=494. General Principles.=—The general analysis of butter fat is
conducted in accordance with the methods described in the part of this
volume devoted to the examination of fats and oils. The methods of
sampling, drying, filtering, and of determining physical and chemical
properties, are there developed in sufficient detail to guide the
analyst in all operations of a general nature. There remain for
consideration here only the special processes practiced in butter
analysis and which are not applied to fats in general. These processes
naturally relate to the study of those properties of a distinctive
nature, by means of which butter is differentiated from other fats for
which it may be mistaken or with which it may be adulterated. These
special studies, therefore, are directed chiefly to the consideration
of the peculiar physical properties of butter fat, to its content of
volatile acids and to its characteristic forms of crystallization as
observed with the aid of the microscope. For dietetic, economic and
legal reasons, it is highly important that the analyst be able to
distinguish a pure butter from any substitute therefor.
=495. Appearance of Melted Butter.=—Fresh, pure butter, when slowly
melted, shows after a short time the butter fat completely separated,
of a delicate yellow color and quite transparent. Old samples of
butter do not give a fat layer of equal transparency. Oleomargarin,
or any artificial butter when similarly treated, gives a fat layer
opalescent or opaque. By means of this simple test an easy separation
of pure from adulterated butter may be effected. In mixtures, the
degree of turbidity shown by the separated fats may be regarded as a
rough index of the amount of adulteration. In conducting the work,
the samples of butter, in convenient quantities according to the size
of the containing vessel, are placed in beakers and warmed slowly at
a temperature not exceeding 50°. After a lapse of half an hour the
observations are made.
If one part of the melted butter be shaken with two volumes of warm
water (40°) and set aside for five minutes the fat is still found as an
emulsion, while oleomargarin, similarly treated, shows the fat mostly
separated. This process has some merit, but must not be too highly
valued.[499]
=496. Microscopic Examination of Butter.=—The microscope is helpful in
judging the purity of butter and the admixture of foreign fats, if not
in too small quantity to be of any commercial importance, can easily
be detected by this means.[500] The methods of preparing butter fat
in a crystalline state are the same as those described in paragraphs
=307-309=. The crystals of butter fat differ greatly in appearance
with the different methods of preparation. When butter is melted,
filtered, heated to the boiling point of water and slowly cooled,
it forms spheroidal crystalline masses as seen by the microscope,
which present a well defined cross with polarized light. This cross
is not peculiar to butter fat, but is developed therein with greater
distinctiveness than in other fats of animal origin.
Pure, fresh, unmelted butter, when viewed with polarized light through
a plate of selenite, presents a field of vision of uniform tint,
varying with the relative positions of the nicols. When foreign fats,
previously melted, as in rendering, are mixed with the butter the
crystallization they undergo disturbs this uniformity of tint and the
field of vision appears particolored. Old, rancid or melted butter may
give rise to the same or similar phenomena under like conditions of
examination. The microscope thus becomes a most valuable instrument for
sorting butters and in distinguishing them in a preliminary way from
oleomargarin.
[Illustration: FIG. 112. THERMOMETER FOR BUTYROREFRACTOMETER.]
=497. Judgment of Suspected Butter or Lard by Refractive Power.=—In
discriminating between pure and adulterated butters by the aid of the
butyrorefractometer (=301=), the absolute reading of the instrument is
of less importance than the difference which is detected between the
highest permissible numbers, for any degree of temperature, and the
actual reading obtained at that temperature. These differences, within
certain limits, do not perceptibly vary with the temperature, and
heretofore they have been determined with the aid of a table, and in
this respect the observations have been made the more laborious.
Wollny has rendered these tables unnecessary by constructing a
thermometer in which the mercury column does not indicate degrees of
temperature, but the highest permissible number for butter or lard
at the temperature of observation. The scale of the instrument is so
adjusted as to include temperatures of from 30° to 40°, which renders
it suited to the examination of butter and lard. The oleothermometer is
shown in Fig. 112.
The side of the scale _B_ is for butter and that marked _S_ for lard.
The use of the instrument is the simplest possible. The sample of fat
is placed in the prisms in the usual manner. When the mercury in the
thermometer is at rest, the scale of the instrument is read. In the
case of a butter, if the reading of the scale give a higher number than
that indicated by the thermometer, the sample is pronounced suspicious
and the degree of suspicion is proportional to the difference of the
two readings.
=498. Estimation of Water, Fat, Casein, Ash and Salt.=—The methods
proposed by the author for conducting these determinations, with
minor amendments, have been adopted by the Association of Official
Agricultural Chemists.[501]
_Water._—The sample held in a flat bottom dish is dried to constant
weight at about 100°. The weight of the sample used should be
proportional to the area of the bottom of the dish, which should be
just covered by the film of melted fat. The dish may be previously
partly filled with sand, asbestos or pumice stone. The drying may take
place in the air, in an inert gas or in a vacuum.
_Fat._—The fat in a sample of butter is readily determined by treating
the contents of the dish after the determination of water with an
appropriate solvent.
