FATS AND OILS
LARD
Lard is very often adulterated with cottonseed oil, cottonseed stearin
and beef stearin. Their being very much cheaper accounts for the
sophistication.
COTTONSEED OIL
_Halphen’s Test._--Dissolve 1 per cent of sulfur in a given volume of
carbon bisulfid. Add an equal volume of amylic alcohol. Mix 3 to 5 cc.
of this reagent with an equal volume of the melted lard in a test tube.
Close with a cotton stopper and boil for 15 minutes in a bath of
saturated brine. The presence of cottonseed oil is indicated by a
deep-red or orange color, little or no color resulting in its absence.
Lard from hogs fed on any of the various cottonseed products may give a
faint reaction when this test is applied.
COTTONSEED STEARIN
Since cottonseed stearin is only the more solid portions of cottonseed
oil, the above test may be applied, but to distinguish it from the
latter it is necessary to make determinations quite beyond the scope of
this set of tests.
BEEF-STEARIN
It is very difficult to identify beef-stearin by chemical tests. It is
usually detected by use of the microscope. Leach gives the following
method: Make a solution of 2 to 5 grams of the fat in 10 to 20 cc. of
ether. Let stand a half day, at about the room temperature. Loosely
stopper the tube with cotton to prevent too rapid evaporation of the
ether. It is well to vary the conditions of heat, amount of solvent, and
rate of crystallization, to get the best possible results. It may often
be well to separate the crystals thus obtained by filtering and
recrystallizing from ether. Separate the crystals that form at the
bottom of the test tube from the liquid portion by pouring on a small
filter. Wash them several times with ether, but not sufficient to remove
the mother liquor entirely. In case it is all removed, and the crystals
are too fragile to mount, add a drop of alcohol. Crystals of lard
stearin are flat rhomboidal plates, one end being oblique to the sides,
and they do not appear to be regularly grouped. Beef-stearin crystals
are rod-shaped, or needles often apparently curved with pointed ends,
and are arranged in clusters like the ribs of a fan, the crystals
radiating from a common point. Under certain conditions the lard
crystals are not irregularly grouped, but are arranged like the parts of
a feather, where one part seems attached to another close at hand.
Considerable experience is necessary to use this test with absolute
certainty.
OLIVE OIL
Olive oil is one of the most commonly adulterated foods. The commonest
adulterant probably is cottonseed oil. Other foreign oils, such as
peanut, sesame, and rape, are sometimes used.
_Preliminary Test._--Pure olive oil turns from a pale to a dark-green
color in a few minutes, when it is shaken with the same volume of
concentrated nitric acid or sulfuric acid. Whenever a reddish to an
orange, or brown coloration results, the presence of a foreign vegetable
oil is indicated (probably a seed oil).
Bach gives the following results of strong nitric acid on the common
oils. Olive oil when shaken with nitric acid gives a pale green, which
changes to an orange yellow after heating five minutes. With similar
treatment peanut oil gives pale rose and brownish yellow; rape oil, pale
rose and orange yellow; sesame oil, white and brownish yellow; sunflower
oil, dirty white and reddish yellow; cottonseed oil, yellowish brown and
reddish brown; castor oil, pale rose and golden yellow.
_Pontet’s Test; Elaiden Test._--Treat 1 cc. of mercury with 12 cc. of
cold nitric acid (sp. gr. 1.42) and shake 2 cc. of this freshly-made
solution with 50 cc. of the sample in a bottle every 10 minutes for 2
hours. Oils which are principally olein, or mixtures of olein and solid
esters like palmatin and stearin, give more or less solid products, but
olive oil is remarkable for the firmness of the canary or lemon-yellow
mass which is formed. After standing a day the mass cannot be pierced
with a glass rod and sometimes it gives forth a sound when struck.
This test requires considerable experience to be used with any great
degree of certainty.
COTTONSEED OIL
Carbon bisulfid containing 1 per cent of sulfur in solution is mixed
with an equal amount of amyl alcohol. Equal volumes (about 3 cc.) of
this reagent and the sample, are mixed in a test tube, which is loosely
stoppered with cotton, and heated in a bath of boiling saturated brine
for a quarter of an hour. The presence of cottonseed oil is shown by the
formation of a deep-red or orange color. Little if any color is produced
in its absence. If no color is produced it is well to add another cc. of
the reagent and heat 5 or 10 minutes more, and to repeat this again if
no color forms. Lard and lard oil from animals fed on cottonseed meal
may give a faint reaction.
PEANUT OIL (ARACHIS OIL)
_Bellier’s Test._--Saponify a gram of the sample with 5 cc. of a
solution of 85 grams potassium hydroxid in a liter of strong alcohol.
This may be done in a small Erlenmeyer flask on the water-bath. Then
boil for two minutes, neutralize exactly with dilute acetic acid (use
phenolphthalein as the indicator). Cool the mixture by placing the flask
in water at 17° to 19° C. A precipitate usually forms. Add 50 cc. of 70
per cent alcohol which contains one per cent by volume of concentrated
hydrochloric acid (sp. gr. 1.2). Shake the flask vigorously and cool
again as before. If no precipitate forms the oil is not adulterated with
peanut oil. The presence of 10 per cent or more of peanut oil produces a
precipitate, even a smaller amount will produce a cloudiness after
standing between 17° and 19° C. for 30 minutes.
Some varieties of olive oil from Tunis give the same turbidity when the
70 per cent alcohol is added. To distinguish these from peanut oil heat
the mixture on the water-bath till everything has dissolved, and cool to
17° to 19°. The cloudiness will not appear if the oil is pure, but will
reappear if peanut oil is present.
SESAME OIL
_Badouin’s Test._--About 0.1 of a gram of cane sugar is dissolved in 10
cc. of hydrochloric acid (sp. gr. 1.20) shaken vigorously with 20 grams
of the sample for a minute or more. After standing for a while the
aqueous solution will separate from the oil. If 1 per cent or more of
sesame oil is present, the aqueous solution will be colored crimson.
_Tocher’s Test._--Dissolve 1 gram of pyrogallic acid in 15 cc. of strong
hydrochloric acid. Add an equal volume of the oil in a separatory
funnel. When it has stood a minute, draw off the aqueous solution and
boil. In the presence of sesame oil it is colored red by transmitted
light, and blue by reflected light.
RAPE OIL
_Palas’ Test._--Make a 1 per cent solution of fuchsin and a 30 per cent
solution of sodium acid sulfite. Mix together 20 cc. of each of these
solutions and add 200 cc. of water and 5 cc. of strong sulfuric acid.
After the solution is decolorized, 10 cc. of the sample is shaken with
it. If rape oil is present, the color will be partially restored. To
prevent the formation of the color by contact with the air have the
vessel full of the mixture.