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ANALYSIS OF MILK
AND
MILK PRODUCTS
LEFFMANN
SANITARY RELATIONS OF THE
COAL-TAR COLORS
BY
THEODORE WEYL
AUTHORIZED TRANSLATION BY
HENRY LEFFMANN
i2mo. 154 Pages. Cloth, net $1.25
EXAMINATION OF WATER
FOR SANITARY AND TECHNICAL PURPOSES
Seventh Edition, Revised
Illustrated. i2mo. Cloth, net $1.25
ORGANIC CHEMISTRY
A COLLEGE TEXT-BOOK
BY
Henry Leffmann and Charles H. La Wall
i2mo. Illustrated. Cloth, net $1.00
SELECT METHODS IN FOOD
ANALYSIS
BY
Henry Leffmann and William Beam
Second Edition, Revised
i2mo. Cloth, net $2.50
I Plate and 54 Illustrations
ALLEN'S COMMERCIAL ORGANIC
ANALYSIS
VOLUME 8 CONTAINS:
Methods of Analysis of Milk and Milk-Prod-
ucts, Meat and Meat-Products, Proteins, Pro-
teoids. Fibroids and Enzyms.
8vo. 696 Pages. $5.00 net
ivifhy
ANALYSIS OF MILK
AND
MILK PRODUCTS
BY
HENRY LEFFMANN, M. D.
PROFESSOR OF CHEMISTRY IN THE WOMAN'S MEDICAL COLLEGE OF
PENNSYLVANIA AND IN THE WAGNER FREE INSTITUTE OF
SCIENCE OF PHILADELPHIA; PATHOLOGICAL CHEMIST
TO JEFFERSON MEDICAL COLLEGE HOSPITAL
FOURTH EDITION, REVISED AND ENLARGED
WITH ILLUSTRATIONS
THE FIRST TWO EDITIONS OF THIS WORK WERE
PREPARED AND ISSUED UNDER THE JOINT AUTHOR-
SHIP OF HENRY LEFFMANN AND WILLIAM BEAM
PHILADELPHIA "^ \
BLAKISTON'S SON & CO.
1012 WALNUT STREET
Copyright, 1915, by Henry Leffmann
THK MAPI<B FHB8B X O K K FA.
PREFACE
This book is intended as a guide to the analysis
of milk and milk products in the routine of the
commercial and food-inspection laboratory.
Only processes of practical value have been given,
and nothing has been said as to the food value
of milk and its products, nor concerning the ef-
fects of the several adulterants that may be
detected.
A notable portion of the text has been taken
from Volume 8 of the Fourth Edition of Allen's
Commercial Organic Analysis. I am indebted to
the courtesy of Messrs. P. Blakiston's Son & Co.
for. permission to use this matter.
An interesting point is to be noted in the com-
parison of this edition with the first, issued about
a score of years ago in association with Dr.
William Beam. In that, a considerable part of
the material was derived from the publications
of foreign workers ; in the present, American in-
vestigations form the basis of many of the im-
portant processes.
" Westward the star of empire takes its way."
H. L.
Philadelphia.
CONTENTS
Milk. Page
Analytic Data and Processes 1-64
Milk Products.
Cream 65-68
Condensed Milk 69-8O
Butter 81-96
Cheese 97-109
Fermented Milk Products 110-113
Index
vii
MILK
ANALYTIC DATA
Milk, the nutritive secretion of nursing mam-
mals, contains water, fat, proteins, sugar, and
mineral matter. Cow's milk is meant in all
cases, unless otherwise stated. Milk as taken
from the animal is generally termed "whole
milk."
Fat. — This occurs in globules varying from
0.0015 mm. to 0.005 J^J^- ill diameter, in a
condition which prevents spontaneous coales-
cence. It is peculiar among animal fats in
containing a notable proportion of acid radicles
with a small number of carbon atoms.
Proteins. — The nature of the proteins of
milk has been much discussed, but it is now
generally conceded that there are at least three
forms, casein, albumin, and globulin, the casein
being present in by far the greatest amount,
and the globulin as traces only.
Casein. — Casein is probably in part in
combination with phosphates. It is precipi-
2 MILK
tated by many substances, among which are
acids, rennet, and magnesium sulfate, but not
by heat. Acids precipitate it by breaking up
the combination with phosphates. The action
of rennet is complex and probably partly hy-
hydrolytic, splitting the casein into several
proteins, some of which are precipitated in
the curd. Films of protein matter occur abun-
dantly in milk, for which reason it is distinctly
opaque, even when nearly all the fat has been
removed by contrifugal action.
The albumin of milk appears to be a distinct
form, and is called lactalbumin. It is not
precipitated by dilute acids, but is coagulated by
heating to 70° — 75°. The proportion in cow's
milk is usually from 0.35 to 0.50%, but col-
ostrum may contain much larger proportions.
Globulin is present only in minute amounts
in normal milk, but colostrum may contain as
much as 8%. It is coagulated on heating.
Lactose. — This is a sugar peculiar to milk.
Citric acid is a normal constituent of the milk
of various animals. In human milk, the quantity
is about 0.5 gram to 1000 c.c; in cow's milk,
from I to 1.5 grams. It is not dependent on
the citric acid present in the food.
Enzyms. — Several enzyms occur in milk but
they are chiefly known by effects and not as
isolated substances. Some are proteolytic, others
ANALYTIC DATA 3
are oxydases, that is, decompose hydrogen per-
oxid and carry oxygen over to other substances.
Lecithin is also a usual ingredient of milk.
Nerking and Haensel found a range in cows'
milk from 0.03 to 0.11%.
Mineral Matter. — The ash of milk contains
calcium, magnesium, iron, potassium, and sodium
as chlorids, carbonates, sulfates, and phos-
phates. It does not exactly represent the salts
present in milk.
Richmond has determined the ratio of the
ash to the solids not fat in 135 samples of milk.
This was found to range from 7.8 to 9.4%,
but more usually from 7.8 to 8.5 (average 8.2) %.
Many ashes were alkaline to turmeric, litmus,
and phenolphthalein, the maximum alkalinity
being 0.025% calculated as sodium carbonate.
Human milk is notable for a low protein
content hence the curd is less bulky and more
friable than that from cows' milk. The milk
of all animals is subject to modification by breed,
climate, season, feed, housing, exercise, time
of lactation, and in human beings (and possibly
in some other animals) by psychic influences.
As regards the proportion of proteins and
lactose, milks of the mare and ass agree closely
with human milk.
Normal milk is an opaque white or yellowish-
white fluid, with an odor recalling that of the
4 MILK
animal, and a faint sweet taste. The opacity-
is due largely but not entirely to the fat globules.
The reaction of freshly drawn milk to litmus is
usually alkaline, but is sometimes amphoteric;
that is, it turns the red paper blue and the blue
paper red. The sp. gr. varies between 1.027
and 1.035. It usually undergoes a gradual
augmentation (sometimes termed Recknagel's
phenomenon) for a considerable time after the
sample has been drawn. The increase may
amount to two units (water being 1000). The
sp. gr. becomes stationary in about five hours
if the milk is maintained at a temperature
below 15°, but at a higher temperature it may
require twenty-four hours to acquire constancy.
The change is not entirely dependent on the
escape of gases.
Unless collected with special care and under
conditions of extreme cleanliness, milk always
contains many bacteria, animal matter of an
offensive character, such as epithelium, blood
and pus cells, particles of feces, and soil.
At ordinary temperature milk soon undergoes
decomposition, by which the milk sugar is
converted principally into lactic acid, and the
proteins partly decomposed and partly coagu-
lated. The liquid becomes sour and the fat is
inclosed in the coagulated casein. In the initial
stages of decomposition the proteins frequently
ANALYTIC DATA 5
undergo transformations into substances which
are the cause of the violent poisonous effects
occasionally produced by ice-cream and other
articles of food into the preparation of which
milk enters.
Boiling produces coagulation of the albumin,
some caramelization of the sugar, and develops
a greater facility of coalescence on the part of
the fat globules. Enzyms are rendered inert
and most microbes are killed.
When milk is allowed to stand, some of the fat
rises gradually and forms a rich layer, constituting
cream. The proportion of cream depends on
several conditions. The amount formed in a
given time cannot be taken as a measure of the
richness of the milk. Water added to milk
causes a more rapid separation of the cream.
Centrifugal action separates nearly all of the fat.
The following figures, given by D'Hout as aver-
ages, show this effect :
Whole Separated ro-.u
Milk Milk Ckeau
Specific gravity 1032 1034 1015
Total solids 14 . 10 9.6 26 . 98
Sugar 4.70 5.05 3.32
Casein 3-50 3 . 62 2 . 02
Ash 0.79 0.78 0.58
Fat 5.05 0.20 21.95
Buttermilk is the residue after removal of the
butter by churning. Vieth gives the following
analyses :
6 MILK
Total «._ Solids not *«„
Solids ^^^ Fat ^^^
9.03 0.63 8.40 0.70
8.02 0.65 7.37 1.29
10.70 0.54 10.16 0.82
Whey or Milk-serum is the liquid freed from
curd after precipitation by rennet or acids. In
most cases it contains a notable amount of
proteins, as shown in the following analyses by
Cochran :
Milk Whey
Total solids Solids not fat Total solids J'emovSd
9.27 9.13 6.62 2.51
927 9.13 6.1 3.03
14.05 8.35 6.62 2.33
7.71 7.61 5.98 1.63
8.91 8.71 6.50 2.21
The whey of any given milk has practically the
same composition, whether taken from the
original milk, skimmed milk, or cream.
Average Proportion of Solids in Milk. — The
most extensive data on this point are those
obtained by Vieth. The total number of samples
was 120,540. The averages of the entire series
are as follows :
Fat 4.1%
Non-fatty solids 8.8%
Total solids 12.9%
Lythgoe gives a table of averages of composi-
tion of 51 samples of genuine milk, each set of
ANALYTIC DATA
averages being deduced by analysis of lo samples.
The following data are selected from this table.
For explanation of the figures in the last column
see page 42.
Total
Solids
Pat
Pro-
teins
Lac
TOSE
Ash
Solids
NOT
Fat
Refraction
OF Copper
Serum 30°
15.70
6.01
4.13
4.79
0.77
9.69
38.1
1500
5.62
3.75
87
0.76
9.38
38.3
14.50
5.30
3.61
82
0.77
9.20
38.3
14.00
4.78
3.51
98
0.73
9.22
38.5
13.50
4.61
3.37
n
0.75
8.89
38.1
13 00
4.24
3.17
86
0.73
8.76
37.9
12.50
3.99
2.84
94
0.73
8.51
38.0
12.00
3.45
2.88
96
0.74
8.55
37.7
11.50
3.33
2.67
80
0.70
8.17
37.3
11.00
302
2.64
63
0.71
7.98
370
10.70
2.90
2.60
49
0.71
7.80
36.4
From these figures Lythgoe derives the riile
that differences in proportion of solids not fat in
unadulterated milks are principally due to dif-
ferences in the amount of proteins. Lactose and
ash are fairly constant. On these facts depend
recently introduced methods of detecting water-
ing milk, as will be pointed out later.
Colostrum. — ^This is the secretion in the early
stages of lactation, and differs from ordinary
milk. It contains characteristic structures,
known as colostrum corpuscles, and usually
contains much less fat than fully developed
milk, but a larger proportion of proteins. Colo-
strum coagulates on boiling. Lactose is in small
amount.
ANALYTIC PROCESSES
Specific Gravity. — The sp. gr. of milk rises
gradually for some time after it has been drawn,
and the determination is to be made only after
this action has ceased. This will require about
five hours after the milk is drawn, if it has been
kept 15°, but at a higher temperature it will be
necessary to allow at least twelve hours. For
all other determinations the milk must be ana-
lyzed as soon as possible. The following figures,
published by Bevan, show that a considerable
loss in total solids may occur in twenty-four
hours :
Evaporated immediately . . .
Evaporated after 24 hours,
Evaporated after 48 hours,
Evaporated after 120 hours.
The decomposition is very irregular, and it is
not possible to determine, by estimation of the
lactic acid or other products, the original compo-
sition of the milk.
Air-bubbles are held rather tenaciously by milk,
and care must be taken in mixing, preparatory
to taking the sp. gr., to avoid as far as possible
8
Total Solids
Loss
11.73
10.79
0.94
10.38
1.35
9.42
2.31
ANALYTIC PROCESSES 9
the inclosure of the air, and to allow sufficient
time for the escape of any bubbles that may be
present. Sp. gr. is understood to be taken at i $ . 5° ;
samples should be brought near to this. If at
a few degrees above or below, it will suffice to
make the determination at once and obtain the
correct figure by reference to the annexed table.
The sp. gr. of normal milk ranges between
1.027 and 1.035. The figure alone does not
indicate the character of the sample, but taken
in conjunction with the figure for fat or for
total solids, it is of value as a check on the
results furnished by other determinations.
The simplest method of determining sp. gr. is
by the lactometer, a delicate and accurately gradu-
ated hydrometer. The instrument must be im-
mersed carefully so as not to wet the stem above
the point at which it will rest. Its accuracy
should be verified by immersion in distilled
water at 15.5° and milks of known sp. gr.
More accurate determinations may be made
with a balance. A special form, the Westphal
balance, is adapted to the determination of
sp. gr. only, the weights being so arranged
that a simple enumeration of them gives the
gravity directly. The cheap forms of this in-
strument are not satisfactory, but some made
by German houses are excellent. The ordinary
lO
MILK
Find the temperature of the milk in one of the horizontal lines
and the sp. gr. in the first vertical column. In the same line
with this and the temperature the correct figure is given.
"F.
50
51
52
53
54
55
56
57
58
59
60
61
62
Sp.Gr.
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
20.2
21.2
22.2
23.2
24.1
25.1
26.1
27.0
28.0
29.0
20.3
21.3
22.3
23.3
24.2
25.2
26.2
27.1
28.1
29.1
20.3
21.3
22.3
23.3
24-3
25.2
26.2
27.2
28.2
29.1
20.420.5
21.4
22.4
23-
24.4
20.6
2I.52I.6
22.5
5
24.5
423
22.6
23
24.6
8
8
8
623.6123.7
24.624.7
720.
721.
722.
92
25.3
26.3
27.
28.3
29.2
25.4
25.5
26.426.5
.427.5
327
28.428.5
29.3
29.4
25
26.6
27.6
28.i
29.6
625
7
26.7
27.7
7
29.7
628
29.930.030.1
30.931.0
31.831.932.0
32.7
33.633.833.934
30.2
31.2
32.1
33.1
.0
30.430.5
31.431.5
30.3
31.3
32.332.432.5
33.2
34.2
33-3
33.5
34.334.5
30.6
31.6
32.6
33.6
34
20.9
21.
22.8
23.8
24.8
25.8
26.8
27.8
28.8
29.8
30.8
31.7
32
33.7
.7
20.9
1.9
22.9
23
24
21.0
21. 1
22.022.1
23.0
O
.0
924
925
23.1
24.1
25.1
25.9
26.9
27.9
28.
29
26.026.1
27.027.1
28.0
.0
o
929
930
634
30.9
31.9
.9
33
34.9
732
31.0
32.0
33.0
.0
35.0
934
28.1
29.1
30.1
31.2
32.2
33.2
34.2
35.2
21.2
22.2
23.2
24.2
25.2
26.2
27.3
28.3
29.3
30.3
31.2
32.3
33.3
34.3
35.3
lO.O
10.5
II. I
11.612.2
12.7
13.3
13.8
14.4
15.0
15.5
16.1
16.6
analytic balance may also be used. A plummet
consisting of a thick glass rod (or short sealed
tube, weighted with mercury) of a bulk of about
10 c.c. is suspended from the hook of the balance
by means of fine platinum wire and the weight
ascertained. It is then submerged in distilled
water and the weight also noted. The water is
contained in a narrow upright cylinder resting
ANALYTIC PROCESSES
II
Find the temperature of the milk in one of the horizontal lines
and the sp. gr. in the first vertical column. In the same
line with this and the temperature the correct figure is given.
63
64
65
66
67
68
69
70
71
72
73 74
75
21.3
22.3
23.3
243
253
21.4
22.4
23.4^23. 523623
24.424.524.6^4
25-425-5
26.3
27.4
28.
29.4
30.
428
17.2
21.5
22.5
21.6
22.6
21.7
22.7
25.625
21.8
22.8
723.8
724.9
7259
26.
27-5
5
29.5
.5
526.
430
27.6
28.6
29.6
30.7
626.7
27.7
26.8
27.8
28.728.8
29.829.9
30.830.9
431
632
31.
32.5
33-5
34-5
35.535-635
•5
32
33.6
34.6
31.
7
33.
