; but the solution should not be filtered, because the filter paper may retain much of the coloring matter.
The dry yellow or slightly orange residue turns blue or violet blue with sulfuric acid, then quickly green, and finally brownish or somewhat violet this final change being variable, according to the purity of the extract.
Saffron can be extracted in the same way; it differs from anatto very decidedly, the most important difference being in the absence of the green coloration.
Genuine butter, free from foreign coloring matter, imparts at most a very pale yellow color to the alkaline solution; but it is important to note that a mere green coloration of the dry residue on addition of sulfuric acid is not a certain indication of anatto (as some books state) because the writer has thus obtained from genuine butter, free from foreign coloring matter, a dirty green coloration, but not preceded by any blue or violet-blue tint.
Blank tests should be made with the ether.
Turmeric is easily identified by the brownish to reddish stratum that forms between the ethereal fat solution and the alkaline solution before they are intimately mixed. It may be even better recognized by carefully bringing a feebly alkaline solution of ammonia in alcohol beneath the ethereal fat solution with a pipette, and gently agitating the two, so as to mix them partially.