NORTH CAROLINA STATE UNIVERSITY LIBRARIES
THE PUBLOW ACID TEST
Questions and Answers
on Milk and Milk-Testing
CHAS. A. PUBLOW, A.B.M.D.CM.
Assistant Professor of Dairy Industry in
HUGH G. TROY, B. S. A.
Agricultural Chemist for the Neiv York State
Department of Agriculture
ORANGE JUDD COMPANY
Kegan Paul, Trench, Trubner & Co., Limited
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Anyone who has had experience in teaching
short-course students in dairying realizes the dif-
ficulty most of these students have in taking notes
and in preparing for examinations. Many of these
men and boys are good cheese and butter makers,
but through lack of preliminary education they
are unable to successfully place on paper the
knowledge they really possess.
It is for these men more particularly that the
authors have prepared this little book.
All up-to-date dairy literature has been freely
consulted with the hope of making these question
compends of the greatest service. Many new facts
that have never appeared in any dairy books have
been added and written in simple language. The
special work on adulterations should be of consid-
erable value to dairy instructors and to those who
wish to prepare for civil service examinations for
state positions in dairy work.
It is the intention of the authors to keep this
book strictly up to date, and they will be grateful
to all readers who may suggest any corrections or
improvements that might be made to further the
usefulness of the book.
CHAS. A. PUBLOW
HUGH C. TROY
Questions and Answers on Milk
What is the average composition of cow's milk?
How does the composition of cow's milk compare
with the composition of human milk?
Human milk contains more sugar, less casein and
albumin and less ash. Konig gives the following
composition of human milk:
Sugar 6.21 %
Casein and albumin 2.29%
The specific gravity of human milk is lower than
cow's milk, being about 1.027.
2 QUESTIONS AND ANSWERS
How does the natural water in milk differ from
Well water, spring water, and water from other
sources varies considerably in composition. So
does the composition of water in milk. But, ordi-
narily speaking, water in milk is not different from
other fresh water.
In what form does fat exist in milk?
In small round globules held in suspension and
forming an emulsion with the other constituents.
These globules vary in size from— ^jq— to ^^f^ of an
inch in diameter.
What can be seen when milk is examined under a
Small fat-globules floating around in the milk
In what form does sugar exist in milk?
What is the composition of milk sugar?
In what form does ash exist in milk?
Part in suspension and part in solution.
What forms of mineral ash are found in milk?
Calcium, sodium, potassium, phosphorus, mag-
ON MILK AND MILK-TESTING 3
In what form does casein exist in milk?
In minute particles held in suspension.
In what form does albumin exist in milk?
Albumin is in solution.
How does the action of casein differ from that of
Casein is in suspension. It is precipitated by
rennet and acids. It is not precipitated by heat.
Albumin is in solution. It is not precipitated by
rennet and acids, but is precipitated by a heat of
What is the composition of casein?
Phosphorus ... .85%
What are the melting points of the important fats ?
Olein 41° F.
Palmatin 142° F.
Myristin 129° F.
These fats become oily when heated and solidify
on cooling, some fats sooner than others.
What is the specific gravity of fat?
QUESTIONS AND ANSWERS
Of what is milk fat formed?
Fatty acids and glycerin.
What fats are present in milk?
What is a volatile fat?
One composed of a soluble volatile fatty acid and
What is a non- volatile fat?
One composed of an insoluble non-volatile fatty
acid and glycerin.
What factors influence the size of fat-globules in
1. Breed of the cow.
2. Individuality of the cow.
3. Character of the food.
4. Period of lactation.
5. Age of the cow.
6. Diseased conditions.
7. The part of the milk examined.
ON MILK AND MILK-TESTING 5
What is the theory of an envelope surrounding fat-
Some chemists have been unable to find any such
covering, but Storch says he has found it to exist,
and that it is composed of 94 per cent water and 64
per cent proteids.
How is the acid in milk, cream starters, or butter-
By an acidimeter.
Describe an acidimeter and the method of testing.
There are several tests for measuring acid, and
sold on the market under different names, such as
Publow's, Mann's, Farrington's, and Marshall's, but
the principle is the same in all of them. An alka-
line solution of known strength and an indicator
called phenol-phthalein are the reagents used. The
purpose of the indicator is to indicate the reaction
of the milk or cream ; that is, it shows whether the
milk or cream is acid, alkaline, or neutral. The
indicator has no color effect in an acid solution,
but it turns an alkaline substance red. . When the
neutral point is reached, the faintly pink color is
To make the test: A known qtfantity of the
milk or cream to be tested is placed in a white cup.
To this a few drops of indicator are added. An
alkaline solution of known strength is then allowed
to run in, drop by drop, from a graduated burette
until the milk or cream assumes a faintly pink
color, which signifies that all the acid in the milk
or cream has been neutralized by the alkali used.
The amount of alkali used can be read on the
6 QUESTIONS AND ANSWERS
burette, and, as its strength is known, it is an easy
matter to figure the amount of acid in the milk or
One c. c. of Yiq normal alkali neutralizes .009
gram lactic acid.
In the test used at Cornell university the alkali
used is a %o normal solution of caustic soda. This
makes a very convenient strength, because when 9
grams of cream or milk are taken .1 c. c. of it neu-
tralizes or represents .01 per cent lactic acid. Thus,
if in testing the milk 4 c. c. of the alkali isoised, the
milk contains .40 per cent of acid.
In Farrington's test the alkali used is made %o
normal by adding 5 tablets in 97 c. c. water. Then
when 17.6 c. c. milk is taken, i c. c. of the alkali
represents .01 per cent acid.
In Mann's test a Yio normal alkali is used and
50 c. c. of milk is tested. The number c. c. of
alkali necessary to neutralize the acid measures in
degrees the amount of acid.
One c. c. of -5- alkali=i degree Mann's test.
To get the per cent acid multiply the number c. c.
alkali used by .009, divide by 50 and multiply by
How can milk or cream be tested on the receiving
1. For acidity by the use of an acidimeter.
2. For odors by sense of smell.
3. For flavors by sense of taste.
4. For insoluble dirt, by eyesight and by allow-
ing samples to stand a few minutes in small glass
jars so that the dirt will settle to the bottom.
ON MILK AND MILK-TESTING 7
5. In cold weather flavors and odors can be de-
tected more readily if milk and cream is warmed up
. 6. By the use of a fermentation test.
7. For adulteration by the use of a lactometer.
8. Samples can be taken for fat-testing in the
Where is milk secreted?
In the mammary glands of all mammals which
suckle their young.
Describe a mammary gland system of a cow.
A cow possesses two mammary glands situated
on either side of the median line of the body on the
under and hind part, and each gland is divided into
two parts, called lobes. Each gland is composed of
glandular tissue, being constructed largely of blood
vessels and epithelial cells. Each of the four lobes
has a small duct opening through which milk is
carried after secretion to the teat outlets.
Describe the udder of a cow.
The udder is the milk reservoir of the cow, and
is situated between her hind legs on the posterior
part of the abdomen. It varies in size and shape
and also in structure. The udder is composed of
glandular tissue such as fatty tissue, milk ducts and
canals, secreting cells, arteries, veins, lymphatics,
nerves, and connective tissue which binds all
the other tissues together. The glands are sup-
ported from the abdomen by a heavy band of
fibrous tissue which extends from the abdomen
through the udder in the median line. The whole
8 QUESTIONS AND ANSWERS
mass, which is more or less grayish red in color,
according to its varied structure, is covered on the
outside by a heavy fold of skin which is covered
with fine hair and has marked elasticity.
Internally the udder is divided into four quar-
ters, the two quarters on the same side communi-
cating with each other and each quarter being sup-
plied with an outlet or teat.
At the upper end of each teat is a fairly large
cavity called a milk cistern, each of which may hold
as much as one-half pint. In these the milk col-
lects after being secreted and carried from the
glandular cells by a more or less complicated series
of milk ducts and canals. At the lower end of
each teat a circular muscle exists, which, when con-
tracted, has the power of closing the lower opening
and preventing the escape of milk.
Considerable muscular tissue exists in the udder,
especially around the walls of milk ducts and their
dividing points. These muscles are well supplied
with nerves so that the animal can by her will
power control to a considerable extent, for a short
time, the evacuation of milk after it has been
secreted by the small cells. She cannot, however,
control the actual secreting process. The milk-
producing power of an udder depends largely upon
the amount of blood carried to and from it through
the arteries and veins.
How and from what is milk secreted?
Milk is secreted from the blood while it passes
through the smallest blood vessels in the udder
called the capillaries and from the lymph while it
passes through the lymphatics.
ON MILK AND MILK-TESTING 9
The water, albumin, casein, and ash all come
directly from the blood stream being more or less
changed as they pass through the very thin walls
of the capillaries and by the action of the glandular
cells. The sugar is formed from the blood. The
fat is derived from the breaking down of the gland
cells by a process of fatty degeneration and from
the lymph stream. The amount of milk secreted
depends upon the amount and composition of the
blood and lymph carried to and from the udder
in a given time and also upon the activity of cell
construction and cell destruction in the mammary
What is colostrum?
Colostrum, or beastings, is the first milk secreted
by a cow after the birth of her calf.
What is the average composition of colostrum?
The composition of colostrum varies in individ-
ual cows to such an extent that only an average
composition can be given.
How does colostrum differ in composition from
Colostrum contains less water, less fat, less sugar,
more casein, more albumin, and more ash. It is higher
lO QUESTIONS AND ANSWERS
in color and strong in odor, and has a laxative
effect upon the bowels of the calf. Varied amounts
of blood and broken-down cells are usually present,
and the viscosity is greater. The specific gravity
is also higher and colostrum is unfit for human
consumption. Examined under the microscope,
large colostrum corpuscles can be seen.
By what tests can colostrum be detected?
1. By the use of a lactometer, which shows a
very high specific gravity.
2. Boiling throws down a large amount of al-
3. Examined under the microscope, colostrum
corpuscles can be seen.
What is the natural color of milk due to?
1. To lactochrome.
2. To the color of the milk fats, especially pal-
What is milk serum?
The serum of milk is that part which is left after
all fat has been removed.
What factors influence the composition of milk?
1. Breed of the cow.
2. Individuality of the cow.
3. Period of lactation.
4. Time of milking.
5. Part of milk tested.
6. Health of the cow.
7. Food and water consumed by the cow.
ON MILK AND MILK-TESTING II
What ferments are present in milk?
1. Organized (Bacteria).
2. Unorganized (Galactase).
What is the difference between an organized and
an unorganized ferment?
An organized ferment is due to the action of bac-
teria and has the power of reproducing itself.
An unorganized ferment or enzyme is formed by
the action of glandular tissue and has not the power
of reproducing itself, although its action may not
be destroyed after performing its function. As an
example of this we have rennet, which does not los»e
its power after coagulating milk.
What are bacteria?
They are the lowest forms of microscopical plant
life, and are composed of protoplasm.
What are spores?
A spore is the breeding cell of a bacterium. All
bacteria do not form spores, many reproducing by
a process known as " fission," the cell simply divid-
ing into two or more parts or bacteria.
What are the three necessities for bacterial growth?
1. Suitable food.
3. A proper temperature.
What bacteria are commonly found in milk?
I. Those that sour milk, called lactic acid bac-
12 QUESTIONS AND ANSWERS
2. Those that produce gas and bad flavors in
milk, called putrefactive bacteria.
3. Those that produce disease called pathogenic
4. Specific bacteria, such as those producing
blue milk, bitter milk, ropy milk, etc.
How do bacteria gain entrance to milk?
1. From the air. The purity of the air deter-
mines the number and character of the bacteria.
The air in unclean stables contains many bacteria.
2. From dirt or dust. All dirt and all dust carry
many bacteria, mostly of the putrefactive type.
3. From the hands, clothing, or body of persons
that have or recently have had or are caring for
persons who have contagious or infectious diseases.
4. From unclean utensils.
5. From infected water supply.
6. From diseased cows.
What effects do bacteria produce in milk?
1. Some forms sour milk.
2. Some forms produce gas in milk.
3. Some produce undesirable flavors.
4. Some cause sweet coagulation.
5. Some cause ropy milk.
6. Some cause bitter milk.
7. Some produce abnormal colors in milk.
8. Some carry disease and render milk unfit for
How is the bacterial content of milk controlled?
I. By absolute cleanliness in all things sur-
rounding the production and handling of the milk.
ON MILK AND MILK-TESTING I3
This tends to prevent the entrance of bacteria into
2. By keeping milk cold. This checks the
growth of bacteria. The lower the temperature, the
more their growth is prevented and the longer will
milk keep sweet.
3. By high temperatures. High temperatures
are used to destroy bacterial life in milk. This is
the principle of pasteurization.
4. Preservatives are used to kill bacteria or to
prevent their growth. The use of preservatives in
milk is prevented by most pure food laws.
5. Electricity has been used to destroy bacteria
6. The use of carbonic acid gas is used to car-
bonate milk and prevent the growth of bacteria.
What methods are used to keep bacteria out of
I. The health of the cows is considered. The
tuberculin test is used to diagnose tuberculosis.
Milk from diseased animals is not used.
• 2. Cows* udders, flanks, and legs are shorn of
hair to make cleaning easy.
3. These parts are washed or wiped with a
damp cloth before milking.
4. Stables are properly ventilated, made free
from dust, whitewashed, or otherwise made sani-
tary by cleanly methods.
5. The health, clothing, hands, and person of the
milkers are regulated in sanitary requirements.
6. Small-top milking pails are used.
7. Milk is strained or filtered in a clean place.
14 QUESTIONS AND ANSWERS
8. Cans, bottles, and all utensils are sterilized
9. Milk is bottled to prevent the entrance of air
10. Milk is cooled to low temperature as soon
as drawn, and kept cold to prevent bacterial
How can bacteria in milk be destroyed?