34-8
.8
731
27.0
28.0
29.0
30.1
31. 1
.832.0
32.933.0
9|34
34.935.0
35.936.1
833
17.7
18.3
18.8
32.2
33.2
.2
35.2
36.2
034
22.0
23.0
24.0
25.0
26.0
27.1
28.1
29.1
30.2
31.2
32.2
33.3
34.3
35.3
36
22.1
23.1
24.1
25.1
26
22.2
23.2
24.2
25.2
.2
126
22.3
23.3
24.3
25.3
26
22.4
23.
24.
25.5
.5
22.5
.5
423
426
22.6
23.7
424.624.7
25.7
8
27.3
28.3
27.427.5
28.
428
27.2
28.2
29.2
30.3
31. 331. 531. 631
29.429.5
30.430.5
628.7
29.729
30.7
.8
433
32.432.5
33
34.5
35.535.635.8
.5
633.7
34.634.7
32.632.832
33.923
34.935.1
436
36.7
36.8
36.0
37.0
19.4
20.020.5
21. 121. 622. 2
25.6
26.
626.
27.727.8
28.9
9
o
.1
30.
31.
829.
931.
932
033
034
I
,2
35.2
36.3
3
237
22.723.3
23.8
on a bench or support above the scale pan.
The loss of weight of the plummet is, of course,
the weight of the biilk of water that it displaces.
The sp. gr. of any sample can be determined by-
weighing the plummet immersed in the sample
and dividing the loss in weight by the loss in
water. The quotient is the sp. gr.
The ordinary pyknometer is not convenient
12 MILK
on account of the liability of the upper layer
of the liquid to be richer in fat than the lower ;
the overflow, therefore, does not represent the
mixture.
Total Solids. — This determination may often
be made with sufficient accuracy for practical
purposes by evaporating a measured volume
(e. g., 3 or 5 c.c.) in a shallow nickel dish from 5
to 8 cm. in diameter. Nickel crucible-covers are
suitable. The thin glass (Petri) dishes used for
microbe culture are convenient. When greater
accuracy is required, and especially when the
ash is to be determined, platinum dishes are the
most satisfactory, but owing to the present price
of this metal, quartz dishes are now much used.
Either the translucent or transparent quartz is
suitable, the former being less expensive.
Good results may be secured as follows : A flat
dish, 3.5 cm. in diameter, with sides 0.5 cm. high,
is provided with a thin flat watch-glass cover
that fits rather closely. The total weight of the
cover and dish is noted. 2 or 3 c.c. of the sample
are run into the dish from the pipet, the watch-
glass placed on, and the weight taken as rapidly
as possible. The glass prevents appreciable
loss from evaporation during an ordinary weigh-
ing. The cover is removed, the dish heated on
the water-bath or in the water-oven, and weighed
from time to time (with cover on it) until the
ANALYTIC PROCESSES 13
weight is sensibly constant. The percentage
of residue can be easily calculated. About three
hours may be required to secure constant weight.
When high accuracy is not essential, it will
suffice to measure the milk. Vieth advised a
pipet graduated to deliver 5 grams, and found
that, working with whole and skimmed milk,
under the ordinary variations of temperature,
the error will not exceed o.i on the total solids
and less on the fat. The pipet should have a
rather wide opening so that no cream will be
retained.
The Massachusetts State Board of Health has
for many years used the routine method of
evaporating 5 grams for two hours in a flat plati-
num basin over boiling water.
The A. O. A. C. method is: Heat at 100° to
constant weight, about 3 grams in a tared plati-
num, aluminum or tin dish of 5 cm. diameter,
with or without the addition of 15 to 30 grams
of sand. Cool and weigh.
Ash. — The residue from the determination of
total solids is heated cautiously over the Bunsen
burner, until a white ash is left.. The result
obtained in this manner is apt to be slightly low
from loss of sodium chlorid. This may be
avoided by heating the residue sufficiently to
char it, extracting the soluble matter with a few
c.c. of water, and filtering (using paper extracted
14 MILK
with hydrofluoric acid). The filter is added to
the residue, the whole ashed, the filtrate then
added, and the liquid evaporated carefully to
dryness. The ash of normal milk is about 0.7%
and faintly alkaline. A marked degree of alka-
linity and effervescence with hydrochloric acid
will suggest the addition of a carbonate.
The method of the A. O. A. C. is as follows : In
a weighed dish put 20 c.c. of milk from a weighing
bottle; add 6 c.c. of nitric acid, evaporate to
dryness, and bum at a low red heat till the ash
is free from carbon.
Fat. — Many methods for fat determination
have been devised. The following will suffice for
all practical work:
Adams' Method. — This consists essentially in
spreading the milk over absorbent paper, drying,
and extracting the fat in an extraction apparatus;
the milk is distributed in an extremely thin layer,
and by a selective action of the paper the larger
portion of the fat is left on the surface. A
paper, manufactured especially for this purpose
by Schleicher & Schuell, is obtainable in strips
of suitable size. Each of these yields to ether
only from o.ooi to 0.002 gram of extract.
Coils made of thick filter-paper, cut into
strips 6 by 62 cm., are thoroughly extracted
with ether and alcohol, or the weight of the ex-
tract corrected by a constant obtained for the
ANALYTIC PROCESSES 1 5
paper. From a weighing bottle about 5 grams
of the milk are transferred to the coil by means
of a pipet, care being taken to keep dry the end
of the coil held in the fingers. The coil is
placed, dry end down, on a piece of glass and dried
for one hour, preferably in an atmosphere of
hydrogen; it is then transferred to an extraction
apparatus and extracted with absolute ether,
petroleum spirit of boiling-point about 45° or,
better, carbon tetrachlorid. The extracted fat
is dried and weighed.
The above procedure is very satisfactory, but
the drying in hydrogen may usually be omitted.
After the coil has received at least twenty wash-
ings, the flask is detached, the ether removed by
distillation, and the fat dried by heating in an
air-oven at about 105°, and occasionally blowing
air through the flask. After cooling, the flask
is wiped with a piece of silk, allowed to stand
ten minutes, and weighed.
Richmond states that to perform a rigidly
accurate determination attention to the following
points is necessary : The ether must be anhydrous
(drying over calcium chlorid and distilling is
sufficient). Schleicher & Schuell's fat-free papers
should be used, and one should be extracted
without any milk on it, as a tare for the others.
Four or five hours' extraction is necessary, and
l6 MILK
the coils should be well dried before extraction is
begun.
Thimble-shaped cases made of fat-free paper
are now obtainable and are convenient for holding
the absorbent material on which the milk is
spread. The fine texture prevents undissolved
matter escaping. A case may be used repeatedly.
Sour milk may be thinned with ammonium hy-
droxid before taking the portion for analysis.
Babcock Asbestos Method. — This is recom-
mended by the A. O. A. C. : Provide a hollow
cylinder of perforated sheet metal 60 mm. long
and 20 mm. in diameter, closed 5 mm. from one
end by a disk of the same material. The per-
forations should be about 0.7 mm. in diameter
and 0.7 mm. apart. Fill the cylinder loosely with
from 1.5 to 2.5 grams of freshly ignited woolly
asbestos free from fine or brittle material.
Cool in a desiccator and weigh. Introduce a
weighed quantity of milk (about 4 grams) and
dry at 100°. The cylinder is placed in the ex-
traction tube and extracted with ether in the
usual way. The ether is evaporated and the fat
weighed. The extracted cylinder may be dried
at 100° and the fat checked by the loss in weight.
A higher degree of accuracy is secured by per-
forming the drying operation in hydrogen.
For thorough extraction, especially with diffi-
culty soluble materials and volatile solvents, the
ANALYTIC PROCESSES 1 7
continuous extraction apparatus devised by
Szombathy, but commonly called the Soxhlet
tube, is most suitable.
The material may be placed in a fat-free paper
thimble and covered with a plug of cotton to
prevent loss of fine particles. In place of the
cotton plug, a porcelain or platinum Gooch
crucible may be used, as shown in the cut.
The top of the thimble should be a short dis-
tance below, and the top of the crucible a short
distance above, the bend of the siphon. The
thimble should be supported by a section of
glass tubing, i to 2 cm. long, with rounded
edges ; the edge on which the thimble rests should
be a little uneven to prevent a close joint, which
would hinder the siphoning of some of the
liquid.
Alundum cylinders will probably be useful.
Loss of solvent by leakage often occurs. It
may be diminished somewhat by soaking the
corks in rather strong hot gelatin solution,
draining them quickly and then exposing them
for some hours to formaldehyde vapor.
The solvents most generally employed are
ether and petroleum spirit, but carbon tetra-
chlorid is well adapted for extraction purposes
as it has high solvent power for fats and is not
easily inflammable.
When extraction is completed, the carton and
l8 MILK
materials may be removed from the tube, and,
replacing the parts of the apparatus, much of
the solvent may be redistilled into the extractor,
thus recovering the liquid. Care must be taken
not to distil the contents of the flask closely or
heat strongly, lest some of the more volatile of
the dissolved matters pass into the distillate.
Roese-Gottlieb Method. — This is now being used
for milk-products as well as for milk. For de-
tailed description, see page 72.
Centrifugal Methods. — Although almost all the
fat of milk may be separated by the centrifuge,
the emulsion is not destroyed and the volume of
cream is merely suggestive as to the fat-content
of the milk. To obtain a clear fatty layer in
condition for close measurement it is necessary
to use chemicals. The methods at present most
employed depend essentially on one devised by
Gustaf DeLaval, who took out a patent in Sweden
for the use of a mixture of twenty volumes of
strong acetic acid and one volume of strong
sulfuric acid. This mixture coagulates and then
dissolves the proteins, destroys the emulsion, but
does not otherwise affect the fat and does not
act on the lactose. By brief whirling in a cen-
trifuge the fat collects in a clear sharply defined
layer. DeLaval took out patents in several
countries subsequent to the above date.
Lefimann and Beam devised a method in which
ANALYTIC PROCESSES 1 9
a small amount of amyl alcohol with an equal
volume of hydrochloric acid was added to the
milk, and the proteins thus coagulated dissolved
by strong sulfuric acid. About the same time
Babcock devised a process in which sulfuric acid
was used alone. Subsequently Gerber published
a process in which the essential feature of the
Leffmann-Beam method, namely, the use of amyl
alcohol, was advised.
The test-bottles have a capacity of about 30 c.c.
and are provided with a graduated neck, each
division of which represents 0.1% by weight
of butter fat.
15 c.c. of the milk are measured into the
bottle, 3 c.c. of a mixture of equal parts of amyl
alcohol and strong hydrochloric acid added,
mixed, the bottle filled nearly to the neck with
concentrated sulfuric acid, and the liquids mixed
by holding the bottle by the neck and giving it a
gyratory motion. The neck is now filled to
about the zero point with a mixture of sulfuric
acid and water prepared at the time. It is then
placed in the centrifugal machine, which is so
arranged that when at rest the bottles are in a
vertical position. If only one test is to be made,
the equilibrium of the machine is maintained by
means of a test-bottle, or bottles, filled with a
mixture of equal parts of sulfuric acid and water.
After rotation for from one to two minutes, the
20 MILK
fat will collect in the neck of the bottle and the
percentage may be read off. It is convenient to
use a pair of dividers in making the reading.
The legs of these are placed at the upper and lower
limits respectively of the fat, allowance being made
for the meniscus; one leg is then placed at the
zero point and the reading made with the other.
Rxperience by analysts in various parts of the
world has shown that with properly graduated
bottles the results are reliable. As a rule, they
do not differ more than o.i % from those obtained
by the Adams process, and are generally even
closer.
For great accuracy, the factor for correcting
the reading on each of the bottles should be de-
termined by comparison with the figures obtained
by the Adams or other standard process.
Cream is to be diluted to exactly ten times its
volume, the sp. gr. taken, and the liquid treated
as a milk. Since in the graduation of the test-
bottles a sp. gr. of 1.030 is assumed, the reading
must be increased in proportion.
A more accurate result may be obtained by
weighing in the test-bottle about 2 c.c. of the
cream and diluting to about 15 c.c. The read-
ing obtained is to be multiplied by 15.45 and
divided by the weight in grams of cream taken.
The mixture of fusel oil and hydrochloric acid
seems to become less satisfactory when long
ANALYTIC PROCESSES 21
kept. It should be clear and not very dark in
color. It is best kept in a bottle provided with a
pipet which can be filled to the mark by dipping.
Rigid accuracy in the measurement is not needed.
[The Leffmann-Beam method is often erro-
neously called the "Beimling" method, but
Beimling was merely the deviser of a cheap
centrifuge. To protect the interest of a manu-
facturer who had invested in the Beimling
machine under the impression that it was a
practicable method for fat estimation, it became
necessary for Leffmann and Beam to take out a
patent (now expired) and assign the same to this
investor.]
Calculation Methods. — Several investigators
have proposed formulae by which when any two
of the data, sp. gr., fat, and total solids, are
known, the third can be calculated. These differ
according to the method of analysis employed.
That of Hehner and Richmond, as corrected
by Richmond, was deduced from results by the
Adams method of fat extraction. It is:
T = 0.25 6^ -j- 1.2 F + 0.14;
in which T is the total solids, G the last two figures
of the sp. gr. (water being looo), and F the fat.
Patrick has proved that with American milks the
constant should be dropped, the formula reading :
T = 0.25 G -{- 1.2 F
22 MILK
Babcock's formula has been much used in the
United States. It is adapted to calculating the
solids not fat. In this formula g is the entire
figure for sp. gr. referred to water as i.
Snf^( ^^^^-^g -x)x2.5 (100-/)
•^ \ioo- 1.0753 /g /^ ^ ^ -^^
Babcock has also given a much simpler form
adapted for total solids. This differs but slightly
from Richmond's.
Total Proteins. — 3 types of processes are
employed for this estimation: Calculation from
the total nitrogen; precipitation and direct
weighing; calculation from the "aldehyde-figure. "
Milk contains appreciable amounts of non-
protein nitrogen, but the fact is usually disre-
garded. According to Munk, this may range, in
cow's milk, from 0.022 to 0.034%, and from
0.014 to 0.026% in human milk. By these
figiu-es, the average protein nitrogen in cow's milk
would be 94%, and in human milk 91%, of the
total nitrogen.
Kjeldahl-Gunning Method. — (Calculation from
total nitrogen).
Reagents :
Potassium sulfate. — A coarsely powdered form
free from nitrates and chlorids should be selected.
Sulfuric acid. — This should have a sp. gr.
1.84 and be free from nitrates and ammonium.
ANALYTIC PROCESSES 23
Standard acid, — ^/a Sulfuric or hydrochloric
acid, the strength of which has been accurately
determined.
Standard alkali. — ^ /jo Ammonium hydroxid, so-
dium hydroxid, or barium hydroxid, the strength
of which in relation to the standard acid must
be accurately determined.
Sodium hydroxid solution. — 500 grams should
be added to 500 c.c. of water, the mixture al-
lowed to stand until the undissolved matter
settles, the clear liquor decanted and kept in a
stoppered bottle. It will be an advantage to
determine approximately the quantity of this
solution required to neutralize 20 c.c. of the
strong sulfuric acid.
Indicator. — Cochineal solution is recommended
by the A. O. A. C, but methyl-orange and sodium
alizarin-monosulfonate are satisfactory. Methyl-
orange solution should be very dilute; i part in
1000. A drop is sufficient for 100 c.c. of liquid.
Phenolphthalein is not well adapted to tritation
of ammonium compounds.
Digestion and distillation flasks. — Jena-glass
round-bottomed flasks with a bulb 12.5 cm.
long and 9 cm. in diameter, the neck cylindrical,
1 5 cm. long and 3 cm. in diameter, flared slightly
at the mouth.
Process
5 c.c. of the sample are placed in a digestion
24 MILE
flask, lo grams of powdered potassium sulfate
and 15 to 25 c.c. (ordinarily about 20 c.c.) of the
strong sulfuric acid are added and the diges-
tion conducted as follows: The flask is placed
in an inclined position and heated below the
boiling-point of the acid for from five to fifteen
minutes, or until frothing has ceased. Excessive
frothing may be prevented by the addition of
a small piece of paraffin. The heat is raised
until the acid boils briskly. A small, short-
stemmed funnel may be placed in the mouth
of the flask to restrict the circulation of air.
No further attention is required until the liquid
has become clear and colorless, or not deeper
than a pale straw.
When Kjeldahl operations are carried out in
limited number, the arrangement used in my
laboratory has been found very satisfactory. A
double- Y, terra cotta drain-pipe, about 20 cm.
internal diameter, is connected by an elbow
directly with the chimney-stack. The digestion
flasks are supported as shown in the rough
sketch, figure i (not drawn exactly to scale).
Two flasks can be operated at once. The
central opening is convenient for other opera-
tions producing fumes. Openings not in use
are closed by circles of heavy asbestos.
Apparatus for use when many determinations
are made are figured in the catalogs of supply-
ANALYTIC PROCESSES 2$
houses. As corrosive vapors are given off, it
must be placed under a hood; but a special
form of apparatus is now made which does not
require an escape-pipe.
