THE BOOK OF ICE-CREAM | Project Gutenberg

Standardizing milk or cream consists in raising or lowering the fat-content to a fixed standard. This is done by adding to the material milk or cream of a higher or lower percentage of fat. In standardization two classes of problems are involved: first, one in which a certain fixed amount of milk is to be made up or a certain amount of standardized milk is desired; and second, in one in which a certain amount of milk or cream is to be used and enough of another product added to make the mixture test a certain percentage of fat. In the latter case, the amount of the mixture is indefinite.

The original method of computing problems in standardization is long and difficult, but a comparatively simple scheme has been devised by R. A. Pearson. The method is as follows:

Draw a rectangle and place in the center of it the percentage of fat desired. Place at the left-hand corners of the rectangle the percentages of fat in the materials to be mixed. Subtract the number in the center from the larger number at the left of the rectangle. Place the remainder on the diagonally opposite right-hand corner of the rectangle. Subtract the smaller number on the left-hand corner from the number in the center and place the remainder on the diagonally opposite right-hand corner of the rectangle.

The two numbers on the right-hand corners of the rectangle represent the number of pounds of material required. If these two numbers are added they will express the number of pounds of the mixture, which will contain a percentage of fat expressed by the number in the center of the rectangle. In each case the number on the right-hand corner corresponds in fat test to the number on the left-hand corner directly opposite.

Problem: How many pounds of 40 per cent cream and 3 per cent milk must be mixed to make milk testing 5 per cent? Using the diagram as described, the result shown in diagram above is obtained.

This means that if 2 pounds of 40 per cent cream are mixed with 35 pounds of 3 per cent milk, the result will be a 37 pound mixture testing 5 per cent. Answer.

Problem: How many pounds of 28 per cent cream and 3 per cent milk will be required to make 500 pounds of a mixture testing 4 per cent? In this problem a definite number of pounds of the mixture is required.

According to the diagram, 1 pound of 28 per cent cream is required to every 24 pounds of 3 per cent milk to make a mixture testing 4 per cent. This would make 25 pounds of the mixture, but 500 pounds is the amount desired. In other words, the number of pounds desired is 20 times larger than the number of pounds on hand (500 ÷ 25 = 20). The amounts must be kept in the proportion of 1 : 24. Therefore, in order to get a 500 pound mixture it is necessary to multiply both the 1 and the 24 by 20. This would give a result of 20 pounds of 28 per cent cream and 480 pounds of 3 per cent milk, which mixed will equal 500 pounds of 4 per cent milk. Answer.

x = 20, number of pounds of 28 per cent cream there will be in the 500 pound mixture. Answer.

If there are 20 pounds of 28 per cent cream in the 500 pound mixture, the remainder will necessarily be 3 per cent milk.

The number of pounds of 3 per cent milk can be found directly by simple proportion:

Proof: In working problems in standardization it is always wisest to prove the answer, as this is the best method of checking the work for mistakes.

According to the conditions of the problem there would be 500 pounds of 4 per cent milk. This amount of milk would contain 20 pounds of fat (500 × .04 = 20). According to the results the 500 pounds would be made up of 480 pounds of 3 per cent milk and 20 pounds of 28 per cent cream. The 480 pounds of 3 per cent milk would contain 14.4 pounds of fat (480 × .03 = 14.4). The 20 pounds of 28 per cent cream would contain 5.6 pounds of fat (20 × .28 = 5.6). 14.4 + 5.6 = 20

Since the 500 pounds contain 20 pounds of fat, and the materials of which the 500 pounds are made up furnish the 20 pounds of fat, the problem is worked correctly.

Problem: How many pounds of 3 per cent milk must be mixed with 150 pounds of 28 per cent cream to make a mixture testing 4 per cent? In this problem the number of pounds to be made up is not definitely known.

Working the problem by the rectangle method, 1 part of 28 per cent cream is required for 24 parts of 3 per cent milk. According to the terms of the problem, 150 pounds of 28 per cent cream must be used, and this is 150 times as large as in the above proportion.

The 28 per cent cream and 3 per cent milk must be kept in the proportion of 1 : 24, and since the amount of 28 per cent cream is to be increased 150 times, the 3 per cent milk must also be increased 150 times. This would give 150 pounds of 28 per cent cream (1 × 150) and 3600 pounds of 3 per cent milk (150 × 24 = 3600), making in all 3750 pounds (150 + 3600 = 3750) of a 4 per cent mixture.

Proof: The 3750 pounds of 4 per cent milk will contain 150 pounds of fat (3750 × .04 = 150).

If the 150 pounds of 28 per cent cream and 3600 pounds of 3 per cent milk furnish 150 pounds of fat, the problem is correct.

The percentage of fat, or solids not fat, or total solids in a given batch may be computed if the percentage composition of the materials is known. Compute the total number of pounds of the desired material in each of the products used and divide by the total weight of the batch. For example, to find the percentage of fat in a batch, compute the pounds of fat in each material and find the total number of pounds of fat. Dividing the result by the total weight of the mix will give the percentage of fat in the mix. The solids not fat or total solids may be computed in the same way. By reversing these calculations, the percentage of fat necessary in the milk or cream to yield a mixture containing a certain percentage of fat can be computed.

171. Benkendorf⁠[48] test for over-run in ice-cream.

—With this simple outfit (Fig. 74), it is possible at all times and without data as to the volume or weight of the “mix,” for the manager of the factory to determine the over-run in any lot of ice-cream made by his employees.

Method of making the over-run test.

To obtain a 50 cubic centimeter sample, the metal sampler should be pressed down into the hardened ice-cream until it is entirely below the surface, and allowed to remain there for a minute or two, to become chilled. Then it should be drawn out and the protruding ice-cream removed from both ends of the sampler with a case knife or small piece of flat metal. (When a continuous freezer is used, a metal sampler with a closed bottom, like a cup, can be held under the spout of the freezer until heaping full, then the surplus scraped off.)

The 200 cubic centimeter flask should be filled exactly to the mark on the neck with hot water and the sampler held in the funnel, the stem of which is inserted in the neck of the 250 cubic centimeter flask, a little of the hot water poured over the sampler until the ice-cream slips out of it, then all the remaining hot water slowly poured over this.

The foam which appears in the neck of the 250 cubic centimeter flask should be destroyed by adding 1 cubic centimeter (or 2 cubic centimeters if necessary) of ether with the pipette. As soon as the foam has disappeared, the flask may be filled with water exactly to the 250 cubic centimeter mark by means of the burette, which has previously been filled to the zero mark.

How to make the calculations.

The number of cubic centimeters of water and ether used to bring the volume up to the 250 cubic centimeters mark, represents the shrinkage which the 50 cubic centimeter sample of ice-cream has undergone when melted. Subtracting this shrinkage from 50 gives the original volume of the “mix” before freezing. To determine the percentage of over-run, the number of cubic centimeters of shrinkage should be divided by the number of cubic centimeters that were in the original mixture.

Example:	Cubic centimeters
Sample used	50
Ether used to reduce foam	1
Water used to bring to 250 c.c. mark	15	.5
Water and ether used (15.5 + 1)	16	.5
Volume of “mix” before freezing (50 - 16.5)	33	.5
Per cent of over-run (16.5 ÷ 33.5)	49	.25	per cent

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.

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.

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.

171. Benkendorf⁠[48] test for over-run in ice-cream.

Method of making the over-run test.

How to make the calculations.

172. Test to determine the hardness of ice-cream.