1. By heating to a high temperature for a time.
Some forms are killed in ten minutes at 140° F.,
while others require a much higher temperature for
a longer period.
2. By electricity.
3. By the use of certain poisons which destroy
What diseases are carried in milk?
1. Typhoid fever.
2. Scarlet fever.
5. Intestinal infections, such as the cholera of
infants and dysentery in adults.
How do the germs of disease enter milk?
1. In dust laden with disease-producing bac-
2. From the body or clothing of milkers who
have had or have been exposed to diseases that
are contagious or infectious.
3. From infected water used in washing or rins-
ing cans or utensils.
ON MILK AND MILK-TESTING 1$
4. From diseased cows, . especially when the
udder is diseased.
5. From the excreta of animals, which may
enter milk in small particles carrying disease-pro-
What causes milk to sour?
The lactic acid bacteria change the milk sugar
into lactic acid, which is sour and as soon as suf-
ficient acid is formed the whole volume of milk
becomes sour to the taste.
What are the causes of bad flavors in milk?
1. Bacteria, which may enter milk in any of the
(o) From dust.
(b) On dirt from the body of the cow.
(c) From the atmosphere.
(d) From hands, body, or clothing of persons
(e) From dirty utensils.
(/) From impure water.
(g) From diseased cows.
2. Flavors absorbed when milk is exposed in
places where strong-smelling substances, such as
turnips and decayed vegetables, are kept.
3. From strong-smelling foods eaten by the cow.
4. Keeping milk at too warm a temperature.
When milk is warm, bacteria present grow rapidly,
and their action on the different constituents of
milk produces bad flavors.
How should milk cans and utensils be washed?
They should be first rinsed with lukewarm
l6 QUESTIONS AND ANSWERS
water, then washed with a brush and hot water
containing some good washing powder. Then
boiling water or steam should be used to sterilize.
The utensils should then be placed in a clean place
free from dust. It is a good plan to expose milk
cans, etc., to the direct rays of the sun, which have
the power of destroying bacteria.
What is pasteurization?
It is the heating of milk to at least 140° F. for
at least ten minutes for the purpose of destroying
bacteria. The milk is then usually cooled to a low
temperature. The word is derived from Louis
Pasteur, an eminent French scientist.
What is sterilization?
It is the heating of milk to at least 212° F. for
the purpose of destroying both bacteria and spores.
How is milk usually pasteurized for commercial
1. By some form of pasteurizing machine in
which steam is the heating agent.
2. By electricity.
What are some of the reliable pasteurizing machines
on the market?
ON MILK AND MILK-TESTING I7
How can buttermilk be prepared from skimmed
Skimmed milk is heated to 165° F. for ten
minutes and then cooled to 70° F., when about 5 per
cent of a good culture of lactic acid is added. The
milk should be softly coagulated in 12 hours. It is
then churned for five minutes and the result is a
fine quality of buttermilk.
How are the fancy acid milk drinks prepared?
By pasteurizing skimmed milk, then cooling and
adding cultures of some acid-producing bacteria
or yeasts. The milk is securely bottled to prevent
What is market milk?
Milk that is produced and marketed solely for its
use as milk.
How is milk marketed?
Milk in its raw state is marketed in one of two
ways, (i) In bulk form. (2) In bottles or sealed
Milk is sold under many descriptive and yet de-
ceiving names, such as aerated, clarified, modified,
pasteurized, standardized, etc. These words usually
indicate some special treatment given to milk by
the producer or dealer.
What is sanitary milk?
Milk that is produced under sanitary conditions.
What is aerated milk?
Milk that has been exposed to the air for the pur-
pose of cooling it or allowing animal odors to pass
1 8 QUESTIONS AND ANSWERS
off. Many forms of aerating devices are used for
this purpose, but aeration has many disadvantages
and practically no advantages in the production of
clean, sweet milk.
What is clarified milk?
Milk that has been run through a separator or
centrifugal machine for the purpose of removing
insoluble dirt. This process has few beneficial ef-
fects on milk. It is much better to keep dirt out
of milk in the first place than try to remedy the evil
What is modified milk?
Milk that is modified for some special purpose,
such as infant feeding, by the addition of such
agents as lime water and barley water, or by the
removal of part of the fat or casein.
What is electrified milk?
Milk that has been treated by a current of elec-
tricity for the purpose of destroying bacteria.
What is pasteurized milk?
Milk that has been heated to a high temperature
(at least 140° F.) for a period of time for the pur-
pose of destroying bacteria. The milk is usually
cooled immediately to at least 50° F. in order to
increase its keeping power. A great deal of the
milk consumed in the larger cities is treated in this
manner, as it is a necessary way for the present
at least, of remedying, in part, defects in milk
caused by carelessness.
ON MILK AND MILK-TESTING I9
What is carbonated milk?
Milk that has been treated with carbonic acid
gas for the purpose of preserving it.
What is malted milk?
Milk that has been heated to a high temperature
for the purpose of killing bacteria, partly con-
densed and then a small quantity of malt added.
What is peptonized milk?
Milk to which some pepsin has been added for
the purpose of making milk more easily digestible.
The pepsin may be added to whole milk, or the milk
may first be partly condensed.
What is condensed milk?
Milk from which a large amount of water has
been extracted by some process of evaporation.
Sometimes cane sugar is added for making what is
known as sweetened condensed milk.
What is the composition of unsweetened condensed
Casein and albumin. 11.92%
Milk sugar i449%
What is the composition of sweetened condensed
Casein and albumin. 11.79%
20 QUESTIONS AND ANSWERS
Milk sugar 13.84%
Cane sugar 36.22%
What is milk powder?
Milk that has been evaporated to dryness and
then placed in a machine which reduces the dried
milk to a finely powdered condition.
What is standardized milk?
Most states have a standard of quality to which
milk must comply before being sold as whole milk.
Some states have a law which requires that milk
must contain at least 3.5 per cent fat and at least
12 per cent total solids. Some breeds of cows do
not give milk that tests that high, so it is necessary
to add some cream or take away some skim milk.
This process is known as standardizing. At the
same time, in some states, milk must comply with
a law which says milk must not be adulterated.
How can the amount of milk or cream necessary
for standardizing be determined?
This problem has been made easy by the use of a
formula and square devised by R. A. Pearson, com-
missioner of agriculture in New York state. Draw
a square and write at the two left-hand corners the
percentages of fat in the milk and the cream or
skim milk that is to be mixed with it. In the cen-
ter write the percentage of fat desired. The dif-
ference between the figures in the center and the
figures at the left are placed on the right-hand cor-
ners with which they stand in line. The figures
at the two right-hand corners then represent the
ON MILK AND MILK-TESTING
proportions in which the milk and the cream or
skimmed milk should be mixed.
The idea can, perhaps, be more easily understood
by working out a problem such as the following:
How much 5 per cent milk must be added to 3.5
per. cent milk to make 1,000 pounds of 4 per cent
.5 jI X 1000 lbs.=333 lbs.
1^ X 1000 lbs.= 666 lbs.
The milk must be mixed .5 part of 5 per cent
milk and i. part of 3.5 per cent milk in every 1.5
parts. Therefore, as figured above we must mix
333 pounds of 5 per cent milk and 667 pounds of
3.5 per cent milk in order to make 1,000 pounds of
4 per cent milk.
Prof. Oscar Erf has also prepared a table to be
used in standardizing milk and cream, but it is not
necessary to give it here.
V/hat means are commonly used to improve the
milk supply of towns and cities?
This work usually is conducted under direction
of the boards of health. In most places all per-
sons delivering milk in towns and cities must com-
ply with the requirements of a special law which
states that all milk sold must be produced and
handled in such a manner that it reaches the con-
sumer in a clean, sanitary condition.
Inspectors are appointed to inspect the dairies
and, if necessary, compel the farmer to improve his
22 QUESTIONS AND ANSWERS
dairy methods. Educational means are used as
far as practicable, but if any man refuses to com-
ply with the sanitary requirements the inspector
reports him to the board of health, which usually
cancels his license and prevents him selling milk
until he fulfils the demands of the board.
For the convenience of both the farmer and the
inspector, and to insure uniform inspections, a
score card is used upon which most conditions can
The score card on pages 24 and 25 is the one
lately devised by the official dairy instructors' as-
sociation, and which is now most used in the United
What is meant by specific gravity?
It means the ratio existing between the weights
of equal volumes of a substance and water at 4
Why is the temperature of 4 degrees centigrade
Because water reaches its greatest density at
What is the specific gravity of whole milk?
The average is about 1.032, but, in some cases, it
may be as low as 1.029, or it may go as high as
1.034 ; that is, if a volume of water weighs 1,000, the
same volume of average whole milk would weigh
How would you calculate the weight of 40 quarts
ON MILK AND MILK-TESTING 23
I quart water weighs 946.4 grams.
I quart milk weighs 946.4X1.032 grams.
453-6 gTams=i pound.
976.6848 grams=2.i53 pounds.
I quart milk weighs 2.153 pounds.
40 quarts milk weigh 2.53X40 pounds=86.i2
How does the weight of 40 quarts milk compare
with the weight of 40 quarts water?
I quart milk weighs 2.153 pounds.
I quart water weighs 2.086 pounds.
40 quarts milk weigh 86.12 pounds.
40 quarts water weigh 83.44 pounds.
The weight of milk is 1.032 times as great as the
same volume water.
What substances make up the milk serum?
Casein and albumin. . 3.4%
Milk sugar 5-0%
Mineral matter 7%
What is the specific gravity of melted milk fat?
Between the temperatures of 120° F. and 160° F.
the specific gravity is .9; that is, when a definite
volume of water weighs 1,000 the same volume of
milk fat weighs 900.
What common proof have we that the specific
gravity of milk fat and milk serum differs?
When milk remains quiet for a time, the globules
of fat rise to the surface in the form of cream.
UNITED STATES DEPARTMENT Or AGRICULTURE.
BUREAU OF ANIMAL INDUSTRY,
SANITIBY INSPECTION OF DAIRIES.
DAIRY SCORE CARD.
Adopted by the Official Dairy Instructors' Assoclatloa
(Subject to revision at future meetioKs.)
Owner or lessee offarm ^
P. 0. address „ _ State.
Total number of cows Number milking ^
Gallons of milk produced daily — _. _
Product is retailed by producer in ,
Sold at wholesale to
For milk supply of — „ _
Permit No. - - Date of inspection _ „ , J90
ApparentiT In Kood hoaltb... I
If iCKted with tubercuUn onee
o year and no tutxirculoFla
h found, or if tested once In
MX months and all reacttoK
animals removed S
(II tested onlT once a year and
rcartliiK anlroali found and re-
mo vul. 2.)
Temperature Of atable. ..%... I
Light: ioursq. ft. otxlasspercow
(Thret sq. ft., 3; Stq.'ft.. 3; 1
CO. ft., I. Deduct for votfren dia-
VentilatlOD. Automatic syatem...
( Adjustable windows, 1.)
Cubic feet of space for cow: 500
to 1.000 leet
(Less than fiOO feet. 2 : less than
400 feet. 1: ics* than 300 feet, 0.)
Location of vUble
Well drained 1
Constructifu of stable ,
Tisht, sound floor and proper
Smootb, tiebt walla and ceU-
Proper stall, tie. and manger. 1
Construction of utensils ,
Water (or cleaning
(Clean, convenient, and abun-
Small-top milking paO
Facilities (or hot water or steam
Clean nOking suite «..
BAICPUNO THS MTUC
Location of milk room
Free from contaminating sur-
Construction of milk room
Floor, walls, and ceiling 1
Light Teiitilation, screens... 1
COWg AXS 8TABLI8.
Cleanliness of cows
Cleanliness of stables
Ceiling and ledges 1
Mangers and partitions 1
Barnyard clean and welldrained.
Removal of manure dally to
field or proper pit
(To 60 feet from aUble. 1.)
trnxsiLS ANO Mn.KiNa.
Care and cleanliness of utensils .
Thoroughly cleansed 5
Inverted In pure air 8
Cleanliness of milking
Clean, dry hands 8
Udders washed and dried .. 6
(Udders cleaned with moist
cloth, 4 ; cleaned with dry cloth
at least IS minutes before milk-
HANDUXO THE MtUC.
Cleanliness of attendants
llilk removed Immediately from
Cleanliness of milk room
Prompt cooling. (Cooled imme-
diately after milking each cow)
Efficient cooling ; below SOP ¥...
(SI" to 55°, 4; 56" to 60<». 2.)
Storage: below 80° F
(51<^tO 56°, 2: 56° to 60°. 1.)
(For jacket or wet blanket al-
low 2: dry blanket or covertrd
Score for equipment + Score for methods = Final score.
NoTt 1.— If any filthy condition Is found, particularly dirty utensils, the total score shall be limited to 49
NoTC 2 —If the water is exposed to danserous contamination or there is evidence of the presence o( 1
dsngerous disease In animals or attendants, the score shall be 0.
26 QUESTIONS AND ANSWERS
How does the fat affect the specific gravity of
The specific gravity of milk fat being only a little
more than .9, it is lighter than the other constituents
and tends to lower the specific gravity.
Why is it that milks, naturally rich in fat, have a
higher specific gravity than milks naturally
poor in fat?
Pure milks, rich in fat, contain larger percentages
of solids not fat than do those of low fat content.
Take, for example, samples of milk of the following
Board of health
Fat Solids not fat lactometer reading
I 3.9 8.6 108.
2 4.9 9.1 III.