When the liquid has become colorless or very
light straw yellow, it is allowed to cool, diluted
with I GO c.c. of water if the smaller form of
Fig. I.
flask has been used, the liquid transferred to
the distilling flask, and the digestion flask rinsed
with two portions of water, 50 c.c. each, which
are also transferred to the distilling flask. With
the larger form of flask the dilution is made at
once by the cautious addition of 200 c.c. of
water. Granulated zinc, pumice stone, or 0.5
26 MILK
gram of zinc dust is added. 50 c.c. of the strong
sodium hydroxid solution, or sufficient to make
the reaction strongly alkaline, should be slowly
poured down the side of the flask so as not to mix
at once with the acid solution. It is convenient
to add to the acid liquid a few drops of phenol-
phthalein or azolitmin solution, to indicate when
the liquid is alkaline, but it must be noted that
strong alkaline solutions destroy the former
indicator. The flask is shaken so as to mix the
alkaline and acid liquids and at once attached to
the condensing apparatus. The receiving flask
should have been previously charged with a
carefully measured volume of the ^ /^ acid (10 c.c.
diluted with distilled water to 100 c.c. is a
convenient amount). The distillation is con-
ducted until about 150 c.c. have passed over.
A small amount of indicator is added, the liquid,
titrated with standard alkali, and the amount
neutralized by the distilled ammonium hydroxid
determined by subtraction. Each c.c. of ^Va
acid neutralized is equivalent to 0.007 nitrogen.
The nitrogen multiplied by 6.38 gives the
total proteins.
The distillation in this operation requires
care, as the amount of ammonium hydroxid is
determined by its neutralizing power, hence
solution of the alkali of the glass will introduce
error. Common glass is not satisfactory. Block
ANALYTIC PROCESSES 27
tin is a good material. Moerrs found that Jena-
glass tubes resist the action of the ammonium
hydroxid. Distillates should be titrated promptly
as alkali may be dissolved from the glass.
A satisfactory condensing arrangement for
general laboratory use is a copper tank of good
size, through which several condensing tubes pass.
Aldehyde Number. — The addition of formalde-
hyde to milk increases the acidity by an action on
the proteins. As commercial formaldehyde is
always acid, the acidity must be either determined
or neutralized in applying the following method.
The application of the reaction to determination
of proteins in milk is due to Steinegger. Rich-
mond and Miller investigated the method and
suggested the use of strontium hydroxid instead
of sodium hydroxid. Richmond gives the
following details:
To 10 c.c. of milk at least i c.c. of a 0.5%
solution of phenolphthalein is added and the
liquid neutralized with standard strontium hy-
droxid solution. To the faintly pink liquid, 2
c.c. or more of 40% formaldehyde solution are
added and the titration made to the same tint
as the former. The strontium hydroxid required
by the formaldehyde solution must be known,
and this being deducted from that which was
used in the titration and the remainder calculated
28
MILK
to c.c. ^/i acid per looo c.c. of milk will give
the ''aldehyd number." Richmond finds that
this multiplied by o. 1 7 gives in most cases a close
approximation to the total proteins obtained by
the Kjeldahl method.
Calculation Method. — Olson has shown that in
normal milks the proteins may be calculated with
close approximation by the formula
p = t-
1.34
in which p is protein and t total solids.
Determination of special proteins. —
Casein and albumin may be determined by S6be-
lein's method: 20 c.c. of the sample are mixed
with 40 c.c. of a saturated solution of magnesium
sulfate and powdered magnesium sulfate stirred
in until no more will dissolve. The precipitate
of casein and fat, including the trace of globulin,
is allowed to settle, filtered, and washed several
times with a saturated solution of magnesium
sulfate. The filtrate and washings are saved for
the determination of albumin. The filter and
contents are transferred to a flask and the
nitrogen determined by the method described
above. The nitrogen so found, multiplied by
6.38, gives the casein.
The filtrate and washings from the determina-
ANALYTIC PROCESSES 29
tion of casein are mixed, the albumin precipitated
by Almen's tannin reagent, filtered, and the
nitrogen in the precipitate determined as above.
The same factor is used.
Almen's reagent is prepared by dissolving 4
grams of tannin in 190 c.c. of 50% alcohol and
adding 8 c.c. of acetic acid of 25%.
In a mixture of milk and whey (prepared with
rennet) in about equal parts, Richmond and
Boseley found about 0.3% of albumoses not pre-
cipitated by the copper sulfate nor by magnesium
sulfate, but precipitable, along with the albumin,
by a solution of tannin. The separation may be
effected by diluting the filtrate from the magne-
sium sulfate precipitation, acidifying slightly with
acetic acid, and boiling, when the albumin will be
coagulated and precipitated. The albumoses
may be separated by filtering the solution and
precipitating with tannin solution. The pre-
cipitated proteins are best estimated by de-
termining the nitrogen in the moist precipitate.
The separation of the proteins may be effected,
though less accurately, but the use of acetic acid,
as recommended by Hoppe-Seyler and Ritt-
hausen.
Leffmann and Beam have modified the process
to avoid the delay and trouble of washing the
precipitate, as follows: 10 c.c. of the milk are
mixed with saturated magnesium sulfate solu-
30 MILK
tion and the powdered salt added to saturation.
The mixture is washed into a graduated measure
with a small amount of the saturated solution,
made up to loo c.c. with the same solution,
mixed, and allowed to stand until the separation
takes place. As much as possible of the clear
portion is drawn off with a pipet and passed
through a dry filter. An aliquot portion of the
filtrate is taken, the albumin precipitated by a
solution of tannin, and the nitrogen in the
precipitate ascertained as above.
The following are A. O. A. C. methods:
I. Provisional Method for the Determination of
Casein in Cows' Milk. — The determination should
be made when the milk is fresh. When it is not
practicable to make the determination within
twenty-four hours, add one part of formaldehyd
to 2 500 parts of milk and keep in a cool place. 10
grams of the sample are diluted with about 90 c.c.
of water at between 40° and 42°, 1.5 c.c. of a
solution containing 10% of acetic acid by weight
added, allowed to stand for five minutes, washed
three times by decantation, pouring the washings
through a filter, and the precipitate transferred
completely to the filter. If the filtrate is not
clear at first, it will generally become so in two
or three filtrations, after which the washing can
be completed. The nitrogen in the washed
precipitate and filter is determined by the
ANALYTIC PROCESSES 3 1
Kjeldahl- Gunning method. The nitrogen, multi-
pHed by 6.38, gives the casein.
In working with milk which has been kept
with preservatives, the acetic acid should be
added in small portions, a few drops at a time with
stirring, and the addition continued until the
Hquid above the precipitate becomes clear or
nearly so.
2. Provisional Method for the Determination of
Albumin in Milk. — The filtrate obtained in the
above operation is neutralized with sodium
hydroxid, 0.3 c.c. of the 10% solution of acetic
acid added, and the mixture heated for fifteen
minutes. The precipitate is collected on a filter,
washed, and the nitrogen determined.
Van Slyke has pointed out that the casein can
be approximately ascertained by multiplying
the figure for total proteins by 0.8.
Modified Proteins, Amino-derivatives and Am-
monium Compounds. — The following procedures
are given by Van Slyke. The filtrate from the
albumin precipitate is heated to 70°, i c.c. of
5% sulfuric acid added, then solid zinc sulfate
to saturation. The mixture is allowed to stand
at 70° until the caseoses settle. The liquid is
cooled, filtered, the precipitate washed with
saturated solution of zinc sulfate slightly acidified
with sulfuric acid and the nitrogen ascertained
by the Kjeldahl method.
32 MILK
For amino-derivatives and ammonium com-
pounds, 50 c.c. of the milk are mixed in a flask
marked at 250 c.c. with i gram of sodium chlorid.
A 12 % solution of tannin is added, drop by drop,
until no further precipitation occurs. The mix-
ture is diluted to the mark, shaken and filtered
through a dry filter. For amino-derivatives, 50
c.c. of the filtrate are treated for nitrogen in the
usual way. For ammonium compounds, 100 c.c.
of the filtrate are mixed with magnesium oxid
and about 50 c.c. distilled, the distillate being
received in a known volume of standard acid.
Large excess of magnesium oxid must be avoided.
Lactose. — For this determination, A. O. A. C.
employs Soxhlet's method with the following
reagents :
Copper sulfate solution. — 34.639 grams of pure
crystallized copper sulfate are dissolved in water
and made up to 500 c.c.
Alkaline tartrate solution, — 173 grams of pure
sodium potassium tartrate and 50 grams of good
sodium hydroxid are dissolved in water and the
solution made up to 500 c.c.
Sodium hydroxid ^ /^,
25 c.c. of the sample in a 500 c.c. flask are
diluted with 400 c.c. of water and 10 c.c. of the
copper sulfate solution and 8.8 c.c. ^/^ sodium
hydroxid solution added. The mixture should
ANALYTIC PROCESSES 33
still have an acid reaction and contain copper in
solution. If this is not the case, the experiment
must be repeated, using a little less of the
alkali. The flask is filled to the mark with water,
shaken, and the liquid passed through a dry filter.
50 c.c. of Fehling's solution, obtained by mixing
equal parts of the above copper sulfate and
alkaline tartrate solutions, are heated to brisk
boiling in a 300 c.c. beaker, 100 c.c. of the filtrate
obtained as above added, and boiling continued
for six minutes ; the liquid then promptly filtered,
and treated according to methods given below.
The amount of lactose is calculated by the table
on page 34 from the copper obtained by table.
The figures for weights of copper between any
two data given in the table may be calculated
with sufficient accuracy for practical purposes by
allowing 0.0008 gram of lactose for each o.ooi
gram of copper.
The precipitated cuprous oxid is usually con-
verted into free copper and weighed as such.
Two methods may be employed for reduction:
by hydrogen or by electrolysis.
Reduction by Hydrogen. — The curpous oxid is
collected on an asbestos filter. This is arranged
most conveniently in a special filtering tube,
which is shown in figure 2. The wider part is
about 8 cm. and 1.5 cm. in diameter, the narrower
portion about 5 cm. long and 0.5 cm. in caliber.
34
MILK
A perforated platinum disk is sealed in just
above the point of narrowing. The asbestos is
placed on this disk, washed free from loose fibers,
dried well, and the tube weighed. The filtering
tube is attached to an exhaustion apparatus by-
passing narrower portion through the cork, and a
Copper
Lactose
Copper
Lactose
Copper
Lactose
O.IOO
0.072
0.205
O.151
0.305
0.228
0.105
0.075
0.210
0.154
0.310
0.232
O.IIO
0.079
0.215
0.158
0.315
0.236
0.II5
0.083
0.220
0.162
0.320
0.240
0.120
0.086
0.225
0.165
0.325
0.244
0.125
0.090
0.230
0.169
0.330
0.248
0.130
0.094
0.235
0.173
0.335
0.252
0.135
0.097
0.240
0.177
0.340
0.256
0.140
O.IOI
0.245
O.181
0.345
0.260
0.145
0.105
0.250
0.185
0.350
0.264
0.150
0.109
0.255
0.189
0.355
0.268
0.155
0.II2
0.260
0.192
0.360
0.272
0.160
O.II6
0.265
0.196
0.365
0.276
0.165
0.120
0.270
0.200
0.370
0.280
0.170
0.124
0.275
0.204
0.375
0.285
0.175
0.128
0.280
0.208
0.380
0.289
0.180
0.132
0.285
0.212
0.385
0.293
0.185
0.134
0.290
0.216
0.390
0.298
0.190
0.139
0.295
0.221
0.395
0.302
0.195
O.I4I
0.300
0.224
0.400
0.306
0.200
0.147
ANALYTIC PROCESSES 35
small funnel is fitted tightly in the top of the tube.
The object of this funnel is to prevent the pre-
cipitate collecting on the upper part of the tube.
The lower end of the funnel should project several
centimeters below the bottom of the cork through
which it passes.
The filtering apparatus must be arranged
prior to the precipitation, so that the cuprous
oxid may be filtered without delay. The pre-
cipitate is transferred as rapidly as possible to
the filter, well washed with hot water, alcohol,
and ether successively, dried, and the cuprous
oxid reduced by gentle heating in a current of
hydrogen. When the reduction is complete,
the heat is withdrawn, but the flow of hydrogen
is continued until the tube is cold. It is then
detached and weighed.
Reduction of Copper by Electrolysis. — The fil-
tration is performed in a Gooch crucible with
an asbestos-felt film and the beaker in which the
precipitation was made is well washed with
hot water, the washings being passed through
the filter, but it is not necessary to transfer
all the precipitate. When the asbestos film is
completely washed, it is transferred with the
adhering oxid to the beaker; any oxid remaining
in the crucible is washed into the beaker by use
of 2 c.c. nitric acid (sp. gr. 1.42), added with a
pipet. The crucible is rinsed with a spray of
36 MILK
water, the rinsings being collected in the beaker.
The liquid is heated until all the copper is in
solution, filtered, the filter washed until the
filtrate amounts to at least 100 c.c, and elec-
trolyzed.
Electrolytic apparatus has been constructed
in a great variety of forms. When the opera-
tion is carried out frequently, it is best to have
an electrolytic table. A platinum basin holding
not less than 100 c.c. is used. A cylindrical form
with flat bottom is convenient. It should rest
on a bright copper plate, which is connected
with the negative pole of the electrical supply.
The positive pole should be also platinum, either
a spiral wire, cylinder, or flat foil. Many
operators use a funnel-shaped perforated ter-
minal for the negative pole; in which case a glass
beaker or casserole will be a suitable container,
the positive terminal being placed within the
negative.
Four cells of a gravity battery will suffice
for a single decomposition, and will operate
two, but more slowly. It is usual to arrange
the apparatus so that the operation may be
continued during the night. When the elec-
tricity is taken from the general supply of the
laboratory, it is usually necessary to interpose
resistance and to have some means of measuring
the current-flow. This is sometimes done with
ANALYTIC PROCESSES
37
u
a gas evolution cell and incandescent lamp, but
an ammeter and adjustable rheostat are better.
Lactose may be determined by the polarim-
eter after removal of the fat and proteins,
which is best effected, as recommended by
Wiley, by acid mercuric nitrate
solution. Wiley prepared this by
dissolving mercury in twice its
weight of nitric acid of 1.42 sp. gr.
and adding to the solution five vol-
umes of water, but Revis and Bol-
ton advise that mercuric oxid
should be used. The A. O. A. C.
optical method is as follows:
For polarimeters reading to 100
for 26.048 grams sucrose (corre-
sponding to 32.98 grams lactose),
measure, in c.c, the amount ob-
tained by dividing double this (i.e.,
65.96) by the sp. gr., add 10 c.c. mercuric nitrate
solution, make up to 102.6 c.c, shake, filter
through a dry filter and examine in a 200 mm.
tube. Half the observed reading will be the per-
Bl centage of lactose. For example, if the sp. gr.
^B of the milk is 1.030, the amount taken will be
^m 65.90 -r- 1.030 = 64 c.c.
^B The allowance for volume of precipitate by
^B making up to 102.6 c.c. is not accurate, except
^B with closely skimmed milks.
K
\
Pig. 2.
38 MILK
The correction may be made more closely by
calculating the actual volune of the precipitate
by multiplying the fat-percentage by 1.075
(average specific volume of fat) and the protein-
percentage by 0.8 (average specific volume of
coagulated proteins), deducting the sum of these
products from 100 c.c. and correcting the ob-
served reading by proportion. For ordinary
milk, the volume of the proteins from 65.96
grams may be taken at 1.68 c.c. Supposing
the sample to contain 4.0% of fat and the
polarimetric reading to be 10, the calculation
would be thus:
65 . 96 X o . 04 = 2 . 63 Amount of fat in milk taken
2 . 63 X 1 . 075 = 2 . 82 c.c. Volume of fat in precipitate
1 . 68 c.c. Est. vol. of proteins in precipitate
4 . 50 c.c. Total volume of precipitate
100 — 4.50 = 9 . 55 c.c. Actual volume of liquid.
100 : 95 . 5 : : 10 : 9.55 9.55 4-2 = 4.75, per cent, lactose.
The employment of a factor for correcting
for the volume of precipitate may be avoided by
Scheibler's method of "double dilution," in
which two solutions of different volume are
compared. The following is a summary of the
method given by Wiley & Ewell: For polari-
meters adapted to a normal weight of 26.048
sucrose, 65.82 grams of milk are placed in a
100 c.c. flask, 10 c.c. of the acid mercuric nitrate
ANALYTIC PROCESSES 39
added, the flask filled to the mark, the contents
well mixed, filtered, and a reading taken. A
similar quantity of the milk is placed in a 200
c.c. flask and treated in the same way. The true
reading is obtained by dividing the product of
the two readings by their difference. If the
observations are made in a 200 mm. tube the
percentage is half the true reading.
The instrument should be accurate, and great
care taken in the work, or the results will be less
satisfactory than by the method first described,
in which an allowance is made for the volume of
the precipitate.
