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The guide to a practical training to pharmaceutical technology of drugs Under edition Yu. A. BLAGOVIDOVA and V. M. Ivanova
"MEDICINE" Moscow — 1972
The management contains all subjects of a practical training on pharmaceutical technology of drugs, copybooks to seminars, recipes for analysis, and also the list of the main and additional literature.
The management to a practical training but pharmaceutical technology of drugs is made also compliance with the program approved by the Ministry of Health of the USSR and the State pharmacopeia of the USSR of the X edition and intends for students of pharmaceutical institutes and pharmaceutical faculties of medical institutes.
DOSING ON WEIGHT. DEVICE AND METROLOGICAL PROPERTIES OF SCALES
Tasks
 To get acquainted with the device and installation of tarirny scales. To make the scheme. To check linearity of a yoke.
 To check sensitivity of tarirny scales.
 To get acquainted with the device of scales: manual, desktop ordinary and torsion.
 To solve problems of definition of errors of weighing.
Lever scales which according to the metrological characteristics belong to the category of technical scales of the 2nd class are applied to dosing on weight in pharmaceutical practice. Metrological properties of scales characterize the following indicators: stability, fidelity, sensitivity, constancy of indications. Stability is called ability of the scales brought out of an equilibrium state to return after fluctuations to initial (zero) situation. Degree of stability of scales depends on distance between the center of gravity of a yoke and a point of support. The below the center of gravity is located, the stability of scales is more. Fidelity is called ability of scales to show a proper correlation between the weighed load and weights. Scales are right on condition of full symmetry and equality of shoulders of a yoke. Sensitivity is called ability of scales to show the minimum distinction between the loads lying on cups. The less size of the load causing a deviation of an arrow of balanced scales the is more sensitive scales.
Sensitivity depends on length of a shoulder of a yoke, its weight, distance from the yoke center of gravity to a point of support, loading of scales and size of a deflection of a yoke — distance from a point of support to the line connecting edges of cargo reception prisms. Constancy of indications is called ability of scales to show identical weight at repeated weighing of the same load. Constancy of indications is reached on condition of strict parallelism of cargo reception prisms each other and their perpendicularity in relation to the yoke plane.
DEVICE AND TARIRNYKH INSTALLATION OF SCALES
Tarirny (prescription) scales consist of the following main parts: yokes, one basic and two cargo reception prisms, two regulators of a container, an arrow, two earrings with holders of cups and two cups. To make their disassembly for acquaintance with parts of tarirny scales. In the course of disassembly of scales to check linearity of a yoke by means of a ruler. To make the scheme of scales. To make their installation and installation.
CHECK OF SENSITIVITY OF TARIRNY SCALES
Check of sensitivity of scales has to be made according to the instruction of Committee of standards, measures and measuring devices at Council of ministers of the USSR. The committee of standards, measures and measuring devices at Council of ministers of the USSR approves admissible errors when weighing on various scales (see the appendix 1). Apparently from the table, errors when weighing increase with loading of scales (sensitivity of scales with loading decreases). Work is performed on tarirny scales with the greatest permissible load of the I kg. When checking sensitivity of scales they are previously balanced. From zero situation to the left on a scale note the point corresponding of 5 mm. Then load the right cup with the weights corresponding to tabular data of an error and define an arrow deviation. A standard deviation the rejection of the index of balance not less than on 5 mm (in accordance with GOST) is considered.
Scales which have a load equal to an admissible error are caused by a deviation less than on 5 mm. are rejected. When checking sensitivity at 1/10 greatest permissible load of a pas both cups of scales place weights on 100 g and try to obtain balance. Then on the right cup of scales add the load equal to an admissible error (see the table in the appendix 1) and define a deviation of an arrow of scales (mm). Similarly make check of sensitivity of scales at the greatest permissible load. The data obtained when checking bring in the table.
Sensitivity of tarirny scales
Underloaded 
At 1/10 greatest permissible load 
At a small permissible load 
small weight weight, causing the noticeable shift of an arrow 
deviation of an arrow, mm 
admissible error, mg 
deviation shooters, mm 
admissible pogreshnost, mg 
deviation of an arrow, mm 






From the obtained data to draw the corresponding conclusions. Note. When checking sensitivity of manual scales it is necessary to consider GOST 35954, p. 3, item 5: "At the provision of scales in balance with the loading equal 1/10 and the greatest admissible, the load corresponding to an admissible error, added to one of loads has to discompose scales so that the arrow went beyond an oboymitsa not less than on a half of the length". Sensitivity of scales nenagruzheny and admissible errors see in the appendix 1. To make their disassembly and installation for acquaintance with the device of manual and desktop ordinary scales. To tie up cups of manual scales. The device and installation of the torsion scales and the rule of weighing on them are described in the appendix 2.