No. 2 contains i per cent more fat and .5 of
I per cent more solids not fat than does No. i.
One per cent of fat lowers the lactometer read-
ing practically 3 degrees, while .5 of i per cent
of solids not fat raises the lactometer at least 6
degrees. Thus we have a final lactometer reading
of III in the richer milk.
What is the specific gravity of the milk solids?
The solids of normal milk have a specific gravity
between 1.25 and 1.34, the average being about
What is the specific gravity of the solids not fat?
The solids not fat are made up of casein, albumin,
sugar, and mineral matter, and have a specific
gravity of about 1.50.
ON MILK AND MILK-TESTING 2/
What is the specific gravity of milk protein?
It is held by some that the specific gravity of
milk protein is about 1.34.
How does milk fresh from the cow differ in specific
gravity from milk several hpurs old?
Fresh milk has a lower specific gravity, due in all
probability to the gases in the fresh milk. For this
reason milk should be several hours old when tested
if accurate results are desired.
What is a lactometer?
It is a form of hydrometer made especially for
taking the specific gravity of milk.
What two forms of lactometers are in common
The Quevenne lactometer and the New York
board of health lactometer.
Describe a Quevenne lactometer.
It consists of a hollow, cylindrical body so
weighted at one end that when floated in milk it
takes an upright position. A stem is attached to
the upper end of the body. The stem contains a
scale so graduated and set that when the instru-
ment is floated in the milk the specific gravity may
be read at the upper surface of the liquid. The
better class of instruments contain a thermometer,
the bulb being melted in the lower end of the body
and the scale appearing directly over the lactometer
28 QUESTIONS AND ANSWERS
Describe the Quevenne lactometer scale.
The scale is graduated from 15 to 40, each gradu-
ation marking one lactometer degree, and figures
denote the reading every five degrees. When the
floating instrument comes to rest with the surface
of the liquid on the 15 mark the liquid has a specific
gravity of 1.015, and when it comes to rest in a
liquid with the surface on the 40 mark the liquid
has a specific gravity of 1.040. Hence to obtain
the specific gravity place the figures i.o in front of
the lactometer readings.
At what temperature should the lactometer read-
ing be taken?
The lactometers are made to be used at 60° F.
If the milk is at a temperature above or below
60° F., can a correction be made on the
Quevenne lactometer reading?
When the temperature of the milk is between
60° F. and 70° F., add .1 to the lactometer reading
for each degree above 60. When the temperature
of the milk is below 60 and above 50 subtract .1
from the lactometer reading for each degree below
60. This correction is only approximate and can-
not be used for wider variations in temperature
than those given above. The temperature of milk
should be brought within those limits before tak-
ing the lactometer reading.
Describe the New York board of health lactometer.
It has the general appearance and form of, and
is made like, the Quevenne lactometer, but the
graduations on the scale are dififerent.
ON MILK AND MILK-TESTING 29
Describe the graduations on the scale of a board of
The scale extends from zero to 120. The zero
point is at the top of the stem at the mark to
which the lactometer sinks in water at 60° F.
When the instrument is floated in cleanly skimmed
milk the surface of the liquid would be near the
120 mark; 100 marks the point below which the
instrument is never expected to settle in pure milk.
There are 60 divisions on the scale, each division
equaling two lactometer degrees.
What is the temperature correction for the board
of health lactometer?
Add .3 to the lactometer reading for each degree
of temperature above 60° F., and subtract .3 for
each degree below 60° F. If the temperature of
the milk is more than 10 degrees from 60 degrees,
bring it within those limits before taking the read-
ing, as the correction cannot be used for greater
variations in temperature.
Compare the scales on the board of health and
The zero point on each is the point to which the
instruments sink when placed in water at 60° F.
The 29 mark on the Quevenne scale corresponds
to the 100 mark on the board of health scale, hence
each board of health lactometer degree is .29 of a
Quevenne lactometer degree, or the latter is 344+
times greater than the former.
How may one lactometer reading be converted to
that of the other?
30 QUESTIONS AND ANSWERS
To convert the board of health lactometer reading
to the Quevenne reading, multiply the board of
health reading by .29; and to convert the
Quevenne reading to board of health, divide the
Quevenne reading by .29.
If a sample of milk read 108 on the board of health
lactometer at 66° F., what would its specific
gravity be at 60° F.?
In this problem the temperature correction may
be made first, then convert to the Quevenne reading
by multiplying by .29, and finally prefix the figures
The specific gravity, therefore, is 1.03 184.
Between what graduations on the board of health
lactometer may normal milks vary?
Between 103 and 115 and in some few cases milk
may read as low as 100 or as high as 118.
Between what graduations on the Quevenne lacto-
meter may normal milks vary?
Between 30 and 34, but in rare cases the milk may
read as low as 29 or as high as 35.
Upon what law of physics does the action of the
It depends upon the fact that a solid body float-
ing in a liquid displaces a weight of the liquid
equaling the weight of the floating body.
ON MILK AND MILK-TESTING 3I
How should the lactometer reading be made?
It may be conveniently made by placing the milk
in a cylinder, 15^ inches in diameter and 10 inches
high, then lowering the lactometer in the milk until
it floats. Let the lactometer adjust itself for about
half a minute before taking the reading. If more
than half a minute elapses before taking the read-
ing, cream may rise and affect the result.
How does the temperature affect the specific gravity
Heat causes milk to expand. A given volume of
cold milk will occupy more space when warmed up.
Hence, heat reduces the specific gravity of milk.
By making use of the differences in specific gravity
of its constituents can one test milk accurately
for its fat content without using a chemical?
No, because some of the milk serum will rise
with the fat, even when great centrifugal force is
used to separate them, and the quantity of serum
remaining with the fat will vary with milks of dif-
What is a lactoscope, and how is it used?
It is an instrument for determining approximately
the amount of fat in milk. It may be of some value
when used in connection with the lactometer. The
instrument consists of a graduated glass barrel with
a tightly fitting stopper at the bottom. The stopper
carries a white glass cylinder with black lines
thereon. The cylinder extends up into the barrel
a short distance. Four c. c. of milk are run into
the barrel and water added with thorough mixing.
32 QUESTIONS AND ANSWERS
until the operator can distinguish the dark lines on
the cylinder through the liquid. The graduations
at the surface of the liquid in the barrel then in-
dicate the percentage of fat in the milk.
What is a pioscope?
It is an instrument for determining roughly the
quantity of fat in milk or whether the milk is of a
high or low grade. It consists of a shallow recep-
tacle with a rim raised slightly above a surround-
ing hard, black disk. Into the receptacle a few
drops of milk are placed and covered with a cir-
cular cover-glass having variously tinted seg-
ments. The milk spreads out in a thin layer and
its color as seen against the dark background may
be matched by one of the tinted glass segments.
The different tinted segments represent different
grades of milk.
Describe in brief the Babcock test.
The test was perfected by Professor Babcock and
given to the public in 1890. It depends upon sul-
phuric acid to free the fat-globules and upon cen-
trifugal force to bring the fat together so that it
may be measured. A definite quantity of the milk
is placed in a glass bottle, sulphuric acid is added,
the mixture well shaken, then placed in a centrif-
ugal machine and whirled to bring the fat to-
gether. Water is then added to the bottles ur.til
the fat rises in the graduated part of the neck,
where the volume of the melted fat can be read
directly in percentage.
ON MILK AND MILK-TESTING 33
Describe the Babcock test machine.
• Various styles are found on the market made to be
run by hand, steam, or electrical power. They vary
in size from the small two- or four-bottle tester,
convenient to carry from place to place, to the
larger machines accommodating 24 or more bottles,
and suitable for f actory~ work. They usually con-
sist of an inclosing frame or covering and a hori-
zontal revolving disk attached to a shaft in the cen-
ter. Swinging pockets for holding test bottles are
attached to the rim of the disk in such a way that
they hold the bottles upright when the disk is quiet,
but in a horizontal position, with the opening
toward the center, when the disk is revolving. In
steam machines a turbine is attached, either to the
upper or lower end of the shaft. These machines
are very satisfactory for factory work where steam
power can be used, while the hand machines are
more suitable for testing small dairies or where a
few tests are made occasionally.
How can one determine the number of revolutions
the disk makes for one revolution of the handle
in a hand machine?
Mark a point on the rim of the disk and turn the
handle slowly once around, counting the number
of times the point on the disk reaches the point at
which it started.
How many revolutions per minute should the disk
in a Babcock machine make in order to do good
The number of revolutions depends upon the
diameter of the circle in which the bottles whirl.
34 QUESTIONS AND ANSWERS
Farrington and Woll have figured out that the num-
ber of revolutions should be those given in the fol-
lowing table :
Diameter of Revolutions
the disk per minute
What conveniences should be attached to a Bab-
cock tester run by steam?
1. Steam gauge.
2. Steam brake for stopping the disk.
3. Speed indicator.
4. Water heater and means of filling bottles
What points should be observed in selecting a
1. The machine should be durable and safe to
2. Should run smoothly.
3. Should have a capacity corresponding to the
work and carry an even number of bottles.
4. Pockets should always swing free so the
bottles may come to an upright position when the
disk comes to rest.
5. The bottles should be protected against the
entrance of oil from the machine.
ON MILK AND MILK-TESTING 35
6. There should be means of ventilation for
7. Bearings should be so placed that heat from
the steam will not affect them.
8. Means should be provided for using a heavy-
oil where the bearings may become heated from
9. The bearings should be protected so that
acid cannot come in contact with them when bot-
tles break in the machine.
How should the milk test bottles be constructed?
1. The graduated portion of the neck should be
2. The bottles should hold about 50 c. c. and be
made of tough glass of even thickness throughout,
and strong enough to stand pressure and sudden
changes of temperature.
3. The top of the body of the bottle should
slant toward its center at an angle not greater than
40 degrees, so that all the fat may rise in the neck.
4. The bottom should be perfectly flat, so that
all points will be supported evenly while being
whirled in the machine.
5. The diameter of the neck should be neither
too large nor too small, and should be the same as
other bottles in the set used.
6. The top should be strong, well annealed, and
flaring, to readily admit the pipette and assist in
preventing loss when milk is introduced.
How is the scale on the neck of the bottle divided?
Each cubic centimeter of space is divided into
five equal parts, each part equaling i per cent.
36 QUESTIONS AND ANSWERS
The latter are divided into five equal parts, each
part equaling two-tenths of i per cent. With a
little practice* one may read accurately to one-tenth
of I per cent.
Why does the scale on the neck of the bottle show
the per cent of fat?
Because the graduated portion holds two cubic
centimeters and the specific gravity of melted but-
ter at 140° F. is .9. One c. c. weighs 0.9 of a gram
and 2 c. c. weigh 1.8 grams, which is 10 per cent
of 18 grams, the weight of milk taken.
What can be done to make the scale easy to read?
Rub it over with a soft pencil, burnt cork or a
paste made by dissolving asphalt in turpentine.
How may the test bottles be marked for identifica-
1. A ground space may be made on the body or
neck of the bottle upon which numbers can be
placed with a lead pencil.
2. Copper bands with stamped numbers can
surround the neck of the bottle.
Describe a skim-milk test bottle.
This has two necks, one having a larger bore.
Substances are introduced through the larger bore,
and the smaller one, which is graduated, is used to
collect the fat.
When placing the bottle in a centrifuge, the large
neck should be turned toward the center of the
ON MILK AND MILK-TESTING 37
What points in the construction of skim-milk bot-
tles need special attention?
1. The scale should be correct and the bore large
enough to admit milk or water freely.
2. The glass should be tough and strong enough
to stand the pressure of whirling and the changes
3. The top of the body should slant gradually
toward the center, with no uneven places where fat
4. The large neck should enter the body at the
base of the graduated tube and extend down
through the center of the body almost to the bot-
tom so that the acid will run under the milk and
not char part of it before they can be properly
How closely can percentage be read on a skim-milk
Some bottles are graduated to measure .01 per
cent while others read only as low as .05 per cent.
On either form one can distinguish easily varia-
tions of .01 per cent.
Describe the different forms of Babcock cream test
1. Bottles with necks having a graduated
capacity from zero to 30 of 40 per cent and a body
so large that an 18-gram quantity may be used,
the graduations reading to i per cent or five-tenths
of I per cent.
2. Bulb-neck bottles of the same capacity as
those above, but graduations reading to two-tenths
of I per cent.
38 QUESTIONS AND ANSWERS
3. Bottles with capacity of 9 grams of cream
and 9 c. c. of acid and a scale showing the percent-
age direct as high as 50 per cent.
4. Bottles with scales showing the percentage
direct, to 50 per cent for 9-gram samples, and
with bodies large enough so the cream may be
diluted with water before adding the acid.
What advantages has a g-gram cream bottle
over other forms when the graduations on it
show the percentage direct and its body holds
about 50 c. c?
1. Accuracy is increased, because a neck of
smaller diameter and a finer scale may be used.
2. In reading the percentage direct any error
is not doubled as occurs with the ordinary bottle
when the sample is divided and the observed read-
ing is doubled.
3. The smaller diameter of the neck reduces
the error due to the difficulty of making proper
allowance for the space occupied by the meniscus.
4. The size of the body allows the addition of
9 c. c. of water before adding the usual amount
of acid, thus diluting the cream and preventing the
acid from attacking the fat, as often occurs when
equal volumes of rich cream and acid are mixed.
5. Richer cream may be tested, as the bottle
may be graduated to give readings of 50 per cent.
How does the graduated portion of the neck in
cream test bottles vary?
I. It varies in capacity, some bottles being
graduated from zero to 50 per cent and others from
zero to 30 per cent, etc.