Multirotation. — When freshly dissolved in cold
water, lactose shows a higher rotation than that
given above. By standing, or immediately on
boiling, the rotary power falls to the point
mentioned. In preparing solutions from the
solid, therefore, care must be taken to bring them
to the boiling-point previous to making up to a
definite volume. This precaution is unnecessary
when operating on milk.
Acidity. — Milk being often amphoteric to lit-
mus, that indicator cannot be employed in
estimating acidity. Phenolphthalein is usually
employed. Several methods differing in details
have been proposed. Probably the best is that
of Thorner. In this, 10 c.c. of milk are diluted
with 20 c.c. of water, a few drops of a dilute
4
40 MILK
alcoholic solution of phenolphthalein added and
the titration made with standard alkali. Thomer
proposes that the number of c.c. required should
be multiplied by lo and the result termed the
*' degree of acidity." Fresh normal milk will
show figures ranging from i6 to i8. When the
degree of acidity is 23 or over, the sample will
coagulate on heating.
The process involves a slight error, in that the
addition of a notable amount of water to a milk
sample disturbs somewhat the relation of the
phosphates and diminishes the acidity. It may
be advisable to titrate the undiluted milk. If
the number of c.c. used is multiplied by 0.9 the
lactic acid equivalent to the acidity of the sample
is given in grams per 1000 c.c.
DETECTION OF ADULTERATION
By far the larger part of the laboratory work on
milk is for assistance in the sanitary control of the
supply, and the analyses are principally directed
to the detection of the ordinary forms of adultera-
tions. The most important of these are: skim-
ming, watering and use of coloring, thickening
and preserving agents. Skimming and watering
are detected by determining fat and total solids;
from these data the solids not fat are calculated.
For the ordinary purposes of milk control, fat
can be estimated with quite sufficient accuracy
by centrifugal methods. The total solids may be
estimated directly as described on page 12, or
calculated from the sp. gr. and fat as indicated on
page 21.
Judgment whether a given sample has been
skimmed or watered depends in many cases upon
the standard for whole milk. Some irregularity
of standards for fat and solids not fat exists, and
the opinion of the analyst will be determined,
therefore, by the standard of the locality. In
most cases the standard for fat is between 3 and
4%, and that for total solids about 8.50%.
As fat diminishes the sp. gr. of milk, and the
41
42 MILK
other solids increase it, it is possible to take off
a small amount of the former and add some
water without disturbing the sp. gr., but, of
course, the above analytical methods will detect
this procedure. It is now admitted that, except
in cases of wide departure from the usual limits,
the adulteration of milk cannot be detected by
the sp. gr. alone but the employment of a care-
fully graduated lactometer is of use in routine
milk inspection.
Direct Detection of Added Water. Serum-refrac-
tion,— Of late years several methods have been
proposed for this purpose but most of them have
no positive value and have not come into general
use. The refractive index of the whey (milk-
serum) offers a rapid and satifactory method for
detecting watering. Several methods of pre-
paring this whey have been proposed, but
Lythgoe has found, as the result of extended
experience, the following to be satisfactory.
Dissolve 7.25 grams of crystallized copper sulfate
in water and dilute to 1000 c.c. If this solution
does not refract 36 on the scale of the immersion
refractometer at 20°, add water or copper sulfate
until the desired result is obtained. To 8 c.c.
of the copper solution add 32 c.c. of milk. Shake
well and pour upon a dry filter. When the filtrate
begins to come through clear, change the receiver,
pour the small quantity of cloudy filtrate upon
At
DETECTION OF ADULTERATION 43
the filter and continue the filtration as usual.
Refract the clear filtrate at 20°, by means of the
Zeiss immersion refractometer. A reading below
36 indicates added water. The advantages of
this method over the acetic acid method are as
follows: It is quicker, heating of the samples is
unnecessary, consequently there is no error due
to evaporation. The range of differences in the
refraction of pure milk is less. 10% of added
water will reduce the refraction of high-grade
milk below the minimum, but it takes 1 5 % in the
acetic acid method. Lythgoe made analyses
of 150 samples of milk of known purity by this
method. The total solids ranged from 17.17 to
10.40%, the fat from 7.7 to 2.45%, the solids not
fat from 10.50 to 7.5% and the refraction of the
copper serum from 36.1 to 39.5. These refrac-
tions were distributed as follows:
Refraction
Number
: OF Samples
39.0 to 39-5
6
38.01038.9
66
37.0 to 37.9
65
36.1 to 36.9
13
150
See also table of refractions on page 7 .
As a result of extended experience, Lythgoe
has recently given the following applications
of some of the methods of milk analysis.
The least variable constituents of milk are
44 MILK
lactose and ash, both of which are valuable data
in detecting added water. It is possible within
reasonable limits to indicate by the total solids
and fat whether a given sample has been watered
or skimmed.
No relation exists between the refraction of
the (sweet) serum and the ash of the sour serum
(see page 66), therefore, if both these data are
below those of normal milk, added water is
positively indicated.
The ratio of protein to fat in normal milk
is always less than i. If the ratio exceeds i,
skimming is indicated. If the protein-fat ratio
is less than 0.7, or the percentage of fat to
total solids is over 35, in samples having a low
serum refraction, these may be declared watered,
the refraction being not necessarily below the
minimum for all samples of known purity.
The sp. gr. of the sweet serum or its total
solids may be used as a datum in place of the re-
fraction; either will be a safe guide.
Lowering of Freezing-point. — Several observers
have shown that watered milk has a lower freezing-
point than pure milk, and that the amount of
depression has a definite relation to the amount
of water added. One of the most recent state-
ments on the subject is by J. W. Leather, who
found the procedure very satisfactory for de-
tecting watering in cows' milk and that of the
DETECTION OF ADULTERATION 45
India buffalo. He states that one observer
has found that a depression to 0.537° indicates
2.3% of added water. The procedure requires
special apparatus and careful manipulation; data
from testing samples of known composition should
be obtained before relying on it in important
cases.
Thickening Agents. — To conceal skimming
and watering many thickening agents have
been used. At least two instances of the use
of brain matter have been reported. Dextrin,
starch, sugar, salt, gelatin and agar have all
been used.
Brain matter can be easily detected by the
microscope, starch jelly by the iodin test,
dextrin by increased polarimetric reading, sodium
chlorid by the increased chlorids in the ash.
Agar is frequently used in certain milk products,
especially the cheap ice-cream sold in American
cities.
Gelatin. — Stokes detects the presence of gelatin
in cream or milk as follows : 10 c.c. of the sample,
20 c.c. of cold water, and 10 c.c. of acid mercuric
nitrate solution (page 37) are mixed, shaken
vigorously, allowed to stand for five minutes,
and filtered. If much gelatin is present, it may
be difficult to get a clear filtrate. A portion
of the filtrate is mixed with an equal bulk
of saturated aqueous solution of picric acid.
46 MILK
Gelatin produces a yellow precipitate. Picric acid
will detect the presence of i part of gelatin in
10,000 parts of water. The picric acid solution
should not give a precipitate with the nitrate
solution.
For sucrose Cotton devised the following tests :
10 c.c. of the sample are mixed with 0.5 gram
of powdered ammonium molybdate, and 10 c.c.
of dilute hydrochloric acid (i to 10) are added.
In a second tube, 10 c.c. of pure milk or 10 c.c.
of a 6 % solution of lactose are similarly treated.
The tubes are then placed in the water-bath and
the temperature gradually raised to about 80°.
If sucrose is present, the milk will become blue,
while genuine milk or milk-sugar remains un-
altered unless the temperature is raised to the
boiling-point. According to Cotton, the reaction
is well marked in the presence of as little as i
gram of sucrose to 1000 c.c. of the milk. For
the detection of other organic thickening agents,
such as pectoses, agar and mixtures of agar and
gelatin, see under '* Cream," page 67.
Calcium Saccharate (Saccharate of Lime). — A
compound produced by the action of lime on
sucrose has been used as a thickening agent. A
test due to Bauer and Neumann is recommended
by Lythgoe, from whose description the following
is taken :
To 25 c.c. of milk (or cream) add 10 c.c. of
DETECTION OF ADULTERATION 47
5 % solution of uranium acetate, shake well, al-
low to stand for five minutes and filter. To lo c.c.
of the clear filtrate (in the case of cream use the
total filtrate, which will be less than lo c.c.) add a
mixture of 2 c.c. saturated ammonium molyb-
date and 8 c.c. dilute hydrochloric acid (i part
25% acid and 7 parts water), and place in a
water-bath at a temperature of 80° for five minutes.
If the sample contains sugar the solution will
have a prussian blue tint. This should always
be compared in a colorimeter with the standard
Prussian blue solution prepared by adding a few
drops of potassium ferrocyanid and 5 drops of
10% hydrochloric acid to a solution of i c.c. of
0.1% ferric chlorid in 20 c.c of water.
It has been claimed that pure milk will give
this test. Occasionally samples of pure milk will
give a pale blue, but this can be entirely removed
by filtration, and the filtrate will be green; while
the color due to sucrose will pass through the
filter, giving the blue solution characteristic of
adulterated samples. The color is due to re-
duction of molybdic acid, and is caused by
levulose and dextrose as well as by sucrose.
Solutions of I gram of lactose, levulose, dextrose
and sucrose in 35 c.c of water were used in com-
paring the amount of color produced when heated
with the molybdenum reagent for five minutes.
Lactose produced no color, levulose gave a heavy
48 MILK
blue, sucrose a weaker blue and dextrose the
weakest blue, corresponding in intensity as
lo 13 :i.
Stannous chlorid and ferrous sulfate give this
color, but the reaction takes place in the cold,
and with small quantities the color disappears on
heating. In order for the color to persist after
heating the sample of cream must contain these
substances to the extent of i % calculated as the
metal. In this case the sample will be completely-
coagulated and the taste will be disagreeable.
Hydrogen sulfid will also give the blue, but it will
disappear on heating. If the solution does not
show blue before heating, it is free from hydrogen
sulfid, ferrous sulfate or stannous chlorid.
As a confirmatory test for sugar, the resorcinol
test may be applied to the serum prepared with
uranium acetate as described. This test is given
by sucrose and levulose, but not by dextrose or
lactose.
The quantitative estimation of sucrose in milk
is given under Milk Products (page 74).
Detection of Heated Milk. — Fresh milk con-
tains one or more enzyms of the "peroxydase**
type, that is, having power to bring about
transfer of oxygen from peroxids to oxidable
substances. As the function of these enzyms
is destroyed by temperatures near 100°, it be-
comes possible to utilize the reaction for deter-
DETECTION OF ADULTERATION 49
mining whether a given sample has been thus heated.
In most cases the action of the enzym is in-
dicated by the production of a deep blue, no
color change occurring when the enzym has been
heated. Hydrogen peroxid is commonly em-
ployed for furnishing the oxygen. A considerable
number of substances have been found to be
susceptible to oxidation under the influence of
the milk enzyms. Benzene derivatives, com-
monly used as photographic developers are
especially susceptible. Guaiacum was first used.
Arnold's Method. — A solution of guaiacum in
acetone is, according to Arnold and Menzel
better than the ordinary tincture. The test is
applied by adding to a small amount of the sample
in a test-tube, about lo drops of the guaiacum
solution, to which a drop or two of hydrogen
peroxid solution has just been added, so that the
reagent will float on the milk. If the sample
has not been heated above 80°, the point of
contact of the liquids will show a deep blue ring.
As guaiacum is liable to changes both in the
solid form and in solution it is important to de-
termine if the reagent is sensitive to raw milk,
hence a control test should aways be made.
Other reagents are now available which are, in the
main, more trustworthy.
Dupouy's Method, — In this method, 1-4 diam-
inobenzene is used. The reagent is dissolved in
50 MILK
water (a weak solution will suffice), a few drops
added to the sample, then a few drops of hydrogen
dioxid solution, and the liquids shaken gently.
Milk that has not been heated above 80° gives
immediately a bright blue. Milk that has been
heated above this temperature shows no color
change at first but may slowly acquire a bluish
tint. This test is much in favor, but it is open
to the objection that the solution of the reagent
does not keep more than few hours, and even in
the solid state some commercial samples soon
decompose.
Benzidin Method. — Wilkinson and Peters sug-
gested this reagent, employing a solution of it
with a few drops of acetic acid followed as usual
by the oxidizing agent. Leffmann finds that
the commercial benzidin hydrochlorid (furnished
for volumetric estimation of sulfates) acts satis-
factorily without acetic aicd.
Wilkinson and Peters' test is performed simi-
larly to those just described, and has a similar
significance. They give experiments to show
that the method is rather more delicate than
with diamino-benzene or guaiacum. The solu-
tion of the benzidin compound keeps better.
They found that milk heated to 77° had lost its
reactivity to guaiacum but retained reactivity
to the other two reagents. Heated to 78° the
reactivity was also lost to these.
DETECTION OF ADULTERATION 51
Leffmann has found that several commercial
photographic developers, e. g., amidol, are ap-
plicable in this test with about the limitations
above noted.
At critical temperatures, however, the results
with all the reagents depend materially on the
length of the heating.
Colors. — Annatto, turmeric, and some coal-tar
colors are much used. Caramel is occasionally-
used, saffron and carotin but rarely. Annatto
may be detected by rendering the sample
slightly alkaline by acid sodium carbonate, im-
mersing a slip of filter-paper, and allowing it to
remain over night. Annatto will cause a reddish-
yellow stain on the paper.
Leys gives the following method for detecting
annatto; 50 c.c. of the sample are shaken with
40 c.c. of 95% alcohol, 50 c.c. of ether, 3 c.c. of
water, and 1.5 c.c. of ammonium hydroxid
solution (sp. gr. 0.900), and allowed to stand for
twenty minutes. The lower layer, which in pres-
ence of annatto will be greenish-yellow, is tapped
off and gradually treated with half its measure of
10% solution of sodium sulfate, the separator
being inverted without shaking, after each addi-
tion. When the casein separates in flakes that
gather at the surface, liquid is tapped off, strained
through wire gauze, and placed in four test-
tubes. To each of these amyl alcohol is added,
52 MILK
and the tubes shaken and immersed in cold
water, which is gradually raised to 80°. The
emulsion breaks up, and the alcohol, holding
the annatto in solution, comes to the surface.
The alcoholic layer is separated from the lower
stratum, evaporated to dryness, and the residue
dissolved in warm water containing a little
alcohol and ammonium hydroxid. Clean white
cotton is introduced and the liquid evaporated
nearly to dryness on the water-bath. The
cotton, which is colored a pale yellow, even with
pure milk, is washed and immersed in a solution
of citric acid, when it will be immediately red-
dened if the milk contains annatto. Saffron,
turmeric, and the coloring-matter of the marigold
do not give a similar reaction.
Coal-tar colors may often be detected by dyeing
wool, but Lythgoe has devised the following
method, which is satisfactory: 15 c.c. of the
sample are mixed in a porcelain basin with an
equal volume of hydrochloric acid (sp. gr.
1.20), and the mass shaken gently so as to break
the curd into coarse lumps. If the milk con-
tains an azo-color, the curd will be pink; with
normal milk the curd will be white or yellowish.
General Method for Colors in Milk. — Leach
devised a general method. 150 c.c. of the
sample are coagulated in a porcelain basin,
with the addition of acetic acid and heating,
DETECTION OF ADULTERATION 53
and the curd separated from the whey. The
curd will often collect in a mass; but if this does
not occur, it must be freed from whey by straining
through muslin. The curd is macerated for
several hours in a closed flask, with occasional
shaking, with ether to extract fat. Annatto
will also be removed by it. The ether and curd
are separated and treated as follows:
The ether is evaporated, the residue mixed
with a little weak solution of sodium hydroxid,
and passed through a wet filter; and when this
has drained, the fat is washed off and the paper
dried. An orange tint shows annatto, which
may be confirmed by a drop of solution of
stannous chlorid, which makes a pink spot.
If the curd is colorless, no foreign coloring-
matter is in it; if orange or brown, it should be
shaken with strong hydrochloric acid in a test-
tube.
If the mass turns blue gradually, caramel is
probably present. The whey should be ex-
amined for caramel (see page 95).
If the mass turns pink at once, an azo-color
is indicated.
Falsification of the "Cream-line,'' — The use of
glass bottles for retail delivery of milk enables
purchasers to make approximate estimations of
the richness of the sample by the depth of cream
formed after standing for some time, this being
54 MILK
of distinctly different tint from the milk below it.
Deception has of late been extensively practised
by a treatment of milk which breaks up the fat
globules and increases the volume of cream
formed, so that a slightly skimmed milk will yield
a fair volume of cream. Determination of fat by
the usual methods will show the fraud. See
page 65.
It has been found that many of the bottles
used for distribution of milk are not of the capac-
ity designated on them, but this is a matter of
police regulation.
