Chapter XIV: Testing (2)

=172. Test to determine the hardness of ice-cream.=--The apparatus[49] used for determining hardness was reproduced from the description of a similar piece of apparatus by A. E. Perkins. It consisted of a wooden frame made of 2 × 4-inch lumber, with cross pieces on the bottom so that it stood firmly in an upright position. A cross piece, about one foot from the bottom of the frame, made the support for holding the sample. At the top of this support was an adjustable wooden screw for holding the electro-magnet. By adjustment with this screw, the magnet could be lowered or raised several inches. This adjustment was necessary so that the height of the needle could be made constant with all samples. The drop frame which holds the needle and which is held up by the magnet until the electric current from the batteries is broken, was made from very light ³⁄₈-inch piping, the width being sufficient to give a free drop without touching the mold, and long enough to reach below the platform when the magnet was at its highest point. The wires from the magnet led to a cut-off key on the side frame and from there to a pair of dry cells from which the current was derived. The needles were of different sizes but the same weight, thus eliminating the necessity of adjustments to obtain constant weight. The needles were marked from their points upward, in centimeters and fractions thereof, to show the depth of penetration. The height of the drop was always 100 millimeters, being measured carefully with a metric rule before each determination.

[49] Holdaway, C. W., and Reynolds, R. R., “Effects of binders upon the melting and hardness of ice-cream,” Va. Exp. Sta., Bul. 211, 1916.

In making the determination, the frame with a suitable needle and weights is suspended from the electro-magnet, and the material to be tested placed in position beneath the needle, the height being regulated as already described. The frame is then released by means of the key. The depth of penetration is ascertained from the marks on the needle and confirmed by measuring with the metric rule. The suspension of the weights far below the needle brings the center of gravity of the falling portion of the apparatus below the point of the needle, causing the latter invariably to assume a vertical position, rendering it much easier to ascertain the true depth of penetration than would be the case if the point of the needle were at or below the center of gravity. After its release by the electro-magnet, the apparatus meets with no resistance in its fall, except that offered by the air, until the point of the needle reaches the surface of the cream. The amount of weight acting on the needle is known and the distance through which it falls is constant. If, however, too much weight or too small a needle is employed, the latter continues to sink slowly, making an accurate reading of the depth of penetration impossible. In the reverse case, with too large a needle or too little weight, the penetration is of course much less and the percentage of experimental error proportionately greater. As there was a large variation in the hardness of the various fillers, three sets of needles were employed and in this way much of the error was eliminated. The size of the needles were: large ⁵⁄₁₆ inch or 7.93 millimeters, medium ⁴⁄₁₆ or 6.35 millimeters, and small ³⁄₁₆ or 4.76 millimeters in diameter. The tests were made by allowing each needle to penetrate the ice-cream three times. The point of penetration was varied from center to points near the edge as there was a possibility of the cream being harder near the edge than in the center. The depth of penetration of each needle was expressed in millimeters. The work was done in a cold storage with the temperature near 0°C.

MOJONNIER TESTER

Considerable time is required to make some of the tests, after the chemical method, such as those for solids in the different milk products. Mojonnier Brothers have devised a test both for fat and solids which is accurate and saves much time. A description of this test follows. The machine is shown in Fig. 75. The numbers on the arrows refer to numbers in the text, as follows:

(1) All tests for butter-fat are made upon this side.

(2) All tests for total solids are made upon this side.

(3) Butter-fat extraction flasks in centrifuge baskets.

(4) Eight 3½ inch aluminum dishes for butter-fat tests (the larger
ones). The one tall counterpoise counterbalances each dish. Fat
dishes have no covers.

(5) Eight 3-inch aluminum dishes for solids tests (the smaller ones).
The one short counterpoise counterbalances each dish. Cover prevents
absorption of moisture from the air during weighing. Counterpoise
balances both dish and cover.

(6) Fat vacuum oven. The temperature in this oven is maintained at
135 deg. C. Thermometer (10) extends into vacuum oven and rests on
hot plate. The mercury bulb fits snugly in removable brass mercury
well. Once a month this mercury well should be refilled with mercury.
Be careful to see that the well always forms good contact with hot
plate. Regulate temperature by rheostat (15).

(7) Cooling chamber. Water at room temperature from the tank (28) in
bottom part of the fat tester, is pumped by means of circulating pump
in power unit (20) through the flat hollow sheet brass plate inside
the cooling chambers and from there into pipe back of tester back
into tank. Operator must watch outlet on cooling chamber and see that
water is flowing at all times while the motor is turned on. If water
is not running, you may know that the water in the storage tank is
low. Keep tank filled at all times. In winter to prevent freezing,
put a gallon of denatured alcohol into tank.

(8) Solids oven. Maintained at 100 deg. C. Regulate temperature by
means of rheostat (16). Follow instructions in (6) above closely for
method of placing thermometer. Keep joints at door clean, and grease
with vaseline sliding surfaces. This insures a more perfect vacuum.

(9) A 250 deg. C. thermometer for solids oven. Wire on rubber
connections.

(10) A 250 deg. C. thermometer for fat oven.

(11) Vacuum gauge is on main suction line from vacuum pump. This
registers vacuum of either oven, or of both ovens simultaneously.

(12) Solids plate. Maintained at 180 deg. C. The thermometer can be
placed in nickel plated mercury well with base that rests directly
upon plate. See that this side is level.

(13) Fat plate. Maintained at 135 deg. C. During the evaporation of
ether from the dishes, the temperature falls. Some operators prefer
to keep temperature at 150 deg. C. to start and place dishes only
halfway upon plate. As the plate cools, the dish may be pushed over
until it is entirely upon hot plate.

