International Prototype Kilogram

For scientific work the fundamental standard of mass is the international prototype kilogram, which is a mass of platinum-iridium alloy made in 1887 and deposited in the International Bureau of Weights and Measures near Paris. Authentic copies of the standard are kept by the appropriate responsible authorities in the various countries of the world these copies are employed for the comparison of secondary standards, which are used in the calibration of weights for scientific work. The unit of mass that is almost universally employed in laboratory work, however, is the gram, which may be defined as the one-thousandth part of the mass of the international prototype kilogram. 

The gram is defined as 1/1000 of the mass of the International Prototype Kilogram. 

The international prototype kilogram is an example of a primary measurement standard its value and uncertainty have been established without relation to another standard of the same kind. When the primary measurement standard is used for calibration, it becomes a primary calibrator. 

Mass The unit of mass in the SI system is the kilogram (symbol kg). The kilogram is defined as the mass of a platinum-iridium alloy cylinder called the International Prototype Kilogram (IPK) that is stored in a vault near Paris. 

The kilogram (unit of mass) is the mass of a particular cylinder of platinum iridium alloy, called the International Prototype Kilogram, which is preserved in a vault at Sevres, France, by the International Bureau of Weights and Measures. 

Mass m kilogram kg The kilogram is the unit of mass it is equal to the mass of the international prototype kilogram, which is a certain platinum-iridium cylinder kept at the International Bureau of Weights and Measures near Paris... 

The mass of an object is a measure of the quantity of material it contains. The SI unit of mass, the kilogram (kg), is used for larger masses, such as body mass. The standard for mass, the international prototype kilogram (IPK), is a cylinder that is made of a platinum-iridium alloy. In the metric system, the unit for mass is the gram (g), which is used for smaller masses. There are 1000 g in one kilogram. In comparison to the U.S. system, the mass of 1 kg is equivalent to 2.205 lb, and 453.6 g is equal to one pound. Some useful relationships between different units for mass follow ... 

Analytical chemists make a distinction between calibration and standardization. Calibration ensures that the equipment or instrument used to measure the signal is operating correctly by using a standard known to produce an exact signal. Balances, for example, are calibrated using a standard weight whose mass can be traced to the internationally accepted platinum-iridium prototype kilogram. 

Kilogram. The kilogram is the unit of mass it is equal to the mass of the international prototype of the kilogram. 

From the definitions and examples above, it should be clear that metrological traceability is established by a series of comparisons back to a reference value of a quantity. In the mass example it is easy to picture a number of scientists with ever more sophisticated balances comparing one mass with another down the chain of masses from the international prototype of the kilogram to bathroom scales. This is known as a calibration hierarchy. A mass farther up the chain is used to calibrate the next mass down the chain, which in turn can be used to calibrate another mass, and so on, until the final measurement of the mass is made. 

The top of the metrological traceability chain is given in figure 7.6. The procedure and system referred to in the figure may be either for the production of the calibrator, such as the international prototype of the kilogram, or for a primary measurement procedure governing a measuring system, as in the use of a coulometric titration. 

In the United States, measurements made with metric units were not legally accepted in commerce until 1866. In 1875 the United States became a signatory to the Metric Convention, and by 1890 it received copies of the International Prototype meter and kilogram. However, rather than converting our measurement system to metric, in 1893 Congress decided that the International Prototype units... 

Balances can be calibrated or verified for accuracy with special weights, called calibrated weights, whose specific mass is known. Calibrated weights vary in quality and tolerance. They are classified by type, grade, and tolerance All calibrated weights are compared directly or indirectly to the international prototype one-kilogram mass to verify their accuracy. 

At the time that the metric system was set up, in 1799, it was intended that the milliliter be exactly equal to the cubic centimeter (cm ). However, it was later found that the relation between the gram, as given by the prototype kilogram, and the centimeter, one one-hundredth of the distance between two engraved lines on a standard platinum-iridium bar, the prototype meter kept in Paris hy the International Bureau of Weights and Measures, is such that the milliliter is not exactly equal to the cubic centimeter, but is instead equal to [.000027 cm . It is obvious that the distinction between ml and cm is ordinarily unimportant. 

Kilogram 1901 One kilogram is the mass of the international prototype which is in the custody of the Bureau International des Poids et Mesures at Sevres, France. 

The kilogram mass definition cannot be realized independently of the international prototype. 

The limitations on the stability of the kilogram defined in terms of the international prototype could be eliminated if the kilogram were defined in terms of a... 

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