The determination of moisture content — КиберПедия 

Механическое удерживание земляных масс: Механическое удерживание земляных масс на склоне обеспечивают контрфорсными сооружениями различных конструкций...

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The determination of moisture content



Of the average model select not less than two slide crackers and grind them on the grater, in the mortar or by knife before obtaining 40-50 g of crumb. Crumb thoroughly is intermixed and from it immediately is taken hinge quantity for determining of humidity and acidity.

Determination of moisture content by desiccation in the cabinets СЭШ. According to the instruction of the committee of standards, measures and meters with the determination of moisture content in the cabinets СЭШ should be used the weighing bottles only of one size (45×20 mm) and dried the hinges quantities at a temperature of 130ºC during 45 min from the moment of load, in this case the duration of drop and rise in temperature after the load of cabinet must be not more than 20 min. For the flatter drying of hinges quantities in the process of drying it is allowed two, triple turning of disk with the weighing bottles.

4-5 g of the analyzed product weigh with an accuracy to 0,01 g on the counterbalances. The prepared hinges quantities in the open weighing bottles, set to the covers taken from them, are placed into the preheated to 130ºC electrical cabinet drier. It is necessary that the deviations from the temperature during the drying indicated would not exceed ± 20. After 40 min, counting from the moment of establishing the temperature 130ºC, cups take out from cabinet by crucible tongs, they cap they transfer into the exsiccate for the cooling, moreover to leave by those not weighted in the exsiccate the cooled hinges quantities not more than 2 h is not allowed.

Humidity, % is determined from the formula:

 

m1 − m2

B = ------------- 100

M

 

m1- the mass of weighing bottle with the product before the desiccation, g;

m2 - mass of weighing bottle with the product after desiccation, g;

m - mass of product, g.

For the humidity assumes arithmetic mean of two parallel determinations.

Between the parallel determinations the divergence is allowed not more than 0,2%, and with the control rooms and arbitration - not more than 0,5%.

 

The acid test

10 g of the ground test is introduced into the dry Erlenmeyer flask. Then from preliminarily measured 100 ml of water (at a temperature of 18-25ºC into the flask pour about 30 ml and they intermix before obtaining of uniform mass. Remaining water is added after this; again they shake up, following then so that it would not remain on the walls of the sticking particles of the analyzed test. Mixtures give to be defended by 15 min, pour the liquid through the close-meshed screen or gauze into the dry vessel, 25 ml of filtrate select from it, they add 5 drops 1% - GO of the solution of phenolphthalein and titrate 0, 1 n. by the solution of alkali before obtaining of the pink dyeing, which does not disappear during the minute. Titration continues, if during the minute painting disappears and does not appear from the addition of 2-3 drops of indicator.

For the expression of acidity in the degrees a quantity of milliliters, gone for the neutralization alkali, measured with accuracy to by 0, 1 ml, they multiply by 4. Eventual result expresses as the mean arithmetic of two titrations, the divergence between which there must not exceed 0, 1 ml.

Divergence as results of acid test in the different laboratories in one and the same test must be not more than 0, 5 deg.

The obtained results compare with the indices, regulated in the All-Union State Stan.s to the appropriate articles.

Control questions:

1. The determination of a quantity of scrap and crackers of the reduced size

2. The determination of swelling

3. The determination of moisture content

 

 

Laboratory work #6

Evaluation of the quality of flour

Theoretical part

Flour is the powder product, obtained via the grinding of grain.

Flour is subdivided into the forms, the types and the sorts. Form is determined by cereal crop, from which is obtained the flour.

Flour is distinguished by the kind of cereals, by the nature of grinding, by the output, by the type.

From the organoleptic indexes most important are the color, smell and taste. Under laboratory conditions determine humidity, acidity, coarseness of grinding, quantity and quality of the gluten of wheaten flour, impurity content and infection by storehouse wreckers.

Materials and the equipment

- a copper or porcelain mortar, a laboratory mill, a sieve with apertures in diameter 1мм, metal weighing bottles in diameter 48mm and altitude 20mm, crucible pincers, an exsiccate, paper, hot water;

- Electric drying cupboard СЭШ-1.

 

Method of performance






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