(14) Rheostat for fat plate. Turning rheostat handle forward
increases temperature. Turning handle backward decreases temperature.
It is important to see that the lever on handle makes good contact
with separate buttons and not with two buttons at a time. As soon as
right button has been found that maintains constant temperature, mark
this point upon rheostat rim. In starting up tester, each day, you
may turn handle on full and then when temperature is up to within 10
degrees of right point, turn handle back to previously marked button.
Same instructions apply for all rheostats.

(15) Rheostat for fat oven.

(16) Rheostat for solids oven.

(17) Rheostat for solids plate.

(18) Handle for centrifuge.

(19) In case the operator forgets temperature and time for treating
samples at various points, he may notice the temperature and time
below each snap switch for each hot plate.

(20) The power unit consists of a high vacuum pump, a water
circulating pump, and a suction fan all driven by a single motor.
Vacuum pump must be submerged in oil furnished with tester. Fill
chamber up to air cock with oil.

(21) Automatic burettes. The cans holding the water, ammonia,
alcohol, ethyl ether and petroleum ether are placed in this order.
This is the order in which these reagents are added to the flasks
containing the weighed sample of milk. Each division delivers the
proper amount for a single extraction.

(22) Place this hood over fat dishes when evaporating off ether, so
that the suction fan may draw off ether fumes to outside of building.

(23) Fasten these legs to floor with lag screws.

(24) This side need not be fastened to floor. In case it is
necessary to take out power unit, it is necessary only to disconnect
connections in rear of machine and move this part of machine forward.

(25) The balance is the heart of the machine. Operator must keep it
level, clean and handle it carefully. Raising and lowering knife
edges must be done gradually and with care. Make it a habit of
cleaning balance daily. The weights must be kept clean, and as soon
as you notice that some of the smaller weights are wearing out, order
new ones.

(26) This cock exhausts vacuum from oven when cock (27) is closed. It
must be kept closed when vacuum is turned on oven.

(27) This cock puts vacuum from main line into vacuum oven. Set of
cocks at right is for solids oven, and at the left for fat oven.

(28) In top of fat plate holder there is a hole communicating with
suction fan on power unit. When the exhaust pipe on suction fan is
run out of window of laboratory and the hood is over the dishes, all
fumes of ether will be driven from the room.

(29) Screw stool to floor.

(30) A wash stand for washing all glassware should be provided.

=173. General preliminary information.=--In the operation of the Mojonnier tester, several steps remain the same regardless of the product being tested. Among these are the following:

(1) _How to use the balance._

Two types of balances are in principal use--namely, the old type with
graduated beam and rider, and the new type called “Chainomatic” with
the chain and vernier. The care to give to either type of balance is
the same. The difference is in the method of balancing the object to
be weighed, and of reading the weight. These points will be discussed
separately.

A balance is a delicate instrument, and care needs to be exercised in
its use at all times. The weights likewise require careful handling.
Lack of care in the weighing operations may lead to entirely
erroneous results, and thus defeat the object aimed at, namely,
accuracy of the tests.

The balance is inclosed in a glass case to shield it from dust,
air currents, and moisture. Perhaps the largest factor affecting
accuracy in weighing,--granting other conditions to be right, is
temperature. If the object to be weighed is of a lower temperature
than the balance case, it will weigh apparently more than its actual
weight. If of a higher temperature than the balance case, it will
weigh apparently less than its actual weight. The object should,
therefore, be as closely as possible of the same temperature as that
of the air in the balance case. The water cooled desiccator used upon
the Mojonnier tester has been designed primarily to facilitate the
equalizing of the temperature between the dishes to be weighed and
the balance case. See, therefore, that the temperature of the water
in the circulating system is as nearly as possible the same as the
temperature of the balance case.

All parts of the balance and weights should be kept free from dust.
A cover to be placed over the balance case at night serves a very
useful purpose. Use a camel’s hair brush to remove the dust from
both the balance and the weights. A small beaker partly filled with
sulfuric acid should be kept in one corner of the balance case.
Replace the sulfuric acid when it becomes saturated with moisture.

Protect the balance against vibration, and see that it is in exact
level. The air bubble in the spirit level should be in the exact
center. This can be readily accomplished by means of the leveling
screws under the balance case.

The balance should be in exact equilibrium at all times. That is, the
pointer should oscillate an equal number of divisions on each side
of zero upon the pointer scale. If the pointer swings too far to the
right, turn the adjusting screw upon the beam to the right. If it
swings too far to the left, turn the adjusting screw to the left.

Place object to be weighed upon the left hand pan, and the weights
or counterpoises upon the right hand pan. Handle the weights with
the forceps only, using the right hand. Use the left hand to release
the beam from the support, and to raise or lower the balance door.
The weights should be placed upon the pan in a systematic order,
beginning with a weight that is judged to be somewhat too heavy.
Lower weights are then tried in succession in a systematic order
until equilibrium results.

Upon the old style balance, adjustments under 5 or 10 milligrams
(depending upon the construction of the balance) are made by means of
the rider. Keep the balance door closed while the final adjustment
is being made. Determine the relation between the divisions upon
the rider beam, and the pointer scale. This relation varies with
different balances, but when once ascertained upon a given balance
it remains a constant value, and if applied in making a weighing,
a great deal of time can be saved. For example, if the pointer
oscillates six divisions to the right of zero, and four divisions
to the left, with a balance having a relation of .0002 gram to one
division upon the pointer scale, the rider is moved .0004 gram to the
right to bring the balance into equilibrium.