ON MILK AND MILK-TESTING 39
2. It varies in per cent represented by the
smallest divisions on the scale, which, in some
bottles, are equal to i per cent, while in others they
represent two-tenths of i per cent.
3. When a cream bottle is made with a bulb in
the neck, the bulb usually represents 10 per cent,
and is not otherwise graduated. The graduated
portion above and below the bulb may be graduated
as fine as two-tenths of i per cent.
What should be the capacity of cream test bottles?
The part below the neck should hold about 50
c. c, even though only 9 grams of cream are used
in making the test.
How should the pipette be made?
1. Of tough glass with a strong annealed tip,
and having an opening large enough to allow the
milk to run out freely, yet not so large as to flood
the neck of the test bottle.
2. The tube below the body should be about
4 inches long, and small enough to enter the neck
of the bottle.
3. The space between the upper end of the
pipette and the mark on the stem should be large
enough so that after filling the pipette, one will
have time to place the finger over the end before
the milk runs below the mark.
How much milk should the pipette deliver?
It should deliver 18 grams of milk, or 17.44 c. c
18-7-1.032 (sp. g. milk)=i7.44.
40 QUESTIONS AND ANSWERS
Why is the pipette marked 17.6?
Because it holds 17.6 c. c. Some milk is always
left in the pipette, and this makes up the difference
between 17.6 and 17.44.
What is meant by *' calibrating " Babcock glass-
It means the determination of the correctness of
the graduations on the glassware.
By what methods can glassware be calibrated?
1. By the use of a plunger
2. By the use of a scale.
3. By the use of mercury.
4. By the use of an accurate pipette or burette.
Describe how milk-testing bottles may be calibrated
by the use of a plunger.
The bottle is filled to the zero mark with some
liquid such as water. Any drops of the liquid
clinging to the walls of the neck above the zero
mark should be removed with a strip of blotting
paper. A brass plunger divided into two sections
connected by a small wire, and each section equal-
ing I c. c, is inserted in the neck of the bottle until
the first section is completely submerged. The
level of the liquid should then be exactly on the
5 per cent mark.
The plunger is then inserted farther into the
bottle until the second section is submerged, when
the surface of the liquid should reach the 10 per
cent mark, if the bottle is correctly graduated.
Bottles showing* a variation of more than .2 per
cent should be rejected.
ON MILK AND MILK-TESTING 4I
How may cream-testing bottles be calibrated by
the use of a plunger?
In the same manner as milk-testing bottles, ex-
cepting thSt a larger plunger is used. Each c. c.
of space occupied by the plunger equals 5 per cent
in the neck of the bottle.
What precautions should be taken in calibrating
with a plunger?
1. Have the surface of the liquid level with the
2. Remove any liquid adhering to the walls of
the neck above zero mark.
3. The plunger should be dry before inserting.
4. There should be no air bubbles in the neck
5. The temperature of the plunger should be the
same as that of the liquid.
6. While calibrating do not allow heat from the
hand to cause the liquid to expand.
How may testing bottles be calibrated by use of
Fill the bottle to the zero mark with water and
balance it on the scales. Add i gram of water. The
surface of the liquid should then be exactly on the
5 per cent mark. On addition of another gram of
water the surface should be level with the 10 per
cent mark. Each two-tenths of a gram equals i
per cent in the neck of the bottle. By this means
any part of the neck of milk or cream bottles may
42 QUESTIONS AND ANSWERS
How may mercury be used to calibrate the testing
From a correctly graduated burette run 2 c. c. of
mercury into the clean and dry test bottle. Then
push a close-fitting stopper into the neck of the
bottle level with the highest graduation. When
the bottle is turned upside down the mercury should
just fill the graduated portion of the neck. The
mercury may be transferred from one bottle to an-
other without loss by connecting the necks with a
piece of closely fitting rubber tubing. In this
manner several bottles may be tested with the
How may the bottles be calibrated by use of a
Fill the bottles exactly to the zero mark with a
liquid. Then run in from the burette liquid to fill
the graduated part of the neck. Each two-tenths
of a c. c. taken from the burette should equal i per
cent in the neck of the bottle. By this means each
per cent of space in the neck may be readily cali-
How may the pipette be calibrated?
By closing the tip and running in 17.6 c. c. of
liquid from a correctly graduated burette. The
surface of the liquid should then be level with the
mark on the stem. Or one may accurately balance
a small vessel on scales. Place 18 grams on the
opposite side of the scales. Then fill the pipette
to the mark with milk having a Quevenne lac-
tometer reading of 32. Allow the milk to run into
the vessel, blowing the drop from the tip of the
ON MILK AND MILK-TESTING 43
pipette into the vessel. The quantity of milk de-
livered from the pipette should just balance the 18
grams placed on the other side of the scales.
How may the acid measure be calibrated?
1. By running into the measure from a gradu-
ated burette 17.5 c. c. water. The upper surface
should then just reach the 17.5 mark.
2. Balance the measure on a scale and place 17.5
grams weight on the opposite side. Then fill the
measure to the mark with water. The weight of
the water should just balance the 17.5 gram weight.
What forms of acid measures are used?
1. A glass cylinder holding 17.5 c. c.
2. The Swedish acid bottle and 17.5 c. c. pipette
What acid is used in the Babcock test?
Sulphuric acid, with a specific gravity of 1.82 to
1.83 and strong enough to produce a light yellow
color in fat.
What substances other than acids are sometimes
Solvents like ether, alcohol, or petroleum spirits
may be used to bring the fat into solution and
separate it from the milk serum.
What are the principal reasons for using an acid in
I. To destroy the sugar and films of casein that
entangle the fat.
44 QUESTIONS AND ANSWERS
2. To destroy the viscosity of the fluid and to
free the fat-globules.
What should be the color of the sulphuric acid?
It should be clear and almost colorless. Organic
matter falling into the acid becomes charred and
darkens the color. This does not spoil the useful-
ness of the acid, unless undissolved particles are
present which would spoil readings.
What are the advantages of using sulphuric acid in
the Babcock test?
1. It quickly dis^lves milk solids other than
fat and destroys viscosity, thus liberating the fat.
2. In combining with the water and solids of the
serum, it generates much heat, which melts the fat.
3. It increases the specific gravity of the liquid
surrounding the. fat, thus making it easy for the
fat to separate.
4. It IS comparatively cheap and easy to obtain.
5. It is non-volatile when hot, and so produces
no injurious gases.
How may one determine if the acid is of proper
By using a form of hydrometer called an acid-
meter. This instrument, when placed in the acid,
should come to rest with the surface of the liquid,
between the graduations 1.82 and 1.83. A little
experience will enable one to judge by the appear-
ance of the fat at the end of the test if the acid is of
ON MILK AND MILK-TESTING 45
If the acid is too strong, how may it be corrected?
1. By adding the acid to a small quantity of
2. By using less acid in testing.
3. By cooling both milk and acid before mixing.
If the acid is too weak, how may it be corrected?
1. By using a larger quantity.
2. By warming both acid and milk before test-
3. If ^rnuch too weak, the acid should be dis-
Will the acid weaken with age?
Not if kept in tightly stoppered containers. It
will, however, absorb water from the air and be-
come weaker if left in open vessels.
Why is it that acid which was of the proper
strength in winter will be apparently too
strong in summer?
During summer the acid, milk and apparatus has
a higher temperature, so the acid appears stronger.
The remedy is to cool both acid and milk.
What kind of stoppers should be used in bottles
containing sulphuric acid?
Glass stoppers only. The acid and its fumes
destroy both cork and rubber.
How may red spots, produced on clothing by acid,
If the acid has not been in contact with clothing
46 QUESTIONS AND ANSWERS
too long, an application of dilute ammonia will re-
move the spots.
What precautions are necessary in handling sul-
1. All vessels containing acid should be plainly
2. It should be kept in tightly stoppered glass
3. Tables, sinks, drains, and pipes which come-
in contact with acid should be covered with lead.
4. In mixing, always add the acid to the other
liquid — not the liquid to the acid.
5. In measuring or pouring, keep acid away from
6. If a bottle breaks in the centrifuge, flush the
machine with plenty of cold water.
7 If acid is spilled it should be cleaned up with
a cloth immediately and the spot covered with a
8. If acid is spilled on the flesh, wash it off im-
mediately with cold water and apply lime water
or some dilute alkali.
9. Refuse material containing acid should be
disposed of where it will not come in contact with
valuable vegetation, animals, or persons.
What kinds of milk may be tested with the Bab-
All kinds from which a fair sample may be
Can a person who has had no chemical training use
a Babcock test?
ON MILK AND MILK-TESTING 47
Yes, anyone capable of following directions and
who will exercise proper care may learn in a short
time to use the test correctly.
How should the milk sample be taken on the
The sample is best secured by using a sampling
tube, because it takes the same proportionate
amount from each quantity sampled and takes a
uniform column from the upper surface to the
bottom of the milk. When the quantity and qual-
ity of the milk varies but little from day to day, it
may be sampled with a small dipper with good
results. A graduated glass tube can be used by
taking lo or 20 c. c. for each 100 pounds of milk,
or I c. c. for each pound when sampling milk from
individual cows. The sample of a patron's milk
at a receiving station should be taken immediately
after it has been poured into the weighing can. It
should be transferred at once to the proper con-
tainer. Several forms of milk samplers or milk
thieves are on the market and most of them give
good results with milk.
How much milk should be taken for a sample?
Enough so that in case of an accident occurring
during the first test you would still have some left
to make another. About 6 ounces is .sufficient.
When the value of a patron's milk is determined by
its fat content, how often should the milk be
Each quantity weighed in should be sampled and
tested either by itself or by a composite.
48 QUESTIONS AND ANSWERS
"What is a composite sample, and why are such
A composite sample is the quantity of milk se-
cured by mixing together samples of different days*
milk. They are taken in order to determine in one
test the average amount of fat in the milk received
for a definite period at different times.
How should composite samples be kept?
In airtight bottles in a cool, dark place conven-
ient to the place where milk is weighed and
sampled. They should be kept under lock and
key, and sufficient preservative should be added to
keep the milk in good condition until tested.
What points should be considered when securing
containers for composite samples?
1. They should be durable and easy to clean.
2. Stoppers should fit tightly and be easily re-
3. They should have large necks so that milk
may be added to or taken from them quickly and
4. They should be of convenient size and prop-
erly marked to identify each sample.
What preservatives are used in composite samples?
1. Corrosive sublimate or mercuric chlorid.
2. Bichromate of potash.
What are the advantages of corrosive sublimate?
I. It is an effective preservative.
ON MILK AND MILK-TESTING 49
2. Small quantities are used.
3. Can be secured in a convenient tablet form.
What are the disadvantages of corrosive sublimate?
1. It is a deadly poison.
2. In excess it hardens milk casein so that the
acid does not dissolve it so readily.
How much preservative should be used?
Enough to keep milk or cream sweet until tested.
Usually one to two tablets of mercuric chlorid will
preserve one-half pint for two weeks. Of formalin
one-half c. c. should preserve the same sample for
two weeks. If bichromate of potash is used, add
enough of it to give the milk a lemon-yellow color.
About 15 grains is usually sufficient to keep a pint
of milk for two weeks.
What are the advantages of formalin?
1. It is a good antiseptic.
2. It is in liquid form.
3. It is not a violent poison.
What are the disadvantages of formalin?
It tends to harden casein so that sulphuric acid
does not readily dissolve it.
What are the qualities of potassium bichromate as
1. It is inexpensive.
2. It is not a violent poison.
3. It colors the milk yellow and the quantity
necessary to add can be determined by the depth
of color of the solution.
50 QUESTIONS AND ANSWERS
The disadvantages are:
1. Excessive amounts are sometimes necessary
in hot weather to preserve the milk.
2. Then it interferes with the acid dissolving the
casein and a clear test is not secured.
3. High acidity of the milk reduces its preserva-
4. Samples containing it may form a tough skin
over the surface, especially in the light, more read-
ily than with other preservatives.
How should the composite bottle be handled while
Each time a bottle is taken from its place it
should be held in an upright position until it has
been quickly whirled in a circle. This mixes the
fat with the remainder of the sample and prevents
it from becoming attached to the sides of the bottle
and drying. The next portion of milk may then
be added and the Sample shaken once more to dis-
tribute the fresh milk and the preservative evenly.
How often should composite samples be shaken,
and how long may they be kept before testing?
Composite samples should be shaken once a day
whether fresh milk is added or not. They should
be tested every ten days or two weeks at the
What special precautions are necessary in the test-
ing of composite samples?
I. Be certain that any cream that may have be-
come attached to the sides of the container is re-
ON MILK AND MILK-TESTIN 5 1
2. That all lumps or dried particles are dissolved
and evenly distributed. This may be accomplished
by warming the sample not higher than 105° to
110° F. and mixing. Then, if necessary, pass the
cream through a fine sieve and mix before drawing
3. Take extra care to have all casein dissolved,
as the presence of a preservative makes it less
What special points should be observed in testing
1. The bottles in a set should all be. of the same
2. They should be graduated to two-tenths of
I per cent.
3. The bottles should have a plain distinguish-
4. Secure a representative sample of the cream.
5. Use the same quantity of cream in each test.
6. Make tests in duplicate.
7. Weigh out samples. on balances accurate to
Yio of a gram.
8. Do not destroy the sample until the results of
the test are written down.
9. The volume of acid used should be the same
as the volume of substance to which it is added.
10. Shake the bottles for some time after the
casein is all dissolved.
11. Be sure the temperature of the fat is right at
the time of reading.
12. Read the scale from the bottom of the fat
column to the bottom of the meniscus.
52 QUESTIONS AND ANSWERS
13. Write down results immediately upon read-
14. If tests are not satisfactory in every par-
ticular, make them over. Honest results cannot be
accomplished without accurate work.