The process is conducted as follows:
The dry butter from the water determination is dissolved in the dish
with ether or petroleum spirit. The contents of the dish are then
transferred to a weighed gooch with the aid of a wash bottle containing
the solvent, and washed till free of fat. The crucible and contents are
heated at the temperature of boiling water till the weight is constant.
The weight of fat is calculated by difference from the data obtained.
The fat may also be determined by drying the butter on asbestos or
sand, and subsequently extracting the fat by anhydrous alcohol free
ether. The extract, after evaporation of the ether, is dried to
constant weight at the temperature of boiling water and weighed.
_Casein or Curd and Ash._—The crucible containing the residue from the
fat determination is covered and heated, gently at first, gradually
raising the temperature to just below redness. The cover may then be
removed and the heat continued till the contents of the crucible are
white. The loss in weight of the crucible and contents represents
casein or curd, and the residue is mineral matter or ash.
_Salt._—It is the usual custom in the manufacture of butter in this
country to add, as a condiment, a certain proportion of salt. In
Europe, the butter offered for consumption is usually unsalted. A
convenient method of determining the quantity of salt is found in the
removal thereof, from the sample, by repeated washing with hot water
and in determining the salt in the wash water by precipitation with
silver nitrate. The operation is conducted as follows: From five to
ten grams of the sample are placed in a separatory funnel, hot water
added, the stopper inserted and the contents of the funnel well shaken.
After standing until the fat has all collected on top of the water, the
stopcock is opened and the water is allowed to run into an erlenmeyer,
being careful to let none of the fat globules pass. Hot water is again
added to the beaker, and the extraction is repeated several times,
using each time from ten to twenty cubic centimeters of water. The
resulting washings contain all but a mere trace of the sodium chlorid
originally present in the butter. The sodium chlorid is determined in
the filtrate by a set solution of silver nitrate, using a few drops of
a solution of potassium chromate as an indicator.
It is evident that the quantity of salt may also be determined from the
ash or mineral matter obtained, as above noted, by the same process.
If desirable, which is rarely the case, the gravimetric method of
estimating the silver chlorid may be used.
=499. Volatile or Soluble Acids.=—The distinguishing feature of butter,
from a chemical point of view, is found in its content of volatile or
soluble fat acids. Among the volatile acids are reckoned those which
are carried over in a current of steam at a temperature only slightly
higher than that of boiling water. As soluble acids are regarded
those which pass without great difficulty into solution in hot water.
These two classes are composed essentially of the same acids. Of these
butyric is the most important, followed by caproic, caprylic and capric
acids. Small quantities or rather traces of acetic, lauric, myristic
and arachidic acids are also sometimes found in butter. Palmitic,
stearic and oleic acids also occur in large quantities. The above named
acids, in combination with glycerol, form the butter fat.
=500. Relative Proportion of Ingredients.=—The composition of butter
fat is given differently by different authorities.[502] A typical dry
butter fat may be regarded as having the following composition:
Per cent.
Butyrin 7.00
Caproin, Caprylin and Caprin 2.30
Olein 37.70
Palmitin, stearin, etc. 53.00
Pure butter fat consists principally of the above glycerids, some
coloring principles, varying in quantity and composition with the food
of the animal, and a trace of lecithin, cholesterol, phytosterol and a
lipochrome.
=501. Estimation of Volatile or Soluble Acids.=—The volatile or soluble
acids in butter fat are estimated by the methods already described
(=349, 351=). In practice preference is given to the method of
determining volatile acids, based on the principle that under standard
conditions practically all the acids of this nature are secured in a
certain volume of the distillate. This assumption is not strictly true,
but the method offers a convenient and reliable manner of obtaining
results which, if not absolute, are at least comparative.
The quantity of acid distilled is determined by titration with tenth
normal alkali and for convenience the data are expressed in terms of
the volume of the alkali consumed. Five grams of normal butter fat
will give a distillate, under the conditions given, requiring about
twenty-eight cubic centimeters of tenth normal alkali for complete
saturation. This is known as the reichert-meissl number. Occasionally
this number may rise to thirty-two or may sink to twenty-five. Cases
have been reported where it fell below the latter number, but such
samples cannot be regarded as normal butter.
The determination of the reichert-meissl number is the most important
of the chemical processes applied to butter fat analysis.
=502. Saponification Value and Reichert Number.=—It may often be
convenient to make the same sample of butter fat serve both for the
determination of the saponification value and of the reichert number.
For this purpose it is convenient to use exactly five grams of the
dry filtered fat. The saponification may be accomplished either under
pressure or by attaching a reflux condenser to the flask as suggested
by Bremer.[503] When the saponification, which is accomplished with
alcoholic potash lye containing about 1.25 grams in each ten cubic
centimeters of seventy per cent alcohol, is finished, and the contents
of the flask are cooled, the residual alkali is titrated with a set
sulfuric acid solution, using phenolphthalein as indicator. When the
color has almost disappeared, an additional quantity of the indicator
is added and the titration continued until the liquid is of an amber
tint. A sample of the alkali, treated as above, is titrated at the same
time and from the two sets of data obtained, the saponification number
is calculated as indicated in paragraph (=345=).