Upon the Chainomatic balance, adjustments under .0500 gram are made
by means of the screw and vernier. Determine the relation between the
divisions upon the vernier, and the pointer scale. If the pointer
swings too far to the right, lower the slide,--if too far to the
left, raise the slide. About .003 gram upon the vernier usually
equals one division upon the pointer scale.

Exercise great care in recording the weights. A double check should
be made by reading both the weights upon the balance pan, and the
weights that are missing from the set. The weights should be placed
upon a paper near the front of the balance case, with the values of
the weights marked upon the place where the respective weights are
kept. Remember that one misread weight will spoil an entire test.
Upon the Chainomatic balance read weights as follows:

(a) Sum of all gram weights equals whole number.

(b) Sum of 100 or multiple of 100 milligrams equals first decimal.

(c) Sum of 10 or multiple of 10 milligrams equals second decimal.

Out of a possible total of 100 milligrams, 50 milligrams are obtained
from the fractional weight, and 50 milligrams from the vernier beam.

(d) The third decimal is obtained from the vernier beam. Read the
value of the line just above the small 0 upon the slide.

(e) The fourth decimal is the value upon the slide that is in an
exact line with any given line upon the vernier beam.

(2) _Care to give to the power unit and the water circulating unit._

Keep the water tank well filled with water. Add about one quart light
machine oil to the water in the tank to keep the water pump well
lubricated. If the tester is located in a cold room in winter, add
one gallon denatured alcohol to the tank to prevent freezing.

Keep the vacuum pump chamber properly filled with the right kind
of oil. The oil should just about reach the top of the pistons, as
indicated by the glass upon the side, or cock upon the end.

Give the motor proper care. It should receive the same attention
as given to any motor, that is, it is to be kept cleaned and well
lubricated.

Should any knocks develop upon the power unit, remedy the same
immediately. The construction is very simple, and with a little
study, the care and operation of the power unit should be readily
learned.

(3) _Care to give to the vacuum ovens and coolers._

Keep sufficient mercury in the mercury well to insure good contact
between the thermometer and the mercury well. The mercury well should
rest directly upon the hot plate. Otherwise incorrect temperature
will be indicated by the thermometer. Keep the ground joint between
the lid and the oven thoroughly cleaned. In case that it is difficult
to get the proper amount of vacuum, look first to this place for
trouble. Sometimes it may be necessary to use a small amount of
vaseline, but as a rule, the best results are obtained by keeping the
ground joints thoroughly clean. Be sure that the thermometer opening,
and the openings upon the bottom of the oven are thoroughly sealed.
It may be necessary to replace the rubber tubing at these points in
case that leakage develops.

Be sure to see that the cooling desiccators are kept from freezing
temperatures. If the water in the cooling plates should freeze, it
would ruin the plates. Watch the water coming out of the coolers, in
order to be sure that the circulation is correct.

(4) _General care of the tester._

Keep the tester clean and free from the accumulation of unnecessary
material at all times. It is impossible to do accurate work if the
apparatus is not in the best of condition. All japanned parts can
be cleaned either with engine oil, applied to a clean cloth, or by
washing with good soap and water.

(5) _How to clean the dishes and the glassware._

The solids dishes should be soaked in water after the test has been
completed, and the solids then removed by means of a brush suited
to the purpose. They should then be thoroughly cleaned and dried,
and placed in the vacuum oven until required for further use. The
fat dishes should be treated with a small quantity of gasoline until
the fat is all dissolved, and this treatment repeated a second time.
Finally, the dishes are to be cleaned with a dry cloth, and placed in
the vacuum oven until needed. Do not use any water upon the fat dish.

All glassware should be washed either immediately after being used,
or it should be placed in water until washed. Extraction flasks
should be thoroughly washed with tap water and then washed out with
distilled water. If flasks become dirty, wash with washing powder
and shot, or use washing powder with a brush specially designed for
this flask. Clean pipettes with brush and water. Use washing powder,
if necessary. Rinse successively with water, alcohol, and ether, and
then dry by holding at exhaust cock leading to the vacuum oven, or
place upon pipette holder between fat oven and cooler.

(6) _How to heat the dishes before weighing._

Give both the solids and the fat dishes the same treatment before
weighing the same empty as is given to them when the same are to be
weighed with the solids or the fat respectively in the same. Do not
attempt to weigh dishes that have not been heated previous to being
weighed.

(7) _How to cool the dishes._

Transfer the solids and the fat dishes from the respective vacuum
ovens to the respective coolers, and weigh the same as rapidly as
possible. Weigh the solids dish with the cover on, and the fat dish
without any cover.

(8) _How to adjust temperatures._

The temperatures upon the two outside hot plates and the two vacuum
ovens can be closely regulated by means of the rheostats. If the
voltage is constant, the temperature will remain very near to the
point desired for a long period of time after the rheostats have been
properly adjusted. Ascertain by test, just where it is necessary to
hold the rheostat in order to get the required temperature. After
this point is once ascertained, the rheostat can be set at the point
required and the temperature allowed to come up automatically, when
starting in the morning.

(9) _How to prepare the samples._

Care and good judgment requires to be exercised in preparing samples
of the various dairy products preparatory to weighing out samples of
the same for the test. This is explained more in detail in the more
extended descriptions following the various products outlined in
these directions.

