Cooperative work on fats and oils, Association of official agricultural chemists, 1906

United States Department of Agriculture,

BUREAU OF CHEMISTRY— Circular No. 27.
H. W. WILEY, Chief of Bureau.

COOPERATIVE WORK ON FATS AND OILS, ASSOCIATION OF OFFICIAL
AGRICULTURAL CHEMISTS, 1906.

By L. M. TOLMAN,

Associate Referee on Fats and Oils.

I. PROVISIONAL METHOD FOR THE TITER TEST, ADOPTED IN 1905.

After two years of cooperative work, the following method was recom-
mended and adopted by the Association of Official Agricultural Chemists
at its meeting November 16-19, 1905, as the provisional method for the
titer test :

METHOD.

Weigh 75 grams of fat into a metal dish and saponify by using 60 cc of 30 per
cent sodium hydrate (36° Baume caustic soda) and 75 cc of 95 per cent by
volume alcohol, or 120 cc of water. Boil down to dryness, with constant stirring,
to prevent scorching. This should be done over a very low flame or over an
iron or asbestos plate. Dissolve the dry soap in a liter of boiling water, and if
alcohol has been used boil for forty minutes in order to remove it, adding suffi-
cient water to replace that lost in boiling. Add 100 cc of 30 per cent sulphuric
acid (25° Baume sulphuric acid) to free the fatty acids, boil until they form a
clear, transparent layer, and then wash the fatty acids with boiling water until
free from sulphuric acid. Collect the fatty acids in a small beaker and place
on the steam bath until the water has settled and the fatty acids are clear, then
decant them into a dry beaker, filter, using a hot-water funnel, and dry twenty
minutes at 100° C. When dried, cool the fatty acids to 15° C or 20° C above
the expected titer and transfer to the titer tube, which is 25 mm in diameter and
100 mm in length (1 by 4 inches) and made of glass about 1 mm in thickness.
This is placed in a 16-ounce, salt-mouth bottle of clear glass, about 70 mm in
diameter and 150 mm high (2| by 6 inches), fitted with a cork, which is per-
forated so as to hold the tube rigidly when in position. The thermometer,
graduated to 0.1° C, is suspended so that it can be used as a stirrer, and the
mass is stirred slowly until the mercury remains stationary for thirty seconds.
The thermometer is then allowed to hang quietly, with the bulb in the center of
the mass, and the rise of the mercury observed. The highest point to which it
rises is taken as the titer of the fatty acids. The titer must be made at about
20° C for all fats having a titer above 30° C and at 10° C below the titer for all
other fats.

The fatty acids are tested for complete saponification as follows :
Three cc of the fatty acids are placed in a test tube and 15 cc of alcohol (95
per cent by volume) added. The mixture is brought to a boil and an equal
volume of ammonia (0.96 sp. gr.) added. A clear solution should result, tur-
bidity indicating unsaponified fat.

I f M i\ I i- • ,

STANDARD THERMOMETER.

A standard thermometer of the following description was also adopted :

The thermometer shall be graduated in one-tenth degrees from 10° to 60° C,
with a zero mark, and have an auxiliary reservoir at the upper end, also one
between the zero mark and the 10° mark. The cavity in the capillary tube be-
tween the zero mark and the 10° mark must be at least 1 cm below the 10° mark.
The 10° mark is to be about 3 or 4 cm above the bulb, the length of the ther-
mometer being about 15 inches over all. The bulb shall be of Jena normal 16U1
glass and the thermometer annealed for seventy-five hours at 450° C. The bulb
shall be of moderately thin glass (so that the thermometer will be quick acting)
and be about 3 cm long and 6 mm in diameter. The stem of the thermometer
shall be 6 mm in diameter and made of the best thermometer tubing, with scale
etched on the stem, the graduation clear-cut and distinct, but quite fine. The
thermometer shall be furnished with a felt-lined case.

It was recommended, however, that further study be made of the
method to be employed in drying the fatty acids.

II. DIFFERENTIATION OF THE " COLD TEST" AND THE "CLOUD TEST."

As a result of correspondence with chemists interested, a collection
of the various methods used in this country in making the cold test has
been made. A study of these methods shows that there seem to be two
well-defined tests commonly classified under the title of "cold test."
One is the temperature at which an oil becomes turbid because of the
crystallization of some of the constituents of the oil, and the other is the
temperature at which an oil will flow. In consideration of the fact that
the cloud test very well describes the clouding due to the separation of
the crystals, it would seem to be better to limit the meaning of " cold
test" to that class of tests where the temperature at which the oil will
flow is determined, and "cloud test" to the class of tests in which the
temperature of clouding is obtained. This will enable us to convey a
definite idea when we speak of " cold test" and "cloud test."