How would you proceed to secure a proper sample
of the milk for testing?
Where possible, mix the milk by pouring it from
one vessel to another two or three times. If the
cream has risen, care should be taken so that it is
all reincorporated with the milk and evenly dis-
tributed. When it is impossible to pour the milk,
use some appropriate instrument to thoroughly stir
it, then while the fat is evenly distributed the
samples must be taken, using a 17.6 c. c. pipette or
18 grams weighed on a scale.
How is the milk transferred to the test bottle?
By sucking it up into a pipette, quickly placing
the forefinger over the end and allowing the milk
to escape until its surface is level with the 17.6 c. c.
mark on the stem. Then place the tip of the pipette
a short distance into the neck while holding the
bottle in a slanting position, so that its opening will
not be entirely closed. By reducing the pressure
with the forefinger the milk will run down the
side of the neck and will not be blown out by es-
caping air. The drop remaining in the tip of the
pipette should be blown into the test bottle.
How much acid is used, and how is it added?
A volume of sulphuric acid equal to the volume
of milk tested is used. It is usually measured in a
ON MILK AND MILK-TESTING 53
small cylinder and transferred to the test bottle,
allowing it to run down the side of the neck. Any-
adhering milk will be washed down if the bottle is
rotated during the process. The acid should run
under the milk until all is added. Then mix it
quickly and thoroughly by holding the bottle in a
slanting position and whirling the body in a circle
while the top remains stationary.
When should the test bottles be whirled in the
Immediately upon mixing with the acid and
while still hot. The test would not be spoiled if
the bottles stood for a time before whirling, but it
would be necessary to heat them to the proper tem-
perature before beginning the operation.
How long and how often should the bottles be
The first whirling should last five minutes.
Water is then added until the fat rises to the base
of the neck. Then whirl for two minutes to wash
the fat free from any undissolved substance. Hot
water is again added until the bottom of the fat
column is some distance above the zero mark. Then
the final whirling is given for one minute.
How should the water be added?
Hot, with some form of pointed tube or pipette
and allowed to fall directly on the fat to wash out
undissolved particles. In the Mitchell-Walker test
the water enters the bottles from a revolving water
centrifuge while the machine is running.
54 QUESTIONS AND ANSWERS
What character of water should be used?
Soft water should be used when possible, but any-
ordinary good water will serve. One or two cubic
centimeters of sulphuric acid added to the water
used for the final filling will aid materially in giv-
ing a clear fat column, especially if the water is
Why does the mixture of milk and acid become
Sulphuric acid, combining with the water of
milk, generates most of the heat. Some heat is
developed by the action of the acid on the milk
Why does the mixture turn dark?
The acid burns or oxidizes the milk solids, which
contain carbon. The darkening process is similar
to burnt wood, becoming dark when burned in air.
If the acid does not completely dissolve the casein
in composite samples, how may the difficulty
1. Have the acid and milk at a slightly higher
temperature than usual at the time of mixing.
2. Use a larger amount of acid than ordinarily.
3. Shake the samples for a longer time than
usual before placing them in the machines.
If the temperature of the fat is not right when
through whirling, how may it be corrected?
1. If too hot, allow the bottles to stand a short
time at room temperature.
2. If too cold, place the bottles in hot water.
ON MILK AND MILK-TESTING 55
3. All bottles should be placed in water of about
140° F. after removal from the machine if accurate
and uniform results are desired.
How should the fat column appear when the test
It should be a light golden yellow throughout its
length, with no specks or particles of undissolved
matter near its base, and the liquid in the neck
under the fat should be as transparent as the air
above it, thus giving the fat the appearance of
resting in the neck without support.
If the column of fat is darkened and contains black
specks or black substance at its bas** what does
It indicates one or more of the following condi-
1. That the acid is too strong.
2. That the temperature of the milk or acid, or
both, was too high.
3. That too much acid was used.
4. Improper mixing.
If the fat column is light in color, containing white
specks or a clouded or white mass at the base,
what does it indicate?
It indicates one or more of the following condi-
1. That the acid is too weak.
2. That not enough acid was used.
3. That the milk and acid were too cold at the
time of mixing.
56 QUESTIONS AND ANSWERS
If the fat has the proper color, but contains undis-
solved substance, what is the trouble?
It usually indicates insufficient mixing before
placing in the centrifuge, but may possibly be due
to improper water.
When should the per cent of fat be read?
Immediately upon completing the whirling, if
the temperature of the fat is correct. The fat
solidifies at about 100° F., and the temperature of
the bottles should be considerably above that dur-
ing the whirling.
How should the fat be measured?
By holding the fat column on a level with the eye
and counting the diyisions on the scale in that part
of the neck occupied by the fat. Give credit
for all the fat between the lowest and highest points
on the fat column. Each division on the scale
usually represents two-tenths of i per cent, but
some bottles are now made upon which each divi-
sion represents one-tenth of i per cent.
How may an instrument assist in measuring the
By using some form of dividers and fixing the
points at the extreme ends of the fat column. Then
change the position until one point rests on the zero
mark and the other on the scale above. The inter-
vening space will have a length equal to that of the
fat column and the per cent may be read directly.
Does all the fat rise in the neck of the bottle?
It has been found by comparing the results with
ON MILK AND MILK-TESTING 57
chemical analysis that about one-tenth of i per
cent will not rise. When credit is given for the
curved spaces that are not occupied by fat at the
ends of the fat column, the results agree closely
with chemical analysis.
How should skim milk be tested for fat?
In the same manner as whole milk, excepting
that a special double-neck test bottle is used.
About I to 1.5 c. c. extra amount of sulphuric acid
is used, and the machine should whirl the bottles
about a minute longer than usual. The fat per-
centage is read on the graduated part of the small
How are buttermilk and whey tested for fat?
In the same manner as skim milk, excepting
that it is not necessary to use more than 17.5 c. c.
of sulphuric acid.
How should cream be tested for fat?
By weighing accurately a representative sample
of the cream into a special cream test bottle, and
then following the method used for testing whole
How may a proper sample of cream be secured?
By pouring the cream from one vessel to another
and having all lumps of dried cream thoroughly dis-
tributed and reincorporated. Then take the sample
with a sampling tube, or, if one cannot be secured,
use a dipper to transfer the cream to the sample
58 QUESTIONS AND ANSWERS
How may cream that is frozen be sampled?
Samples should not be taken until the cream is
thawed and properly mixed.
Can sour cream be accurately sampled?
If it were absolutely necessary, approximate re-
sults might be secured by adding solid caustic soda
to neutralize the acid and dissolve the casein, then
take the sample after properly mixing.
What quantity of cream should be used in the test
That depends upon the capacity of the graduated
neck and the richness of the cream. If the neck
were graduated from zero to 30 per cent and the
cream tested more than 30 per cent, less than 18
grams of cream would have to be used, and the per
cent would be as much greater than the observed
reading as the quantity taken was smaller than 18
How should cream in sample bottles be prepared
If the cream is in a fluid condition it may be
mixed by pouring from one bottle to another several
times, but if it is lumpy and thick, or has dried on
the bottle, it should be warmed to 105° F., then
properly mixed and sampled. To destroy lumps,
pass it through a fine sieve, then mix and test
Heating above 105° F.' is liable to separate some
fat from the rest of the cream.
Why should the cream sample be weighed rather
ON MILK AND MILK-TESTING 59
1. Because with every change in the per cent of
fat in cream there is a change in the specific gravity,
so that a pipette that would hold the proper amount
of cream of one quality would not hold the right
amount of cream of another quality.
2. Cream is viscous and a variable amount re-
mains in the pipette.
3. Air bubbles become incorporated during the
mixing and gases from fermentation also cause
bubbles which are retained in the cream on account
of its viscosity, so that in measuring out such
cream too small a quantity would be secured.
How should the per cent of fat be read?
By counting the graduations between the bottom
of the fat column and the bottom of the meniscus
at the upper surface of the fat.
Why do we not read to the top of the meniscus as
in the case of milk bottles?
Because the diameter of the neck is greater and
the space occupied by the meniscus is larger in
cream bottles and is altogether too large a quantity
to allow for the fat that does not rise.
When the whole of the fat column has the clouded
appearance and color of muddy water, how may
it be corrected?
I. It may be corrected by shaking the mixture of
cream and acid for several minutes before whirling,
in the meantime keeping the bottles hot. After
the whirling is completed the condition of the test
may be improved by allowing the fat to solidify.
60 QUESTIONS AND ANSWERS
Then rehuat and whirl for a short time in the
machine before reading.
2. In filling after first whirling use a mixture of
equal volumes of sulphuric acid and water.
How often should the test bottles be washed?
The bottles should be thoroughly washed after
each test, not only to remove the fat, but also to
remove other foreign matter that would become too
firmly attached to remove if left in while making
How should the test bottles be washed?
1. Shake them well when emptying.
2. Rinse with hot water containing some good
3. Rinse thoroughly with plain hot water.
What can be done to hasten the washing process?
Special devices which enable the operator to
handle several bottles at a time may be used.
These consist of racks for holding bottles securely,
trays for submerging large numbers of bottles in
the washing solutions, and sprays for rinsing.
How may unsweetened condensed milk be tested
by the Babcock method?
Thoroughly mix the sample and weigh 20 grams
into a bottle or flask. Add 40 c. c. of water and
shake until thoroughly mixed. Test in duplicate,
weighing 18 grams into a milk test bottle and pro-
ceed as in testing milk. Multiply the reading of the
fat by three to obtain the per cent.
ON MILK AND MILK-TESTING 6l
How may the fat in sweetened condensed milk be
determined by the Babcock test?
The method devised by Farrington is practically
Dissolve 40 grams of the condensed milk in 100
c. c. of water. Measure into a milk-testing bottle
a Babcock pipette full to the mark of this sokition.
Add about 3 c. c. of the sulphuric acid used in
testing milk and shake the mixture vigorously.
The coagulated casein incloses the fat and they are
thrown down together by whirling in the machine
at a high speed and a temperature of 200° F. The
liquid containing much of the sugar is carefully
poured off. Ten c. c. of water is then added and
the mass of curd is broken up and thoroughly
shaken with the water to remove more sugar ; 3 c. c.
of acid is again added and the bottle whirled as
before. The liquid is again poured off. The test
is now completed by adding 10 c. c. of water and
17.5 c. c. of sulphuric acid and proceeding as in the
fat test for milk. Multiply the fat reading by 3.2
to obtain the per cent.
C. B. Cochran proposes the following method for
fat in sweetened condensed milk:
" Weigh out 25 g^ams of the sample, dissolve in
water and make up to 100 c. c. Transfer 6 c. c. to
a double tube milk flask provided with a small bore
tube graduated to give percentage of fat for 5 c. c.
of milk. Add 4 c. c. of ether and 4 c. c. acetic acid
(80 per cent or more absolute acid). Acetic acid
of this strength will dissolve the curd, but has no
effect on the sugar. Place the flask in a vessel of
warm water and heat until the ether is expelled.
A layer of milk fat will now be seen floating on a
62 QUESTIONS AND ANSWERS
clear and colorless liquid. Fill the flask with hot
water, thus raising the fat into the graduated tube.
The percentage of fat can now be read. The sam-
ple is then whirled in a centrifugal machine and
another reading made. Multiply the reading by-
Why is it impossible to test sweetened condensed
milk by the Babcock method in the ordinary
Because the acid chars the cane sugar and does
not dissolve all of it. The blackened and undis-
solved sugar rises with the fat and makes it impos-
sible to secure a clear reading.
How may the fat content of dried milk or milk
powder be determined?
Van Slyke has had quite satisfactory results by
combining the Gottlieb and Babcock methods as
" Dissolve lo grams of milk powder in lOO c. c.
of water. Take lo c. c. of this solution in a loo
c. c. glass cylinder. Add i c. c. of strong ammonia
and shake until thoroughly mixed with the solution.
Then add the following reagents, one after the
other, shaking vigorously after each addition be-
fore adding the next material : lo c. c. of 92 per cent
alcohol, 25 c. c. of washed ether, and 25 c. c. of
gasoline or, better, petroleum ether (boiling point
below 80° C). The cylinder is closed with a
tightly fitting, moistened cork stopper. The con-
tents of the cylinder, after thorough shaking, are
poured into a 200 c. c. beaker, the cylinder being
rinsed with a little gasoline, and this added to the
ON MILK AND MILK-TESTING 63
beaker. The beaker is then placed on a steam bath
or in boiling water, and kept there until the ether,
alcohol, and gasoline are completely evaporated.
The remaining liquid is then poured into a milk-
testing bottle and the beaker is rinsed with a little
ether, which is also added to the test bottle. The
test bottle is then placed in boiling water for a few
minutes to evaporate the ether. After cooling the
contents of the test bottle to about 70° F., add 17.5
c. c. of sulphuric acid and complete the operation
as in the case of milk by the Babcock test. The
reading is multiplied by 18. In some cases, as in
dried skim milk, it is desirable to make the original
solution more concentrated by having 20 or more
grams in 100 c. c. of solution.
" The following precautions must be observed in
using this method :
" I. The milk powder solution must be made
uniform before sampling.
" 2. The shaking of the mixture must be vigor-
ous and thorough after the addition of each of the
" 3. The evaporation of the reagents added must
be complete, otherwise the final results are apt to
be too high.
"4. The evaporation must not be carried so far
as to cause any appearance of solid particles in the
liquid. When this happens, the fat column con-
tains darkened material, which makes the results
" This method is applicable to skim milk, whey,
and buttermilk, which usually do not give high
enough results by the Babcock method."