A few drops of the alcoholic lye are added to the contents of the flask
and the alcohol removed by evaporation. The residual soap and potassium
sulfate are dissolved in 100 cubic centimeters of recently boiled
water, some pieces of pumice added, and the volatile acids removed by
distillation in the usual way after adding an excess of sulfuric acid.
It is important to conduct blank distillations in the same form of
apparatus to determine the magnitude of any corrections to be made.
The size of the distilling flask and the form of apparatus to prevent
mechanical projection of sulfuric acid into the distillate should be
the same in all cases.
=503. Modification of the Reichert-Meissl Method.=—Kreis has proposed
the use of strong sulfuric acid for saponifying the fats, the
saponification and distillation being accomplished in one operation.
A source of error of some inconvenience in this method is due to the
development of sulfurous acid by the reducing action of the organic
matter on the oil of vitriol. Pinette proposes to avoid this difficulty
by adding, before the distillation is begun, sufficient potassium
permanganate to produce a permanent red coloration. By this means the
sulfurous acid is completely oxidized and its transfer to the standard
alkali during distillation entirely prevented. The same result is
accomplished by Micko by the use of potassium bichromate. The details
of the manipulation are as follows:[504]
About five grams of the fused fat (butter or oleomargarin) are placed
in a flask of approximately 300 cubic centimeters capacity. After
cooling, there are added ten cubic centimeters of sulfuric acid
containing three grams of water to each ninety-seven grams of the
strongest acid.
The fat and acid are well mixed by a gentle rotatory motion of the
flask and placed in a water bath at a temperature of 35° (_circa_) for
fifteen minutes. At the end of this time the flask is removed from
the bath and 125 cubic centimeters of water added, little by little,
keeping the contents cool. Next are added four cubic centimeters of a
four per cent solution of potassium bichromate. The contents of the
flask are vigorously shaken and, after five minutes, a solution of
ferrous sulfate is added gradually from a burette until the reaction
with a drop of potassium ferrocyanid shows a slight excess of the iron
salt. The volume of the liquor in the flask is then increased to 150
cubic centimeters by the addition of water and 110 cubic centimeters
distilled. After mixing and filtering through a dry filter, the acid
in 100 cubic centimeters is determined by standard tenth normal barium
hydroxid solution and the number thus obtained increased by one-tenth
representing the total acid obtained.
=504. Elimination of Sulfurous Acid.=—Prager and Stern[505] propose to
eliminate the sulfurous acid by a stream of air, succeeded by one of
carbon dioxid, and proceed as follows: Five grams of the butter fat are
brought into a liter flask, ten cubic centimeters of strong sulfuric
acid are added and the flask is kept for ten minutes at 30-32° with
constant agitation. When the liquid is cold, air is bubbled through
it until the odor of sulfurous acid has disappeared. One hundred
cubic centimeters of water are added, with precautions against rise
of temperature, and carbon dioxid is bubbled through for ten minutes.
This is then displaced by a stream of air for another ten minutes, the
delivery tube is washed into the flask with fifty cubic centimeters
of water and the distillation is effected. The following results are
quoted:
Cubic centimeters of tenth normal alkali required by five grams of
butter fat:
Reichert-Meissl. Prager-Stern.
Sample _a_ 29.86 29.60
” _b_ 30.23 29.65
” _c_ 28.34 27.76
” _d_ 28.20 28.10
The authors do not comment on the possibility of loss of acids
other than sulfurous in the stream of air, but they admit that
further investigation is requisite to render the suggestion of Kreis
serviceable.
=505. Errors Due to Poor Glass.=—The easy solubility of the glass
holding the reagents is the cause of some of the difficulties attending
the determination of the saponification value. The separated silica
tends to carry down, mechanically, a part of the alkali. This is shown
by the fact that after the color has been discharged by titration
with acid and the flask set aside a reappearance of the red color is
noticed, after a time, beginning at the bottom of the flask.[506] In
order to avoid difficulties of this nature, either cold saponification
should be practiced or the digestion vessels used for moist combustion
in sulfuric acid be employed.
Errors may also be easily introduced by the use of uncalibrated
burettes and from the employment of varying quantities of the
phenolphthalein solution.
=506. Estimation of the Molecular Weight of Butter and Butter
Substitutes.=—Garelli and Carono have proposed a method for
discriminating between butter and its substitutes by the kryoskopic
determination of molecular weights.
The molecular weights of stearin, palmitin and olein are 890, 806
and 884, and of butyrin, caproin and caprylin 303, 386 and 470
respectively. Pure butter, therefore, has a lower mean molecular weight
than margarin.
The method and apparatus of Beckmann are used in the determination,
fifteen grams of benzol being employed as a solvent.
The constant for the molecular depression of the benzol is found to be
53.
The molecular weight obtained with samples of pure butter varied from
696 to 716, and for oleomargarin from 780 to 883.
The figures obtained with mixtures of twenty, twenty-five, thirty-three
and fifty per cent of margarin with butter were 761, 720, 728 and 749
respectively. The method can be relied upon to classify samples as
follows: