Best laboratory test

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1. 2. 3, 4.

s.

6. 7. 8. 9.

(This chapter has been completely revised) CHAPTER 12

BEET LABORATORY TESTS TABLE OF CONTENTS General

Preparati°'p of Sample . . . . Care of the Rasp . . . .. ... . Determination of Sugar by Cold Water Digestion ... . Determination of Sugar by Hot Water Digestion.~ ... . General Checks on Beet Laboratory Work . . . . Percentage of Pulp Produced ... ... . Care of Beet Sample Bags . . . . Apparent Purity . . . .. . . . 1. GENERAL Page 1201 1201 1203 1204 1205 1206 1206 1206 1207

The purpose of the beet laboratory tests is to determine the quality of the beets during the latter part of the growing season and at the time of delivery during the harvest season.

Determine on each sample:

(a) Sugar by Cold Water Digestion. Determine as often as required:

(b) Sugar by Hot Water Digestion. (c) Apparent Purity.

As delivery samples will come from the tareroom in open baskets, and the beets are subject to both rapid evaporation and deterioration on standing, such samples must be worked up as fast as received and must not be ·allowed to accumulate. Any accumulation necessary as a small reserve, or resu\ting from the difference

in starting time between the beet laboratory and the tareroom, must be kept in bags of such material as will best prevent evaporation, and tqe b~gs must be tied with string.

2. PREPARATION OF SAMPLE

Some samples of beets, such as field samples, will be broug9t to the beet laboratory in rubberized bags. These should not be removed from the bags until shortly before analysis.

The samples should be cleaned, if necessary; and freed from dirt with a wire brush or other suitable appratus, avoiding as much as possible injury to the outside surface. Field samples, and sometimes "piled!' samples will require cleaning.

If a record of the average weight is desired, count and weigh the beets constituting the sample, and enter the data on the envelope or ticket accompanying the sample.

The Great Western Sugar Company

Chemical Department

-1201-Methods of Analysis Beet Laboratory Tests

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Reduce a segment of each beet of the sample to a fine pulp by passing the beet thru the automatic rasp. A conical rasp, such as the Keil disc, has been found by·careful tests to takE;l, in the long run, an average sample

of the entire

beet, but the accuracy of the sample obtained is dependent on the observation of the following points:

(a) The edge of the segment ta.ken from the beet must be at the exact center by having the V disc-support shiJIJIQed to the proper height, and the segment must coincide with the axis of the beet.

(b) Take the segment from the first beet at the smaller diameter, that from the second beet at the larger diameter, or vice versa, and so on alternately with the remaining beets of the sample.

(c) All small and broken beets must be rasped, because they constitute a part of the sample and should not be discarded.

(d) See that the rasp is always up to the required speed of 2000-2200 revolutions per minute.

(e) The rubber wipers and metal backing plates at the small end of the cone of the bucket should clear the opening so that the beet tails will not jam against them. These wipers should be replaced as soon as they become ineffective.

(f) The speed of the buckets should be approximately fifty per minute. A slower speed is not objectionable if capacity can be maintained.

(g) Keep the rasp in proper mechanical condition as described under Section

3,

"Care of the Rasp".

The round bottomed pan in which the pulp is caught must be properly cleaned between samples and must be removed from the rasp as soon as the last beet of the sample has passed over the Keil disc, in order to limit the evaporative effect of the air current produced by the revolving disc. If there is a temporary delay in rasping, the last sample of pulp should not be left under the rotating disc. Sample of pulp may be allowed to stand in the mixing bowls in still air for 10

minutes without determinable evaporative error.

In unusual cases, excessively dry or wilted beets cannot be rasped without noticeable heating from friction. Samples of this type should be quartered, and one quarter of each beet should be ground in a meat chopper (cossette grinder), the sugar being determined by hot water digestion. Beets which are very small and give insufficient pulp may be re-rasped at

90°

to the original segment, or

handled as above. ·

Hand Rasps

Similar instructions, as far as applicable, apply also to hand rasps. The speed of the Keil disc of the hand rasp should, however, be about 1000-1200 R .• P. M., as this rasp is not designed-for a higher disc speed. In hand rasping

it is important to push ea~h beet over the disc at a slow, uniform speed in order to obtain pulp of the necessary fineness.