Perservatives. — These are largely used, es-
pecially in the warmer season, as a substitute for
refrigeration. Many of them are sold under
proprietary names which give no indication of
their composition. Preparations of boric acid
and borax were at one time the most frequent
in use, but at present formalin^ a 40% solution
of formaldehyd, has come into favor. Sodium
benzoate is now in common use as a preservative
of cider, fruit- jellies, and similar articles, and
may, therefore, be found in milk. Salicylic
acid is not so much employed. Sodium car-
bonate is occasionally used to prevent coagula-
tion due to slight souring. Fluorids and abrastol
may be used. A mixture of boric acid and borax
is more efficient than either alone. The quantity
generally used is equivalent to about 0.5 gram of
DETECTION OF ADULTERATION 55
boric acid per looo c.c. Formaldehyde is an
efficient antiseptic. In the proportion of 0.125
gram to 1000 c.c, it will keep milk sweet for a
week. Hydrogen peroxid, ozone and dichro-
mates have been used. The almost universal
decree of sanitary authorities is that milk
must be free from any added material, but
owing to its comparatively high cost, liability
to decomposition and the marked characters
of even incipient decomposition, great tempta-
tion to use preservatives exists and any anti-
septic, not actively poisonous, may be used. It
has been found that milk drawn and marketed
under strict sanitary precautions will keep for
a considerable time, even at moderate tempera-
tures. The only permissible method of pre-
serving milk is by refrigeration.
In addition to the descriptions of the detec-
tion and estimation of preservatives given below,
see also under "Cream."
Formaldehyde. Hehner's Test. — Hehner found
that when milk containing formaldehyde is
mixed with sulfuric acid containing a trace
of a ferric compound, a distinct blue appears.
Richmond and Boseley showed that the delicacy
of the test is much increased if the milk is
diluted with an equal volume of water and
sulfuric acid of 90 to 94%, added so that it
forms a layer underneath the milk. Under
5
56 MILK
these conditions, milk, in the absence of for-
maldehyde, gives a slight greenish tinge at
the junction of the two liquids, while a violet
ring is formed when formaldehyde is present
even in so small a quantity as i part in 200,000
of milk. The color is permanent for many
hours. In the absence of formaldehyde, a
brown ring may form in the course of a few
hours, but it is below the junction line of the
two liquids.
Phenylhydrazin Test. — The following test
avoids the fallacy of some other tests. A pinch
of phenylhydrazin hydrochlorid is added to a
few c.c. of the sample, the liquid shaken, then a
drop of a fresh solution of sodium nitroprussid
and a few drops of sodium hydroxid solution.
A greenish tint is at once produced if formalde-
hyde is present. If the test is applied to the
liquid obtained by distilling milk the color will be
deep blue.
Phloroglucol Test. — A small amount of a 1%
solution of phloroglucol is added to the sample
and then a considerable volume of sodium
hydroxid solution. In the presence of formalde-
hyde a distinct rose tint will be produced. It
is best to add the phloroglucol by means of a
tube passed to the bottom of the test-tube.
Bonnet's test utilizes the vapor of formalde-
hyde, and avoids the fallacies of some of the
DETECTION OF ADULTERATION 57
older tests. A solution is made by dissolving
0-035 gram pure morphin sulfate in lo c.c. of
sulfuric acid. This solution does not keep well.
A convenient amount of the sample is placed in
a dish or beaker, a watch-glass containing i c.c.
of the above solution is floated on it, and the dish
covered with a glass plate. The materials are
allowed to remain undisturbed at room-tempera-
ture for several hours. Formaldehyde is in-
dicated by the development of a color ranging
from pink to dark blue. A black discoloration
is disregarded. Bonnet found that with i part
of formaldehyde to 25,000 parts of sample a
distinct color appeared in one hour.
In testing ice-cream and similar articles it
must be borne in mind that some of the flavor-
ing materials being aldehydic in nature may
simulate formaldehyde. La Wall has found
that vanillin may act thus. The phenylhydrazin
and Bonnet tests are least liable to fallacy in this
respect.
Nitrites and Formaldehyde. — Mixtures of these
substances are now sold under fanciful and mis-
leading names, for milk preservatives as a
nitrite prevents the reactions of formaldehyde
with some of the tests.
Leffmann has found that the phenylhydrazin
test will react promptly with formaldehyde in
presence of notable amount of nitrite and also
58 MILK
that the well-known test for nitrites (sulfanilic
acid and alphanaphthylamine) reacts in the
presence of formaldehyde. The reactions are
obtained in fresh samples and in those that have
stood for twenty-four hours.
Determination of Formaldehyde. — In the case
of milk the proportion of formaldehyde is almost
always small and it may be in great part removed
from milk by distillation especially in a current
of steam. B. H. Smith found that if loo c.c.
of the sample are distilled with i c.c. of dilute
sulfuric acid (1:3), one- third of the formaldehyde
present will come over with the first 20 c.c.
Distillation of milk is troublesome owing to
bumping, but Smith found that it could be safely
conducted with a flat evaporating burner. It is
advisable to put a few pieces of pumice into the
flask.
Shrewsbury and Knapp recommend the fol-
lowing method for estimation of formaldehyde.
An oxidizing reagent is prepared by mixing o.i
gram of pure nitric acid (sp. gr. 1.52) with 100 c.c.
of strong hydrochloric acid are mixed. This
mixture should be freshly made.
5 c.c. of milk are treated with 10 c.c. of the
reagent, the mixture well shaken and kept for ten
minutes in a water-bath at 50°. The depth of
color is proportional to the amount of formalde-
hyde present and by means of milk containing
DETECTION OF ADULTERATION 5g
known amounts of the preservative estimations
may be made.
Hydrogen Peroxid. — Many tests have been
devised for detection of this substance. Among
the most convenient and satisfactory is the
reaction with vanadic acid first given by Werther.
It may be carried out by adding to lo c.c. of the
milk, lo drops of a i% solution of vanadic acid
in dilute sulfuric acid. This solution may be
conveniently made by dissolved commercial
sodium ortho vanadate in the dilute acid.
In the presence of hydrogen peroxid a distinct
red will appear promptly. Barthel states that a
proportion of o.oio gram of the peroxid in loo
c.c. of milk can be detected positively using only
ID c.c. of the sample.
Benzoates and Salicylates. — The following
method covers both these preservatives.
lo c.c. of dilute sulfuric acid (5%) are added
to 20 c.c. of 95% alcohol and into this 50 c.c. of
the milk are poured in a fine stream with constant
stirring. After a few moments, the mixture is
filtered, the filtrate being returned until it passes
clear. A sufficient volume of the filtrate is
extracted in the usual manner with an equal
volume of ether or similar solvent. The solvent
is divided into two portions that are separately
evaporated and tested for benzoic and salicylic
acids respectively as given below.
6o MILK
Benzoates. — This is detected by a modification
of Mohler's method by Von der Heide and
Jakob as given by U. S. Bureau of Chemistry.
The residue that is to be tested for benzoic
acid is dissolved in a Httle water, the solution
mixed with from i to 3 c.c. of normal sodium hy-
droxid and evaporated to dryness. To this resi-
due is added from 5 to 10 c.c. of concentrated sul-
furic acid and a small crystal of potassium nitrate
and the mixture heated either for ten minutes
in a glycerol bath between 120° and 130° or for
twenty minutes in boiling water. If heated in
the glycerol bath the temperature must not be
permitted to go over 130°. Metadinitrobenzoic
acid is formed. After cooling i c.c. of water is
added, the liquid made decidedly ammoniacal,
boiled to break up ammonium nitrite, and some
fresh colorless ammonium sulfid solution added
so that the liquids do not mix. A brown ring at
junction indicates benzoic acid. The liquids
being mixed, the color diffuses and on heating
changes to greenish-yellow. The last reaction
distinguishes benzoic acid from salicylic and
cinnamic acid as these latter form amino-deriva-
tives which are not destroyed by heating.
Phenolphthalein interferes with this process.
Salicylic Acid.— The other portion of the
ether-extract may be evaporated and tested for
DETECTION OF ADULTERATION 6 1
salicylic acid in the usual manner with a ferric
compound.
Saccharin. — A suitable amount of the sample
(50 or 100 c.c.) is acidified with dilute (25%)
sulfuric acid and extracted with a mixture of
equal parts of petroleum spirit (boiling below 60°)
and ether. The solvent is evaporated at a gentle
heat. The presence of saccharin in the residue
may be detected by the taste. 2 c.c. of a
saturated solution of sodium hydroxid are added
and the dish heated until the residue dries and
then to 2io°-2i5°, and maintained thus for half
an hour. The saccharin is converted into salicylic
acid, which may be detected in the residue by
acidulating it with sulfuric acid and applying the
ferric chlorid test. If salicylic acid be present
originally in the sample, the residue from the
petroleum spirit and ether solution is dissolved
in 50 c.c. of dilute hydrochloric acid, bromin
water added in excess, the liquid shaken well,
and filtered. Salicylic acid is completely removed
as a brominated derivative. The filtrate is made
strongly alkaline with sodium hydroxid, evapo-
rated, and fused as described above.
Sodium Carbonate and Sodium Acid Car-
bonate.— These substances are occasionally added
to milk to prevent acidity due to decomposition.
Barthel recommends a test devised by Hilger.
50 c.c. of the milk are diluted with 250 c.c. of
62 MILK
water, the mixture is heated, precipitated with a
small amount of alcohol and a convenient
volume filtered. The filtrate is evaporated to
half its bulk. The presence of an alkali-carbon-
ate is easily ascertained by the usual tests.
Borates. — Jenkins' method is convenient and
reasonably delicate. lo c.c. of milk are mixed
with 7 c.c. of hydrochloric acid, filtered, a strip
of turmeric paper dipped in the filtrate, and then
dried on a watch-glass on the water-bath. The
paper becomes red in the presence of borates.
A simple test is to mix in a porcelain basin a
drop or two of the milk, a drop of hydrochloric
acid and a drop of alcoholic solution of turmeric
and evaporate to dryness on the water-bath.
The residue touched with ammonium hydroxid
will show a distinct greenish stain in the presence
of very small amounts of borates.
It is obvious that the delicacy of both these .
tests may be materially increased by concen-
trating the sample. As boric acid is volatile
with steam it is best to render the sample slightly
alkaline with sodium hydroxid before evaporating.
Abrastol (Asaprol). — This is a calcium beta-
naphthol-sulphonate that has marked antiseptic
powers and has been used as a food preservative.
The following test suggested by Leffmann will
detect very small amounts. lo c.c. of the
sample are mixed with 0.5 c.c. of the solution of
DETECTION OF ADULTERATION 63
mercuric nitrate described on page 37. In
the presence of abrastol a distinct yellow tint is
produced in a few minutes. Greater delicacy
can be obtained by using the same proportion
of the reagent with 10 c.c. of milk known to be
pure.
Organic Contamination. — Sanitary control of
market-milk also involves tests for animal prod-
ucts, such as pus cells, and the identification
of specific microbes, such as those causing tuber-
culosis and typhoid fever. These investiga-
tions, however, are mostly outside of the scope
of a work on chemical analysis. For informa-
tion concerning these recourse must be had to
works on pathology and bacteriology.
Several chemical tests have been published
by which it is claimed that approximate deter-
mination of these contaminating organisms and
substances can be made but they are not capable
of replacing the exact methods of the pathologic
and bacteriologic laboratory. One of these is
the following. A dilute solution of methylene
blue is prepared by adding 5 c.c. of a saturated
alcoholic solution of the dye to 200 c.c. of water.
0.5 c.c. of this solution is added to 10 c.c. of
the sample. If the color is discharged promptly,
the sample contains over 100,000,000 bacteria
per c.c.
Hydrogen dioxid has been shown by the in-
64 MILK
vestigations of Rentschler to kill quickly many
forms of microbes, and may be applicable to the
purification of milk, when, as in war, systematic
protection and inspection are not possible.
Preservation of Samples. — For the preservation
of milk samples for a day or two, refrigeration
is the best method. Sterilization in the ordinary
steam sterilizer used in preparing culture-media,
will enable milk to be kept for a considerable
time if in a flask closed with a cotton plug.
Several preservatives have been proposed for
keeping samples . Richmond found small amounts
of hydrofluoric acid effective, but it has been but
little used. Formaldehyde is very efficient; in
large amount it increases the total solids, inter-
feres with the reactions of the proteins and simu-
lates some of the reactions of the carbohydrates.
A couple of drops of commercial formalin to 25
c.c. will preserve a sample for several days.
MILK PRODUCTS
CREAM
Cream differs from whole milk principally in
the fat-content; the analytic procedures, there-
fore, follow those indicated under "Milk," except
that the high fat may render some modifica-
tions advisable. It is better, for instance, to
weigh rather than measure cream, and it is
often advisable to dilute it with a known
weight of water. For the determination of fat
the Rose- Gottlieb method is much in favor
(see page 72). The following are some special
procedures.
Imitation Cream. — By means of special ma-
chinery, the fat globules of milk may be broken
into very small portions without causing them
to coalesce. This is termed "homogenizing"
and will give to poor cream an appearance of
richness. It is also possible to incorporate
butter with skim-milk, producing an article
resembling cream. Of course, unsalted, un-
colored butter must be used. As butter made
in the usual manner, always contains water, the
65
66 MILK PRODUCTS
adulteration may be detected by the change
in the refractive power of the serum as described
on page 42. H. C. Lythgoe, who has investi-
gated this question, finds that samples adulter-
ated with butter will give a refraction below 36.0.
Results may be confirmed by taking the ash
of the sour serum. A large amount of the
sample is taken (as the yield of serum is small),
soured with a pure culture of lactic acid bacillus,
or with a little sour milk, shaken in a bottle
until the fat and curd have separated, the serum
drawn off and the ash of 25 c.c. taken. It
should not be below 0.73%. The homogizing
of cream without the addition of fat can be
detected by microscopic examination.
Formic Acid. — ^Revis and Bolton state that
glucose containing this may be found in cream
and give the following method for its detection.
100 grams are diluted with an equal weight of
water, 20 c.c. of a 20% solution of phosphoric
acid added, and 100 c.c. distilled, the end of the
condenser dipping below the surface of milk of lime
containing at least i gram of calcium hydroxid
and 2 c.c. of 3% acetic acid, free from formic.
The distillate is evaporated to dryness, sealed
in a small tube of hard glass, drawn out at one
end that dips into a small U-tube containing
2 c.c. of water, arranged so that none of the water
can be drawn into the tube, and heated until
CREAM 67
distillation ceases. The water in the U-tube is
mixed with 2 c.c. of SchiflE's reagent. If formic
acid was present, the mixture will become violet
within a half hour.
Schiff's reagent is obtained by dissolving i
gram of rosanilin hydrochlorid in 10 c.c. of
water, adding a mixture of 2 c.c. saturated
solution of sodium acid sulfite and 0.5 c.c. strong
hydrochloric acid, then water to make 100 c.c.
The solution keeps for some time in the dark.
Agar. — This is now often used as a thicken-
ing agent. Although characteristic diatoms are
found in it, the detection of the substance by
isolation of these has not been practically
successful. Revis and Bolton recommend the
following method.
50 grams of the sample are diluted with 100
c.c. of water, heated in boiling water and cleared
with 5 c.c. of 10% calcium chlorid solution.
The mixture is filtered, preferably in a hot-water
funnel, cooled and mixed with about two-thirds
its volume of strong alcohol. The precipitate
(containing any agar that may have been in the
sample) is separated, and boiled with 5 c.c. of
water until dissolved. If it contains agar, the
solution will gelatinize on cooling. To detect
the presence of gelatin in association with agar,
the procedure is the same, except that when the
precipitate is dissolved, a few c.c. of the solution
68 MILK PRODUCTS
are treated with picric acid solution. A pre-
cipitate indicates gelatin. In this case, the re-
mainder of the solution is evaporated to small
bulk, and mixed with a io% solution of tannin
until no more precipitate is produced. The
liquid must in this treatment not have a tem-
perature of over 60°. To it a few c.c of white of
egg are added and the mixture heated to boiling
for thirty minutes, filtered hot, concentrated
to small bulk on the water and allowed to cool
and gelatinize.
CONDENSED MILK
Commercial condensed milks present two prin-
cipal forms, sweetened and unsweetened. In the
latter sucrose is generally used. Often consti-
tuting more than half the solids of the product.
Up to recent years, unsweetened condensed milk
was largely sold in the United States as "evapo-
rated cream" but this is now forbidden by the
federal food law and by many State enactments.
Dried milk has also been manufactured but
does not seem to have met with much favorable
reception. Commercial evaporation of milk is
conducted at a low temperature so that less
modification of the ingredients is produced than
in ordinary boiling, but some modification of the
lactose may occur which will make polarimetric
readings less accurate than with unheated milk.