(10) _How to weigh samples for the fat test._

Several methods are in use for weighing the samples for the fat test,
depending on the product that is being tested. The weighing cross
with the short pipettes can be used successfully on a number of
dairy products. Numerous advantages are gained by using this method,
provided the product to be tested permits of its use. Five different
samples can be weighed with only six weighings, and if care is taken,
great accuracy is obtainable. Several products can be pipetted out,
taking ten grams and where possible, this is a very accurate method.
The pipettes are graduated to discharge ten grams of whole milk at
60 deg. F., allowing 15 seconds for draining the pipette after the
milk has all run out, and then blowing out the last drop of milk in
the pipette. Again, when sample shows signs of separation of fat,
the only satisfactory method is to warm up the sample until the fat
is melted, and mix thoroughly. While stirring the well mixed sample,
pipette out a sample into a cleaned, dried and weighed extraction
flask suspended from the balance beam. If flask is wet on inside it
should be weighed with cork.

(11) _Size of samples to take for the fat test._

The size of sample to use varies, depending on the product being
tested, and it ranges from one gram in the case of butter, to ten
grams in the case of raw milk. See instructions in diagram.

(12) _How to add the reagents._

The reagents should be added in the following order: Water, ammonia,
alcohol, ethyl ether and petroleum ether. The burettes upon the
dispensing cans are graduated to deliver the proper charge required.
See instruction diagram.

(13) _How to shake the flask._

If only one sample is being tested, this can be shaken by hand.
As many as four samples can be shaken at one time in the shakers
furnished with the equipment. The flask should be held with large
bulb down and small bulb extending upward. In this position they are
shaken vigorously lengthwise of flask. After shaking five or six
times, allow liquid in small bulb to run back into large bulb. Repeat
this operation at least four times. There is no danger in shaking the
samples too much, but rather of not shaking them enough.

(14) _How to centrifuge the flask._

If only one sample is being centrifuged at a time, place a
counterpoise upon the opposite side of the centrifuge in order to
balance the head. Always see that there is about the same weight upon
both sides of the centrifuge.

(15) _How to pour off the ether solutions._

Remove the cork by twisting carefully from the flask. Pour off the
ether solution as completely as possible, taking care not to allow
any of the liquid under the ether to flow out of the flask. This can
be avoided if the dividing line between the ether solution and the
remaining solution is carefully watched, while pouring off. In the
first extraction, a larger amount of the ether solution can remain in
the flask than in the second extraction. In the second extraction the
fat dish should be placed on the tester top, and the operator should
look down on the ether solution as it is being poured off, observing
the point where the ether has been all removed. By following this
method, all but one or two drops of the ether solution should be
recovered, provided the dividing line was in the right place before
pouring off.

(16) _How to bring up the dividing line._

Inability to pour off the ether solution closely is due to the fact
that the dividing line between the ether solution and the remaining
solution is too low in the lower bulb of the flask. At the end of
the first extraction, the dividing line can remain without change,
taking care to pour off the ether solution as closely as possible,
regardless of the position of the dividing line. At the end of the
second extraction, remove the stopper from the flask, and drop in
sufficient distilled water from the burette into the extraction flask
to raise the dividing line to the desired point. This should be done
just before pouring off the ether. If this procedure is followed, it
becomes possible to remove the ether almost to the last drop.

(17) _How to evaporate the ether from the dish._

It is important to maintain the proper temperature upon the outside
hot plate. If the temperature is allowed to go below 135 deg. it
takes too long to evaporate the ether solution. On the other hand,
if it rises much above 135 deg. there is danger of the ether boiling
out over the top of the dish. If the plate is too hot, it is best to
place only part of the dish in contact with the plate. We recommend
that the hood be placed over the dishes, and that the ether fumes
be blown out of the room by means of the blower. It is dangerous to
allow the ether fumes to evaporate into the working room, and besides
it makes it very unpleasant for the operator to work in contact with
these vapors.

(18) _How to heat the fat dish in the oven._

Do not transfer the fat dish to the vacuum oven until all of the
ether solution has been evaporated upon the outside plate. If this
is not done, the contents of the dish are quite likely to spatter in
the oven. It is very important to maintain the proper temperature
conditions, and also the proper vacuum upon the fat dishes, while
the same are being heated in the oven. If for any reason, there
should be difficulty in attaining either the proper heat or the
proper vacuum, the trouble should be immediately investigated and
removed.

(19) _How to weigh the fat dish._

The fat dishes are to be transferred from the vacuum oven to the
cooler, in which they are to remain for seven minutes before being
weighed. The weighing should be done as promptly as possible.

(20) _How to calculate the percentage of butter-fat._

Divide the weight of the butter-fat by the weight of the sample
taken. Multiply the result thus obtained by 100 in order to arrive at
the percentage of butter-fat in the sample.

(21) _Weight of sample to take for the solids test._

This varies with the product to be tested, ranging from .25 of a gram
in the case of sweetened condensed milk, to 2 grams in the case of
fresh milk.

(22) _How to weigh the solids sample into the dish._

The samples can be weighed from the weighing cross, or in several
cases it is advantageous to weigh the samples directly into the
solids dish.

(23) _How to add water to the samples in the dish._

For this purpose, always use best distilled water. It is well to run
a blank upon the water to determine if it is free from solid matter.
Reject any water that may contain any solid matter. Add sufficient
water to make up the total volume, not to exceed 2 cubic centimeters.
Agitate the sample with the water in the dish so that the remainder
will be uniformly distributed over the bottom of the dish.

(24) _How to treat the sample upon the outside hot plate._

It is very important to have the outside hot plate as nearly 180
deg. as possible. If the temperature is less than 180 deg. there
will be insufficient bubbling of the sample, so that the surface
will be improperly broken. If a temperature above 180 deg. is used,
there is great danger of the samples spattering out of the dish.
Heat the samples in the dish until they just begin to turn brown.
This is one of the most important steps in the entire operation, and
unless properly watched, an error may be introduced at this point.
Insufficient heating may give high results, and over heating may give
low results.

(25) _Temperature and vacuum to maintain in solids oven._

Keep the solids oven at a temperature of as nearly 100 deg. as
possible. This applies to all products to be tested. Also see that
there is at least 20 inches of vacuum upon the vacuum oven. If the
tester is properly operated, it should be possible to maintain 25
inches of vacuum at all times.

(26) _How long to retain the dish in the solids oven._

This varies with the products to be tested. The minimum time is ten
minutes and in the case of sweetened condensed milk, in order to get
absolute results, it is best to dry the samples an hour and a half.

(27) _How to cool the solids dish._

Transfer the dish from the oven to the cooler promptly, and keep the
same in the cooler for five minutes with the water circulating during
this time.

(28) _How to heat the solids dish._

Always weigh the solids dish with the dish cover upon the dish. Make
the weighings as rapidly as possible, as otherwise the sample is
quite likely to absorb moisture from the atmosphere.

(29) _How to calculate the percentage of total solids._

Divide the weight of the total solids by the weight of the sample
taken, and multiply the result by 100, which will give the percentage
of total solids in the sample.

(30) _Order of operations in testing evaporated milk for butter-fat
and total solids with Mojonnier tester._

In the following outline, the procedure described is that used in the
case of evaporated milk. The procedure in the case of other products
is much the same, but as described in directions, differences may
occur in the methods of weighing the samples; the size of the samples
to use; the quantity of water or the reagent to add; the method of
shaking, and the method of centrifuging. The outline presumes that
only one operator is doing the work. When speed is required, a helper
to the operator can materially shorten the time required. In that
case, the order of operations will need to be slightly modified.

(1) See that respective dishes have been in vacuum oven at least five
minutes while ovens are heated with vacuum on.

(2) Place respective dishes in cooling ovens, turn pump on, and set
bell for five minutes for solids and seven minutes for fat.

(3) Weigh solids dish first--being careful to put cover on dish, and
record weight and number upon laboratory report. Put dish back into
cooling oven.

(4) Weigh fat dish without cover. Record weight and number upon
laboratory report, and put fat dish back in cooling oven.

(5) Fill one 5-gram and one 1-gram pipette with milk, and place upon
weighing cross.

(6) Weigh above and note weight on laboratory report under “pipettes
plus milk” column.

(7) Transfer milk in 5-gram pipette to extraction flask, and return
empty pipette to weighing cross.

(8) Weigh again, and note weight in fat column under “pipettes.”

(9) Put above weight in solids column of laboratory report, also
under heading of “pipettes plus milk.”

(10) Transfer milk from one gram pipettes to the weighed solids dish,
and return pipette to weighing cross.

(11) Place weighing cross upon balance, weigh, and record weight
under the heading “pipettes.”

(12) Add equal volume of distilled water to solids dish, distribute
evenly, and place on solids hot plate.

(13) When evaporation has taken place, put in solids oven.

(14) Turn on vacuum and set bell for ten minutes.

(15) At this point take extraction flasks with milk in and make first
extraction, centrifuge and pour ether into fat dish.

(16) Make second extraction, same as 15.

(17) During above period solids bell will ring and solids dish should
be transferred to cooling oven, and bell set for five minutes.

(18) As soon as ether has evaporated, place dish in fat oven, turn
vacuum on, and set bell for five minutes.

(19) When solids bell rings, weigh dish and record weight.

(20) When fat test bell rings, transfer to cooling oven, and set bell
again for seven minutes.

(21) Complete subtractions on laboratory report.

(22) Weigh fat dish, turn pump off, and finish calculations.

(23) From tests obtained, determine what material to add to
standardize batch.

=174. Testing evaporated, sweetened condensed, bulk condensed milk ice-cream (mix or melted), for fat and total solids.=--The process is outlined in the following steps:

(1) Wash solids dishes with warm water and fat dishes with gasoline.
Dry with a towel and place into heated vacuum oven for five minutes,
with vacuum on. At the end of five minutes, put these dishes into
cooler and with pump still running, keep them there for five minutes
before weighing. Do not turn off motor until last dish is weighed out
of cooling chamber.

(2) While dishes are being heated and cooled, wash pipettes with
water, alcohol and ether, and dry by applying vacuum at exhaust cock
upon tester. Always use clean and dry pipettes for each different
sample. Aim to clean pipettes as well as all glassware, immediately
after using.

(3) It is very important to keep the extraction flasks clean. Wash
these with warm water immediately after extraction is finished. Wash
with washing powder and shot when necessary.

(4) Keep solids dishes in cooler for at least five minutes, weigh
accurately to .0001, using the proper counterpoise. Weigh solids
dishes with cover on. Keep fat dishes in cooler for seven minutes
before being weighed. Fat dishes do not have cover.

(5) Use pipettes as follows: Fill 5-gram pipettes up to 5 gram mark
for butter-fat and 1 gram pipette up to 1 gram mark for total solids.
If duplicates are to be run, fill two pipettes from the same sample.
As pipettes are filled, place lower end into cleaned and dry rubber
tubes which are pressed upon knobs at ends and center of weighing
cross. Either five or less samples for butter-fat or five or less for
total solids may be pipetted out.

(6) Weigh the cross with the pipettes containing the milk on chemical
balance accurately to .0001 gram. Run milk from pipette into proper
flask, or 3 inch dish if making solids test. The pipettes may be
distinguished by the number upon each cross. Replace pipette and
weigh again. Difference in weight gives weight of sample. Repeat
until all samples are run into proper flasks, and into weighed solids
dishes if solids are determined along with the fat.

For fat in sweetened condensed milk use a 5-gram sample. The 5-gram
pipette delivers approximately 5 grams between the 5 gram mark and
the base of the bowl of the pipette.

Some operators prefer to mix 200 grams of sweetened condensed milk
with 200 grams of water, weighing these carefully upon a Harvard trip
scale sensitive to .1 gram. In this case, care must be exercised to
obtain the exact weight of both milk and water and to stir these
thoroughly with glass or metal rod before taking sample. A tall
tumbler, a one-pound bottle or a quart cup, make good containers in
which to make mixture. A 10-gram sample of this mixture is used.
This is best weighed out by using two 5-gram pipettes on weighing
cross.

For total solids, weigh out ¹⁄₂ (.5000) to ³⁄₄ (.7500) gram of this
mixture. If the undiluted milk is used, take as nearly ¹⁄₄ (.2500)
gram as possible.

For regular 8 per cent plain bulk condensed milk, use same size
samples and treat same as evaporated milk. For 12 per cent
superheated condensed milk, mix 100 grams milk with 300 grams water
upon Harvard trip scale. Weigh 10 gram sample of this mixture into
flask for fat, and a 2 gram sample into solids dish for solids.
Multiply percentages obtained by 4 for correct percentages, when a 1
to 4 dilution is made.

=175. Fat determination.=--The following steps should be followed when making the fat test.

(1) Remove flask from holder and run 4 cubic centimeters water (one
charge on water burette) into each flask. Be careful not to add more.
Shake well until all of sample is mixed with water. This can be done
without inserting cork.

For sweetened condensed milk, if not diluted with water, add 8 cubic
centimeters of hot water with a pipette. To get hot water, place fat
dish filled with distilled water upon solids plate. If sweetened milk
has been previously diluted with water and a 10 gram sample has been
used, it is not necessary to add water. It is very necessary to shake
the flasks containing the sweetened condensed milk very thoroughly
after the addition of each reagent. Sweetened condensed milk requires
more shaking than any other liquid milk product.

(2) Before replacing flask into holder, add 1¹⁄₂ cubic centimeters C.
P. ammonia, one charge on burette. Shake well so that all of sample
is well mixed with ammonia. This can be done without inserting cork.

(3) Add 10 cubic centimeters of 95 per cent alcohol. Insert cork,
twisting cork in firmly, using best quality corks only. Replace the
flask into flask holder. Shake thoroughly, and see that no milk
adheres to any part of flask undissolved. In case particles of milk
stick to side of flask, shake thoroughly until these are washed away.
It is of utmost importance to shake thoroughly at this point.

(4) Add 25 cubic centimeters ethyl ether, insert corks and shake
vigorously, lengthwise of flask, with liquid in large bulb of flask,
and small bulb extended upward. Stop shaking at end of five seconds
until all liquid has run into large bulb and repeat vigorous shaking
for four five-second periods.

(5) Add 25 cubic centimeters petroleum ether and shake in same way.

(6) Place extraction flasks into centrifuge and whirl for thirty
turns at speed of about 600 revolutions a minute. Have centrifuge
balanced with small oil sample bottles furnished with tester. Double
time for sweetened condensed milk.

(7) Place four 3¹⁄₂ inch dishes in line on shelf adjoining hot plate,
keeping them in order in which their weights were posted on record
sheet. Aim to have numbers on flasks correspond with number of dishes.

(8) Pour ether extraction above dividing line into proper dishes
and slide dishes over onto hot plate which should be held at a
temperature of 135 deg. C, as indicated by thermometer inserted in
nickel plated mercury well. Be careful to pour off no solid matter.
Cover dishes with hood.

(9) Repeat the extraction, shaking first to prevent formation of
precipitate, then adding successively 5 cubic centimeters of 95 per
cent alcohol, then 25 cubic centimeters ethyl ether and then 25 cubic
centimeters petroleum ether, and shake vigorously after the addition
of each of above three reagents for four five-second periods.

(10) Whirl in centrifuge for thirty turns.

(11) Move aluminum dishes back upon shelf adjoining hot plate, when
almost dry, and pour the second extraction into proper dishes. Never
pour extraction into hot dish. Remove dish from hot plate as soon as
ether is all evaporated.

(12) When all of ether has evaporated, place dishes into vacuum
oven which should have a temperature of 135 deg. C. Keep them there
for five minutes after the vacuum gauge shows at least 22 inches of
vacuum.

(13) Place dishes into cooler for seven minutes, with pump outfit
running. See that water is running through cooling plates.

(14) Place counterpoise for dish and the approximate weight for fat
on right hand balance pan.

(15) Transfer dish to left hand balance pan and weigh quickly to 0.10
milligram (0.0001 gr.).

(16) Weight of fat divided by weight of sample taken, multiplied by
100 represents percentage butter-fat.

=176. Total solids determination.=--The steps in making the test are as follows:

(1) The temperature of the hot plate in the solids vacuum oven must
be 100 deg. C. The temperature of the outside solids plate must be
170 deg. to 180 deg. C.

(2) To weighed milk in solids dish, add about 1 cubic centimeter
water and distribute mixture evenly over bottom of dish, immediately
after weighing. For sweetened condensed milk, use hot water, or place
momentarily on hot plate and distribute evenly over dish by shaking
sidewise very carefully after cold water is added.

(3) Place not more than two dishes at once upon hot plate, which must
be perfectly level. Allow all visible moisture to evaporate. During
the evaporation turn the dishes around with crucible tongs slowly so
as to produce an even boiling over the whole bottom surface of the
dishes. The dishes must be watched carefully during the evaporation.
This step should require not more than two minutes. The end point is
reached when bubbling and crackling ceases and sample shows first
trace of brown. Vigorous boiling without spattering and complete
evaporation are fundamentally essential.

(4) Place dishes into vacuum oven which must be at 100 deg. C. and
turn on the vacuum. Heat for ten minutes. In the case of sweetened
condensed milk keep it for ninety minutes in vacuum oven, or heat for
twenty minutes and deduct 30 per cent from result. The gauge should
register not less than 22 inches of vacuum. If for any reason you
cannot obtain at least 22 inches of vacuum, then leave your dishes in
oven for twice the regular time.

(5) Remove from oven and place into cooler. Allow dishes to cool for
five minutes.

(6) Weigh dishes with covers on, being careful to weigh quickly and
very exactly.

(7) Weight of dry solids divided by weight of milk taken, multiplied
by 100, represents percentage total solids.

=177. Testing butter.=--Both the fat and the moisture may be determined by this test. The sample may be prepared in either of two ways:

_Method I._ Remove about one-half pound butter from the different
parts of the churn or tub with a butter trier, and put this into
wide-mouthed bottle or Erlenmeyer flask fitted with rubber stopper
having a thermometer in the center of the stopper, and reaching down
into the mass of butter. Heat bottle in hot water until thermometer
reaches 40 deg. C. or 104 deg. F. If this temperature is not
exceeded, there is very little danger of the butter-fat spreading
rapidly from the curd. Shake vigorously.

_Method II._ Another very satisfactory method of preparing butter for
sampling is to put butter as it comes from churn or tub into Mason
jar, beaker, glass tumbler, or wide-mouthed bottle, any of which may
be covered tightly to prevent evaporation. Allow these to stand in
warm room or in warm water until the butter is soft enough so that it
may be stirred thoroughly with table knife, spatula, or a mechanical
stirrer. At temperature of about 75 deg. to 80 deg. F. butter stirs
into a waxy form from which water or casein will not separate. In
this form, it is put into boat or flask to be weighed.

Fat determination:

(1) If sampling method I is used, measure (about) 1 gram into weighed
butter boat. Weigh quickly and insert boat into flask. If sampling
method II is used, put about 1 gram of the butter sample into weighed
boat, weigh quickly, and insert into extraction flask.

(2) Remove flask from holder and add to extraction flask 9 cubic
centimeters hot water from aluminum dish placed on fat plate. Mark
10-gram pipette up to 9 cubic centimeter and use this for measuring
hot water. Shake vigorously so as to mix butter thoroughly with water.

(3) Before replacing flask into holder, add 1¹⁄₂. cubic centimeters
C. P. ammonia and shake thoroughly, making sure that butter is
thoroughly mixed with ammonia.

(4) Add 10 cubic centimeters of 95 per cent alcohol. Insert cork.
Replace flask into flash holder. Shake flask thoroughly with cork
inserted. Use best quality corks only.

(5) Cool flask by running cold water over lower end of extraction
flask, if flask is very hot. This is not ordinarily necessary.

(6) Add 25 cubic centimeters ethyl ether. Insert corks, shake
vigorously until all butter is dissolved out of boat. Then add 25
cubic centimeters petroleum ether and repeat operation.

(7) Centrifuge flasks, turning handle thirty turns after centrifuge
has reached a speed of about 600 revolutions a minute.

(8) Pour off extractions into proper weighed 3¹⁄₂ inch aluminum
dishes. Repeat above extraction, adding successively 5 cubic
centimeters of 95 per cent alcohol, then 25 cubic centimeters of
each ether. Excepting for very accurate work, a third extraction is
not necessary. The second extraction will remove all but .10 to .15
per cent of the butter-fat. For factory control work this would be a
good margin of safety.

(9) Evaporate off ether at 135 deg. C. on “fat plate,” and when all
of ether is off, dry fat in fat oven held at 135 deg. C. for five
minutes after the vacuum has reached at least 22 inches.

(10) Cool, weigh, and calculate percentage butter-fat as in regular
fat test.

To determine moisture in butter:

If sampling method I is used, keep butter at 140 deg. F. and mix
thoroughly and while well mixed, weigh 1 gram into the solids dish
as quickly as possible to prevent evaporation. If second method of
sampling is used, weigh 1 gram of butter into the solids dish. Heat
on hot plate at 180 deg. C. until foaming ceases, and then place
in vacuum oven held at 100 deg. C. for seven minutes. Cool, weigh
and calculate percentage solids; 100 less this figure represents
percentage moisture.

=178. Testing fresh milk, skim-milk, whey, buttermilk for fat and total solids.=--The fat test is made as follows:

(1) Use the 10 gram pipettes for measuring out 10 grams of milk into
cleaned but not necessarily dried Mojonnier extraction flask. Use
only 10 gram pipettes furnished with tester and do not use 10 cubic
centimeter pipettes. The pipette is graduated to deliver 10 grams of
milk, after allowing all milk to run out and letting it drain for
fifteen seconds longer, then blowing gently to remove last drop.
The pipette must be perfectly clean and dry before being used. Wash
frequently with sulfuric acid, water, alcohol, and ether to insure
having a clean pipette.

(2) Make extractions exactly as in test for butter-fat in condensed
milk, excepting that no water need be added, and in second extraction
only 15 cubic centimeters of each ether need be used.

(3) Percentage butter-fat is obtained by multiplying the weight of
the extracted butter-fat by 10.

(4) If any of these products have soured badly, double the quantity
of ammonia in the regular extraction and shake until all particles
are dissolved.

Total solids determination:

Determining total solids as in evaporated milk, excepting that a
2-gram sample is weighed out, and no water need be added to spread
the milk over the bottom of the dish.

=179. Testing powdered milk, cocoa, malted milk and milk chocolate for fat and total solids.=--

Mix the sample thoroughly, making sure that it is sufficiently
pulverized, and representative of the entire lot to be tested. In the
case of milk chocolate, pulverize the sample very thoroughly, in a
close grained mortar. Transfer the pulverized sample promptly to a
sealed jar. Mix before removing portions for testing.

Butter-fat determination:

(1) Weigh out rapidly, to prevent absorption of moisture from the
air, about 1 gram of milk powder into butter boat. In case of malted
milk, milk chocolate and cocoa, weigh out a 0.5 gram sample.

(2) Add 8.5 cubic centimeters of hot water to flask. Insert cork.
Heat flask in water boat, and shake thoroughly until the sample is
well mixed.

(3) Add 1.5 cubic centimeters (one charge) ammonia, and shake
thoroughly.

(4) Add 10 cubic centimeters of 95 per cent alcohol. Shake
thoroughly. Cool the flask, if necessary.

(5) Continue the extraction exactly as directed under the butter-fat
determination, paragraphs 4, 5, 6, and 7, inclusive.

Total solids determination:

Use .3000 gram sample. Add 2 cubic centimeters distilled water to the
sample in this dish. Otherwise continue the determination exactly as
directed under total solids determination in cheese.

=180. Testing cream for fat and total solids.=--

Mix sample thoroughly in the container. If the cream has been
homogenized, it can be weighed with the weighing pipettes as
described under 5, page 230 of these directions. If the cream is
churned or lumpy it has to be heated until the fat is all just barely
melted, and the entire mixture is uniform. Cream is a product that
is subject to many variations in composition, degree of acidity, and
physical condition. For these reasons, the operator needs to exercise
the best judgment possible. The method of operation may require, at
times, slight modification, depending on the condition of the sample.

Butter-fat determination:

(1) For cream testing under 15 per cent butter-fat, take about a 2
gram sample, using 2-gram pipette. For cream testing over 15 per
cent butter-fat take a 1-gram sample. If practicable, weigh out of
pipette as described under 5, page 230. Otherwise weigh the sample in
the butter boat, or directly into the extraction flasks, which were
previously weighed.

(2) Remove flask from the holder and add enough water to make a total
of 10 cubic centimeters. Insert cork and mix thoroughly.

(3) Before replacing flask in holder, add 1.5 cubic centimeters (one
charge) of ammonia. If the cream is sour add 3 cubic centimeters of
ammonia. This is very important.

(4) From this point to the end of the test, continue as stated on
page 231, beginning at paragraph 2 to paragraph 16, inclusive. At
the end of the second extraction it may be necessary to add quite a
little more alcohol, in order to bring the dividing line up to the
required height.

Total solids determination:

Use a 1.0 gram sample. Add 1 cubic centimeter distilled water to the
sample in the dish. Otherwise proceed exactly as directed in sections
3 to 7 of page 233.

=181. List of precautions to observe in operating Mojonnier tester.=--

(1) Before the reagents are put into the cans, be sure that the cans
are thoroughly cleaned by washing all parts, first with warm water,
then alcohol and then ether. Every third or fourth time cans are
filled, empty out last portion of reagents, and use for cleaning
purposes.

(2) The bottoms of all dishes should be kept as flat as possible. Any
bulging may be worked out by resting dishes upon marble plate in
front of balance, rubbing entire bottom surface with thumbs. Operator
should observe this every time dishes are cleaned. This is very
important.

(3) The calcium chloride in the coolers should be changed every three
or four weeks. The same calcium chloride may be used over and over by
drying the used calcium chloride in tin dishes placed upon hot plate
held at 135 deg. C. for at least five hours.

(4) The bottles should be whirled in the centrifuge until the ether
extraction is perfectly clear. About thirty turns at a normal speed
are to be recommended. For sweetened condensed milk this time must be
doubled.

(5) Be sure to keep extraction flasks perfectly clean. Wash often
with sulfuric acid and washing powder, if necessary. If particles
cling to the sides put in small shot, washing powder and hot water,
and shake thoroughly.

(6) Keep temperature regulated as nearly to standard temperature as
possible.

(7) Never pour off extraction into a hot dish. Remove dish from plate
before second extraction is run into dish.

(8) Be careful to pour off ether into dishes slowly at first and
gradually increase stream until full stream is running.

(9) In using weighing pipettes, make sure that neck of flask is free
from water when pipette is inserted.

(10) Always use clean and dried pipettes.

(11) If the samples for solids have to stand for any length of time,
add the water just as soon as they are measured out, otherwise
there is a tendency to dry and a good mixture with water cannot be
obtained. Keep dishes upon marble plate beside the balance, and not
on hot plate support.

(12) Redistill ethyl ether and petroleum ether, unless they are known
to be pure. This is unnecessary if these are bought from a reliable
firm.

(13) Make sure that water is always running through cooling plate.
Watch pipe back of cooler. If tester is located in cold room in
winter, add a gallon of denatured alcohol to tank to prevent freezing.

(14) Always aim to weigh empty dishes just before you are ready to
use them. It is not advisable to weigh them a long time before they
are used.

(15) It is fundamentally important to see that weights are read and
posted rightly. Operator should-keep his weights in systematic order
upon balance pan. When a reading is taken, it should be checked at
least three times. Learn to make weighing absolutely correct. One
figure misread may cost a month’s salary.