The Great Western Sugar Company Chemical Department

-1202-Methods of' Anarys is Beet Laboratory Tests July 20, 195:3

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3. CARE OF THE RASP

The disc must be mounted on the shaft so that the edge will run true

with-out oscillation. New discs should be tested to see that they are true, as

other-wise it will be impossible to mount them properly.

The disc should rotate at the rate of 2000-2200 revolutions per minute.

T h e ~ of rasping is dependent on the sharpness of the teeth, but the

fineness of t h e ~ is dependent on a n ~ contour of the edges of the teeth.

The reliability of the cold water digestion method in giving the correct percentage

of sugar depends on the fineness of the pulp .. Too coarse pulp will give low

results because of incomplete extraction of the sugar. If a rasp is found to give

too coarse pulp, the disc should be faced by holding a file or carborundum stone

against both the sides and the edge of the rotating disc. Very often this

pro-cedure can be improved upon by first going over the disc and filing down all teeth

which project perceptibly above the general contour; large side teeth close to the

edge of the rasp are particularly objectionable and should be reduced by filing.

After this treatment very little facing will usually be necessary to put the rasp

into such condition that i t will produce pulp of the proper fineness. The facing

should be done gradually and the character of the pulp tested by comparative cold

and hot water digestion, until a point is reached where the rasp yields fine pulp,

but is still sufficiently sharp so that the beets may be ground without undue

effort. Ne'w discs will commonly require facing before the pulp is satisfactory.

The qu~lit~·of the pulp can be judged only approximately by observation and must be

determined by the average difference between series of comparative hot and cold

water digestion tests. This difference should be less than 0.1 per cent on the

weight of the beets, and, if it exceeds this figure, the rasp should be given

attention.

When the disc becomes dull, as usually determined when the percentage of

pulp becomes small and a clean cut segment is not removed from the beet, the edge

teeth should be sharpened with a cant file, care being taken to keep the teeth of

as uniform size and even contour as possible. The edge should then be faced

lightly, if necessary, as previously described. As the edge becomes wider from

wearing down, it will be found increasingly difficult to obtain fine pulp, until a

point is eventually reached where the disc wil.l have to be discarded.

A ~cale of calcium oxalate frequently deposits on the disc, especially

when immature beets are being rasped. As this forms a polished surface, its

presence is easily overlooked. It has the effect of filling up the interstices

between the teeth and thereby making the rasp dull. This scale can be removed

mechanically, or very readily by immersing the disc in strong hydrochloric or

nitric acid diluted with an equal volume of water. The scale formation will be

lessened if the disc is washed with hot water whenever the rasp is shut down for

any length of time. Experience has indicated the desirability of acid cleaning

the discs at the end of every day's work.

The mixing bowl should not be allowed to come into contact with the rotating

disc when it is removed after the rasping of each sample.

At the end of every day the rasp should be thoroughly washed and scrubbed,

and then dried well, even if it is not acid washed. When acid washed, care should

be used to see that the last traces of acid are removed so that none will

contami-nate the first ensuing sample rasped.

Chemical Department

-1203-Methods of Analysis

Beet Laboratory Tests

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4.

DETERMINATION OF SUGAR

BY

COLD WATER DIGESTION

Special Apparatus

(a) A torsion balance, equipped with an air dashpot, or a pulp balance of suitable capacity and sensitivity.

(b} Counterpoised squares or vegetable parchment paper, about 3-3/4 x 3-1/2 inches.

(c) A sufficient number

of

Monel metal capsules about 3 inches high by 3 inches in diameter. (Drawing S-1170).

(d) Automatic pipettes which have been carefully standardized to deliver 177+ 0.20

ml,

as described under Volumetric Apparatus, p. 4201, and

"Specifica-tions", page 4 (d). (Drawing S-3098).

(e) Aluminum discs with a round hole in the middle, provided with rubber envelopes, to serve as capsule covers. (Drawing S-1170).