The analysis of unsweetened condensed milk
can be conducted along the same lines as those
for ordinary milk and cream, the sample being
diluted about three times by adding a known
volume of water. It must not be forgotten, that
lactose may crystallize from condensed and dried
milks, and excessive polarimetric rotation occur in
recently made dilutions, unless these are heated
to brief boiling and cooled (see page 39). Com-
69
70 MILK PRODUCTS
mercial condensed milks usually represent whole
milk concentrated to about one-third or two-
sevenths of its original volume. A small amount
of invert-sugar may be present. The most com-
mon defect in condensed milks is deficiency
in fat, due to preparation from closely skimmed
milks. Preservatives (other than sucrose) and
coloring-matters are rarely used, nor is it likely
that foreign fats will be present.
The fat of unsweetened condensed milk can be
readily determined by the L-B method (page i8).
In a recent publication, Bigelow andFitzgerald
give the following detailed description of the
application of the Leffmann and Beam method
to the examination of unsweetened condensed
milk:
Weigh 9 grams of evaporated milk into an
8% Babcock milk bottle. Add lo c.c. of water.
Thoroughly mix by shaking and add 3 c.c. of a
mixture of equal parts of amyl alcohol and con-
centrated hydrochloric acid. Shake thoroughly
and add 10 c.c. of concentrated sulfuric acid
(1.84 sp. gr.) in three or four portions, mixing
after each addition. If too much heat develops
the bottle may be cooled somewhat in water
during the addition of the acid.
Fill the bottle to near the base of the neck with
a hot fresh mixture of equal parts of sulfuric
acid and water. Thoroughly mix the contents
CONDENSED MILK 7 1
of the bottle by shaking. Raise the fat column
to the top of the scale by means of the acid and
water mixture, and whirl for five minutes.
Read promptly (see page 20) from the extreme
bottom of the fat column to the bottom of the
upper meniscus. Multiply the reading by 2 , and
deduct 0.25; the remainder is the per cent, of
fat.
If an electric centrifuge without heat has been
employed, the fat column will be somewhat cool
and should be heated, before reading, in a water-
bath about 60°.
The same authors give the opinion that the
centrifugal methods are not sufficiently accurate
to be depended upon for determining if evapo-
rated milk is up to standard. The Rose-Gottlieb
method is best for this purpose. If the centrif-
ugal methods are employed, considerable allow-
ance must be made for inaccuracies. Results
obtained are inaccurate unless the fat column
is clear, with the meniscus at the bottom of the
column perfect and not distorted by either char
or milky appearance. •
The percentage of solids as calculated from
the sp. gr. is not sufficiently accurate to
determine whether the milk complies with the
standard unless the correction factor for the for-
mula of calculation is ascertained frequently by
the determination of solids by drying.
6
72 MILK PRODUCTS
The full analysis of sweetened condensed milk
is difficult, and many of the published figures are
erroneous. The sucrose interferes with the ex-
traction of the fat by solvents. The same
difficulty occurs in the analysis of some prepared
infant-foods, such as mixtures of milk with malt
and glucose.
For the general operations, a portion of the
well-mixed contents of a freshly opened can
should be accurately weighed, diluted with a
known amount of water, and well mixed, from
which mass the portions for analysis may be
taken and the results calculated to the original
sample. 50 grams mixed with 150 c.c. of water
will be a convenient quantity. For the polar-
imetric determination of lactose, a special pro-
cedure will be necessary ; but for determination of
solids, ash, total proteins, and total reducing
sugars, the examination may be made as with
ordinary milk upon this diluted sample.
Fat. — The Adams method is not satisfactory
under ordinary conditions, owing to the sucrose.
The Rose- Gottlieb method is now largely used
and generally approved. The following descrip-
tion is given by Bigelow and Fitzgerald :
Weigh from 4.5 to 5.0 grams evaporated or
condensed milk into a Rose-Gottlieb tube, add
water to make about 11 grams and ij^ to i}4
CONDENSED MILK 73
c.c. concentrated ammonium hydroxid, and thor-
oughly mix by shaking.
Add 10 c.c. 95 % alcohol and shake thoroughly.
Fill up to the level of the side tube with water, if
necessary, and shake. Add 25 c.c. ether and
shake well for one minute . Add 250.0. petroleum
spirit (b. p. below 65°) and shake well for one
minute.
Allow tube to stand until layers separate
well. Draw off ether-fat solution as completely
as practicable and run it through a small quick-
acting filter into a weighted flask (weighted by
counterpoising, if the test is not finished the day
it is started.)
Re-extract the liquid in tube as before with
15 c.c. of each of petroleum spirit and ether,
shaking after each is added. Before the addition
a little alcohol may be added and the contents
of the tube mixed by shaking, to bring the layer
of ammoniacal liquid close up to the outlet tube,
for by repeated extractions the surface of sepa-
ration is lowered.
Run the solution from the second extraction
through the filter into the flask, and wash end of
spigot, filter paper, and lower surface of the
funnel with ether; or, better, with a mixture of
equal parts of ether and petroleum spirit which
has been allowed to stand for separation of
water.
74 MILK PRODUCTS
In the examination of cream a third extraction
is necessary, but with evaporated and condensed
milk the third extraction does not recover more
than 0.02 or 0.03 % of fat, and may be omitted.
Evaporate the liquid slowly on a steam bath
and dry the fat in steam oven until its weight is
constant. Weigh after one hour and then at half-
hour intervals. As soon as the fat begins to gain
in weight stop drying and take the next previous
weight. Increase of weight is due to oxidation
after all moisture and alcohol are gone. In all
cases the drying should be completed the day it
is begun.
Double Extraction. — The following is given as a
provisional A. O. A. C. method: Extract with
ether, as usual, about 5 grams of a 40% solution,
dry, leave the tubes in a dish containing at least
500 c.c. of water, dry, extract again with ether for
four hours.
Sugars. — If regard is to be given to the
presence of invert-sugar, a special method must
be followed. The processes first given consider
lactose and sucrose only. The heating employed
in the manufacture of condensed milk may
reduce the rotatory power of lactose sufficiently
to cause error in the polarimetric method. The
reducing power with alkaline copper solutions
is not seriously affected.
Determination of sucrose may be made by
CONDENSED MILK 75
difference; that is, subtracting the sum of the
other ingredients from the total soHds. This will
serve for ordinary inspection purposes, since
the amount present is almost always large, gener-
ally more than the total of milk-solids, and a
slight error does not affect the judgment as to
the wholesomeness of the sample. Exact work
requires, however, that the sucrose be de-
termined directly. Several processes have been
devised for the purpose. Sucrose exerts but
little action on Fehling's solution, but invert-
sugar acts powerfully, and some processes depend
on determining the reducing power before and
after inversion. Since the polarimetric reading is
also markedly changed by the inversion, the
difference in polarization may be employed.
Fermentation may be so conducted as to re-
move the sucrose (also any form of glucose) while
the lactose is unaffected. This method is chiefly
valuable for recognizing invert-sugar or either of
its constituents.
Inversion Methods. — These must be such as to
secure prompt inversion of the sucrose without
affecting the lactose. Experiment shows that
citric acid and invertase are the most suitable
agents. Stokes & Bodmer have worked out the
citric acid method substantially as follows:
25 c.c. of the diluted sample are coagulated by
addition of i% of citric acid, without heating,
76 MILK PRODUCTS
and made up to 200 c.c. plus the volume of the
precipitated fat and proteins (see page 38). The
liquid portion, which now measures 200 c.c, is
passed through a dry filter. The reducing power
with alkaline copper solutions is determined at
once upon 50 c.c. of this filtrate. To another
50 c.c, 1% of citric acid is added, the solution
boiled at least thirty minutes, and the reducing
power also determined. The increase over that
of the first solution is due to the invert-sugar
formed by the action of the citric acid on the
sucrose. It is necessary to bear in mind that the
reducing equivalents of lactose and invert-sugar
are not the same. Volumetric methods may be
employed.
The following method is based on the difference
in polarimetric reading before and after action of
invertase. 75 c.c of the diluted milk are placed
in a loo-c.c flask, diluted to about 80 c.c,
heated to boiling, to correct birotation, cooled,
and 10 c.c of acid mercuric nitrate solution
(page 37) added. The mixture is made up to 100
c.c, well shaken, filtered through a dry filter, and
the polarimetric reading taken at once. It will
be the sum of the effect of the two sugars. The
volume of the sugar-containing liquid is calcu-
lated by allowing for the precipitated proteins
and fat, as described on page 38.
50 c.c of the filtrate are placed in a flask
CONDENSED MILK 77
marked at 55 c.c, a piece of litmus paper dropped
in, and the excess of nitric acid cautiously neu-
tralized by sodium hydroxid solution. The
liquid is then faintly acidified by a single drop of
acetic acid (it must not be alkaline), a few drops
of an alcoholic solution of thymol are added,
and then 2 c.c. of a solution of invertase, prepared
by grinding half a cake of ordinary compressed
yeast with 10 c.c. of water and filtering. The
flask is corked and allowed to remain at a tem-
perature of 3 5 ° to 40° for twenty-four hours. The
cane-sugar will be inverted, while the milk-sugar
will be unaffected. The flask is filled to the mark
(55 c.c.) with washed aluminum hydroxid and
water, mixed, filtered, and the polarimetric
reading taken. The amount of cane-sugar can
be determined from the difference in the two
readings by the formula
^ _ 100 a + b
t
142.68
in which 5 is the percentage of sucrose; a, the
reading before, b, after inversion; /, the
temperature.
Lactose, Sucrose and Invert-sugar. — Bige-
low and McElroy propose the following routine
method to include invert-sugar. The reagents
are:
78 MILK PRODUCTS
Acid Mercuric lodid. — Mercuric chlorid, 1.35
grams; potassium iodid, 3.32 grams; glacial acetic
acid, 2 CO. ; water, 64 c.c.
Alumina-cream. — A cold saturated solution of
alum is divided into two unequal portions, a
slight excess of ammonium hydroxid is added
to the larger portion and the remainder added
until a faintly acid reaction to litmus is obtained.
The entire contents of the can are transferred
to a porcelain dish and thoroughly mixed. A
number of portions of about 25 grams are
weighed carefully in 100 c.c. flasks. Water is
added to two of the portions, and the solutions
boiled. The flasks are then cooled, clarified by
means of a small amount of the acid mercuric
iodid and alumina cream, made up to mark,
filtered, and the polarimetric reading noted.
Other portions of the milk are heated in the
water-bath to 55°; one-half of a cake of com-
pressed yeast is added to each flask and the
temperature maintained at 55° for five hours.
Acid mercuric iodid and alumina-cream are
then added, the solution cooled to room tem-
perature, made up to mark, mixed, filtered, and
polarized. The amount of sucrose is determined
by formula given above. Correction for the
volume of precipitated solids may be made by the
double-dilution method. The total reducing
sugar is estimated in one of the portions by one of
CONDENSED MILK 79
the reducing methods, and if the sum of it and
the amount of sucrose obtained by inversion is
equal to that obtained by the direct reading of
both sugars before inversion, no invert-sugar is
present. If the amount of reducing sugar seems
to be too great, the lactose must be re-determined
as follows: 250 grams of the condensed milk are
dissolved in water, the solution boiled, cooled to
80°, a solution of about 4 grams of glacial phos-
phoric acid added, the mixture kept at 80° for
a few minutes, then cooled to room temperature,
made up to mark, shaken, and filtered. It may
be assumed that the volume of the precipitate
is equal to that obtained by mercuric iodid solu-
tion. Enough sodium hydroxid is then added to
not quite neutralize the free acid, and sufficient
water to make up for the volume of the solids
precipitated by the phosphoric acid. The mixture
is then filtered and the filtrate is measured in
portions of 100 c.c. into 200-c.c. flasks. A
solution containing 20 milligrams of potassium
fluorid and half a cake of compressed yeast is
added to each flask, and the mixture allowed to
stand for ten days at a temperature between 25°
and 30°. Invert-sugar and sucrose are fermented
and removed by the yeast in the presence of a
fluorid ; lactose is unaffected. The flasks are filled
to the mark and the lactose determined either
by reducing or by the polariscope. The amount
8o
MILK PRODUCTS
of copper solution reduced by the lactose and
invert-sugar, less the equivalent of lactose re-
maining after fermentation, is due to invert-
sugar.
BUTTER
Butter is a mixture of fat, water, and curd.
The water contains lactose and the salts of the
milk. Common salt is usually present, being
added after the churning. Artificial coloring
is frequently used.
Butter-fat is distinguished from other animal
fats in that it contains a notable proportion of
acid radicles with a small number of carbon atoms.
Thus, about 91% consists of palmitin and olein
and the remainder of butyrin and caproin, along
with small amounts of caprylin, caprin, myristin,
and some others. According to the experiments
of Hehner & Mitchell, stearin is present only in
very small quantity. The exact arrangement of
the constituents is unknown.
The composition of good commercial butter
usually ranges within the following limits:
Fat 78% to 94%
Curd I % to 3%
Water 5% to 14%
Salt 0% to 7%
Butter containing over 40% of water is some-
times sold. Such samples are pale and spongy,
lose weight, and become rancid rapidly.
81
82 MILK PRODUCTS
The official methods of the A. O. A. C. for the
analysis of butter are as follows:
Preparation of the Sample. — If large quantities
of butter are to be sampled, a butter trier or
sampler may be used. The portions thus drawn,
about 500 grams, are to be perfectly melted in a
closed vessel at as low a temperature as possible,
and when melted the whole is to be shaken vio-
lently for some minutes until the mass is homo-
geneous and sufficiently solidified to prevent
the separation of the water and fat. A portion
is then poured into the vessel from which it is
to be weighed for analysis, and should nearly or
quite fill it. This sample should be kept in a
cold place until analyzed.
Water. — From 1.5 to 2.5 grams are dried to
constant weight at the temperature of boiling
water, in a dish with fiat bottom, having a surface
of at least 20 sq. cm. The use of clean dry sand
or asbestos with the butter is admissible, and
is necessary if a dish with round bottom be
employed.
Fat. — The dry butter from the water deter-
mination is dissolved in the dish with absolute
ether. The contents of the dish are then trans-
ferred to a weighed Gooch crucible with the aid
of a wash-bottle filled with the solvent, and are
washed until free from fat. The crucible and
BUTTER 83
contents are heated at the temperature of boiling
water till the weight is constant.
The fat may also be determined by drying the
butter on asbestos or sand, and extracting by
anhydrous alcohol-free ether. After evaporation
of the ether the extract is heated to constant
weight at the temperature of boiling water and
weighed.
Casein, Ash, Chlorin. — The crucible con-
taining the residue from the fat determination is
covered and heated, gently at first, gradually
raising the temperature to just below redness.
The cover is removed and the heat continued until
the material is white. The loss in weight rep-
resents casein, and the residue mineral matter.
In this mineral matter dissolved in water slightly
acidulated with nitric acid, chlorin may be
determined gravimetrically with silver nitrate,
or, after neutralization with calcium carbonate,
volumetrically, using potassium chromate as
indicator.
Salt. — About 10 grams are weighed in a beaker
in portions of about i gram at a time taken from
different parts of the sample. Hot water (about
20 c.c.) is now added to the beaker, and after
the butter has melted, the mass is poured into
the bulb of a separating funnel, which is then
closed and shaken for a few moments. After
standing until the fat has all collected, the water
84 MILK PRODUCTS
is allowed to run into an Erlenmeyer flask, with
care not to let fat globules pass. Hot water is
again added to the beaker, and the extraction
is repeated from ten to fifteen times, using each
time from lo to 20 c.c. of water. The resulting
washings contain all but a mere trace of the salt
originally present in the butter. The chlorin is
determined volumetrically in the filtrate by
means of standard silver nitrate and potassium
chromate indicator and calculated to sodium
chlorid.
Butter -substitutes. — The chief adulteration of
butter consists in the substitution of foreign fats,
especially the product known as oleomargarin.
When fats are saponified and the soap treated
with acid, the individual fatty acids are obtained.
It is upon the recognition of the peculiar acid
radicles existing in butter that the most satis-
factory method of distinguishing it from other
fats is based. Since the relative proportion of
these radicles differs in different samples, the
quantitative estimation cannot be made with
accuracy; but when the foreign fats are substi-
tuted to the extent of 20% or more, the adultera-
tion an be detected with certainty and an
approximate quantitative determination made.
The detection of adulteration of butter-fat by
other fats is generally carried out by the deter-
BUTTER 85
mination of the volatile acid, but some other
confirmatory processes are occasionally employed.
Qualitative Tests. — Two tests are convenient
for preliminary examinations, especially for sort-
ing out, when many samples are to be tested.
The experience of Dr. William Beam and myself
in testing many hundred samples for the Dairy
and Food Commissioner of Pennsylvania showed
that the methods are satisfactory and useful.
Heating test. — When butter is heated in a
small tin dish directly over a gas flame, it melts
quietly, foams, and may run over the dish.
Oleomargarin, under the same conditions, sput-
ters noisily as soon as heated and foams but little.
Even mixtures of butter and other fats show this
sputtering action to a considerable extent. The
test is not applicable to butter which has been
melted and reworked (renovated or process
butter).
Saponification test. — An alcoholic solution of
sodium hydroxid, boiled up with butter, and then
emptied into cold water, gives a distinct odor of
pineapples, while oleomargarin gives only the
alcoholic odor.
Quantitative Methods. Volatile Acids. —
This method, suggested by Hehner & Angell,
systematized by Reichert, is generally called the
Reichert process. In this form it is carried
out by saponifying 2.5 grams of the fat, adding
86 MILK PRODUCTS
excess of sulfuric acid, distilling a definite portion
of the liquid, and titrating the distillate with
^/lo alkali. The number of c.c. of this solution
required to overcome the acidity of the distillate
is called the Reichert number. E. Meissl sug-
gested the use of 5 grams, and the number so
obtained is called the Reichert- Meissl number.
Alcoholic solution of potassium hydroxid was
originally used for saponification, but the solu-
tion devised by Leffmann & Beam, namely,
sodium hydroxid in glycerol, is more satisfactory.
This procedure is now official in the U. S. and
several European countries. The reagents and
operation are as follows:
Glycerol-soda. — 100 grams of good sodium
hydroxid are dissolved in 100 c.c. of distilled
water and allowed to stand until clear. 20 c.c
of this solution are mixed with 180 c.c. of pure
concentrated glycerol. The mixture can be con-
veniently kept in a capped bottle holding a 10-
c.c. pipet, with a wide outlet.
Sulfuric Acid. — 20 c.c. of pure concentrated
sulfuric acid, made up with distilled water to
100 c.c.
Sodium Hydroxid. — An approximately ^/lo,
accurately standardized, solution of sodium
hydroxid.
Indicator. — Solution of phenolphthalein.
A 300-c.c. flask is washed thoroughly, rinsed
BUTTER 87
with alcohol and then with ether, and thoroughly
dried by heating in the water-oven. After
cooling, it is allowed to stand for about fifteen
minutes and weighed. (In ordinary operation
this preparation of the flask may be omitted.)
A pipet, graduated to 5.75 c.c, is heated to about
60° and filled to the mark with the well-mixed
fat, which is then run into the flask. After
standing for about fifteen minutes the flask and
contents are weighed. 20 c.c. of the glycerol-
soda are added and the flask heated over the
Bunsen burner. The mixture may foam some-
what; this may be controlled, and the operation
hastened by shaking the flask. When all the
water has been driven off, the liquid will cease
to boil, and if the heat and agitation be continued
for a few moments, complete saponification will
be effected, the mass becoming clear. The whole
operation, exclusive of weighing the fat, requires
about five minutes. The flask is withdrawn from
the heat and the soap dissolved in 135 c.c. of water.
The first portions of water should be added drop
by drop, and the flask shaken between each
addition in order to avoid foaming. When the
soap is dissolved, 5 c.c. of the dilute sulfuric acid
are added, a piece of pumice dropped in (this
must not be omitted), and the liquid distilled
until no c.c. have been collected. The con-
densing tube should be of glass, and the distilla-
7
88
MILK PRODUCTS
tion conducted at such a rate that the above
amount of distillate is collected in thirty minutes.
The distillate is usually clear; if not, it should
be thoroughly mixed, filtered through a dry
filter, and loo c.c. of the filtrate taken. A little
of the indicator is added to the distillate, and the
standard alkali run in from a buret until neutrali-
FiG. 3.
zation'is attained. If only 100 c.c. of the dis-
tillate have been used for the titration, the c.c.
of alkali used should be increased by one-tenth.
The distilHng apparatus shown in figure 3 is
that recommended by the A. O. A. C. (and since
adopted in Great Britain), and the directions for
BUTTER 89
preparing the flask are also from the same
source.
When it is intended merely to distinguish
butter from oleomargarin, it will be sufficient to
saponify 3 c.c. of the clarified fat, dilute, acidify,
distil 100 c.c. in the ordinary manner and titrate
as directed. ** Straight oleos," that is, samples
containing inappreciable amounts of butter, will
give a distillate requiring only a few c.c. of alkali.
Butter (5 grams) yields a distillate requiring
from 24 to 34 c.c. of ^/jo alkali. Several instances
have been published in which genuine butter has
given a figure as low as 22.5 c.c, but such results
are uncommon. The materials employed in
the preparation of oleomargarin yield a distillate
requiring less than i c.c. of alkali. Commercial
oleomargarin is usually churned with milk in
order to secure a butter flavor, and, thus acquiring
a small amount of butter-fat, yields distillates
capable of neutralizing from i to 2 c.c. of alkali.
If coconut oil has been used in the preparation
of the oleomargarin, the figure will be higher, but
there will still be no difficulty in distinguishing
pure butter.
The determination of the Reichert number will
usually give sufficient information as to the
nature of a butter sample. In doubtful cases it
may be of advantage to apply other tests as
corroborative evidence.
90 MILK PRODUCTS
Index of Refraction. — This datum differs nota-
bly in different oils, but it is not of much value
in detecting adulteration unless considerable of
the adulterant be present. Several instruments
have been devised for making refraction de-
termination; a familiar one is the butyrorefrac-
tometer of Zeiss.
The butyrorefractometer has been strongly
recommended for the examination of butter.
It is equally adapted for the general examination
of fats and oils, and may be used for the de-
termination of the index of refraction as well.
As these instruments are made by only one firm
and are furnished with directions for use, further
description will not be required.
Renovated Butter. — So-called "process" or
'* renovated" butter, made by melting old or in-
ferior samples, purifying the fat, coloring and
salting, is now a familiar article. When heated in
a dish such butter sputters, with but little foam-
ing as does oleomargarin, but yields with alcoholic
solution of sodium hydroxid the pineapple odor.
The fat or process butter gives refractometric
data and Reichert-Meissl data similar to ordinary
butter. Hess and Doolittle state that the curd
of process butter has characteristic qualities, and
propose the following method for detecting it.
50 grams of the sample are melted in a beaker
at about 50°. Ordinary butter yields a clear
BUTTER 91
fat almost as soon as melted, while with process
butter the fat may remain turbid for a long while.
When the curd has largely settled, as much of the
fat is poured off as possible, and the remaining
mixture is thrown on a wet filter, by which the
water will drain away, carrying the soluble
proteins and salt. A few drops of acetic acid
are added to the filtrate and the mixture is
boiled. The filtrate from ordinary butter gives
a slight milkiness, but that from process butter
gives a fiocculent precipitate. Quantitative ex-
amination is made by dissolving 50 grams of the
sample in ether ; if it is ordinary butter, the curd
is so finely divided that it remains suspended for
some time. As much as possible of the solution
is decanted and the mass transferred to a sepa-
rator, the casein, water, and salt removed, and the
remainder washed three times, at least, with
ether to remove the fat. The curd is collected
on a filter, washed with water, and the nitrogen
determined by treating the precipitate with the
filter by the Kjeldahl- Gunning method. The
filtrate from the curd is made slightly acid with
acetic acid, boiled, the precipitated proteins
collected on a filter, and the total nitrogen de-
termined. The factor 6.38 may be used in each
case for converting the nitrogen into proteins.
A distinction between ordinary and process
butter may often be made by microscopic ex-
92 MILK PRODUCTS
amination under polarized light with crossed
nicols (i. e., dark field), when the process butter
appears mottled, owing to the presence of
crystals.
Butter Colors. — Butter and butter- substitutes
are usually artificially colored. Turmeric and
annatto or azo-colors allied to methyl-orange are
used.
Azo-colors. — These may be detected by the
test devised b}'- Geisler. A small amount of the
sample, or, better, the fat filtered from it, is mixed
on a porcelain plate with a little fullers' earth.
Azo-colors give promptly a red mass; if they are
not present, the mixture becomes only yellow or
light brown. All samples of fullers' earth are
not equally active, and tests should be made with
different samples by using fat known to contain
the azo-compound until a good specimen of the
earth is secured.
For the detection of very minute quantities of
the color, the sample may be dissolved in light
petroleum, and the fullers' earth added to the
solution, when the pink color will appear as a
distinct ring or zone at the edge of the deposited
layer of the reagent.
Low has proposed the following test for the
yellow azo-color: A few c.c. of the filtered
fat are mixed in a large test-tube with an
equal volume of a mixture of one part strong
BUTTER 93
sulfuric acid and four parts glacial acetic acid.
The contents of the tube are then heated almost
to boiling and thoroughly mixed by violently
agitating the bottom of the tube. When now
allowed to stand and separate, the lower layer of
mixed acids will be strongly colored wine-red if
the azo-color be present. Pure butter-fat im-
parts no color to the acids, or, at most, only a faint
brownish tinge.
Turmeric and Annatto. — Martin's test will
usually be satisfactory: 2 c.c. carbon disulfid
are mixed with 15 c.c. of alcohol, by adding small
portions of the disulfid to the acohol and shaking
gently; 5 grams of the butter-fat are added to
this mixture in a test-tube and shaken. The
disulfid falls to the bottom of the tube, carrying
with it the fatty matter, while any artificial
coloring-matter remains in the alcohol. The
separation takes place in from one to three
minutes. If the amount of the coloring-matter
is small, more of the fat may be used. If the
alcoholic solution be evaporated to dryness and
the residue treated with concentrated sulfuric
acid, annatto will be indicated by the production
of a greenish-blue color. With many samples
of oleomargarin, a pink tint will be produced,
which indicates an azo-color.
Palm oil has been used as a coloring agent in
butter-substitutes. Crampton & Simons have
94 MILK PRODUCTS
found that two tests devised for detection of
rosin-oil can be satisfactorily adapted to detec-
tion of palm oil. Success depends on several
points. The sample must be kept in a cool
dark place until used, filtered at a temperature
not above 70°, the heating as brief as possible,
and promptly tested. The reagents must be
pure and colorless. Cochran finds that annatto
will simulate palm oil in these tests, and hence
the absence of the former must be assured
(see above) before inferring the presence of the
latter.
Halphen method. — 100 c.c. of the filtered fat
are dissolved in 300 c.c. petroleum spirit and
shaken out with 50 c.c. of potassium hydroxid
solution (o. 5 % of hydroxid) . The water is drawn
off, made distinctly acid with hydrochloric acid,
and shaken out with 10 c.c. of carbon tetrachlorid.
This solution is drawn off, and part of it tested
by adding to it 2 c.c. of a mixture of i part crys-
tallized phenol in 2 parts carbon tetrachlorid. To
this add 5 drops of hydrobromic acid (sp. gr. 1.19).
The test is best performed in a porcelain basin and
the contents mixed by agitating gently. Palm oil
gives almost immediately a bluish-green liquid.
Liebermann-S torch method. — 10 c.c. of the
filtered fat are shaken with an equal volume of
acetic anhydrid, one drop of sulfuric acid (sp.
gr. 1.53) is added and the mixture shaken for
BUTTER 95
a few seconds. If palm oil be present, the heavier
layer separating will be blue with a tint of green.
Egg-yolk has been proposed as a color for
oleomargarin, and although its use is unlikely,
the possibility of it should be borne in mind.
To detect it, about lo grams of the filtered fat
should be shaken with warm alcohol, the liquid
drawn off as closely as possible and evaporated
to dryness. The coloring matter of egg-yolk
is soluble in alcohol, but insoluble in water. It
may be distinguished from turmeric by moisten-
ing it with a few drops of a mixture of boric and
hydrochloric acids, and drying at a gentle heat.
Turmeric becomes brown ; egg-color is not affected.
Egg-yolk contains considerable lecithin, a phos-
phoric acid derivative. Pure fats contain no
phosphorus compound. If, therefore, a few
grams of the fat, carefully freed from water or
curd, are charred and the mass extracted by
boiling with nitric acid, the filtered solution
should not give an appreciable precipitate with
ammonium molybdate.
Vegetable colors may be detected by boiling
up the filtered fat with water, drawing off the
watery liquid, adding a few drops of hydrochloric
acid and heating the mixture with a piece of clean,
undyed wool. True butter colors will not dye
wool under these circumstances.
Caramel may be detected by shaking the
g6 MILK PRODUCTS
watery solution with fuller's earth and filter-
ing. The filtrate is notably paler if caramel is
present. Fuller's earth differs in efficiency, and
each sample should be tested on known solutions.
Preservatives. — The preservatives used in milk
may be found in limited amount in butter, but a
mixture of boric acid and borax is often added as
a substitute for salt.
Glucose is sometimes used as a preservative,
especially in butter intended for export to tropical
countries. Crampton found as much as io%
in a sample of highly colored butter intended
for exportation to Guadeloupe. For the de-
tection of glucose the phenylhydrazin test might
be used. For determination Crampton used the
following method: lo grams of the sample were
washed with successive portions of convenient
bulk, the solution made up to 250 c.c, and an
aliquot portion determined, as given for lactose
on page 32. The solution may also be clarified
by alumina-cream or acid mercuric nitrate and
examined in the polarimeter.
Boric Acid. — 25 grams of the sample are melted,
the watery portion separated and tested as de-
scribed on page 62.
Cheese is the curd of milk which has been
separated from it, pressed, and undergone some
fermentation. The precipitation is produced
either by allowing the milk to become sour
— when the lactic acid is the agent — or by rennet.
The first-named method is mainly applied to the
manufacture of so-called Dutch or sour-milk
cheese, green Swiss cheese, and cottage cheese.
More commonly cheese is obtained by means of
rennet derived from the fourth stomach of the
calf. The action is due to an enzym which
acts directly on the proteins and does not pro-
duce its affect through the intervention of acids.
The curd (cheese) undergoes, by keeping, various
decompositions, some essentially putrefactive,
and due to the action of microbes. The de-
composition of the cheese is termed "ripening."
In the sour milk cheeses, ripening is restricted
intentionally, since there is liability to an irregular
and miscellaneous bacterial growth by which the
fermentations may be carried too far, undesirable
and even harmful products being formed. Such
cheeses are intended for prompt use.
Cheese contains no casein, if by this term
97
98 MILK PRODUCTS
is meant the protein as it exists in milk, or as
precipitated from milk by acids. When milk
is coagulated by rennet, only a part of the
proteins enter into the curd ; true casein contains
about 15.7% of nitrogen, but the protein matter
of cheese contains about 14.3%. Under the
process of ripening this is further decomposed,
amino- and ammonium compounds, peptones
and albumoses being formed.
The following figures, obtained by Van Slyke,
will serve to give some idea of the extent to which
the curd is changed in ripening. The figures
represent average percentage on the total nitrogen.
The cheese was an American cheddar:
Green After Pivb
Cheese Months
Soluble nitrogen compounds ... 4 . 23 35-52
Soluble amino compounds none 11 .66
Soluble ammonium compounds none 2.92
Van Slyke 's experiments seem also to indicate
that the cheese ripened more rapidly when the
curd was precipitated by a larger quantity of
rennet and, especially, that cheese rich in fat
ripened more rapidly than skim-milk cheese.
In addition to the fat and nitrogenous com-
pounds just mentioned, cheese may contain a
small amount of lactose and of lactic and other
organic acids. There is present also a certain
proportion of mineral matter, alkaline and earthy
CHEESE 99
phosphates, along with any salt that has been
added. Traces of nitrates have been found.
Skimmed milk is not infrequently used for the
production of cheese. Partially-skimmed milk is
used in the preparation of certain Dutch cheeses.
Foreign fats, such as are used in the manufacture
of oleomargarin, are sometimes incorporated, the
article being known as "filled cheese."
The common American cheese is known as
Cheddar. According to Van Slyke, this has,
when ripe, the following average composition:
Water 31 -50%
Fat 37.00%
Proteins 26.25%
Ash, sugar, etc 5.25%
The ash of cheese consists largely of calcium
phosphate and salt. Mariani & Tasselli de-
termined the total ash, chlorin, calcium, and
phosphoric acid in 15 samples of cheese. The
amounts of salts (calculated from the chlorin)
depend on the mode of salting. The proportion
of phosphoric oxid was always greater than that
necessary to form tricalcium phosphate, ranging
from 1.07 and 1.08 equivalents of phosphoric
anhydrid to calcium oxid in cheese made from
sour milk to 1.56 to i in Gorgonzola, 1.67 to i
in skim-milk cheese, and 1.75 to i in Edam cheese.
The largest quantities of calcium and phosphoric
oxid were found in sheep 's-milk cheese and in
lOO MILK PRODUCTS
cheese made from sour milk, whence it follows
that acidity does not prevent the precipitation of
calcium phosphate in the curds. The excess of
phosphoric oxid obtained was attributed to acid
phosphates.
The salt in cheese usually ranges between i and
4%.
Analytic Methods.— The analytic points usu-
ally determined in regard to cheese are water, fat,
casein, ash, the presence of fats other than
butter-fat, and coloring-matters.
In addition to this, especially in comparing the
qualities of genuine cheeses, the proportion of
proteic, aminic, and ammoniacal nitrogen is of
value.
Care should be taken to select for analysis a
sample which represents the average composition
of the entire cheese.
The following methods for the determination
of water, fat, ash, total nitrogen, and acidity
have been adopted by the A. O. A. C. :
Sampling. — When the cheese can be cut, a
narrow wedge-shaped segment, reaching from
the outer edge to the center of the cheese, is
taken. This is to be cut into strips and passed
through a sausage-grinding machine three times.
When the cheese cannot be cut, samples are taken
by a cheese trier. If only one plug can be
obtained, this should be perpendicular to the
CHEESE lOI
surface, at a point one-third of the distance from
the edge to the center of the cheese. The plug
should reach entirely through, or only half-way
through, the cheese. When possible, draw three
plugs — one from the center, one from a point
near the outer edge, and one from a point half-
way between the other two. For inspection
purposes, the rind may be rejected; but for
investigations requiring the absolute amount of
fat in the cheese, the rind is included in the
sample. It is preferable to grind the plugs in a
sausage machine, but when this is not done,
they should be cut very fine and carefully
mixed.
Water. — Between 2 and 5 grams of the sample
should be placed in a weighed platinum or
porcelain dish which contains a small amount of
material, such as freshly ignited asbestos or sand,
to absorb the fat that may run out. This is then
heated in a water-oven for ten hours and weighed ;
the loss in weight is considered as water. If
preferred, the dish may be placed in a desiccator
over concentrated sulfuric acid and dried to con-
stant weight, but this may require many days.
The acid should be renewed when the cheese
has become nearly dry.
Fat. — The extraction-tube described on page 16
is prepared as follows : The perforations in the
bottom of the tube are covered with asbestos,
I02 MILK PRODUCTS
on which is placed a mixture containing equal
parts of anhydrous copper sulfate and pure dry-
sand to the depth of about 5 cm., packed loosely,
and the upper surface covered with a film of
asbestos. On this are placed from 2 to 5 grams
of the sample, the mass extracted for five hours
with anhydrous ether, then removed and ground
to fine powder with pure sand in a mortar. The
mixture is replaced in the extraction tube, the
mortar washed free from all matters with ether,
the washings being added to the tube, and the
extraction is continued for ten hours. The fat so
obtained is dried at 100° to constant weight.
Here, as in most extractions, carbon tetra-
chlorid can be substituted for ether, but the
results obtained are not necessarily equivalent,
and in official analyses the official method must
be used.
Total Nitrogen. — This is determined by the
Kjeldahl- Gunning method, using 2 grams of the
sample. The percentage, multiplied by 6.38,
gives the nitrogen compounds.
Ash. — The dry residue from the water de-
termination may be taken for the ash. If the
cheese is rich, the asbestos will be saturated there-
with. This mass may be ignited carefully, and
the fat allowed to burn off, the asbestos acting as
a wick. No extra heating should be applied
during the operation, as there is danger of spurt-
CHEESE 103
ing. When the flame has died out, the burning
may be completed in a muffle at low redness.
When desired, the salt may be determined in
the ash by titration with silver nitrate and potas-
sium chromate.
Provisional Method for the Determination of the
Acidity on Cheese. — Water at a temperature of
40° is added to 10 grams of finely divided cheese
until the volume equals 105 c.c, agitated
vigorously, and filtered. Portions of 2 5 c.c. of the
filtrate corresponding to 2.5 grams of the cheese
are titrated with decinormal solution of sodium
hydroxid, using phenolphthalein as indicator.
The amount of acid is expressed as lactic acid.
The above processes may be advantageously
modified in some respects. The determination
of water may be made by the extraction of the
cheese with alcohol and ether and drying of the
alcohol-ether extract and fat-free solids sepa-
rately. Blyth recommends this method as more
accurate and less tedious than the direct drying.
In the determination of ash it will be better to
extract the charred mass with water and pro-
ceed as described in the determination of the ash
of milk.
The fat extracted by ether may be examined
for other than butter-fat by the distillation
method in the usual way. When the composition
of the fat is alone desired, it may often be ex-
8
104 MILK PRODUCTS
tracted by simple methods. Pearmain & Moor
recommend that 50 grams be chopped fine and
tied up in a muslin bag, which is placed in a water-
bath. When the water is heated, the fat will
generally run out clear. If not clear, it can be
filtered through paper.
Henzold suggests the following: 300 grams
of the powdered cheese are agitated in a wide-
neck flask with 700 c.c. of 5 % solution of potas-
sium hydroxid previously warmed to 20°. In
about ten minutes the cheese dissolves, the fat
floats, and by cautious shaking may be col-
lected in lumps. The liquid is diluted, the fat
removed, washed in very cold water, keaded
as dry as possible, melted, and filtered. It is
claimed that the fat is not altered in composition
by the process.
The fat of cheese may be estimated by the
centrifugal method, as follows:
About 3 grams of the mixed cheese in small
fragments are weighed and transferred to the
bottle, the last portions being washed in with the
acid of water. A few drops of ammonium hy-
droxid are added, and sufficient water to make
the liquid about 15 c.c. The liquid is warmed
with occasional shaking until the cheese is well
disintegrated, and then treated as a sample of
milk. The percentage of fat is found by mul-
tiplying the percentage reading by 15.45 and
CHEESE 165
dividing by the number of grams of cheese taken
for analysis.
Chattaway, Pearmain & Moor use the follow-
ing modification: 2 grams of the cheese are
placed in a small dish and heated on the water-
bath with 30 c.c. of concentrated hydrochloric
acid until a dark, purplish-colored solution is
produced. The mixture is now poured into
the test bottle, portions of solution remaining in
the dish rinsed with the hydrochloric acid fusel-
oil mixture into the bottle, and, finally, enough
strong hot acid added to fill the bottle up to the
mark. It is then whirled for about a minute.
The difficulty in this method is to get all the fat
into the bottle. It is best to weigh the cheese
in the bottle.
For accurate determination of fat, Revis and
Bolton recommend the Schmid-Bondyzynski
method, as follows: About 1.5 grams are weighed
in a small flask, 5 c.c. of hydrochloric acid and
a little powdered sulfur added and the mixture
boiled gently. (For dry cheese, acid of sp. gr.
1.125 is best, for moist cheese, sp. gr. 1.19.)
The mixture is cooled, transferred to the appara-
tus used for Rose- Gottlieb method, by the use of
two portions of 2.5 c.c. each of alcohol and then
small quantities of ether until 12.5 c.c. have been
used. The contents are mixed, 12.5 c.c. light
I06 MILK PRODUCTS
petroleum added and the analysis carried out
as described on page 72.
Lactose. — This may be estimated by boiling the
finely divided cheese with water, filtering, and
determining the reducing power of the filtrate
on Fehling's solution.
Determination oj Albuminoid Nitrogen (Stutzer's
Method). — 0.7 to 0.8 gram of the cheese are
placed in a beaker, heated to boiling, 2 or 3 c.c.
of saturated alum solution added to decompose
alkaline phosphate, then copper hydroxid mix-
ture (see below) containing about 0.5 gram of
the hydroxid, and stirred in thoroughly; when
cold, the mass is filtered, washed with cold water,
and, without removing the precipitate from the
filter, the nitrogen determined by the Kjeldahl-
Gunning method. Before distillation, sufficient
potassium sulfid solution must be added to pre-
cipitate the copper.
The special reagent is prepared as follows:
100 grams of copper sulfate are dissolved in 5000
c.c. of water, 25 c.c. of glycerol added, and then
a dilute solution of sodium hydroxid until the
liquid is alkaline. The mass is filtered, the
precipitate is mixed well with water containing
5 c.c. of glycerol per liter, and washed until the
washings are no longer alkaline. It is then
rubbed up with a mixture of 90% water and 10%
glycerol in sufficient quantity to obtain a uniform
CHEESE 107
magma that can be measured with a pipet. The
quantity of copper hydroxid per c.c. should be
determined. It should be kept in a well-closed
bottle.
Ammonium compounds. — ^About 5 grams of
cheese are rubbed up in a mortar with water,
transferred to a filter, and washed with a liter
of cold water. The filtrate is concentrated by
boiling (if alkaline, it must be neutralized before
heating), barium carbonate added, the liquid
distilled, and the ammonium hydroxid in
the distillate estimated by titration with stand-
ard acid.
According to Stutzer, magnesium oxid or
magnesium carbonate (the latter usually contains
some oxid) should not be used as some of the
amino-compounds may be decomposed.
Amino-compounds. — The nitrogen as amino-
compounds is estimated by subtracting from
the figure for total nitrogen the sum of the
protein and ammoniacal nitrogen. If nitrates
are present, the nitrogen as such should also be
determined and subtracted.
Van Ketel & Antusch propose the following
methods for estimating the nitrogen compounds:
Ammonium compounds. — The sample, pow-
dered with the addition of sand, is distilled with
water and barium carbonate, and the distillate
received in a measured quantity of standard
I08 MILK PRODUCTS
sulfuric acid, and, after boiling, the excess of acid
is neutralized with standard sodium hydroxid,
using rosolic acid as indicator.
Amino-compounds. — These are determined by-
macerating the powdered cheese in water for
fifteen hours at the ordinary temperature. After
adding a little dilute sulfuric acid (1:4), the pro-
teins and peptones are precipitated by phospho-
tungstic acid. The precipitate is filtered off and
washed with water containing a little sulfuric acid.
The filtrate is made up to a definite bulk, and the
nitrogen is determined in an aliquot portion of
the liquid by the Kjeldahl-Gunning process,
allowance being made for the nitrogen existing as
ammonium.
Peptones and Albumoses. — These are deter-
mined jointly by boiling the powdered cheese
(mixed with sand as before) with water and
filtering from the imdissolved casein and albumin.
In an aliquot portion of the filtrate the peptones
and albumoses are precipitated by adding dilute
sulfuric acid and phosphotungstic acid. After
washing with acidulated water the nitrogen in
the precipitate is determined by the Kjeldahl-
Gunning process.
The total nitrogen of the cheese is also deter-
mined, and after allowing for the nitrogen ex-
isting as other forms, the remainder is calctilated
to casein.
CHEESE 109
Poisonous Metals. — ^Lead chromate has been
found in the rind of cheese, and finely divided
lead in a number of Canadian cheeses. In
England zinc sulfate has been employed under
the name of cheese spice to prevent the heading
and cracking. Arsenic has also been found; it
may be detected by Reinsch's test. Lead, zinc,
and chromium may be detected by ashing a
portion of the sample in a porcelain crucible and
applying the usual tests.
FERMENTED MILK PRODUCTS
The usual fermentation of milk is the con-
version of the lactose into lactic acid, but by
special methods other changes may be substituted.
These modified fermentations are of rather
ancient origin, and being produced by mixture
of organisms, the products are complex and
irregular. The proteins are more or less changed
into proteoses and peptones.
Kumiss is milk which has undergone alcoholic
fermentation. The inhabitants of the steppes
of Russia prepare it from mares' milk. When
cows* milk is used, sucrose must be added. It
is often made by adding sucrose and yeast to
skim-milk.
Vieth gives the following analysis of kumiss at
successive stages of fermentation :
Kumiss from Cows' Milk
One One One Three
Day Week Month Months
Alcohol I.I 0.9 l.o I.I
Solids 1 1. 3 8.9 8.6 8.5
Fat 1.6 1.4 1.5 1.5
Casein 2.0 2.0 1.9 1.7
Albumin 0.3 0.2 0.2 o.i
Carbohydrates 6.1 3.1 2.2 1.7
Lactic acid 0.2 0.9 1.3 1.9
Lactoprotein and peptone. 0.3 0.5 0.7 0.9
Soluble ash o.i 0.2 0.2 0.2
Insoluble ash 0.4 0.3 0.3 0.3
IIO
i
FERMENTED MILK PRODUCTS HI
The item "lactoprotein and peptone" refers
to the substance precipitated by tannin after
removal of the casein and albumin.
Kumiss from Mares' Milk
At the Alco- Nitrogenous Lactic Lac-
End of: hol Fat Matters Acid tose Ash
I day 2.47 1.08 2.25 0.64 2.210.36
8 days 2.70 i . 13 2.00 1.16 0.690.37
22 days 2.84 1.27 1.97 1.26 0.510.36
Kejyr. — This is usually made from cows' milk.
It has been used in the Caucasus for centuries.
For its preparation a peculiar ferment is used,
which is contained in the kefyr grains. These
are first soaked in water, by which they are
caused to swell and rendered more active, and
then added to the milk. If taken out of the milk
and dried, the grains may be used repeatedly.
The following are analyses of kefyr:
KdNiG Hammarsten
Alcohol 0.75 0.72
Fat 1.44 3.08
Casein 2.88 2.94
Albumin 0.36 0.18
Hemialbumose 0.26 0.07
Peptone o . 04
Lactose 2.41 2 . 68
Lactic Acid i . 02 o . 73
Ash 0.68 0.71
According to Konig, good kefyr will not
contain more than i % of lactic acid.
Analytic Methods. — SoUds and ash are deter-
I
112 MILK PRODUCTS
mined by evaporation as described on page 13.
Acidity is determined by titration with ^/i<,
alkali, using phenolphthalein or methyl-orange as
an indicator. The amount of acidity is expressed
in terms of lactic acid. The Kjeldahl-Gunning
method will give the total nitrogen. For further
examination of the nitrogenous bodies, the
methods given on pages 106 to 108 may be applied.
Total reducing carbohydrates may be estimated
as given on page 32. If sucrose and common
yeast have been added, the fermented material
will be likely to contain invert-sugar, with un-
changed lactose and sucrose, and the method of
examination of sweetened condensed milk may
be applicable. Fat can, probably in all cases,
be determined with sufficient accuracy by the
L-B. process. If it be desired to make polari-
metric readings, the liquid should be clarified
with acid mercuric nitrate solution (page 37), as
some partly hydrolyzed proteins which have
rotatory power may not be precipitated by other
reagents. The determination of alcohol accu-
rately is difficult, as the quantity is usually
small. The cautious distillation of a conader-
able volume of the material previously neutral-
ized with a little sodium hydroxid will yield
a distillate in which alcohol may be detected
and determined by the usual methods.
FERMENTED MILK PRODUCTS II3
Preservatives are not likely to be used, since
they would interfere with the fermentation, but
attempts may be made to secure better keeping
by adding some preservative after the fermenta-
tion has occurred. In some cases, therefore, tests
for boric acid, formaldehyde, and salicylic acid
should be made, as these will be most likely to be
used.
INDEX
Abrastol, 62.
Acidity, 39.
Acid mercuric iodid, 78.
nitrate, 37.
Adams' method, 14.
Agar, 67.
Albumin, 2, 28, 31.
Aldehyde number, 27.
Almen's reagent, 29.
Alumina-cream, 78
Amphoteric milk, 39.
Annatto, 51, 53, 93.
Asaprol, 62.
Ash, 3, 13.
Babcock's method, 16.
Benzoates, 59-
Boiled milk, detection of, 48.
Borax and boric acid, 62,
Butter, 81.
colors, 92.
fat, 81.
, process, 90.
renovated, 90.
Butyrorefractometer, 90.
Calcium saccharate, 46.
Calculation methods, 21, 28.
Caramel, 95.
Casein, 28, 30.
Cheese, 97.
Citric acid, 2.
Colors in butter, 92.
milk, 51.
Colostrum, 7.
Condensed milk, 69.
Cream, 65.
, evaporated, 69.
Cryoscopy, 44.
Egg-yolk in oleomargarin, 95.
Enzyms in milk, 2.
Evaporated cream, 69.
Fat 9f milk, i.
Fehling's solution, 32.
Fermented milk, iio.
Filled cheese, 99.
Formic acid, 66.
Formaldehyde, 55.
Formalin, 55.
Gelatin, detection of, 45.
Globulin, 2.
Glucose, detection of, 96.
Glycerol-soda, 86.
Hydrogen peroxid, 59.
Imitation cream, 65.
Kefyr, iii.
Kjeldahl-Gunning method, 22.
Kumiss, no.
Lactose, 2, 32.
Lecithin, 3.
Leflfmann-Beam method, 19, 86.
Mercuric iodid, acid, 78.
nitrate, acid, 37.
Metals in cheese, 109.
Milk-sugar, 2, 32.
Multirotation, 39.
Nitrites in milk, 57.
Oleomargarin, 84.
Palm oil, detection of, 93.
Preservation of samples, 64.
Process butter, 90.
Proteins, determination of, 22.
Recknagel's phenomenon, 4.
Refraction index, 42.
Refractometer, 90.
Reichert-Meissl number, 86.
Renovated butter, 90.
Roese-Gottlieb method, 72.
Saccharin, 61.
Saccharate of lime, 46.
Salicylic acid, 61.
Separated milk, 5.
Serum-refraction, 42.
Sodium carbonate, 61.
benzoate, 59.
Soxhlet's method, 32.
Specific gravity, 8.
Sucrose, 46, 74.
Turmeric, 93.
Volatile acids, 85.
Whey, 6.
115
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