There seems to be no doubt that these two tests represent different
determinations. The cloud test gives the temperature at which the
more solid fats or oils begin to crystallize, and when we consider that
all oils are made up of substances varying widely in their crystallizing
points, it would seem hardly possible that the information given by this
test could have the same meaning as a determination of the congealing
point of the whole oil, which is the information given by the cold test.
Moreover, there are two classes of oils to consider — first, the edible oil,
which must remain clear at a certain temperature, and, second, the
lubricating oil, which must flow at a certain temperature. A test like
the "cloud test" is the one to be applied to the edible oils, while the
" cold test," which gives information regarding the temperature at which
the oil will flow, will be the only satisfactory test to apply to lubricating
oils.

COLD TEST.

There seem to be several objections to the method for the cold test
as given by the Prussian State Railway Direction, some of which are
based on its complications, although it seems that the method might
be readily modified so as to be extremely practical and rapid. The
chief objection, however, is the fact that the oil is not stirred in anyway
while cooling, and it is a well-known fact that oils can be cooled to a
considerable degree below their crystallizing points if kept perfectly
quiet, while lubricating oils in actual use are in motion. The chief
advantage of the method is that it eliminates the personal equation as
to whether the oil flows or not. It seems to be the consensus of opin-
ion, however, that a simpler method, such as that used by the Penn-
sylvania Railroad and by the United States Navy Department, with
perhaps some slight modification in the manner of carrying out the test,
would satisfy every requirement of accuracy and speed.

A number of valuable suggestions have been brought out by corre-
spondence with the various chemists. W. H. Low, of the Cudahy
Packing Company, says: "The trouble with all flow tests is that the
solidified oil may move as a piston, owing to the sides of the container
being warmer than the body of the oil." This trouble is overcome to a
certain extent by the scheme suggested by J. P. Millwood, of the Brook-
lyn Navy- Yard, of insulating the bottle with a holder of asbestos pipe
covering. It seems to the referee, however, that even this insulating of
the bottle might be insufficient in many cases, and that perhaps warm-
ing up in a bath not far from the flowing temperature would give better
results. It seems also that the oil should be stirred as it is cooled, in
order to give it a more uniform texture and make the melting more
even. Oil is a mixture of fats of various crystallizing points, and only
by continued stirring while cooling can the various constituents be uni-
formly mixed.

The need of a special thermometer which can be read without remov-
ing from the bottle was noted by Robert Job, of the Philadelphia and
Reading Railroad, and by J. P. Millwood, of the Brooklyn Navy- Yard.
The latter thus describes the thermometer used by him: "The special
thermometers used are graduated in degrees from 0° to 100° F and are
18 inches long, with the zero point about 7 inches above the bulb,
which brings it outside the bottle."

The importance of the element of time in the test has been empha-
sized by several chemists, and it is on this point that we find the greatest
divergence in practice. The experience of many indicates that definite
conditions as regards time will have to be made. It is possible, how-
ever, that in a method requiring continued stirring the time factor would
not be so important.

Thomas Gladding suggests making the cold test by placing the oil in

a bottle which is placed inside another bottle, thus surrounding it with
an air jacket. This is set in a bath of cold water. The oil is constantly
stirred by a mechanical stirrer until it begins to thicken as shown by
the slowing down of the stirrer. Mr. Gladding would have the tempera-
ture lowered very slowly and make the determination in much the same
way as the titer of the fatty acids. He is, however, determining the
congealing point, which is not the determination made in the cold test
as ordinarily practiced, i. e., the melting point of the mixed oils, and
it is hardly to be expected that the congealing points and melting points
will be the same.

In testing the lubricating oils, the oils should be dried, while in test-
ing salad oils where it is desired that the oils remain clear it is evident
that the water must not be removed.

CLOUD TEST.

The cloud test is given by Dr. Manns as follows:

1. The oil must be perfectly dry, because the presence of moisture will produce
a turbidity before the clouding point is reached.

2. The oil must be heated to 150° C over a free flame, immediately before
making the test.

3. There must not be too much discrepancy between the temperature of the
bath and the clouding point of the oil. An oil that will cloud at the tempera-
ture of hydrant water should be tested in a bath of that temperature. An oil
that will cloud in a mixture of ice and water should be tested in such a bath.
An oil that will not cloud in a bath of ice and water must be tested in a bath of
salt, ice, and water.