Special Reagent

(a} Dilute lead acetate: Mix one part or basic lead acetate solution

of standard strength (556

Brix) with 30 parts

of

water. The milky solution ·may be usea without being allowed to settle, but precipitation will be minimized

if

reasonably pure water is used tor dilution. The solution should be at approxi-mately room temperature and should not be excessively cold. Only tap

water

should be used for this dilution to prevent any contamination by sugar.

Determination

Mix the sample

ot

tine pulp thoroughly with the Smith mixer. Weigh out 26 grams on a counterpoised parchment paper, discarding any fragments or skin, rootlets, etc., which may occasionally be discovered. Weigh the pulp within a precision

ot

20 milligrams, and do not waste time in attempting to weigh any more closely. Transfer the parchment paper with the pulp to a Monel capsule, add 177 ml

ot

the dilute lead acetate solution from the automatic pipette, cover, and shake vigorously for a few seconds. Let the covered capsule stand for at least

20 minutes, again shake vigorously, remove the cover, tilter, and polarize in a

400 mm continuous tube. The reading gives directly the percentage of sugar. When frozen beets are encountered, the time of standing in the capsules

before filtration should be considerably lengthened, in order to insure complete

diffusion and temperature equalization. Do not use dilute lead acetate above

room temperature to hasten diffusion because of volume error upon cooling.

Special Precautions

Check the balance frequently for equilibrium and sensitivity. The

equilibrium should be checked with the customary load of 26 grams, and the balance

used for hot water digestion weighings should be checked also with the load of

the counterpoised metal dish plus 26 grams. The balances should be protected from drafts.

Check the normal weight frequently with standard analytical weights or

with a calibrated standard normal weight.

When selecting a parchment paper from a package for use as a counter-poise, instead of taking one at random make it a rule to balance several papers

against one another and select one of median weight. The Great Western Sugar Company

Chemical Department

=12

04-Methods of Analysis Beet Laboratory Tests

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\

The Ninegar polariscope tube or the Koontz-Huleatt rubber-capped tube is

recommended on account of the avoidance of cover glass strain and the ease of removing the caps and cover glasses for cleaning. Check the tube frequently for optical

acitivity, p,articularly if not of the Ninegar type, after cleaning and before use

by filling it with distilled water and reading it in the polariscope. This should be done at least once a shift. To minimize corrosion, use an ammonium acetate solution rather than muriatic acid for cleaning the tube.

If difficulty is encountered in preventing the Ninegar tube from leaking,

an application of a light coating of stopcock lubricant or vaseline to the end

surfaces of the tube is recommended.

The polar~scope should be checked with a +16° quartz plate (with National Bureau of Standards Certificate) at least 4 times a day, oftener if the instrument tends to show a variable reading. It should be set so as to give the correct quartz plate reading whether or not the instrument always reads exactly zero with

this setting when the quartz plate is removed. An occasional polariscope will

give a few hundredths difference but in such a case the quartz plate reading should govern.

The thoroughness of mixing cannot be overemphasized, as upon this operation depends the accuracy of the sugar determination. This should be checked occasion-ally by making sugar determinations on several samples taken at random from

different parts of the same bowl of pulp and also by taking several samples,

remix-ing, and polarizing. The mixer should not be overburdened with other duties to the extent that this important phase is neglected. A high plus difference between hot and cold tests may be explained by the presence of rootlets or fragments of a beet, but high minus differences must in the long run be ordinarily due to imperfect mixing.

5. DETERMINATION OF SUGAR BY HOT WATER DIGESTION

Check the accuracy of the cold water digestion tests by making hot water

digestions on some of the regular samples of rasped pulp. M~ke at least three hot water tests per shift on days of reasonable activity. If these show an erratic tendency, this number should be increased.

The hot water digestion should be carried out exactly as in the case of cossettes, page 303 of the Methods of Analysis, and all operations should be

per-formed with equal care and with the same detailed procedure. Particular care should be given to the removal of occluded air by evacuation under a good vacuum, which should preferably be at least 20 inches of mercury and should be measured by a gage or manometer. Dea~ration should be longer than for cossettes and should be carried to the point where no foam forms on the liquid at the end of the digestion

"

period. After digestion and cooling, a further deaeration is recommended. For an efficient make of filter pump refer to the Chemical Bulletin, pp. 399 and 405.

Chemical Department

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6. GENERAL CHECKS ON BEET LABORATORY WORK

The hot water checks to be made regularly in the beet laboratory are

qesoribed in section 5 preceding.

As an additonal check, the cold and hot filtrates from the beet

labora-tory check determinations, or composite samples made up of equal portions of the

hot and corresponding cold filtrates respectively may be saved and polarized in

the factory laboratory. If the composite samples become dark on standing, they

may be refiltered with Filter-Cel before polarization.

Once or twice a day during the delivery season, exchange samples for

sugar determination between the beet laboratory and factory laboratory. Such

samples may be either beet laboratory pulp or ground cassettes; the latter, if

used, must be analyzed by both laboratories by hot digestion. The analyst of the

factory laboratory, when analyzing beet laboratory pulp, should be cautioned about

the necessity for complete remoyal of air by proper evacuation. A permanent record

of these exchange samples should be made and after the beet laboratory has closed

for the season, a recapitulation giving the individual tests and the average of all

tests should be transmitted to the General Chemist.

As a check on the polarizations as read in the beet laboratory, a

compos-ite should be made of the filtrates from approximately each 100 samples. This can

be made by taking a definite volume from each sample or by pouring all the filtrate

through the polarization tube, care being taken that the filtrates are very nearly

equal in volume, and collecting the entire filtrate in a closed container. After

thorough mixing and filtering, a portion is read in the beet laboratory as wel-1 as

in the factory laboratory, and these polarization~ are compared with the

arith-metical average of the sample tickets which it represents. These polarizations

must be carefully recorded on the Beet Laboratory Foreman's Notes for use in the

factory laboratory office.

7. PERCENTAGE OF PULP PRODUCED

To check the performance of the disc, weigh about six samples of beets

and the yield of pulp obtained from these beets. Calculate the percentage yield

of pulp on beets. The weight of pulp of several samples may be weighed as one

unit.

8. CARE OF BEET SAMPLE BAGS

During the testing season suitable attention should be paid to the care

and accounting of beet sample bags. It is considered best to keep them in

continu-ous circulation to avoid deterioration of damp bags. As heating of a high stack

of bags has been observed within 22 hours, attention should be given the bag

storage on days when the beet laboratory is not operating. It is recommended that

the bags be piled not over 100 high for 24 hours storage, to prevent possible fire

hazard as well as damage to the bags.

As the end of the season it is important to see that all sample bags are

thoroughly dtied_poth inside and outside. If possible they should be suspended in

such a manner that the inside as well as the outside will be dried, in order to

avoid turning the bags, which is hard on the cemented seam. If there is any doubt

as to the dryness of the inside of the bags they should then be turned.

Chemical Department -

1206-Methods of Analysis

Beet Laboratory Tests

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After drying, any loose dirt is removed by and the gum-coated side is dusted with Filter-Cel. on racks in loose piles of not too great height in suitable location.

shaking or gentle brushing, The bags should then be stored the beet laboratory or other

The bags should be inspected at occasional intervals during the inter-campaign, to make sure that they are under suitable storage conditions and that no mold or heating is in evidence.

Bags which have given way at the cemented seams but are otherwise in good condition, should be sewed along the seam.

9. APPARENT PURI'IY

Purity determinations are not regularly required on delivery samples. Purity determinations on field samples should be made in the following manner. Squeeze out the juice from the ground pulp at a good pressure, preferably in an hydraulic press, and collect and mix all the juice expressed. Dilute to diffusion juice density (11-12° Brix) with water low in solids, and dea~rate thoroughly under a good vacuum. Then determine apparent purity in the regular manner according to the General Methods.

Purity determinations on experimental and special samples should be made by the procedure requested by those furnishing such samples.

In all purity determinations particular attention should be paid to the complete removal of air by evacuation. The time of evacuation needed should be established by repeating the evacuation and redetermining the Brix on a few samples.

Chemical Department