64 QUESTIONS AND ANSWERS
Can butter be tested for fat by the Babcock method?
Yes; but not with as much accuracy as many
other dairy products.
How is butter tested for its fat content?
1. By the ether method. Evaporate a known
weight (2 to 3 grams) to dryness in a flat-bottom
dish. Then wash the total contents of the dish
upon a weighed filter paper, using about 50 c. c. of
ether or naphtha. Then wash free from fat the
residue on the filter paper with ether or naphtha.
The filter is then dried at 100° C. to constant weight
and weighed. The percentage fat is determined by
the difference between the weight of butter and the
weight of fat.
2. By Babcock test. Weigh 4 grams of butter
into a cream bottle, adding enough water to make
18 grams in the bottle. Add 17.5 c. c. of sulphuric
acid and after thoroughly mixing whirl in the cen-
trifuge for five minutes. Add hot water at 200° F.
to raise the fat in the graduated neck of the bottle.
Whirl again for two minutes, then multiply the
reading on the bottle by 4.5.
How should the scale be read in testing butter?
The same as in testing cream, giving credit for
that part of the scale between the bottom of the
fat column and the bottom of the meniscus. The
temperature of the fat should be between 130° and
What is meant by an aliquot part of a quantity?
It is the part that results from dividing a quan-
tity by a whole number, which leaves no remainder.
ON MILK AND MILK-TESTING t$
Example: 20 is an aliquot of 100, resulting from
the division of 100 by 5.
How may a representative sample of cheese be se-
cured for the fat test?
Where possible, cut a wedge-shaped piece reach-
ing from the circumference to the center of the
cheese. When this is impossible, three plugs
should be taken with a trier reaching halfway or all
the way through the cheese, one near the circum-
ference, one halfway to the center, and the third
near the center. In either case the sample secured
may be made fine by passing through a meat
grinder or by cutting to very fine pieces. Thor-
oughly mix before taking the sample.
How much cheese is taken for the test and how is
the per cent calculated?
^ix grams gives good results, but 4.5 grams or 9
grams may bemused. In either case, when the ordi-
nary cream test bottle is used, to obtain the per
cent of fat divide 18 by the weight of cheese taken
and multiply the observed reading by the quotient.
Example : If 6 grams of cheese were taken and the
observed reading was 12, what was the per cent
i2X3=36=per cent of fat.
How is the fat in cheese determined by the Babcock
Weigh into a cream bottle the quantity to be
used. If 6 grams are taken, add 12 c. c. of hot
water to make 18 grams in the bottle, shake thor-
66 QUESTIONS AND ANSWERS
oughly, let stand about five minutes and while it is
still quite warm add 17.5 c. c. of sulphuric acid. It
is well to add half the above amount of acid first,
shake thoroughly and then add the remainder and
shake until the casein is all dissolved. The test
is then completed in the same manner as for cream
It the casein in the fat test of cheese does not read-
ily dissolve, how may it be brought into solu-
1. Let the cheese soak in the hot water in the
test bottle for 10 or 15 minutes before adding the
2. Have the mixture of cheese and water quite
hot at the time of adding the acid and add the
acid in small quantities, shaking between each addi-
3. Add an excess of acid.
Describe the Gerber fat test for milk.
The Gerber test depends upon the same prin-
ciples for separating the fat that are used in the
Babcock fat test. Eleven c. c. of milk, 10 c. c. of
sulphuric acid (specific gravity 1.825) and i c. c.
of amyl alcohol are used. The cork is inserted and
the contents of the bottle thoroughly mixed. ^ The
cork should then be forced in until the liquid ex-
tends well into the narrow graduated neck at the
ooposite end of the bottle. The mixture is centri-
fuged five minutes, the bottles resting on the
corked ends meanwhile. The fat column is then
read the same way as in the Babcock test.
ON MILK AND MILK-TESTING 6^
How is the Russian Babcock fat test bottle con-
The bottle consists of a cylinder and a graduated
neck. The cylinder is about an inch in diameter
and 55^ inches long, having a constriction a short
distance above the surface of the liquid, when the
milk and acid are mixed. The funnel-shaped lower
end of the graduated neck rests on the shelf formed
by the constriction, while the upper end extends a
short distance out of the cylinder.
How is the Russian Babcock fat test operated?
The neck is removed from the bottle while adding
the milk. It is replaced before whirling the bottle
in the centrifuge. After whirling for five minutes
at the speed proper for the size of the machine
(usually 1,200 revolutions per minute), hot water
is added. The special construction of the machine
and the bottle make it possible to add hot water
without stopping the whirling. The bottle is
whirled for one minute after adding the full amount
of water. The per cent of fat is read as in the regu-
lar Babcock fat test.
What are the features peculiar to the Russian Bab-
cock fat test?
1. A specially constructed test bottle.
2. The use of one-half the amount of milk and
acid taken in the Babcock fat test.
3. A specially constructed centrifuge, enabling
the operator to add hot v/ater without stopping the
68 QUESTIONS AND ANSWERS
Give four formulas used in determining the solids
not fat in milk.
1 L+ 7F __ gQ^^is j^Qt fat.
2 ^ + .2 F + .14 = solids not fat.
3 J + .2 F = solids not fat.
L + F
solids not fat.
In each of these formulas L=lactometer read-
ing and F=fat.
How do the results secured by the different
No. I gives the highest results, while No. 3 gives
the lowest. Nos. 2 and 4 give about the same re-
sults excepting on rich milks, when No. 4 gives
results that are nearly as high as those secured
with formula No. i.
With what class of milks does each of the formulas
give best results?
Formula No. i gives results that correspond
fairly well with chemical analysis for milks having
a Quevenne lactometer reading of 33 or more and
having more than 4.5 per cent of fat. Formula
No. 2 gives its best results in milks having a
Quevenne reading between 31 and 33 and a fat
content between 3.7 and 4.5 per cent.
Formula No. 3 gives best results on all milks
having a Quevenne reading of less than 31 and a
fat content of 3.7 per cent or less.
Formula No. 4 will give good results with milk
of average quality or richer milks.
ON MILK AND MILK-TESTING 69
How may the per cent of total solids be deter-
By adding the fat as determined by the Babcock
test to the solids not fat, as determined by the
application of the formula.
Is there a formula for determining the per cent of
protein in milk?
The following formula has been developed by
G. A. Olsen:
In this formula T S=total solids, A=ash, and
P=protein. The ash is to be called .75 in all
Below what percentage do the solids not fat of
pure milk rarely go?
The solids not fat of pure milk are usually more
than 8.5 per cent, and they very rarely go below
8.4 per cent.
How does the addition of water to milk affect the
Since the specific gravity of water is less than the
specific gravity of milk, the addition of water to
milk reduces the specific gravity of the mixture.
How does the skimming of milk affect its specific
Since the specific gravity of the fat is less than
the specific gravity of the other constituents of
milk, skimming increases the specific gravity.
yO QUESTIONS AND ANSWERS
Why is it that the specific gravity is not a sure
indication that milk has been neither skimmed
Because a sample of milk might be skimmed, or
partly skimmed, and then just water enough added
to reduce the specific gravity to what it was be-
fore the skimming took place ; thus there would be
no change in the specific gravity, although the milk
What is the approximate proportion of fat to solids
not fat in normal pure milks?
One cannot state the proportion definitely, since
the relative quantity of the constituents in milks
from different cows, breeds, etc., varies. In gen-
eral it will be found that the pure milk of a herd
contains fat and solids not fat closely approaching
some one of the proportions given in the following
Fat not fat Total solids
3.00 8.40 11.40
3.25 8.47 11.72
350 8-55 12.05
3.75 8.62 12.37
4.00 8.70 12.70
4.25 8.77 13.02
450 8.85 13.35
4.75 8.92 13.67
5.00 9.00 14.00
5.25 9.07 14.32
5.50 9-15 14.65
5.75 9.22 14.97
6.00 9.30 15.30
ON MILK AND MILK-TESTING 7I
What are the different forms of adulteration of
milk often found?
3. Watering and skimming.
4. The addition of preservatives.
5. Addition of coloring matter.
6. The addition of acid neutralizers.
How does watering affect the percentage of the
different milk solids?
It reduces the percentage of all the milk solids,
and reduces them in the same proportion.
How does skimming affect the percentage of the
It reduces the percentage of the fat and slightly
increases the percentage of all other constituents.
How may the presence of added water in milk be
Since the water of milk has the same chemical
composition as pure water from any source, and
the water content of milk varies to some extent, the
presence of added water in small amounts cannot
be determined directly. When the low lactometer
reading, low fat content, or physical characteristics
of the milk lead one to suspect that it is adulter-
ated a control sample of the milk as produced by
the cow or herd should be procured if possible. The
composition of the two samples should be com-
pared. If the suspected milk is to any great extent
lower in quality, and especially if the per cent of
72 QUESTIONS AND ANSWERS
solids not fat is reduced, it is safe to conclude that
the milk was watered.
If a sample of milk gives a Quevenne lactometer
reading of 29, and *is found, upon testing and
applying the formula for solids not fat, to have
4 per cent of fat and 8 per cent of solids not fat,
was it adulterated? How much, and what was
the form of adulteration?
One may conclude that any milk having 4 per
cent of fat should have at least 8.6 per cent of
solids not fat. It would then be plain that the milk
was watered, since the solids not fat are, reduced
approximately 7 per cent, determined as follows:
.6-^8.6=.o697X 100=6.97 per cent of added water.
How may one detect when a sample of milk has
If the suspected sample has a low percentage of
fat, higher lactometer reading, and an equal or
larger percentage of solids not fat than the control
sample, then it is safe to conclude that the milk
If a sample of milk has a Quevenne lactometer read-
ing of 33 and contains 3 per cent of fat, was it
adulterated? ' In what way was it adulterated,
and how much?
Determine the solids not fat by the formula :
-^ +.2F=solids not fat.
8.25+.6o=8.85^olids not fat.
ON MILK AND MILK-TESTING 73
By referring to the table given in answer to ques-
tions on page 70, it appears that milk haying 8.85
per cent of solids not fat should contain 4.5 per cent
4.5 — 3=1.5 per cent of fat missing.
i-5^4.5=-3333X 100=33.33 per cent of the fat re-
moved by skimming,
How may one detect when milk has been skimmed
Milk has been skimmed and watered if the per-
centage of all the solid constituents are reduced and
the per cent of fat is reduced to a much greater
extent than the other solids.
If a sample of milk contains 2.8 per cent of fat and
8.2 per cent of solids not fat, and the control
sample contains 4.5 per cent of fat and 8.85
per cent of solids not fat, how was the milk
adulterated and what was the per cent of
By comparing the solids not fat in the two
samples it will be seen that the milk has been
watered, because the solids not fat are reduced.
Calculate the per cent of added water by determin-
ing the quantity of solids displaced by it.
.65 -f-8.85=.0734X 100=7.34 per cent of added
Next determine how much the fat is reduced.
1. 7-^-4.5=. 3777X100=37.7 per cent of fat miss-
Since we know that the solids not fat have been
74 QUESTIONS AND ANSWERS
reduced 7.34 per cent, and that watering reduces all
milk solids in the same proportion, it follows that
the fat was also reduced 7.34 per cent by watering.
The total reduction of the fat minus 7.34 must have
been lost by skimming.
Therefore, the milk was watered 7.34 per cent,
and 30.43 per cent of the fat was removed by skim-
How should a factory man or shipping station
agent determine whether milk has been
watered or skimmed when it is impossible to
secure a control sample?
First determine the composition of the suspected
milk. Then compare the results with some stan-
dard. When suspected milk is furnished by an
original producer it usually is not difficult to learn
at least the breed of cattle producing the milk. If
the herd is of a breed that produces milk of a high
quality, then one should use a higher standard for
comparison than in the case where the milk is from
a herd of a breed that naturally produces milk of a
low quality. If the herd is composed of mixed
breeds or common stock it may be assumed that
the pure milk is of average quality. To judge milk
in this manner would be a difficult problem for
one having no experience in dairy work, but an
experienced factoryman or agent in a shipping
station should have little trouble in gaining in-
f )rmation sufficient to w^irrant a fairly reliable con-
ON MILK AND MILK-TESTING 75
If a sample of milk contained 8.5 per cent of solids
not fat and 3.3 per cent of fat, should it be con-
sidered as adulterated?
If one -should learn that the milk was produced
by a herd of Jersey cows, it should be considered
adulterated. In that case the composition of the
original milk would be at least 4.4 per cent of fat
and 8.8 per cent of solids not fat. Those figures
could be used as a basis for computing the kind and
amount of adulteration. If the milk was produced
by a Holstein herd, there would be the possibility
that it was adulterated only in the sense that a
herd of cows was selected which gave a low grade
of milk, thus bringing the quantity of total solids
below the legal standard of 12 per cent. If such
milk was sold and no information could be gained
regarding the character of the herd producing it,
then it would be considered as having been actually
What is the Hart casein test?
It is a method of testing milk for the percentage
of casein it contains.
Upon what principles is the Hart casein test based?
1. That dilute acetic acid coagulates casein in an
insoluble form heavier than the milk serum.
2. The ability of chloroform to extract the fat
from the precipitated casein and form a solution
heavier than the milk serum or coagulated casein.
3. Adopting a graduated tube and a volume of
milk so that the volume of collected casein indicates
on the scale the percentage of casein in the milk.
76 QUESTIONS AND ANSWERS
4. Applying centrifugal force to separate the
serum, the casein, and the chloroform fat solution.
What pieces of apparatus are used in the Hart
1. A 5 c. c. pipette for measuring the milk.
2. A cylinder holding 2 c. c. to the mark, for
measuring the chloroform.
3. A strong test tube 5.6 inches long. About
2.6 inches of one end is formed into a graduated
neck one-half the diameter of the remainder, which
forms the body. The body of the tube should hold
35 c. c. and the graduated part exactly 5 c. c. Each
graduation on the scale represents .1 of i c. c, or .2
per cent of casein. The opening is at the large end
of the tube.
4. A strong centrifuge properly constructed for
holding the test tubes and geared to give a speed
nearly twice as great as would be required in a
Babcock fat test machine having a revolving disk
of the same size.
5. A thermometer for determining the tempera-
ture of the milk and acid solution.
What reagents are used in the Hart casein test?
Dilute acetic acid and chloroform of the best
How much and of what strength is the acetic acid
used in the Hart casein test?
Use 20 c. c. of a solution containing 0.25 per cent
of acetic acid.
ON MILK AND MILK-TESTING *jy
How may an acetic acid solution of proper strength
Add to lo c. c. of pure glacial acetic acid 90 c. c.
of water. Take 25 c. c. of this solution and make
it up to 1,000 c. c. by the addition of water. The
solution then contains 0.25 per cent of acetic acid.
How is the Hart casein test carried out?
Add 2 c. c. of the chloroform, 20 c. c. of the dilute
acid, and 5 c. c. of the milk, in the order named, to
the test tube. The temperature of the milk and
acid solution must be within 5° of 70° F. A lower
temperature tends to give a higher reading, and a
higher temperature has the reverse eflfect. The
thumb is placed over the opening and the tube
inverted several times and shaken with some vigor
for not more than 20 nor less than 15 seconds. The
agitation must be just sufficient to thoroughly mix
the contents and yet not form an emulsion. The
tubes may be whirled in the centrifuge at once or
may stand 20 to 25 minutes before whirling, if
necessary. The speed of a revolving disk 15 inches
in diameter should be approximately 2,000 revolu-
tions per minute, and should continue seven and
one-half to eight minutes. If the test has been
properly made there will be found in the bottom of
the tubes on taking them from the centrifuge a
layer of the chloroform fat solution and immedi-
ately over it the layer of casein. Allow the tubes
to stand 10 minutes after removing from the ma-
chines to allow the casein to come to a constant
volume. Then read the test.
78 QUESTIONS AND ANSWERS
What points should receive special attention in
making the Hart casein test?
1. The temperature of the milk and acid solu-
tion must be right.
2. The mixture must be shaken properly and for
the right length of time.
3. The speed of the centrifuge must be sufficient,
yet not too great.
4. Allow ten minutes to elapse after complet-
ing the whirling before reading the test.
What coloring matters are sometimes added to
2. Coal-tar colors.
How does artificially colored milk differ in appear-
ance from uncolored milk?
In uncolored milk the natural yellow is contained
largely in the cream. In colored milk the color
remains after the cream has risen or been removed.
The skim milk does not show the familiar bluish
tint when coloring matter has been added.
What is the nature of annatto coloring matter?
Annatto is a reddish-yellow coloring matter ex-
tracted by weak alkaline solutions from the pulp
inclosing the seeds of a shrub that grows in South
America and the West Indies. The alkaline solu-
tion is used for coloring purposes.
Give a simple test for annatto coloring in milk.
In a tig^htly corked vial or test tube shake
ON MILK AND MILK-TESTING 79
vigorously 10 c. c. of milk and an equal volume of
ether. If annatto is present the amount will be in-
dicated by the depth of the yellow coloring in the
ether layer which forms on the surface when stand-
How may foreign color be detected in milk?
The following method was developed by Leach:
1. Warm about 150 c. c. of milk in a porcelain
dish and add about 5 c. c. of acetic acid, after which
slowly continue the heating to the boiling point
while stirring. Gather the curd, when possible,
into one mass by the stirring rod and pour off the
whey. If the curd breaks up into small flakes,
separate from the whey by straining through a
sieve. Press the curd free from adhering liquid,
transfer to a small flask, and macerate for several
hours (preferably overnight) in about 50 c. c. of
ether, the flask being tightly corked and shaken at
2. Detection of annatto in the ether extract.
Decant the ether as obtained above into an evapo-
rating dish and evaporate the ether over hot water.
Make the fatty residue alkaline with sodium hy-
droxide, and pour upon a very small wet filter while
still warm. After the solution has passed through,
wash the fat from the filter with a stream of water
and dry the paper. If, after drying, the paper is
colored orange, the presence of annatto is indicated.
Confirm by applying a drop of stannous chlorid
solution, which, in the presence of annatto, produces
a characteristic pink on the orange-colored paper.
3. Detection of coal-tar color (" aniline orange ")
in the curd. The curd of an uncolored milk is per-
80 QUESTIONS AND ANSWERS
fectly white after complete extraction with ether,
as is also that of milk colored with annatto. If the
extracted fat-free curd is distinctly dyed an orange
or yellowish color, aniline orange is indicated. To
confirm the presence of this color, treat a lump of
the fat-free curd in a test tube with a little strong
hydrochloric acid. If the curd immediately turns
pink, the presence of aniline orange is assured.
4. Lythgoe's test for aniline orange is as follows:
Treat about 10 c. c. of the milk with an equal
volume of hydrochloric acid (specific gravity 1.20)
in a porcelain casserole and give the dish a slight
rotary motion. If an appreciable amount of aniline
orange is present, a pink color will at once be im-
parted to the curd particles as they separate.
5. Detection of caramel (in the curd). If the
fat-free curd, after extraction with ether, is colored
a dull brown, caramel is to be suspected. Shake
a lump of the curd with strong hydrochloric acid in
a test tube and heat gently. In the presence of
caramel the acid solution will gradually turn a deep
blue, as will also the white fat-free curd of an un-
colored milk, while the curd itself does not change
color. It is only when this blue coloration of the
acid occurs in connection with a brown curd, which
itself does not change color, that caramel is to be
suspected, as distinguished from the pink colora-
tion produced at once under similar conditions by
Name several of the preservatives that are some-
times used in milk.
2. Borax and boric acid.
ON MILK AND MILK-TESTING 8l
4. Benzoates and benzoic acid.
5. Carbonate and bicarbonate of soda.
6. Salicylic acid.
How may the presence of peroxides in milk be de-
Add to 15 or 20 c. c. of milk in a milk test bottle
or test tube a quantity of paraphenylenediamin
hydrochlorid the size of a pea and shake the mix-
ture vigorously for five or ten seconds. If per-
oxides are present the milk will turn blue within
a few minutes. When the blue solution is made
alkaline the color changes to a yellowish light red.
If the peroxide has been in the milk for a long time,
the test may not work well.
How may borax or boric acid in milk be detected?
To 50 c. c. of the milk add enough sodium hydrate
to make alkaline. Evaporate the solution to dry-
ness and incinerate. Acidify the ash with a small
amount of strong hydrochloric acid. A strip of
tumeric paper is then soaked in the solution for a
few minutes -and afterward dried on a clean glass
or porcelain surface. If the paper when dry is a
reddish color and turns to a dark olive green on
the addition of dilute ammonia, the presence of
boric acid or borates is assured.
How may the presence of formaldehyde in milk be
To 15 or 20 c. c. of milk in a Babcock milk test
bottle or in a test tube add 4 or 5 drops of a 10 per
cent solution of ferric chlorid. Then add a volume of
82 QUESTIONS AND ANSWERS
sulphuric acid equal to the volume of milk taken.
Shake the bottle in a circle, but not sufficient to
mix the milk and acid to any great extent. In the
presence of formaldehyde a deep bluish-violet color-
ation appears in the circle where the milk and acid
join. Hydrochloric acid having a specific gravity
of 1.2 may be substituted for sulphuric acid in the
How may the presence of carbonates in milk be de-
1. The ash of milk containing carbonates will
effervesce upon the addition of a few drops of
diluted hydrochloric acid. This is a strong indica-
tion of added carbonates.
2. Add to lo or 15 c. c. of the milk an equal
volume of alcohol and a few drops of a i per cent
solution of rosalic acid. In the presence of car-
bonates a rose-red color appears, while pure milk
shows a light yellowish-red color.
How may the presence of benzoic acid in milk be
Add 5 c. c. of dilute hydrochloric acid to 50 c. c.
of the milk in a flask and shake to curdle. Extract
the curdled milk with successive portions of ether.
Transfer the ether to a separatory funnel and shake
with dilute ammonia, which separates the benzoic
acid from the fat, in the form of ammonium ben-
zoate. Draw off the ammoniacal solution and
evaporate in a dish over hot water until all free
ammonia has disappeared, but before dryness is
reached add a few drops of ferric chlorid reagent.
A flesh-colored precipitate indicates benzoic acid.
ON MILK AND MILK-TESTING 83
All free ammonia should be driven off, otherv/ise
ferric hydrate would be formed.
How may the presence of salicylic acid in milk be
The acid is seldom used as a preservative in milk.
If its presence is suspected, proceed exactly as in
testing for benzoic acid. On applying the ferric
chlorid to the solution after the evaporation of the
ammonia a violet color indicates the presence of
How can the presence of starch in milk be de-
To 10 or 15 c. c. of milk in a test tube or vial add
a few drops of an iodine solution. If starch is
present it will be colored blue by the iodine.
How may milk that has been heated to 175° F. be
1. To 15 or 20 c. c. of milk in a small bottle or
test tube add i c. c. of a concentrated starch solu-
tion and 6 or 8 drops of a 10 per cent solution of
potassium iodid. Next add 4 or 5 drops of a 2 per
cent solution of hydrogen peroxid. Upon shak-
ing the mixture it will turn to a dark blue color if
the milk has not been heated to 175° F.
2. In the same manner as above, add a quantity of
paraphenylenediamin hydrochlorid about the size
of a pea and 4 or 5 drops of a 2 per cent solution
of hydrogen peroxid. The mixture turns blue on
shaking if the milk has not been heated to 175° F.
84 QUESTIONS AND ANSWERS
What causes the color of the milk to change in the
tests for heated milk?
The enzymes of the milk set free oxygen from
the hydrogen peroxid and the free oxygen sets
free iodine from the potassium iodid. Then the
free iodine colors the starch blue. When the
enzymes are destroyed by heat no action takes
place and the milk remains white.
In the second test the oxygen, set free by the
enzymes, acts upon the other reagent, causing it to
change to a blue color.
What are the common ways of adulterating cream?
1. By diluting the cream with milk.
2. By the addition of thickeners.
3. By the addition of preservatives.
4. By the addition of acid neutralizers.
How may the tendency to dilute the cream be over-
By buying and selling cream upon the basis of
the fat content.
How may the presence of condensed milk or con-
densed skim milk in cream be detected?
Separate the fat of the cream from the serum.
Determine the per cent of solids not fat in the
serum. If the serum contains a greater percentage
of milk solids not fat than is found in skim milk,
the presence of condensed milk or condensed skim
milk is assured.
How may the presence of gelatin in cream be de-
ON MILK AND MILK-TESTING 85
Prepare an acid solution of mercuric nitrate by-
dissolving mercury in twice its weight of nitric acid
of 1.42 specific gravity, and diluting the solution to
25 times its bulk with water. To 10 c. c. of the
cream to be examined, add an equal volume of
acid mercuric nitrate solution, shake the mixture,
add 20 c. c. of water, shake again, allow to stand
five minutes, and filter. If much gelatin is present
the filtrate will be opalescent and cannot be ob-
tained very clear. To a portion of the filtrate con-
tained in a test tube add an equal volume of a
saturated aqueous solution of picric acid. A yellow
precipitate will be produced in the presence of any
considerable amount of gelatin, while smaller
amounts will be indicated by a cloudiness. In the
absence of gelatin the filtrate obtained will be per-
fectly clear. The test will work equally well for
determining the presence of gelatin in milk.
How may the presence of starch in cream be de-
By adding a small amount of iodine solution as
in the test for starch in milk. A slightly larger
quantity of the iodine solution should be added, as
the greater amount of fat in cream will absorb
more of the iodine.
What substances are often used as cream thicken-
1. Sucrate of lime (viscogen).
2. Condensed milk or condensed skim milk.
S6 QUESTIONS AND ANSWERS
How is sucrate of lime made?
Slake 3 pounds of freshly burned lime in hot
water. Make the quantity up to 5 gallons by add-
ing water. Dissolve 10 pounds of sugar in five
gallons of water. Mix the two solutions and stir
at intervals for about three hours. Let settle and
use the clear solution.
How may the presence of viscogen in cream be
Determine the number of c. c. of -f^ acid re-
quired to neutralize the ash from 100 grams of the
cream. The -^ acid should be added in excess
and titrated back with -^ alkali. If more than
14 c. c. are required it is a strong indication that
viscogen is present in the cream.
How may the presence of preservatives in cream
The methods used for detecting preservatives in
milk may be applied to cream as well. In some
cases it may be necessary to dilute the cream before
applying the tests.
How may the presence of acid neutralizers in cream
The substances used to neutralize the acid are
alkalies or carbonates and the methods for detecting
them are the same as those used on milk.
How is butter sometimes adulterated?
1. By substituting a foreign fat for the whole or
a part of the butter fat.
2. By selling renovated butter as fresh butter.
ON MILK AND MILK-TESTING 87
3. By incorporating an excess of moisture dur-
ing the process of manufacture.
4. By the addition of preservatives.
How may renovated butter and oleomargarine be
distinguished from butter?
1. Melt some of the substance in a spoon by
holding it over a small flame. Let the melted fat
boil vigorously. Renovated butter and oleomar-
garine snap and sputter with noise while boiling
and very little, if any, foam is formed. In boiling,
butter makes little noise and a large amount of
2. On melting butter and allowing the casein
and water to settle a transparent oil results. With
oleomargarine or renovated butter the oil remains
How may renovated butter and oleomargarine be
Heat about half a pint of milk in a tin cup to
140° F. Add. to this a tablespoonful of the sub-
stance. Stir with a wooden stirring rod until
melted. Then set the cup in ice cold water and
stir until the fat hardens. It may then be collected
into a lump with the wooden stirring rod if it is
oleomargarine, but will remain separated in fine
granules if it is butter or renovated butter.
What is one of the best methods for distinguishing
butter from oleomargarine?
By determining the Reichert-Meissl number.
88 QUESTIONS AND ANSWERS
What is meant by the Reichert-Meissl number?
It means the number of c. c. -^ alkali required
to neutralize the volatile acids from 5 grams of the
How is the Reichert-Meissl number determined?
Five grams of the fat are placed in a clean, dry-
flask of 300 c. c. capacity, 10 c. c. of 95 per cent
alcohol added, and 2 c. c. of a saturated aqueous
solution of sodium hydrate. Place a funnel in
the neck of the flask and heat on the water bath
with occasional shaking until saponification is com-
plete, when the solution will be free from fat-glob-
ules and perfectly clear. Then remove the funnel
and continue heating over the bath to dryness.
Add 135 c. c. of water and warm on the water bath
with shaking until the soap is dissolved. Cool and
add a few small pieces of pumice stone, to prevent
lumping while boiling, and 5 c. c. of dilute sul-
phuric acid (200 parts of acid to 1,000 parts water).
Connect the flesk with a condenser and distill oflF
no c. c. in about 30 minutes. Titrate the entire
distillate with tenth-normal alkali, using phenol-
phthalein as indicator. The number of cubic cen-
timeters of tenth-normal alkali required express
what is called the Reichert-Meissl number.
How does the Reichert-Meissl number for butter
and for oleomargarine differ?
The size of the Reichert-Meissl number for oleo-
margarine usually depends to a great extent upon
the per cent of butter present in the oleomargarine.
This number is not often more than 5 for oleomar-
garine and rarely less than 24 for butter. The
ON MILK AND MILK-TESTING 89
Reichert-Meissl number for butter is usually be-
tween 24 and 31.
What fats are sometimes used to adulterate butter?
Lard and beef fat or products manufactured
therefrom, as lard stearin and beef stearin. Stearin
derived from cottonseed oil is also used. Fats or
oils from any source may be used provided they
have the proper melting point when mixed and no
What fats are used in the manufacture of oleo-
Neutral lard, beef fat stearin and cottonseed oil
stearin are the principal fats used in nearly all the
oleomargarine now manufactured. Cottonseed oil
stearin is probably not used to so great an extent as
the others. Small quantities of a few other oils
are sometimes added to change the color to more
nearly resemble that of butter.
What is neutral lard and lard stearin?
Neutral lard is the best quality of lard made
from hog fat. The fat is rendered at a low tem-
perature and the product washed with water con-
taining a little sodium carbonate, salt, or dilute
acid. The product then has only a slight acidity
and is almost tasteless. Its principal use is in the
manufacture of oleomargarine. Lard stearin is
made by melting lard and holding it at a tempera-
ture between 50° and 60° F., until the stearin sep-
arates in crystals. It is then filtered and pressed
in cloth sacks. The oil obtained is used for illumi-
nating and lubricating purposes. The stearin
90 QUESTIONS AND ANSWERS
which is collected in the sacks is mixed with other
fats and manufactured into oleomargarine or com-
pounds like lard and cottonseed oil.
How is oleomargarine manufactured?
The process of manufacture depends somewhat
upon the ingredients used and the markets to be
supplied. When the product goes to a tropical
country oils of higher melting points are used in
larger quantity than when the product goes to
colder climates. In general the oleo oil from beef
tallow, the neutral lard or lard stearin from hog
fat, and the cottonseed oil stearin are mixed in pro-
portions giving a melting point about that of butter.
The mixture is then churned with skim milk or
whole milk and the process thereafter is practically
the same as that for the making of butter from
What preservatives may be used in butter?
1. Boric acid or borates.
3. Salicylic acid.
4. Sulphurous acid.
How may the presence of boric acid or borates be
detected in butter?
Melt an ounce or two of the butter at the tem-
perature of boiling water and collect the aqueous
solution at the bottom. To a small amount of the
aqueous solution add a few drops of hydrochloric
acid. Then apply tumeric paper to the liquid. If
the paper turns red upon drying and turns to a dark
ON MILK AND MILK-TESTING 9I
olive green upon being made alkaline with ammonia
the presence of boric acid is assured.
How may the presence of formaldehyde in butter
Melt the butter at a low temperature and sep-
arate some of the water solution that collects at
the bottom. To this add milk free of formaldehyde.
Then test the mixture for formaldehyde by adding
a few drops of ferric-chlorid solution and con-
centrated sulphuric or hydrochloric acids, as in the
case with milk. A violet blue color assures the
presence of formaldehyde.
How may the presence oi salicylic acid in butter be
Separate some of the water solution that settles
to the bottom on melting the butter and follow the
directions given for the detection of salicylic acid in
How may the presence of sulphurous acid in butter
Separate some of the water solution that settles
out on melting the butter. Distill off a part of it
and to the distillate add bromine water and barium
chlorid. A precipitate indicates the presence of
sulphurous acid or a sulphite in the butter.
How is butter tested for its salt content?
I. Weigh into a glass beaker 10 grams of butter.
Add about 20 c. c. water. Warm it to melt the
butter and then transfer the butter and water to a
separatory funnel. Insert the stopper. Shake for
92 QUESTIONS AND ANSWERS
a few moments. Allow the mixture to stand a few
minutes until any remaining fat has collected on
the surface. Then draw the water into a flask, being
sure that no fat passes through. Again add hot
water to the beaker and repeat the washing in the
funnel several times, using 15 c. c. of water each
Determine the sodium chlorid in a measured
part (10 c. c.) of the liquid by titrating with stand-
ard silver nitrate solution, using potassium chro-
mate as an indicator, i c. c. -g- silver nitrate solu-
tion=.oo5837 grams of salt.
To determine the total amount of salt divide the
total number c. c. of water used by 10 and multiply
by .005837. This will give the total number grams
of salt in 10 grams of butter. Then, knowing the
amount present in 10 grams, it is an easy matter to
determine the amount in 100 grams by multiplying
by 10. This gives the percentage of salt in the
2. Gray's salt test. A representative lo-gram
sample of butter is placed in a small glass dish.
The dish is then half filled with boiling water and
the mixture of fat and water poured into a 500 c. c.
glass flask. The dish is rinsed several times with
hot water and each time the rinsings are poured into
the flask. The flask is then filled to the 500 c. c.
mark with boiling water and thoroughly shalcen.
Then allow the contents of the flask to cool and
after the fat has collected on top and hardened,
measure with a pipette 50 c. c. of the clear solution
beneath the fat and place it in a clean glass dish.
Fifty c. c. of a potassium chromate indicator is
then added and the solution titrated with a standard
ON MILK AND MILK-TESTING 93
silver nitrate solution. The strength of this silver
nitrate solution is such that i c. c. of it represents
one-tenth of i per cent of salt.
3. The Fitch salt test. A representative 3.5-
gram sample of butter is placed in a 300 c. c. glass
flask and 180 c. c. of boiling water added. The
flask is then corked and thoroughly shaken, care
being taken to remove the cork often tt) relieve the
pressure. The mixture is then allowed to cool and
after the fat has collected on the top and solidified
17.6 c. c. of the clear solution beneath the fat is
placed in a white cup. Then 17.6 c. c. of potassium
chromate indicator is added and the solution
titrated with a standard silver nitrate solution meas-
ured from a graduated cylinder till the solution be-
comes a permanent reddish color. The number
c. c. silver nitrate used divided by io=per cent salt.
How is the moisture content of butter determined?
1. By chemical analysis.
2. By practical moisture tests.
What are the names of the more commonly used
1. Cornell test.
How should a representative sample of butter be
secured and prepared for making a moisture,
salt, or fat test?
From the mass of butter to be tested take several
94 QUESTIONS AND ANSWERS
samples from various parts. The samples when
added together should make about 6 ounces. These
are placed in a wide-mouth sample bottle or fruit
jar and placed in hot water until the butter melts to
the consistency of thin cream. While melting, the
butter should be thoroughly and continuously
stirred with a table knife or similar instrument.
The bottle should then be well shaken to secure a
uniform mixing of the sample. The bottle is then
placed in cold water to solidify, but while cooling
the butter should be stirred continuously. As soon
as the butter has become fairly solid or plastic, the
sample for testing can be secured. If in melting
the butter becomes oily great care and skill must
be used to reincorporate the water evenly during
Describe and give directions for using the Irish
A representative lo-gram sample of butter is
placed in a small metal cup and held over a flame
with a pair of special forceps until all the moisture
has evaporated from it. While the butter is heat-
ing it foams considerably. As soon as the foaming
has ceased, and before the fat begins to char, a
small mirror is held over the cup to show if any
moisture still remains. When the sample is thus
freed from moisture it is cooled to room tempera-
ture, 60° F. to 70° F., and reweighed upon a special
scale by which the difference between the weight
of the butter before and after heating is indicated
in the form of percentage by the use of small
ON MILK AND MILK-TESTING 95
Describe and give directions for using Gray's
This test consists of a scale, glass flask, gradu-
ated glass tube, condenser, amyl reagent, and an
A representative lo-gram sample of butter is
placed in the glass flask. To this 6 c. c. of amyl re-
agent is added and the different parts of the test
then connected for use. The condenser is filled
with cold water. The butter and amyl mixture is
heated over a flame, the moisture is driven off and
collects in the graduated glass tube, where it can be
read in the form of percentage. The heating is
stopped as soon as the mixture in the flask becomes
brown and the crackling noise ceases. This usually
requires about six minutes.
Should heat be applied too severely to the flask
the steam may go above the 15 per cent mark.
This should be prevented by withdrawing the heat
for a short time. Great care must be exercised in
collecting all the moisture in the graduated tube if
reliable readings are to be secured.
Describe and f^ive directions for using Farrington*s
In Farrington's test 10 grams of a representative
sample of butter is placed in a small dish. The
dish is then placed in a special oven heated to from
240° F. to 270° F. under steam pressure. Here the
butter is left until all moisture has been evaporated,
indicated by the browning of the casein in sample.
This usually takes about 30 minutes. After the
moisture has been evaporated the dish and its con-
tents is reweighed and the difference from the
g6 QUESTIONS AND ANSWERS
original weight determined. The per cent moisture
can thus be easily determined. Occasionally a re-
verse beam scale is used upon which the per cent
moisture evaporated can be read direct.
Describe and give directions for using the Cornell
This is a simple, accurate, and durable test re-
cently prepared by Mr. H. E. Ross of the dairy-
department of the New York state college of agri-
culture. The test resembles the Irish test, but has
several important improvements.
A lo-gram sample of butter is secured in the
usual way. This is placed in a special cast alum-
inum cup and the cup held over a flame with special
forceps or placed on some heated surface. The
important features of the test are the use of this cup
and the use of a thin sheet of asbestos between
flame or heated surface and the cup. The asbestos
prevents all the sputtering of the heating butter and
eliminates a great deal of the danger of charring.
The sample is heated till all moisture is driven off.
This usually requires about 25 minutes, and is in-
dicated by the casein losing its snow-white color
and becoming brown. The sample is then cooled
and reweighed with a special scale upon which the
per cent moisture can be read directly and accu-
Describe and give directions for using the Mitchell-
The apparatus in this test consists of a meial
evaporating cup, condenser, graduated glass re-
ceiver, scale for weighing sample, spirit lamp, amyl
ON MILK AND MILK-TESTING 97
acetate reagent, and a stand to support the appa-
A representative lo-gram sample of butter is
placed in the metal cup. To this is added 10 c. c.
of the amyl acetate reagent. The apparatus is
then connected and the condenser filled with cold
water. The alcohol flame is then applied under
the evaporating cup. In about a minute the water
and reagent will begin to pass over and drop from
the condenser tube into the receiver. After all the
water has been evaporated from the cup, the reagent
will cease dropping for a moment and then begin
again as soon as it has reached its own boiling
point, which is higher than that of the water. Con-
tinue to apply the flame until practically all the re-
agent is driven oif and it ceases to drop freely from
the condenser tube. By this means all the water
is washed out of the condenser tube and the major
portion of the reagent is recovered. The flame is
now extinguished. The mouth of the receiver is
corked and taken by the top and shaken a few
times to detach any drops of water that may
adhere to the sides.
The per cent moisture can now be read in the
graduated receiver. The water is withdrawn from
the receiver, and then the reagent, which is collected
in a bottle and preserved for use in later tests.
tests for li 5, 6
Babcock test 33, 39
Buttermilk 17, 57
cream bottles 41
nlilk bottles 40
composition of 9
tests for 10
sampling 51, 57
solids not fat 68
Gerber fat test 66
Mammary gland 7
adulteration 69, 74
composition of 1, 2, 10
contamination 14, 15
fat 3, 4
Milk — Continued
secretion 8, 9
serum 10, 23
weight of 23
tests for 87
Preservatives 48, 80
Reichert-Meissl ntmiber 88
Score cards 24, 25
Specific gravity 22, 23, 26
Spores 11, 12
acid , 1, 5, 6
benzoic acid 82
boracic acid 81
condensed milk 60, 61
fat 66, 67
foreign color 79
moisttire 92, 95
pasteurized milk 83
renovated butter 87
salicylic acid 83
skimmed milk 57
sucrate of lime 86
sulphurous acid 91
Viscogen •• 8^