The test is conducted as follows: The oil is heated in a porcelain casserole
over a free flame to 150° C, stirring with the thermometer. As soon as it can
be done with safety, the oil is transferred to a 4-ounce oil bottle, Which must be
perfectly dry. One and one-half ounces of the oil is sufficient for the test. A
dry Fahrenheit thermometer is placed in the oil, and the bottle is then cooled by
immersion in a suitable bath. The oil is constantly stirred with the thermome-
ter, taking care not to remove the thermometer from the oil at any time during
the test, so as to avoid stirring air bubbles into the oil. The bottle is frequently
removed from the bath for a few moments. The oil must not be allowed to
chill on the sides and bottom of the bottle. This is effected by constant and
vigorous stirring with the thermometer. As soon as the first permanent cloud
shows in the body of the oil, the temperature at which this cloud occurs is noted.

With care, results concordant to within 1° F can be obtained by this method.
The Fahrenheit thermometer is used merely because it has become customary to
report results in degrees Fahrenheit.

The oil must be tested within a short time after heating to 150° C, and a
retest must always be preceded by a reheating to that temperature. The cloud
point should be approached as quickly as possible, yet not so fast that the oil is
frozen on the sides or bottom of the bottle before the cloud test is reached.

This method seems to be entirely satisfactory except that the drying
would not be legitimate when the test is used on salad oils, as moisture
would affect the clearness of these oils as much as crystallized fats. If
the cloud test, as given by Dr. Manns, can be substituted in the testing

of salad oils for the test as given by the New York Produce Exchange,
it would be a great saving of time. It seems to the referee that a
method in which the oil is allowed to remain perfectly quiet can never be
satisfactory.

III. CONCLUSION.

To sum up, it appears from the correspondence that it is practically
agreed that the cloud test and the cold test represent different methods
and do not furnish the same information, but, as Dr. Dudley says, there is
need for both tests; also, that the cloud test is suitable for salad oils
and for testing lubricating oils when the temperature at which they cloud
is desired, and that some modification of the flowing test must be used
for testing lubricating oils. The work thus separates itself into two
parts — first, a study of a method for lubricating oils, and, second, a.
method for salad oils.

As a basis, however, the following method for the cold test is offered
as a starting point. This is practically the one used by J. P. Millwood,
with a few added details suggested by the experience of others.

COLD TEST (MILLWOOD).

Warm the oil until all the stearin is dissolved and filter, through several thick-
nesses of filter paper, into a dry 4-ounce wide-mouth bottle, li ounces of the oil
to be tested; place in a freezing mixture and stir until the oil becomes solid,
then cork and' leave for one hour in the freezing mixture. Take the bottle from
the freezing mixture, wipe it dry, and place in a holder of ordinary magnesia,
asbestos pipe covering, or any suitable holder which will insulate the sides of
the bottle. The frozen oil is broken up and well stirred with the special cold-
test thermometer previously described, and at every degree rise in the tempera-
ture the bottle is inverted ; continue till the oil will run to the other end of the
bottle. The temperature registered at this stage is to be considered the cold test.

The questions at issue on lubricating oils are —

1. Method to be used :

(a) A flowing test ?
(I)} A clouding test?

2. Preparation of oil for analysis :

(a) Shall it be dried, and how?
(6) Shall it be filtered ?

3. Method of cooling:

(a) Shall it be stirred until solid ?

(b) Shall it stand a definite time; and if so, how long?

4. Method of melting :

(a) Shall it be allowed to warm up at room temperature ?
(&) Shall it be warmed up in a bath ?

As regards salad oils —

Can the cloud test be used for the testing of salad oils such as winter cotton-
seed oil ?

Cooperative work along the following lines is requested for the pur-
pose of answering the questions enumerated above :

6

A number of samples of oil will be sent out by the referee to the vari-
ous chemists to be tested —

1. By the method in use in the respective laboratories.

2. By the cloud test as given by Dr. Manns.

3. By the cold test of the Pennsylvania Railroad as modified by
Millwood.

4. In regard to the other points at issue as far as is practicable.

Report of the results should be sent to the referee as soon as possible,
as this is only a preliminary investigation. In the report make any
suggestions or criticisms that may seem pertinent.

Approved :

JAMES WILSON,

Secretary of Agriculture.

WASHINGTON, D. C., February 5, 1906.

O

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