Kilogram in France: Double-Bell or Triple-Bell Jar?

[elPhys]

Some sources say it's held in a double-bell jar while others say it's a triple-bell jar. What's the scoop?

 

[f95toli]

There is a photo on the BIPM website, so see for yourself

http://www.bipm.org/en/scientific/mass/pictures_mass/prototype.html

 

[elPhys]

But in the third edition of Halliday and Resnick it shows a picture of it in what appears to be a double bell jar.

So is there some history I'm missing? Was it originally in a double bell jar and then another bell jar added later?

Or maybe the outer "bell jar" isn't considered by some to be a true bell jar (since it doesn't have a knob at the top), and the Halliday and Resnick photo was zoomed into take a picture of just the inner two jars?

 

[lisab]

Free the kilogram! Free the kilogram!11!

 

[LudusRex]

I can provide some clarification on the discrepancy regarding the use of double-bell and triple-bell jars for the kilogram in France. The kilogram is currently defined by the International System of Units (SI) as the mass of a specific platinum-iridium alloy cylinder known as the International Prototype of the Kilogram (IPK). This cylinder is housed in a special container, known as the International Bureau of Weights and Measures (BIPM) jar, which is designed to protect it from environmental factors and maintain its mass.

The BIPM jar has evolved over the years, and there have been different versions used in France. In the early 20th century, the jar was made of a double-bell design, with the IPK suspended in the center and two bells on either side. However, in the 1980s, the jar was redesigned to a triple-bell design, with the IPK suspended in the center and three bells surrounding it.

Both versions of the jar have been used in France, and there is no definitive answer as to which is currently being used. However, it is important to note that the design of the jar does not affect the mass of the IPK, as the IPK is the actual standard for the kilogram, not the jar. The jar is simply a protective container.

In conclusion, while there may be conflicting information about the type of jar used to house the kilogram in France, it is ultimately not a significant factor in the accurate measurement of the kilogram. The important thing to remember is that the kilogram is defined by the mass of the IPK, and this standard is carefully maintained by the BIPM.